The top 10 weight loss programs, according to science
, medical review by Dr. Bret Scher, MD
Evidence basedWith so many weight loss plans available, it can be challenging to know which one to choose — especially since there isn’t one diet that’s the best fit for everybody.
If you want to lose weight and improve your health — with a plan that works for you — you’ve come to the right place.
In this review, we rank the 10 best weight loss programs based on the scientific evidence supporting their effectiveness. We’ll also explore each plan’s pros and cons to help you decide which option is right for you.
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There is strong evidence that many different types of diets can help people lose weight.1
However, some diets may lead to more dramatic weight changes than others. Certain diet plans may also provide greater improvements in health markers — like blood sugar control and heart disease risk factors — compared to other eating patterns.
Finding a diet that you enjoy and can stick with is important, too. If you view your diet as a long-term healthy lifestyle change rather than a quick fix, you’re more likely to lose weight and keep it off.
We’ve ranked the most popular weight loss plans primarily by their effectiveness for weight loss, and secondarily for improvements in health markers, based on the strength of the evidence to date.2
Each diet received a score on a scale of 1 to 5 for weight loss and health changes, for a combined overall score out of 10. Importantly, any rating system of this nature can involve some level of subjectivity, and the exact scores can of course be debated.3
We’ve also provided a description of the diets, along with their advantages and disadvantages.
If you’re ready to lose weight and keep it off, read our detailed review of the top 10 weight loss programs to find out which one is best for you.
1. Keto or very low carb diet
Our top pick for weight loss, improvement in health markers, and sustainability? A keto or very low carb diet.
Pros
- Often more effective for losing weight than other diets
- Suppresses appetite, leading to weight loss without deliberate calorie restriction or hunger
- Significantly improves blood sugar control and other markers of metabolic health
Cons
Rating
| Weight loss score: | 4.5/5 | |
| Health benefits score: | 4.5/5 | |
| Overall score: | 9/10 |
Keto diet basics
A ketogenic (keto) diet minimizes carbohydrate (carb) intake while allowing more generous amounts of protein and fat.
Carbohydrates are found in starches (bread, potatoes, pasta), sweets (cookies, cake), milk, and fruit, among other foods.
On a ketogenic diet, you reduce carbs to the point where your body stops using glucose as its primary energy source and instead uses mainly fat — either the fat you eat or your stored body fat. This fat-burning state is known as ketosis.
A keto diet emphasizes eating adequate protein (meat, fish, eggs, cheese, or tofu), adding fat such as butter or olive oil for flavor and fullness, and including above-ground vegetables at most meals. Nuts and small amounts of berries are sometimes included.
How many carbs can you eat and still get into or stay in ketosis? This varies from person to person.4 However, in studies, ketogenic or very low carb diets typically provide less than 50 grams of total carbs per day.5
Weight loss
In several reviews of studies testing low carb diets against low fat and other diets, low carb has been found as effective — and frequently more effective — for losing weight.6
And when data from these trials are looked at individually, very low carb diets typically produce the most dramatic weight and fat loss — even when people are allowed to eat as much of the keto foods as they need to feel satisfied.7
In one of these trials, overweight adults who followed a non-calorie-restricted keto diet lost 26 pounds (12 kilos) and 5.8% of their body fat within 24 weeks, whereas those who ate a calorie-restricted low fat diet lost 14 pounds (6.5 kilos) and 2.8% of their body fat.8
More recent studies have also found that keto diets produce impressive weight loss.9
One reason keto diets are so effective for losing weight is because they typically suppress appetite, causing people to naturally eat less without deliberately restricting calories.10
Health benefits
Aside from weight loss, very low carb diets often provide metabolic health benefits.
Of the three macronutrients — protein, carbs, and fat — carbs raise blood sugar the most.11When people with type 2 diabetes eat very low carb diets, they typically experience profound improvements in blood sugar control and can quickly reduce or discontinue their diabetes medication.12
Very low carb diets often reduce triglycerides and increase HDL cholesterol levels (changes that are considered beneficial) more than other diets.13 They can also lower blood levels of small, dense LDL — the type of LDL with the strongest link to heart attack risk.14 And they can be very effective for lowering blood pressure.15
To learn more about losing weight and improving your health with a keto diet, read our complete beginner’s guide to ketogenic diets.
2. Low carb diet
Pros
- As effective or more effective for losing weight compared to other diets
- Less restrictive than a keto diet, with side effects such as keto flu less likely
- Often significantly improves blood sugar control and other markers of metabolic health
Cons
- Typically produces more gradual weight loss than keto or very low carb diets
- May not provide as much appetite suppression as keto or very low carb diets
- Requires medical supervision in people who take medications for diabetes or blood pressure
Rating
| Weight loss score: | 4/5 | |
| Health benefits score: | 4.5/5 | |
| Overall score: | 8.5/10 |
Low carb diet basics
A low carb diet provides about 50 to 130 grams of total carbs per day.16 That’s more than a keto or very low carb diet, but considerably less than the estimated 200 to 300 grams of carbs most people eat every day.17
A low carb diet includes all of the foods on a keto diet — meat, eggs, above-ground vegetables, fats, and berries — plus a few others that are slightly higher in carbs, such as fruits, carrots, and possibly small amounts of starchy foods like sweet potatoes.
Weight loss
In reviews of trials lasting between eight weeks and 24 months, researchers have concluded that low carb diets often lead to greater weight loss than low fat diets.18
In several of those trials, people who ate non-calorie-restricted low carb diets lost more weight than those who ate calorie-restricted low fat diets.
In a 2014 trial, 148 people were assigned to eat less than 40 grams of carbohydrate per day, or a low fat diet. Although the low carb group ended up averaging about 100 grams of carbs per day, they lost about 12 pounds (5.3 kilos) — more than twice as much as those in the low fat diet group.19
Some research suggests that following a low carb diet might even help keep people’s metabolism from slowing down during weight maintenance.20
Health benefits
Low carb diets also outperform low fat and other dietary interventions for lowering blood sugar levels in people with diabetes.21
Additionally, low carb diets may be beneficial for reducing markers of heart disease risk, particularly triglycerides and blood pressure.22 And results from a two-year trial suggest that losing weight via a low carb diet may help reduce the amount of plaque in the arteries of people with heart disease.23
To learn more about how to follow a low carb diet, including tips for getting started, read our complete low carb diet for beginner’s guide.
3. Intermittent fasting
Pros
- Typically as effective or more effective for weight loss compared to chronic calorie restriction
- Does not restrict type or amount of food during eating windows
- Reduces time spent preparing, eating, and cleaning up after meals
Cons
- For some, it may be difficult to fast for several hours or eat few to no calories on alternate days
- May cause some side effects
- Requires medical supervision in people who take medications for diabetes or blood pressure
Rating
| Weight loss score: | 4/5 | |
| Health benefits score: | 4/5 | |
| Overall score: | 8/10 |
Intermittent fasting basics
Intermittent fasting involves going for extended periods without eating. It includes time-restricted eating (skipping one or two meals every day) and alternate-day fasting (eating normally one day and fasting or eating very few calories the next day).
Unlike other weight loss plans, intermittent fasting specifies when you eat rather than what you eat.
