Top 17 low carb & keto controversies
, medical review by Dr. Bret Scher, MD
, Dr. Michael Tamber, MD
Evidence basedHowever, our goal of making low carb simple also requires us to be upfront and honest about potential problems and how to handle them; some adverse effects can and do occur on low carb.
Here are the most common controversies about low carb and what the best available scientific evidence can tell us about them.
1. Will saturated fat clog my arteries and give me a heart attack?
No. This is probably one of the biggest nutrition myths of the last few decades.2
First of all, the mechanisms by which we develop heart disease are not analogous to the way a sink develops a clog. There are many potential contributing factors to the development of heart disease, including genetics, inflammation, and metabolic health conditions, such as diabetes.3 Further, the interaction of diet with these other variables can vary greatly from one individual to another.
In terms of scientific evidence, links between saturated fat and heart disease are weak and inconsistent. Although some reviews of the literature do find a weak relationship, an increasing number of meta-analyses and systematic reviews find that there is no significant connection between saturated fat and heart disease.45 The weakness of the evidence against saturated fat is catching on in the mainstream media as well.6
Because the evidence is so weak and because the individual response to dietary fats varies significantly, population-wide recommendations to avoid saturated fat may have been a mistake.
Watch doctors explain why saturated fat is neutral
2. Does a low-carb diet cause high cholesterol?
Low-carb diets tend to improve the cholesterol profile by increasing levels of HDL (“good”) cholesterol and decreasing levels of potentially harmful triglycerides.7 They may also improve the size profile of the LDL particles.8
These beneficial changes in the lipid profile are also associated with decreased insulin resistance, suggesting that overall health is likely improved.
Regarding LDL (“bad”) cholesterol, most people experience no significant changes on low carb.9
However, in some people, LDL levels decrease or (more often) increase somewhat.10
A minority of people will see their LDL cholesterol increase dramatically on a low-carb, high-fat diet.11 In this situation, it may be worth adapting the diet to lower LDL. Depending on your overall risk profile, you may want to work closely with your doctor to monitor for any evidence of cardiovascular disease.
To learn more about how to evaluate rising LDL on a low-carb diet, see our dedicated educational guides:
LDL low carb hyper-responders
Is elevated LDL harmful?
How to lower LDL on a low carb diet
The bottom line: Low-carb, high-fat diets generally improve the lipid profile and reduce most risk factors for heart disease.12 This effect is emphasized by a 2010 study that showed a reduction in atherosclerosis after two years on a low-carb, high-fat diet.13
Low carb and cholesterol – the full guide
3. Doesn’t the brain need dietary carbs?
No. On a strict low-carb diet the brain can be primarily fueled by fat — or technically, by ketones. When carb intake is very low, your liver converts body fat or fat from the food you’ve eaten into ketones, which can be used by the brain as fuel.14
Furthermore, your body can produce any glucose it needs through a process called gluconeogenesis, converting other nutrients to glucose – even if you don’t eat any carbs at all.15
There is no need for carbohydrates in the diet; the brain functions fine without them.
Learn more in our full guide:
Food for thought: Does the brain need carbs?
Learn more about ketones and ketosis4. Is low carb bad for the environment?
This question needs to address the following:
1- Does eating low carb mean you have to eat more meat?
2- Is meat by definition bad for the environment?
It’s a common misunderstanding that a low-carb diet requires eating a lot of meat. This is simply not true.
A low-carb diet is just that — low carb. You can otherwise eat however you want, be it vegan, vegetarian, carnivore, or anything in between.
The amount of protein usually stays moderate — about 1.2 to 2.0 grams per kilo per day.16 This amount of protein may be more than many people are eating, but it doesn’t have to come from meat. It’s very possible to eat a vegetarian or vegan low-carb diet, should you want to.