Weight loss
Reviews of studies exploring time-restricted eating and alternate-day fasting have shown that they are as effective or more effective than daily calorie restriction for losing fat and improving health markers.24
One review of clinical trials found that while alternate-day fasting or chronic calorie restriction led to similar weight and fat loss, people who practiced alternate-day fasting retained more muscle mass than those who ate a low-calorie diet every day.25
Health benefits
A 2019 review of trials found that intermittent fasting lowered blood sugar and increased insulin sensitivity compared to control diets.26
In one trial, people with type 2 diabetes who practiced intermittent fasting for 12 months improved their blood sugar control as much as people who followed calorie-restricted diets.27
One problem with intermittent fasting trials is that people are usually advised to eat whatever they want during non-fasting periods — which could include processed foods high in sugar and other refined carbs.
Regardless of how often you eat, getting adequate essential nutrition — especially protein — and limiting less nutritious foods is important for sustainable weight loss and overall health.
If you are going to practice intermittent fasting, choose nourishing, minimally processed foods whenever you eat.
To learn more about time-restricted eating and alternate-day fasting, read our intermittent fasting for beginners guide.
4. Mediterranean diet
Pros
- Typically produces greater weight loss than low fat diets
- Provides a wide variety of minimally processed foods
- May improve blood sugar control and other markers of metabolic health
Cons
- Weight loss results are usually modest
- May require deliberate calorie restriction for weight loss
- Metabolic benefits may not be as impressive compared to low carb diets
Rating
| Weight loss score: | 4/5 | |
| Health benefits score: | 4/5 | |
| Overall score: | 8/10 |
Mediterranean diet basics
A “Mediterranean diet” is a way of eating based on the traditional cuisine of people living in the countries that border the Mediterranean Sea, including Italy and Greece.
Many people consider a Mediterranean diet healthy because the most common version features large amounts of vegetables, fruits, whole grains, fish, legumes, nuts, and olive oil, with moderate amounts of meat, eggs, dairy, and alcohol.28
Weight loss
One review comparing different diets found that a Mediterranean diet can provide modest weight loss benefits in people with type 2 diabetes.29
Occasionally, this way of eating may also produce rapid results. For example, in one study, people who followed a Mediterranean diet lost up to 7.5 pounds (3.4 kilos) and 2.74% of their body fat in only four weeks.30
Researchers who reviewed several trials testing different diets found that a Mediterranean diet was more effective than low fat diets for losing weight but not more effective than low carb diets for losing weight.31
Indeed, low carb versions of Mediterranean diets typically lead to more impressive weight loss results compared to low fat diets and traditional Mediterranean diets.32
Health benefits
In 2015, researchers who conducted a sweeping review of Mediterranean diet trials in people with type 2 diabetes found that they are more effective for lowering blood sugar, HbA1c, and reducing heart disease risk factors than low fat diets.33
Results from a two-year trial suggest that losing weight by following a Mediterranean diet can potentially help reduce the amount of plaque on artery walls in people with heart disease.34
To learn more about how to follow a Mediterranean diet, read our Mediterranean diet guide.35
5. Paleo diet
Pros
- May produce modest weight loss
- Emphasizes nourishing, minimally processed foods
- May improve blood sugar control and insulin sensitivity more than low fat diets
Cons
- Some may find the diet too restrictive to follow, especially when dining out
- Because the diet allows potatoes and honey, some carb-sensitive individuals may see little improvement in blood sugar levels
- Requires attention to ensure adequate intake of iodine-rich seafood and non-dairy sources of calcium
Rating
| Weight loss score: | 4/5 | |
| Health benefits score: | 3.5/5 | |
| Overall score: | 7.5/10 |
Paleo diet basics
A paleo or paleolithic diet — also known as the hunter-gatherer diet, caveman diet, and Stone-Age diet — includes only foods that could have been eaten by our prehistoric ancestors who lived roughly 10,000 to 2 million years ago.
On a paleo diet, you avoid not only processed foods, refined flour, and sugar, but also whole grains, dairy products, and legumes. Foods to eat include meat, fish, fruit, vegetables, tubers (potatoes and yams), nuts, and seeds.
A modern-day paleo lifestyle gained fame and popularity through the writings of exercise physiologist Loren Cordain in his best-selling 2002 book, The Paleo Diet.
This way of eating focuses on getting back to natural foods to improve health and prevent metabolic disease.
Weight loss
In 2019, researchers reported that in nine of eleven trials, people who ate a paleo diet lost more weight than people who ate their usual diets or diets recommended by health authorities.36
In a 12-week trial, people with type 2 diabetes ate a non-calorie-restricted paleo diet while following standard exercise recommendations or participating in supervised one-hour exercise sessions three times a week. By the end of the study, both groups lost nearly 16 pounds (7.1 kilos) and decreased their HbA1c by about 1%.37
Other trials have shown more modest weight loss results in people who ate paleo diets.38
Health benefits
In some trials, people who followed paleo diets had greater improvements in blood sugar, insulin sensitivity, and triglyceride levels compared to those who followed other diets.39
Because the paleo diet provides a wide variety of animal and plant foods, people who follow this way of eating are unlikely to develop nutrient deficiencies. A possible exception may be calcium deficiency due to avoiding dairy.40
However, you can meet your calcium needs on a paleo diet by including non-dairy sources of calcium, such as canned salmon or sardines, almonds, seeds, and leafy green vegetables.
Additionally, some people may fall short on iodine because iodized salt is typically not permitted on paleo diets.41 Fortunately, consuming fish and shellfish regularly can help prevent iodine deficiency.
To learn more about how to follow a paleo diet, read our full guide.
6. Vegan diet
Pros
- Slightly better weight loss than some other diets, often without deliberate calorie restriction
- May lower blood sugar, insulin, and LDL cholesterol levels
- May be less expensive than diets that contain meat, seafood, and other animal products
Cons
- May be difficult for some to consistently meet protein and other nutrient needs; requires supplementation of vitamin B12 and likely other nutrients, such as vitamin D
- May be difficult to dine out or socialize with non-vegan friends or colleagues
- Some vegan foods are highly processed
Rating
| Weight loss score: | 4/5 | |
| Health benefits score: | 3.5/5 | |
| Overall score: | 7.5/10 |
Vegan diet basics
On a vegan diet, all animal products are off the table. This means avoiding eggs, meat, fish, dairy products, and gelatin (which comes from animal bones and hides). Vegan staples include legumes, grains, nuts, seeds, vegetables, and fruits.
Both vegan and plant-based diets have become very popular in recent years. Although people sometimes use these terms interchangeably, they mean different things. Unlike vegan diets, plant-based diets may include small amounts of animal products.
Weight loss
Overall, vegan diets have been shown to produce slightly better weight loss than standard dietary advice in overweight people and those with type 2 diabetes.42
In some studies, people have lost significantly more weight with a vegan approach compared to other higher carb diets.43
In a recent 16-week trial, 122 overweight adults who ate a low fat vegan diet lost an average of nearly 14 pounds (6.4 kilos), reduced their body fat by 10%, and became more insulin sensitive. Although they were allowed to eat as much as they wanted, they ended up averaging 500 fewer calories per day than their baseline diet.44
One six-month trial that compared different types of non-calorie-restricted plant-based diets found that participants who ate vegan diets lost more weight than those who ate vegetarian and semi-vegetarian diets.45
A low carb vegan diet combines two popular eating patterns. Although only one study has explored this approach, results suggest that it may help some people lose weight and improve heart health markers.46
Health benefits
In some, but not all studies, vegan diets have been shown to reduce blood sugar and insulin levels, along with markers of heart disease risk.47
A vegan diet requires supplementation with vitamin B12, which is only found in animal products. Additionally, people who eat a vegan diet are at higher risk of protein, vitamin D, calcium, iron, and zinc deficiencies.48
To stay healthy on a vegan diet, it’s crucial to include a protein source (legumes, nuts, seeds) and vegetables at every meal and to take supplements as needed based on lab results.
To learn more about vegan diets, read Vegan for Life.49
If you’re interested in following a low carb version of a vegan diet, read our full guide.
7. Vegetarian diet
Pros
- May lead to modest weight loss
- Less restrictive and easier to dine out compared to vegan diets
- May lead to modest improvements in blood sugar and heart health markers
Cons
- May require deliberate calorie restriction for weight loss
- Unlikely to improve diabetes control more than meat-containing diets with similar macronutrient composition
- Unlikely to reduce heart disease risk more than meat-containing diets with similar macronutrient composition
Rating
| Weight loss score: | 3.5/5 | |
| Health benefits score: | 3.5/5 | |
| Overall score: | 7/10 |
Vegetarian diet basics
Vegetarian diets exclude meat but — with the exception of vegan diets — include some animal products. Lacto-ovo vegetarians eat dairy and eggs, lacto vegetarians eat dairy but avoid eggs, and pescatarians eat seafood, eggs, and dairy.
Like vegan diets, vegetarian diets are typically rich in legumes, grains, and vegetables. Although many highly processed foods are technically vegetarian, health-focused vegetarians recommend avoiding them.
Weight loss
Reviews of vegetarian diet trials suggest that this way of eating may help some people lose weight.50
However, vegetarian diets haven’t been shown to be more effective than other diets for weight loss, at least long term.
In a review of 12 trials, people who ate vegetarian diets initially lost an average of 4.4 pounds (2.2 kilos) more than those who ate meat-containing higher carb diets, and the largest weight loss occurred in those who ate vegan or calorie-restricted vegetarian diets. Yet in trials lasting a year or more, weight loss was similar between those eating vegetarian vs. non-vegetarian diets.51
Health benefits
Similarly, vegetarian diets may not improve all heart health markers more than diets that include meat.
For example, in one trial, 118 overweight adults followed a calorie-restricted vegetarian diet and a calorie-restricted Mediterranean diet for three months and lost about 4 pounds (1.8 kilos) during each diet. Although the vegetarian diet lowered their LDL cholesterol more, the Mediterranean diet lowered their triglyceride levels more.52
To learn more about losing weight while following a vegetarian lifestyle, check out the Vegetarian for Weight Loss cookbook.53
If you are interested in a diet that combines a vegetarian diet with a keto approach, read our full guide.
8. DASH diet
Pros
- Typically produces equal or slightly better weight loss when compared to other calorie-restricted diets
- Allows a wide range of minimally processed foods
- Typically lowers blood pressure slightly and may improve some markers of metabolic health
Cons
- Deliberate calorie restriction may be needed for weight loss
- May be challenging to follow long term due to being low in both fat and salt
- Unlikely to lower blood sugar levels significantly
Rating
| Weight loss score: | 3/5 | |
| Health benefits score: | 3/5 | |
| Overall score: | 6/10 |
DASH diet basics
The Dietary Approaches to Stop Hypertension (DASH) diet is designed to lower blood pressure.54
It emphasizes minimally processed foods high in potassium and other minerals, such as fruits, vegetables, whole grains, lean protein, and low fat dairy products. The DASH diet limits sugar and saturated fat, and most versions restrict sodium.
Weight loss
Although the DASH diet’s primary focus is lowering blood pressure to decrease heart disease and stroke risk, some research suggests it may help people lose weight, especially when combined with calorie restriction.
For instance, a review of 13 trials found that the DASH diet led to slightly greater weight loss when compared to control diets.55
In an eight-week trial in people with fatty liver disease, participants who ate a calorie-restricted DASH diet lost 8 pounds (4.8 kilos), while those who ate a calorie-restricted control diet lost 5 pounds (2.3 kilos).56
Health benefits
The DASH diet may improve some health markers.
In the eight-week trial described above, the DASH diet group had greater improvements in liver enzymes, insulin sensitivity, triglycerides, and markers of inflammation compared to the control group.57
The DASH diet seems to live up to its name. A 2020 review of 50 trials found that the DASH diet slightly lowered blood pressure compared to control diets.58 Interestingly, the DASH diet reduced blood pressure the most when sodium intake was not restricted to less than 2,400 mg per day.59
For a weight loss–focused version of the DASH diet, read The DASH diet weight loss solution.60
9. WW (formerly Weight Watchers)
Pros
- May produce modest weight loss
- Does not restrict any foods
- Points system encourages consumption of adequate essential nutrients, including protein
Cons
- Limited published evidence supporting its effectiveness for weight loss
- Very limited published evidence supporting its effectiveness for improving health markers
- Fee required to join the WW online program
Rating
| Weight loss score: | 3/5 | |
| Health benefits score: | 2/5 | |
| Overall score: | 5/10 |
WW basics
WW — known as Weight Watchers until 2018 — is a diet program that assigns point values, called SmartPoints, to foods based on their calorie and nutritional content.61
Although a food’s calories form the basis of its point value, saturated fat and sugar increase the number, while protein lowers it.
Many fruits, vegetables, legumes, and lean proteins are assigned a point value of zero to encourage people to eat as much as they want of these foods. Depending on the eating plan a person chooses, they can eat other foods totaling up to 100, 200, or 300 points per day.
Weight loss
While there isn’t a lot of research on the WW points system for weight loss, a few trials suggest that it may work for some people.62
In a 2016 trial, adults with prediabetes who followed the WW points plan lost 5.5% of their body weight within 12 months, compared to a 0.2% loss in those who followed a diet based on the National Diabetes Education Program guidelines. 63
In a study of 297 overweight adults, those who followed the Weight Watchers online program lost 6 pounds (2.7 kilos) within three months, while those who received a WW newsletter but did not join the program lost 3 pounds (1.3 kilos).64
In the 2005 A to Z trial, people who were assigned to the Weight Watchers program lost about 7 pounds (3 kilos) in one year, which was similar to participants who were assigned to the Atkins, Ornish (low fat, plant based), or Zone (high protein) diet.65
Health benefits
Although studies on the WW program have focused on changes in weight, some have also reported improvements in health markers.