Furthermore, the impact of meat production on the environment depends on many factors. Do you buy locally raised, grass fed or pasture raised meat or poultry? If so, these can be raised in a manner that is environmentally friendly! They may potentially reduce the pesticide burden and nutrient depletion of soils, as well as allowing for more carbon dioxide to be stored in the ground.17
However, if most of your meat comes from industrial meat production sites, also known as CAFOs, then there may be a significant contribution to greenhouse gasses.18
Finally, a low-carb diet often results in people eating less food, because it’s so satiating.19 After significant weight loss, people need even less food. Needing less food, and needing to eat less often, is of course good for the environment.
Bottom line: A low-carb diet doesn’t require you to eat more meat. If you choose to eat more meat, you can search for meat from regenerative ranchers, which may provide a net benefit to the environment. Eating meat from CAFOs will likely contribute to increased greenhouse gasses.
Six ways to stay environmentally friendly on a low-carb or keto diet
Diet Doctor Podcast with Professor Frank Mitloehner and another with Diana Rodgers.
TED / Allan Savory: How to fight desertification and reverse climate change
Watch one of the smartest men in the world explain the real problem for the environment (Hint: it’s fossil fuels)
5. Can you get nutrient deficiencies on low carb?
Probably the opposite is more often true. The foods consumed on a low-carb diet are highly nutritious.20 For example, eggs (a staple for many people on low carb) may provide the most complete nutrition of any food on the planet.21
Consider that a complete chicken can be formed from the nutrients inside the egg. There’s no way for the chicken to pop out and get some vitamins and minerals while growing in the egg; everything has to be there. And by eating an egg, we humans get all those nutrients.
Meat, fish, and vegetables are also highly nutritious foods. And many people eating low carb tend to replace nutrient-poor pasta, rice, and potatoes with more nutrient-rich vegetables.
Studies show that a low-carb diet can be nutritionally complete.22
Compared to the more complete nutrition of a low-carb diet, refined flour is more or less devoid of any nutrition apart from pure starch. Usually, it’s legally required to add vitamins to flour, so that people who eat a lot of it do not get vitamin deficiencies.
Also, grains like wheat are high in phytic acid that can potentially reduce the absorption of many minerals.23
Another concern with low-carb diets is the lack of fruit, often thought to be necessary for proper nutrition. This is a misunderstanding. Apart from vitamin C, there are very few nutrients in most modern fruit.24 These days, they are modified to be large and very sweet. We think of fruit as candy from nature, which should probably be eaten in moderation. Fruit juice is even worse, given the concentrated sugar and lack of fiber to help slow the absorption.25
Modern fast food and snack food also contain a lot of calories and minimal if any nutrition.26 And low-fat products are low in essential fat-soluble vitamins, which are found in full-fat versions of yogurt, cheese, and other whole foods.
Bottom line: Switching from a standard Western diet to a low-carb diet based on real foods is likely to significantly increase the amount of vitamins and minerals you get from your diet.
6. Can low carb damage your thyroid?
Not likely. If you eat a well-formulated low-carb diet, it’s very unlikely it will affect your thyroid negatively.27
Although some studies of low-carb, high-fat diets have shown a decrease in the active thyroid hormone T3, it seems unlikely that this represents a clinical problem.28 For instance, some hypothesize that our bodies become more sensitive to thyroid hormone and therefore have a different “normal” range. Others suggest fat is more metabolically efficient, and therefore less thyroid hormone is required to metabolize it.29 While these are just hypotheses at this point, they highlight how a change in a single lab value does not automatically signify a problem or deleterious change.
In fact, some people who lose significant amounts of weight on low carb may end up needing less thyroid medication, and a few individuals may even be able to stop taking it completely.30 This may just be an effect of a smaller body needing less thyroid hormone – there isn’t any research showing that carbohydrate reduction itself can improve thyroid function.
This means that if you have hypothyroidism and supplement with thyroid hormone, you can start a low-carb diet like anybody else and continue to do regular checkups per usual. If you lose a lot of weight, it may be wise to do an extra check of your thyroid blood tests once in a while, e.g. every time you’ve lost 30 pounds (15 kilos). It’s not impossible that your dose may need to be adjusted.
Bottom line: Eating a healthy, low-carb diet should not negatively affect your thyroid.