In the 2016 trial in people with prediabetes described above, those who followed WW reduced their HbA1c values and increased their HDL cholesterol levels more than those who followed standard diabetes recommendations.66
And in the 2005 A to Z trial, participants in the Weight Watchers group experienced slight reductions in LDL cholesterol levels, similar to those in the Atkins, Ornish, and Zone groups.67
To learn more about the WW online program, visit the WW site.10. Zone diet
Pros
- May produce slight to modest weight loss
- Allows a wide range of minimally processed foods
- High in protein and other essential nutrients
Cons
- Limited published evidence supporting its effectiveness for weight loss
- Very limited published evidence supporting its benefits for metabolic health
- “Block” system may be time-consuming and challenging to follow long term
Rating
| Weight loss score: | 3/5 | |
| Health benefits score: | 2/5 | |
| Overall score: | 5/10 |
Zone diet basics
The Zone diet was created by Dr. Barry Sears, who published his bestselling book Enter the Zone in 1995.
It involves eating a specific macronutrient ratio — 40% carbs, 30% protein, and 30% fat — at each meal.
The diet also emphasizes choosing low-glycemic-index carbohydrates (vegetables, sweet potatoes, apples), lean proteins (chicken breast, fish, egg whites), and unsaturated fats (olive oil, nuts).
To achieve the 40/30/30 macronutrient ratio, people eat Zone “blocks” that contain 7 grams of protein, 9 grams of carbs, and 1.5 grams of fat. Zone dieters are assigned a daily quota of blocks based on their weight and body composition.
Weight loss
There has been very little published research on the Zone diet’s effects on weight and health to date.
In a small study, Italian researchers reported that participants who followed the Zone diet supplemented with omega-3 fatty acids lost more body fat than those who followed standard dietary recommendations with omega-3 fatty acid supplementation.68
In a six-month trial of 96 overweight women, participants who followed a non-calorie-restricted Zone diet lost 15 pounds (6.7 kilos), which was slightly less than those who followed the Atkins diet and significantly more than those who followed a high carb, high fiber diet.69
In some trials, the Zone diet hasn’t been found as effective for weight loss as other diets. For instance, in the 2007 A to Z trial, overweight women assigned to follow the Zone diet lost significantly less weight than those assigned to the Atkins diet, and slightly less weight than those assigned to the Ornish diet or LEARN (low fat) diet.70
Health benefits
Limited research suggests the Zone diet might improve some health markers. For instance, in a 2005 trial, people who followed the Zone diet or Atkins diet had greater reductions in triglycerides than those who ate a high carb, high fiber diet.71
To learn more about the diet, read Enter the Zone.72
What about high protein diets?
You may have noticed that we don’t have a section on high protein diets on this list. Can high protein eating be a healthy, effective approach for weight loss? Absolutely!
Strong science shows that high protein diets can help people feel full, eat less, and lose body fat while preserving resting metabolic rate and preventing loss of muscle mass.73
Fortunately, you can do a high protein version of any of the diets discussed above. So, for the greatest healthy weight loss success, we suggest combining a high protein approach with one of our top 10 diets.
Learn more in our complete guide, High protein diet: What it is and how to do it.
Summary
Ratings summary
| 1. Keto diet | 9.0/10 | |
| 2. Low carb diet | 8.5/10 | |
| 3. Intermittent fasting | 8.0/10 | |
| 4. Mediterranean diet | 8.0/10 | |
| 5. Paleo diet | 7.5/10 | |
| 6. Vegan diet | 7.5/10 | |
| 7. Vegetarian diet | 7.0/10 | |
| 8. DASH diet | 6.0/10 | |
| 9. WW | 5.0/10 | |
| 10. Zone diet | 5.0/10 |
You can lose weight in many different ways. While some diets seem to be more effective for taking off pounds or kilos than others, there isn’t one diet plan that is best for everyone.
All of the diets on this list emphasize choosing minimally processed, nutritious foods and avoiding refined flour and sugar.
When you eliminate refined carbs, you get rid of many foods that cause people to gain weight.
The best diet plan for you is the one that allows the foods you love, helps you feel full and satisfied, and improves your health markers. If you struggle to stay true to a specific way of eating and constantly crave “forbidden” foods, the diet likely won’t be sustainable for you.
When you find a way of eating that you can enjoy as a lifestyle for years to come, you’ll be on your way to losing weight and keeping it off for good.
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The top 10 weight loss programs, according to science - the evidence
This guide is written by Franziska Spritzler, RD and was last updated on February 5, 2024. It was medically reviewed by Dr. Bret Scher, MD on December 23, 2020.
The guide contains scientific references. You can find these in the notes throughout the text, and click the links to read the peer-reviewed scientific papers. When appropriate we include a grading of the strength of the evidence, with a link to our policy on this. Our evidence-based guides are updated at least once per year to reflect and reference the latest science on the topic.
All our evidence-based health guides are written or reviewed by medical doctors who are experts on the topic. To stay unbiased we show no ads, sell no physical products, and take no money from the industry. We're fully funded by the people, via an optional membership. Most information at Diet Doctor is free forever.
Read more about our policies and work with evidence-based guides, nutritional controversies, our editorial team, and our medical review board.
Should you find any inaccuracy in this guide, please email andreas@dietdoctor.com.
Systematic reviews of randomized controlled trials (RCTs) — considered the strongest form of evidence — have shown this:
British Medical Journal 2020: Comparison of dietary macronutrient patterns of 14 popular named dietary programmes for weight and cardiovascular risk factor reduction in adults: systematic review and network meta-analysis of randomised trials [systematic review of randomized trials; strong evidence]
Journal of the American Medical Association 2014: Comparison of weight loss among named diet programs in overweight and obese adults: a meta-analysis [systematic review of randomized trials; strong evidence] ↩
Not included in this list are diet programs that require eating less than 1,000 calories per day, meal replacements (shakes or bars), or pre-packaged meals. We don’t believe these are sustainable options to achieve and maintain a healthy weight. ↩
The ratings reflect our interpretation of the amount of high-quality research supporting the effectiveness of each diet.
For instance, the keto or very low carb diet received a 4.5 for weight loss and a 4.5 for health benefits due to the large volume of clinical trials showing that it often outperforms other diets in these areas.
The Zone diet received a 3 for weight loss and a 2 for health benefits due to the limited number of clinical trials supporting its effectiveness. Additional research demonstrating positive effects would increase its score.
We also considered nutritional completeness when ranking the diets in order. So although a vegan diet received a 4 for weight loss and a 3.5 (7.5 overall) for health benefits, we listed it after the Paleo diet (which also scored 7.5 overall) because a vegan diet requires supplementation. ↩
In a trial of 77 healthy adults, some participants achieved ketosis while eating a diet providing 25% of calories from carbs (about 90 grams of total carbs a day on a 1,500-calorie diet). However, not everyone can achieve ketosis with this level of carb intake. Some will require much less. In this study, keeping carb intake below 5% of total calories resulted in ketosis for all participants:
Nutrition: X 2019: Effects of differing levels of carbohydrate restriction on mood achievement of nutritional ketosis, and symptoms of carbohydrate withdrawal in healthy adults: A randomized clinical trial [randomized trial; moderate evidence] ↩
At Diet Doctor, we provide the amount of net carbs (total carbs minus all fiber) in our visual guides.
We recommend aiming for 20 or fewer grams of net carbs per day, as this level virtually guarantees ketosis. Diets with less than 50 grams of total carbs likely provide less than 30 grams of net carbs per day. ↩
In a review comparing trials that tested different popular diets, researchers concluded that the low carb Atkins diet produced the greatest weight loss in both the long and short term:
Nutrients 2017: Effects of popular diets without specific calorie targets on weight loss outcomes: systematic review of findings from clinical trials [systematic review of randomized trials; strong evidence]
Other trials report similar results:
PLoS One 2015: Dietary intervention for overweight and obese adults: Comparison of low carbohydrate and low fat diets. A meta-analysis [strong evidence]
The British Journal of Nutrition 2016: Effects of low carbohydrate diets v. low fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials [strong evidence]
Obesity Reviews 2016: Impact of low carbohydrate diet on body composition: meta-analysis of randomized controlled studies [strong evidence] ↩
Of 16 RCTs lasting between eight weeks and two years that were included in several meta-analyses, eight of the nine very low carb diets led to significantly greater weight loss than other diets. In contrast, all seven of the more moderate low carb diets resulted in similar or slightly more weight loss than comparator diets:
PLoS One 2015: Dietary intervention for overweight and obese adults: Comparison of low carbohydrate and low fat diets. A meta-analysis [strong evidence]
The British Journal of Nutrition 2016 Effects of low carbohydrate diets v. low fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials [strong evidence]
Obesity Reviews 2016: Impact of low carbohydrate diet on body composition: meta-analysis of randomized controlled studies [strong evidence]
Here are a few examples of results from very low carb diet studies:
In a 12-week trial, people with metabolic syndrome who ate a very low carb diet lost 22 pounds (10 kilos), while those who ate a low fat diet lost 11 pounds (5.2 kilos):
Lipids 2009: Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat diet [randomized trial; moderate evidence]
In a four-month trial, obese women who ate a non-calorie-restricted keto diet lost 22 pounds (9.8 kilos), whereas those who ate a calorie-restricted low fat diet lost 14 pounds (6.2 kilos):
The Journal of Clinical Endocrinology and Metabolism 2005: The role of energy expenditure in the differential weight loss in obese women on low fat and low carbohydrate diets [randomized trial; moderate evidence] ↩
Annals of Internal Medicine 2004: A low carbohydrate, ketogenic diet versus a low fat diet to treat obesity and hyperlipidemia: a randomized, controlled trial [randomized trial; moderate evidence] ↩
In a recent eight-week trial, older adults who ate a keto diet lost 13 pounds (5.9 kilos) and 9.7% of their body fat, while those who ate a low fat diet lost 2 pounds (0.9 kilo) and 2% of their body fat:
Nutrition and Metabolism 2020: Effects of weight loss during a very low carbohydrate diet on specific adipose tissue depots and insulin sensitivity in older adults with obesity: a randomized clinical trial [randomized trial; moderate evidence]
Other studies reported similar results:
Nutrition & Diabetes 2017: Twelve-month outcomes of a randomized trial of a moderate carbohydrate versus very low carbohydrate diet in overweight adults with type 2 diabetes mellitus or prediabetes [randomized trial; moderate evidence]
Journal of Medical Internet Research 2017: An online intervention comparing a very low carbohydrate ketogenic diet and lifestyle recommendations versus a plate method diet in overweight individuals with type 2 diabetes: a randomized controlled trial [randomized trial; moderate evidence] ↩
Obesity Reviews 2015: Do ketogenic diets really suppress appetite? A systematic review and meta-analysis [strong evidence]
In one crossover study, obese men followed a non-calorie-restricted keto diet or a non-calorie-restricted moderate carb diet for four weeks each. Participants reported being less hungry on the keto diet and lost an average of 14 pounds (6.3 kilos), compared to 10 pounds (4.3 kilos) on the moderate carb diet:
The American Journal of Clinical Nutrition 2008: Effects of a high protein ketogenic diet on hunger, appetite, and weight loss in obese men feeding ad libitum [randomized trial; moderate evidence] ↩
Diabetes Care 2004: Dietary carbohydrate (amount and type) in the prevention and management of diabetes [overview article; ungraded] ↩
This has been demonstrated in several clinical trials:
Cureus 2020: Effects of the ketogenic diet on glycemic control in diabetic patients: Meta-analysis of clinical trials [strong evidence]
In one trial of adults with type 2 diabetes who followed a ketogenic diet for 16 weeks, people in the keto diet group reduced their hemoglobin A1c (HbA1c) — a long-term measure of blood sugar control — by 1.5%. Additionally, 95% of participants discontinued or reduced the dosages of their insulin and other diabetes medications:
Nutrition and Metabolism 2008: The effect of a low carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus [randomized trial; moderate evidence]
In a two-year trial, people with type 2 diabetes who ate a keto diet reduced their HbA1c by an average of 0.9%, and 67% of participants were able to eliminate insulin and oral diabetes medications (other than metformin) altogether. For those who still used insulin or other diabetes medications after two years, dosages were greatly reduced:
Frontiers in Endocrinology 2019: Long-term effects of a novel continuous remote care intervention including nutritional ketosis for the management of type 2 diabetes: A 2-year non-randomized clinical trial [non-randomized study; weak evidence] ↩
In a systematic review of RCTs, low carb diets were found to lower triglycerides and increase HDL cholesterol more than low fat diets, and these effects were most dramatic in diets providing fewer than 50 grams of carbs per day:
Nutrition Reviews 2017: Effects of carbohydrate-restricted diets on low-density lipoprotein cholesterol levels in overweight and obese adults: a systematic review and meta-analysis [systematic review of randomized trials; strong evidence] ↩
Cardiovascular Diabetology 2020: Impact of a 2-year trial of nutritional ketosis on indices of cardiovascular disease risk in patients with type 2 diabetes [nonrandomized study; weak evidence] ↩
The following meta-analysis reported consistent blood pressure benefits from very low carb diets:
Obesity Reviews 2012: Systematic review and meta-analysis of clinical trials of the effects of low carbohydrate diets on cardiovascular risk factors [strong evidence]
In a small study, people with metabolic syndrome who followed a ketogenic diet for 12 weeks experienced significant reductions in blood pressure, going from an average of 141/89 to 123/76:
Journal of Medicinal Food 2011: A pilot study of the Spanish ketogenic Mediterranean diet: an effective therapy for the metabolic syndrome [weak evidence]
Other trials report similar results:
Archives of Internal Medicine 2010: A randomized trial of a low carbohydrate diet vs orlistat plus a low fat diet for weight loss [moderate evidence]
Cardiovascular Diabetology 2018: Cardiovascular disease risk factor responses to a type 2 diabetes care model including nutritional ketosis induced by sustained carbohydrate restriction at 1 year: an open label, non-randomized, controlled study [weak evidence] ↩