7. Can low carb damage your kidneys?
Highly unlikely.31 Many people still believe that a low-carb diet or even a high-protein diet could put a strain on the kidneys. This is a myth based on two misunderstandings.
First, a well-formulated low-carb diet is moderate in protein — around 1.5 grams per kilo per day.32
As a low-carb diet doesn’t need to be very high in protein — for example, 3 grams per kilo per day — the whole “problem” behind this controversy simply does not exist.
Secondly, people with normal kidney function can handle high amounts of protein without any problem for the kidneys.33
Even if people choose to eat excessive protein, this will only be a problem if the kidneys are already severely damaged. An example of this would be end-stage kidney disease that is close to requiring dialysis. If you have severe kidney disease and you’ve been told to limit protein, you should of course do so.34 But you might still be able to successfully eat a low-carb, high-fat diet.
To summarize: For people without kidney disease, there’s no reason to worry about the effect of excessive protein on your kidney health.
Bottom line: A low-carb diet is fine for your kidneys.
In fact, by lowering elevated blood sugars in people with diabetes, a low-carb diet may actually protect the kidneys from one of the most common causes of damage.35
What you need to know about a low-carb diet and your kidneys
Watch doctors explain how low carb affects your kidneys How to reverse your type 2 diabetes8. Can low carb make you depressed?
Not likely. But during the first week or two of a low-carb diet, it’s common to experience symptoms similar to those of depression (such as lethargy, tiredness, irritability, brain fog).36
These problems usually disappear within a few days to a couple of weeks. They can often be avoided or mitigated by getting enough fluid and salt – for example a cup of bouillon 1-2 times a day.
Long term, a low-carb diet often has the opposite effect. Getting into ketosis can make some people feel very energetic and might increase mental performance and endurance.37 People sometimes mention the “mental clarity” they feel.
Studies of the mental state on low-carb diets generally show either no clear change or a slight improvement, compared to before starting the diet.38
If someone does feel depressed, however, it could be related to having what resembles an addiction to reward from high-carb, sweet foods.39 Eliminating these high-reward foods may result in temporary feelings of loss and sadness, similar to symptoms of depression. It may be analogous to the effect of withdrawing from nicotine or alcohol when addicted to these substances.
Fortunately, after early withdrawal symptoms have passed, getting free of an addiction is incredibly liberating and enables people to lead fuller and happier lives.40 So it can definitely be worth the struggle.
Finally, to make a low-carb diet feel great long term requires tasty food and a simple and enjoyable lifestyle. Feel free to use our resources to speed up the process.
9. Is low carb bad for exercise?
Low carb can be good, bad, neutral or even fantastic for exercise. It depends.
During the first couple of weeks when you’re switching from a diet rich in carbs to a low-carb diet, your capacity in the gym will most likely go down.41 This is due to the low-carb flu and not being fully fat-adapted, but it will likely improve within several weeks.42
After a few weeks of adaptation, people often report feeling at least as good as before when exercising, especially if they make sure to get enough fluids and salt.43
Furthermore, for endurance athletes, there are many potential benefits to being fat-adapted and eating LCHF.44 For example, Chris Froome won Tour de France multiple times after adopting a low-carb diet.
But the findings are not universal. Two studies out of Australia report that race-walk times decreased after 12 weeks of eating a keto diet, despite improved fat oxidation.45
When it comes to powerlifting and weightlifting, low-carb diets have demonstrated benefit.46 Additionally, following a ketogenic diet might improve body composition when combined with resistance training.47
However, more carbs may be needed for non-endurance sports such as sprinting, etc.48 In these cases, it might be a good idea to take in some more carbs on the day you need to perform.
The bottom line is that scientific evidence is mixed on how ketosis affects athletic performance. Individual variability, different effects for different types of exercise, and the importance of fat-adaptation all need to be taken into consideration.