At Diet Doctor, we define a low carb diet as one that provides up to 100 grams of net carbs (total carbs minus fiber) per day. However, researchers often define a low carb diet as one that provides up to 130 grams of total carbs per day. ↩
Recent survey data suggests that in the US, people consume an average of 50% of their calories as carbohydrates, or 250 grams on a 2,000-calorie diet. However, this is self-reported data, and people often under-report the amounts of food they eat:
Journal of the American Medical Association 2020: Trends in dietary carbohydrate, protein, and fat intake and diet quality among US adults, 1999-2016 [cross-sectional survey; weak evidence] ↩
PLoS One 2015: Dietary intervention for overweight and obese adults: Comparison of low carbohydrate and low fat diets. A meta-analysis [strong evidence]
The British Journal of Nutrition 2016: Effects of low carbohydrate diets v. low fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials [strong evidence] ↩
The low carb group also had greater improvements in high-density lipoprotein (HDL) cholesterol, triglycerides (TG), and other cardiovascular disease risk factors than the other group:
Annals of Internal Medicine 2014: Effects of low carbohydrate and low fat diets: a randomized trial [randomized trial; moderate evidence] ↩
In a 2012 study, 21 adults who’d lost weight on a calorie-restricted diet were found to burn around 300 calories more per day during weight maintenance if they followed a low carb diet compared to a low fat diet:
Journal of the American Medical Association 2012: Effects of dietary composition during weight loss maintenance: a controlled feeding study [randomized trial; moderate evidence]
In a similar but larger study in 164 people, participants who’d previously lost weight were found to burn between 200 to nearly 500 more calories per day on a low carb maintenance diet compared to a higher carb maintenance diet:
British Medical Journal 2018: Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial [randomized trial; moderate evidence] ↩
A 2017 systematic review of nine trials found that in addition to reducing weight, diets providing between 20 grams and 130 grams of total carbs per day led to significant improvements in HbA1c, blood sugar, and triglyceride levels:
Diabetes Research and Clinical Practice 2017: Efficacy of low carbohydrate diet for type 2 diabetes mellitus management: A systematic review and meta-analysis of randomized controlled trials [strong evidence]
More recently, an 18-month trial demonstrated that people with poorly controlled type 2 diabetes who consumed 90 grams of carbs per day decreased their HbA1c by 1.6% and were able to reduce their diabetes medication dosage significantly more than participants who consumed a low fat diabetes diet:
PloS One 2020: Effect of a 90 g/day low carbohydrate diet on glycaemic control, small, dense low-density lipoprotein and carotid intima-media thickness in type 2 diabetic patients: An 18-month randomised controlled trial [randomized trial; moderate evidence] ↩
Two recent systematic reviews have concluded that low carb diets reduced triglycerides and blood pressure in overweight adults:
PloS One 2020: The effects of low carbohydrate diets on cardiovascular risk factors: A meta-analysis [systematic review of randomized trials; strong evidence]
Nutrition Reviews 2017: Effects of carbohydrate-restricted diets on low-density lipoprotein cholesterol levels in overweight and obese adults: a systematic review and meta-analysis [systematic review of randomized trials; strong evidence] ↩
In this study, researchers tracked signs of carotid atherosclerosis (fatty deposits in the carotid arteries) over two years in participants who ate either a low carb diet, a Mediterranean diet, or a low fat diet. By the end of the trial, there was significant regression of measurable carotid artery wall volume in all three diet groups, implying a reduction of atherosclerosis. According to the researchers, the improvement was likely due to loss of weight and reduced blood pressure resulting from the dietary changes:
Circulation 2010: Dietary intervention to reverse carotid atherosclerosis [randomized trial; moderate evidence] ↩
In a 2020 review of 18 RCTs lasting between eight and 52 weeks, participants who practiced intermittent fasting lost between 3.2% to 13% of their body weight, which was similar to participants who followed daily calorie restriction:
Canadian Family Physician 2020: Intermittent fasting and weight loss: Systematic review [strong evidence]
The following review also showed similar weight loss for the continuous calorie restriction and intermittent fasting groups:
Obesity Reviews 2017: Short‐term intermittent energy restriction interventions for weight management: a systematic review and meta‐analysis [strong evidence]
Other systematic reviews of RCTs suggest that intermittent fasting may lead to slightly greater decreases in fat and waist circumference compared to chronic calorie restriction and control diets:
JBI Database of Systematic Reviews and Implementation Reports 2018: Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis [strong evidence]
Journal of Clinical Medicine 2019: The effectiveness of intermittent fasting to reduce body mass index and glucose metabolism: A systematic review and meta-analysis [strong evidence] ↩
Obesity Science and Practice 2016: Alternate‐day versus daily energy restriction diets: which is more effective for weight loss? A systematic review and meta‐analysis [systematic review of non-randomized trials; moderate evidence] ↩
Journal of Clinical Medicine 2019: The effectiveness of intermittent fasting to reduce body mass index and glucose metabolism: A systematic review and meta-analysis [strong evidence] ↩
JAMA Network Open 2018: Effect of intermittent compared with continuous energy restricted diet on glycemic control in patients with type 2 diabetes: a randomized noninferiority trial [moderate evidence] ↩
The American Journal of Medicine 2015: The Mediterranean diet, its components, and cardiovascular disease [review article; ungraded] ↩
A 2015 systematic review of clinical trials in people with type 2 diabetes found that a Mediterranean diet was one of only two diets that led to a 5% or greater loss of weight in 12 months. People randomized to a Mediterranean diet lost an average of 13.5 pounds (6.2 kilos) and achieved significant improvements in HbA1c, lipids, and blood pressure:
Journal of the Academy of Nutrition and Dietetics 2015: Lifestyle weight-loss intervention outcomes in overweight and obese adults with type 2 diabetes: a systematic review and meta-analysis of randomized clinical trials [strong evidence] ↩
Journal of Translational Medicine 2018: Influence of FTO rs9939609 and Mediterranean diet on body composition and weight loss: a randomized clinical trial [randomized trial; moderate evidence] ↩
The American Journal of Medicine 2016: Systematic review of the Mediterranean diet for long-term weight loss [strong evidence] ↩
In an 18-month trial, 278 people with abdominal obesity were assigned to eat either a low fat diet or a low carb Mediterranean diet (up to 70 grams of carbs per day). By the end of the study, those in the low carb Mediterranean diet group lost 3.1% of their body weight and significantly more liver fat than the low fat group:
Journal of Hepatology 2019: The beneficial effects of Mediterranean diet over low fat diet may be mediated by decreasing hepatic fat content [randomized trial; moderate evidence]