Watch doctors explain how low carb can be good for exercise
Learn more about how to increase physical performance on low carb
10. Is low carb bad for your gut bacteria?
Probably not. There is currently a lot of research being conducted about gut bacteria and the microbiome.49 The main problem with much of the reporting on gut bacteria and diet is the confusion of statistical correlations with causality, i.e. taking weak clues and mistakenly calling them proof.50
Not much can be said about the health effects of changes to the microbiome on a low-carb diet — only that it changes.51 However, many people report that they have less gastrointestinal distress and bloating after starting a low-carb diet.
Watch a presentation on the possible benefits of slow carbs to feed the microbiome
11. Can you get constipated on low carb?
Yes. Constipation is a possible side effect that can occur, especially during the first time on a low-carb diet, as your digestive system may need time to adapt.52
It can usually be alleviated by either drinking more water and increasing salt intake, taking in more fiber or, if necessary, adding Milk of Magnesia.53
Note that just because some people have a bowel movement less often does not mean they are constipated. Many people report decreased stool frequency on low carb, but as long as they don’t feel bloated or have abdominal pain, it isn’t a concern.54
It’s important to note that, if you do suffer from constipation when starting low carb, it will usually be temporary.
Learn more about preventing or curing constipation on low carb
12. Can you get osteoporosis on low carb?
No. There is a lingering idea that eating a diet low in carbohydrates and rich in protein could result in osteoporosis, due to making the blood “acidic” and leaching minerals from the bones. But this theory has been disproven in several ways.
For example, under normal circumstances the pH of the blood does not change depending on what you eat.55 Blood pH is tightly controlled within a very narrow range – if it wasn’t, we would die.
Further, the theory that more dietary protein leads to weaker bones has been discredited by clinical trials – people who eat more protein actually tend to have stronger bones.56 Looking at all available science, higher protein intake hasn’t been shown to harm bone health, and it may even help protect against bone loss in the lower spine.57
Finally, repeated studies show no effect on bone density in people eating low carb, even after several years.58
Read our complete guide on bone health and low-carb diets.
13. Does low carb cause hair loss?
Occasionally. Temporary hair thinning can occur for many different reasons, including any big dietary change.59 This is especially common when severely restricting calories (e.g. starvation diets, meal replacements) but it can also occasionally happen on a low-carb diet.60
After a period of losing more hair than usual, the lost hairs then grow out again, so that the hair ends up as thick as before.
It’s safe to say that the large majority of people who try a low-carb diet never experience this. Furthermore, it’s likely possible to minimize the risk by not doing a low-carb and low-fat diet at the same time, i.e. by avoiding starvation. Make sure to eat enough fat to feel satisfied and a moderate amount of protein.61 Learn more about low carb & temporary hair loss
14. Does low carb cause ketoacidosis?
No. Many people mix up ketoacidosis with ketosis.
Ketoacidosis (also known as diabetic ketoacidosis, or DKA) is a rare and dangerous medical condition that mainly occurs in people with type 1 diabetes if they don’t take enough insulin, especially when they are ill.
People with type 2 diabetes who take certain medications (e.g. SGLT-2 inhibitors) can also develop DKA, although this is relatively rare.62 However, eating a ketogenic diet while taking these medications might potentially increase the risk of DKA.63
Also, in rare cases, women eating a very low-carb diet can develop ketoacidosis while breastfeeding.64
Ketosis (sometimes referred to as nutritional ketosis), on the other hand, is a 100% natural and safe state for most people.65
Nutritional ketosis can be achieved by eating a low-carb diet or by a brief period of fasting.66
Being in ketosis usually means that the body is efficiently metabolizing and burning fat, which can be good for weight loss.67
15. Do you get a shortage of whole grains on low carb?
Do you need to eat whole grains – like bread or pasta – to stay healthy? While the fiber in whole grains may slow down the absorption of glucose and lower the glycemic index of food (possibly a good thing), it’s less clear what the benefit is on a low-carb diet.68 There’s likely much less benefit of slowing down the absorption of carbs if you don’t eat many carbs.
Furthermore, there is no high-quality science proving a need to eat whole grains to prevent disease or prolong life. A Cochrane review of high-quality nutrition science found no evidence for that idea.69
There’s a widely-held belief that people need to eat grains to get specific nutrients. However, other foods that are lower in carbs are often more nutritious.
Finally, there’s an idea that the microbiome in our guts may benefit from the fiber in whole grains. This is still a controversial topic with a lack of high-quality science. However, there are many other sources of fiber that are far lower in carbs than whole grains.
16. Is salt dangerous for your health?
A low-carb diet is not necessarily higher in salt than other diets. But it’s often recommended to increase salt intake when starting, to reduce the risk of side effects. Many people are concerned about increasing their salt intake — even temporarily — because of longstanding dogma that salt is dangerous.
It turns out that the evidence behind this common piece of health advice is fairly weak. Read more in our comprehensive guide to salt.
Also check out our news post detailing how salt restriction lacks credible evidence
17. Is red meat dangerous?
A low-carb diet is not necessarily higher in red meat than other diets. It’s even possible to eat a vegetarian low-carb diet. However, many people eat a low-carb diet with red meat. Here’s our guide to what the scientific evidence tells us about it:
Low-carb side effects & how to cure them
Common early problems
Induction flu 
Leg cramps 
Heart palpitations 
Bad breath Later potential issues
Potential danger when breastfeeding 
Gallstones 
Lowered tolerance to alcohol 
Keto rash Main guides
Practical low-carb guides
Dining out 
How to eat more fat 
Low-carb cheating 
No cooking 
Breakfasts 
Meals 
Bread 
Snacks and desserts 
Instead of potatoes, pasta, rice 
Traveling 
Low carb for kids 
Questions & answers 
Cheap low carb 
Low-carb living in a high-carb world
Visual guides
Vegetables 
Fruits 
Nuts 
Low-carb snacks 
Low-carb alcohol
Top 17 low carb & keto controversies - the evidence
This guide is written by Dr. Andreas Eenfeldt, MD and was last updated on June 17, 2022. It was medically reviewed by Dr. Bret Scher, MD on March 4, 2021 and Dr. Michael Tamber, MD on February 28, 2022.
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.
This advice coincided with — and may have contributed to — the obesity epidemic.
Nutrition 2015: Statistical review of US macronutrient consumption data, 1965-2011: Americans have been following dietary guidelines, coincident with the rise in obesity [overview article; ungraded]
Some argue that very few individuals actually adhered to the dietary recommendations, and therefore we cannot blame the guidelines for the rise in obesity and metabolic disease. However, it does seem clear that the advice to lower fat — at a minimum — led to increased carb consumption. At Diet Doctor, we believe that this has contributed to an overall decline in health.
↩Current Nutrition Reports 2018: Saturated fat: part of a healthy diet [overview article; ungraded] ↩
Journal of Natural Science 2017: Linking chronic inflammation with cardiovascular disease: From normal aging to the metabolic syndrome. [overview article; ungraded]
Frontiers of Endocrinology 2018: Type 2 diabetes mellitus and cardiovascular disease: Genetic and epigenetic links.
[overview article; ungraded]The following observational study reported a much greater risk of developing heart disease for those with metabolic disease, such as diabetes or insulin resistance, as compared to those with elevated LDL cholesterol. You can read our review of the study here.
JAMA Cardiology 2021: Association of Lipid, Inflammatory, and Metabolic Biomarkers With Age at Onset for Incident Coronary Heart Disease in Women [observational study with HR>2, weak evidence]
↩Here are four meta-analyses showing no connection between saturated fats and heart disease:
- Open Heart 2016: Evidence from randomised controlled trials does not support current dietary fat guidelines: a systematic review and meta-analysis [strong evidence]
- Nutrition Journal 2017: The effect of replacing saturated fat with mostly n-6 polyunsaturated fat on coronary heart disease: a meta-analysis of randomised controlled trials [strong evidence]
- Annals of Internal Medicine 2014: Association of dietary, circulating, and supplement fatty acids with coronary risk: a systematic review and meta-analysis [meta-analysis of observational studies and RCTs; moderate evidence]
- PLOS ONE 2016: Is butter back? A systematic review and meta-analysis of butter consumption and risk of cardiovascular disease, diabetes, and total mortality [meta-analysis of observational studies; very weak evidence]
When looking at RCTs, this review found no relationship between saturated fat and heart disease, though it did find a relationship when looking at observational studies.