In another trial, overweight people with diabetes followed either a low carb Mediterranean diet, a traditional Mediterranean diet, or a low fat diet based on American Diabetes Association (ADA) recommendations for one year. At the end of the study, people in the low carb Mediterranean diet group lost an average of 22 pounds (10.1 kilos), while those in the traditional Mediterranean diet group lost an average of 16 pounds (7.3 kilos), and those in the ADA diet lost 17 pounds (7.7 kilos). Those in the low carb Mediterranean diet also increased their HDL cholesterol levels (beneficial) and reduced their HbA1c’s more than the those in the other diet groups:
Diabetes, Obesity & Metabolism 2010: A low carbohydrate Mediterranean diet improves cardiovascular risk factors and diabetes control among overweight patients with type 2 diabetes mellitus: a 1-year prospective randomized intervention study [randomized trial; moderate evidence] ↩
BMJ Open 2015: A journey into a Mediterranean diet and type 2 diabetes: a systematic review with meta-analyses [strong evidence] ↩
In this study, researchers tracked signs of carotid atherosclerosis (fatty deposits in the carotid arteries) over two years in participants who ate either a Mediterranean diet, a low carb diet, or a low fat diet. By the end of the trial, there was significant regression of measurable carotid artery wall volume in all three diet groups, implying a reduction of atherosclerosis. According to the researchers, the improvement was likely due to loss of weight and reduced blood pressure resulting from the dietary changes:
Circulation 2010: Dietary intervention to reverse carotid atherosclerosis [randomized trial; moderate evidence]
However, another team of researchers who conducted a recent systematic review of 30 RCTs concluded that it is still unclear whether eating a Mediterranean diet helps prevent heart disease:
Cochrane Database of Systematic Reviews 2019: Mediterranean-style diet for the primary and secondary prevention of cardiovascular disease [strong evidence] ↩
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Nutrition Journal 2019: Influence of Paleolithic diet on anthropometric markers in chronic diseases: systematic review and meta-analysis [strong evidence] ↩
Diabetes Metabolism Research and Reviews 2017: Benefits of a Paleolithic diet with and without supervised exercise on fat mass, insulin sensitivity, and glycemic control: a randomized controlled trial in individuals with type 2 diabetes [moderate evidence] ↩
In a randomized trial of 70 postmenopausal women lasting two years, women who ate a non-calorie-restricted paleo diet lost significantly more body fat than women who ate a diet based on Nordic Nations dietary recommendations after six months. However, after two years, changes in fat loss between the two groups were less dramatic: The paleo group lost 10 pounds (4.6 kilos) of fat, and the control group lost 6.5 pounds (2.9 kilos) of fat:
European Journal of Clinical Nutrition 2014: Long-term effects of a Palaeolithic-type diet in obese postmenopausal women: a 2-year randomized trial [moderate evidence]
In a small trial, people with type 2 diabetes who ate a Paleo diet lost about 5 pounds (2.3 kilos) in two weeks:
European Journal of Clinical Nutrition 2015: Metabolic and physiologic effects from consuming a hunter-gatherer (Paleolithic)-type diet in type 2 diabetes [moderate evidence] ↩
European Journal of Clinical Nutrition 2014: Long-term effects of a Palaeolithic-type diet in obese postmenopausal women: a 2-year randomized trial [moderate evidence]
European Journal of Clinical Nutrition 2015: Metabolic and physiologic effects from consuming a hunter-gatherer (Paleolithic)-type diet in type 2 diabetes [moderate evidence] ↩
In a pilot study, people who consumed a paleo diet were found to be at higher risk of inadequate calcium intake because of the lack of dairy products in their diet:
European Journal of Clinical Nutrition 2008: Effects of a short-term intervention with a paleolithic diet in healthy volunteers [non-controlled study; weak evidence] ↩
In the two-year trial of menopausal women, some participants developed iodine deficiency:
European Journal of Clinical Nutrition 2018: A Paleolithic-type diet results in iodine deficiency: a 2-year randomized trial in postmenopausal obese women [moderate evidence] ↩
In a systematic review of RCTs comparing a low fat vegan diet to an omnivore diet, vegan diets resulted in greater or equal weight loss, although results varied due to different dietary protocols in the trials:
Diabetes, Metabolic Syndrome and Obesity 2020: Effects of plant-based diets on weight status: A systematic review [strong evidence]
In one study, overweight postmenopausal women who followed a vegan diet for two years lost an average of 11 pounds (4.9 kilos) in the first year, while those who followed dietary recommendations from the National Cholesterol Education Program (NCEP) lost 4 pounds (1.8 kilos). However, the women in the vegan group regained some weight during the second year, completing the trial at 7 pounds (3.2 kilos) less than their baseline weight, compared to 2 pounds (0.8 kilos) less in those who followed NCEP guidelines:
Obesity (Silver Spring) 2007: A two-year randomized weight loss trial comparing a vegan diet to a more moderate low fat diet [randomized trial; moderate evidence]
In another trial, adults with type 2 diabetes followed either a non-calorie-restricted low fat vegan diet or a calorie-restricted diet based on conventional American Diabetes Association (ADA) guidelines for 74 weeks. By the end of the trial, those in the vegan group had lost 10 pounds (4.4 kilos), compared to 7 pounds (3 kilos) in the ADA diet group. The vegan group also achieved slightly greater reductions in HbA1c (about 0.2% more) and LDL cholesterol levels than the other group:
The American Journal of Clinical Nutrition 2009: A low fat vegan diet and a conventional diabetes diet in the treatment of type 2 diabetes: a randomized, controlled, 74-wk clinical trial [randomized trial; moderate evidence]
In a 14-week trial, overweight postmenopausal women who ate a non-calorie-restricted vegan diet lost 13 pounds (5.8 kilos), whereas the group who followed a non-calorie-restricted diet based on National Cholesterol Education Program guidelines lost 8 pounds (3.8 kilos). The women in the vegan diet group also experienced a slightly greater increase in insulin sensitivity compared to the control group:
The American Journal of Medicine 2005: The effects of a low fat, plant-based dietary intervention on body weight, metabolism, and insulin sensitivity [randomized trial; moderate evidence] ↩
For instance, in a 22-week trial, people with type 2 diabetes who followed a non-calorie-restricted vegan diet lost 14 pounds (6.5 kilos) — more than twice as much as those who followed a calorie-restricted diet based on American Diabetes Association guidelines:
Diabetes Care 2006: A low fat vegan diet improves glycemic control and cardiovascular risk factors in a randomized clinical trial in individuals with type 2 diabetes [randomized trial; moderate evidence] ↩
JAMA Network Open 2020: Effect of a low fat vegan diet on body weight, insulin sensitivity, postprandial metabolism, and intramyocellular and hepatocellular lipid levels in overweight adults: a randomized clinical trial [randomized trial; moderate evidence] ↩
At six months, the vegan group had lost an average of 7.5% of their body weight, compared to 3.1% to 3.2% in the other vegetarian groups:
Nutrition 2015: Comparative effectiveness of plant-based diets for weight loss: a randomized controlled trial of five different diets [randomized trial; moderate evidence] ↩
In a two-part trial, 47 overweight people with high cholesterol levels were randomly assigned to follow either a calorie-restricted lower carb vegan diet or a calorie-restricted higher carb vegetarian diet that included eggs and dairy.