Annals of Internal Medicine 2009: Dietary fat and coronary heart disease: Summary of evidence from prospective cohort and randomized controlled trials [moderate evidence]
A 2020 Cochrane review of RCTs showed a modest reduction in cardiovascular events for lower saturated fat intake. But it found no benefit to lowering saturated fat intake for heart attack, stroke, cardiovascular death, or all-cause death.
Cochrane Database of Systemic Reviews 2020: Reduction in saturated fat intake for cardiovascular disease [systematic review of randomized trials; strong evidence]
Beyond studies looking at saturated fat as a macronutrient, studies examining specific natural foods have not convincingly proven that they cause heart disease. For example, red meat, butter, and coconut oil have not been proven to increase heart disease risk.
While many nutritional epidemiology studies have suggested a link between red meat and heart disease, meta-analyses of randomized controlled trials have not found a cause/effect relationship:
Annals of Internal Medicine 2019: Effect of lower versus higher red meat intake on cardiometabolic and cancer outcomes: a systematic review of randomized trials. [strong evidence]
American Journal of Clinical Nutrition 2017: Total red meat intake of ≥0.5 servings/d does not negatively influence cardiovascular disease risk factors: a systemically searched meta-analysis of randomized controlled trials [strong evidence]
PloS One 2016: Is butter back? A systematic review and meta-analysis of butter consumption and risk of cardiovascular disease, diabetes, and total mortality [systematic review of nutritional epidemiology studies; very weak evidence]
Indian Heart Journal 2016: A randomized study of coconut oil versus sunflower oil on cardiovascular risk factors in patients with stable coronary heart disease [moderate evidence]
Dairy fat, including yogurt and cheese, has been shown to be protective against heart disease in observational studies.
Advances in Nutrition 2019: Effects of full-fat and fermented dairy products on cardiometabolic disease: Food is more than the sum of its parts [nutritional epidemiology study; very weak evidence]
As leading scientists claimed in their 2020 review paper, we should discuss the health implications of specific foods, rather than lumping them all together as “saturated fats.”
Journal of the American College of Cardiology 2020: Saturated fats and health: A reassessment and proposal for food-based recommendations: JACC State-of -the-Art Review [overview article; ungraded] ↩
Here are a few examples.
TIME: Eat butter. Scientists labeled fat the enemy. Why they were wrong.
Nutrition Reviews 2018: Effects of carbohydrate-restricted diets on low-density lipoprotein cholesterol levels in overweight and obese adults: a systematic review and meta-analysis [meta-analysis of randomized controlled trials; strong evidence]
Annals of Internal Medicine 2010: Weight and metabolic outcomes after 2 years on a low-carbohydrate versus low-fat diet: a randomized trial [moderate evidence]
↩Small, dense LDL particles are thought to be more tightly linked with risk of heart disease, as opposed to larger, less dense LDL particles.
Lipids 2009: Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat diet [randomized controlled trial; moderate evidence]
A nonrandomized trial showed that a ketogenic diet reduced the percentage of small LDL and increased large LDL. This trial also showed no significant increase in plaque buildup in the carotid artery at two years, even in those who demonstrated the largest overall increases in LDL cholesterol.
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]
↩A meta-analysis showed no significant change on average.
Nutrition Reviews 2019: 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]
Another study in people with type 2 diabetes found that LDL cholesterol increased by roughly 10%, on average, after one year on a very-low-carb diet. Most of that increase was attributable to an increase in the large LDL subfraction, thought to be less tightly linked to heart disease risk, as compared to the small LDL subfraction.
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] ↩
This can vary quite a bit from person to person. For instance, in a 3-week study of healthy people who followed a low-carb diet, LDL cholesterol levels increased by as little as 5% in some and as much as 107% in others.