Although weight loss was similar in both groups, the low carb vegan group had greater reductions in markers of heart disease risk. Additionally, people in the lower carb vegan group seemed happier with their diet:
Archives of Internal Medicine 2009: The effect of a plant-based low carbohydrate (“Eco-Atkins”) diet on body weight and blood lipid concentrations in hyperlipidemic subjects [randomized trial; moderate evidence]
For the second part of the study, each group was allowed to eat as much of the permitted foods as they wanted. At the end of six months, the lower carb vegan group lost slightly more weight, raised their HDL cholesterol levels, and lowered their LDL cholesterol and triglyceride levels more than the other group:
BMJ Open 2014: Effect of a 6-month vegan low carbohydrate (‘Eco-Atkins’) diet on cardiovascular risk factors and body weight in hyperlipidaemic adults: a randomised controlled trial [moderate evidence] ↩
A 2020 systematic review of RCTs found that in five out of nine studies, a vegan diet significantly improved markers of blood glucose control, whereas in the other four it did not improve glycemic control significantly:
Diabetes, Metabolic Syndrome and Obesity 2020: Effects of plant-based diets on outcomes related to glucose metabolism: A systematic review [strong evidence]
In a study comparing a vegan diet to an American Diabetes Association (ADA) diet in people with type 2 diabetes, the vegan group lost twice as much weight and reduced their LDL cholesterol levels twice as much as the other group, in addition to reducing their HbA1c by 1%:
Diabetes Care 2006: A low fat vegan diet improves glycemic control and cardiovascular risk factors in a randomized clinical trial in individuals with type 2 diabetes [randomized trial; moderate evidence]
However, in another trial testing a vegan diet against an ADA diet in people with type 2 diabetes, the vegan diet did not lead to significant changes in HbA1c or other measures of blood sugar control:
Journal of Nutrition 2011: Decreases in dietary glycemic index are related to weight loss among individuals following therapeutic diets for type 2 diabetes [randomized trial; moderate evidence]
A 2018 trial tested a vegan diet against a diet recommended by the American Heart Association for reducing c-reactive protein (CRP), a marker of inflammation linked to increased heart disease risk. The vegan group experienced a significantly greater reduction in hs-CRP and slightly better reduction in LDL cholesterol levels compared to the AHA diet:
Journal of the American Heart Association 2018: Anti-inflammatory effects of a vegan diet versus the american heart association-recommended diet in coronary artery disease trial [randomized trial; moderate evidence] ↩
Journal of the International Society of Sports Nutrition 2017: Vegan diets: practical advice for athletes and exercisers [overview article; ungraded]
Nutrients: Comparison of nutritional quality of the vegan, vegetarian, semi-vegetarian, pesco-vegetarian and omnivorous diet [review article; ungraded]
American Journal of Clinical Nutrition: Health effects of vegan diets [review article; ungraded] ↩
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Journal of General Internal Medicine 2016: Vegetarian diets and weight reduction: a meta-analysis of randomized controlled trials [strong evidence]
Journal of the Academy of Nutrition and Dietetics 2015: A systematic review and meta-analysis of changes in body weight in clinical trials of vegetarian diets [strong evidence] ↩
Journal of General Internal Medicine 2016: Vegetarian diets and weight reduction: a meta-analysis of randomized controlled trials [strong evidence] ↩
Circulation 2018: Low-calorie vegetarian versus Mediterranean diets for reducing body weight and improving cardiovascular risk profile: CARDIVEG study (Cardiovascular Prevention With Vegetarian Diet) [randomized crossover trial; moderate evidence] ↩
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Journal of the American Medical Association 2020: The DASH diet, 20 years later [review article; ungraded] ↩
Overall people lost an average of 3 pounds (1.4 kilos) more on a DASH diet compared to their usual diets or control diets with similar levels of calorie restriction:
Obesity Reviews 2016: The effect of dietary approaches to stop hypertension (DASH) diet on weight and body composition in adults: a systematic review and meta-analysis of randomized controlled clinical trials [strong evidence] ↩
Liver International 2016: The effects of DASH diet on weight loss and metabolic status in adults with non-alcoholic fatty liver disease: a randomized clinical trial [randomized controlled trial; moderate evidence] ↩
Liver International 2016: The effects of DASH diet on weight loss and metabolic status in adults with non-alcoholic fatty liver disease: a randomized clinical trial [randomized controlled trial; moderate evidence] ↩
On average, blood pressure dropped by 3/2 mm Hg. This was statistically significant, but many question if it is clinically significant ↩
Advances in Nutrition 2020: Dietary Approaches to Stop Hypertension (DASH) diet and blood pressure reduction in adults with and without hypertension: A systematic review and meta-analysis of randomized controlled trials [strong evidence] ↩
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In August of 2019, WW launched Kurbo, a nutrition and weight loss app for children and teens, which we at Diet Doctor do not condone. ↩
The WW program also provides group support via weekly meetings. In studies, participants who attend these meetings in addition to following the WW points system tend to lose more weight than those who don’t attend meetings regularly:
Obesity 2013: Combining behavioral weight loss treatment and a commercial program: a randomized clinical trial [randomized controlled trial; moderate evidence]
The American Journal of Medicine 2013: A randomized controlled trial of a community-based behavioral counseling program [randomized controlled trial; moderate evidence] ↩
The American Journal of Public Health 2016: Comparison of commercial and self-initiated weight loss programs in people with prediabetes: A randomized control trial [randomized controlled trial; moderate evidence] ↩
Although average weight loss was similar in both groups after 12 months, twice as many people who joined the WW program lost more than 5% of their body weight:
Obesity (Silver Spring) 2017: Weight loss in Weight Watchers Online with and without an activity tracking device compared to control: A randomized trial [randomized controlled trial; moderate evidence] ↩
Journal of the American Medical Association 2005: Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial [randomized controlled trial; moderate evidence] ↩
The American Journal of Public Health 2016: Comparison of commercial and self-initiated weight loss programs in people with prediabetes: A randomized control trial [randomized controlled trial; moderate evidence] ↩
Journal of the American Medical Association 2005: Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial [randomized controlled trial; moderate evidence] ↩
European Journal of Clinical Investigation 2005: Blood profiles, body fat and mood state in healthy subjects on different diets supplemented with Omega-3 polyunsaturated fatty acids [moderate evidence] ↩
Diabetalogia 2005: Comparison of high fat and high protein diets with a high carbohydrate diet in insulin-resistant obese women [moderate evidence] ↩
Journal of the American Medical Association 2007: Comparison of the Atkins, Zone, Ornish and LEARN diets for change in weight and related risk factors among overweight premenopausal women. The A to Z weight loss study: a randomized trial [randomized controlled trial; moderate evidence]
In a previous A to Z trial, overweight adults assigned to the Atkins, Ornish, Weight Watchers, or Zone diet lost similar amounts of weight and had similar improvements in heart disease risk markers:
Journal of the American Medical Association 2005: Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial [randomized controlled trial; moderate evidence] ↩
Diabetalogia 2005: Comparison of high fat and high protein diets with a high carbohydrate diet in insulin-resistant obese women [moderate evidence]
And in the 2005 A to Z trial previously discussed, participants in the Zone group experienced slight reductions in LDL cholesterol levels, similar to those in the Atkins, Ornish, and Weight Watchers groups:
Journal of the American Medical Association 2005: Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial [randomized controlled trial; moderate evidence] ↩
Diet Doctor will not benefit from your purchases. We do not show ads, use any affiliate links, sell products or take money from industry. Instead we’re funded by the people, via our optional membership. Learn more ↩
Journal of the American College of Nutrition 2004: The effects of high protein diets on thermogenesis, satiety and weight loss: a critical review [systematic review of randomized trials; strong evidence]
Nutrition Reviews 2016: Effects of dietary protein intake on body composition changes after weight loss in older adults: a systematic review and meta-analysis [systematic review of randomized trials; strong evidence]
The American Journal of Clinical Nutrition 2012: Effects of energy-restricted high protein, low fat compared with standard protein, low fat diets: a meta-analysis of randomized controlled trials [systematic review of randomized trials; strong evidence] ↩