Atherosclerosis 2018: Effect of low carbohydrate high fat diet on LDL cholesterol and gene expression in normal-weight, young adults: A randomized controlled study [moderate evidence]
↩These individuals are often referred to as “hyper-responders.” Read more about LDL hyper-responders. ↩
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 for improved risk factors]
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]
Progress in Lipid Research 2008: Dietary carbohydrate restriction induces a unique metabolic state positively affecting atherogenic dyslipidemia, fatty acid partitioning, and metabolic syndrome [overview article; ungraded]
Learn more about this and other studies on low carb and risk factors ↩
All three diets induced weight loss and resulted in signs of reduced atherosclerosis, compared to baseline.
The low-carb, high-fat diet – defying expectations – did not do worse. Instead the non-significant trend was towards a stronger positive effect on low carb:
Circulation 2010: Dietary intervention to reverse carotid atherosclerosis [randomized controlled trial; moderate evidence] ↩
Although the brain always requires some glucose, a significant portion of its energy needs can be met by ketones.
Critical Care 2011: Clinical review: ketones and brain injury [overview article; ungraded]
Journal of Cerebral Blood Flow & Metabolism 2017: Inverse relationship between brain glucose and ketone metabolism in adults during short-term moderate dietary ketosis: a dual tracer quantitative positron emission tomography study [non-randomized study; weak evidence]
↩American Journal of Clinical Nutrition 2009: Gluconeogenesis and energy expenditure after a high-protein, carbohydrate-free diet [randomized controlled trial; moderate evidence] ↩
In many LCHF studies showing health benefits, people are advised to eat a moderate amount of protein and as much fat as needed to feel satisfied.
Diabetes Therapy 2018: Effectiveness and safety of a novel care model for the management of type 2 diabetes at 1 year: an open-label, non-randomized, controlled study [weak evidence]
Applied Physiology, Nutrition and Metabolism 2017: A 12-week low-carbohydrate, high-fat diet improves metabolic health outcomes over a control diet in a randomised controlled trial with overweight defence force personnel [moderate evidence]
↩Environmental Health 2017: Human health implications of organic food and organic agriculture: a comprehensive review [overview article; ungraded]
Nature Communications 2015: Emerging land use practices rapidly increase soil organic matter [non-randomized study; weak evidence]
Agricultural Systems 2017: Impacts of soil carbon sequestration on life cycle greenhouse gas emissions in Midwestern USA beef finishing system [non-randomized study; weak evidence] ↩
There is disagreement about animal emissions compared to those from transportation, home energy, and industrial energy. But as discussed in a podcast with environmental scientist Frank Mitloehner, PhD, the greenhouse gas emissions from coal-burning far outweigh the emissions from cattle. ↩
Many studies have shown that when people eat low-carb, high-fat diets, their appetite decreases. As a result, they naturally end up eating less without consciously restricting how much they eat.
Obesity Reviews 2014: Do ketogenic diets really suppress appetite? A systematic review and meta-analysis [strong evidence]
↩These include natural fats, meat, poultry, seafood, eggs, vegetables and berries.
Nutrients 2015: Egg and egg-derived foods: effects on human health and use as functional foods [overview article] ↩
For example this one:
BMJ Open 2018: Assessing the nutrient intake of a low-carbohydrate, high-fat (LCHF) diet: a hypothetical case study design [very weak evidence] ↩
Phytic acid binds to important minerals like calcium, iron, potassium, and magnesium, which impairs your body’s ability to absorb and use them.
Journal of Zhejiang University. Science. B 2008: Phytate: impact on environment and human nutrition. A challenge for molecular breeding [overview article]
↩Here are the nutrition profiles for commonly consumed modern fruits. Fruits are also high in sugar, with the exception of avocados. ↩
Studies have shown that consuming fruit juice results in greater weight gain than consuming fresh fruit.
Obesity (Silver Spring) 2012: Beverage vs. solid fruits and vegetables: effects on energy intake and body weight [randomized controlled trial; moderate evidence]
The Lancet Diabetes and Endocrinology 2014: Fruit juice: just another sugary drink? [overview article; ungraded]
↩The Journal of Clinical Lipidology 2015: JCL roundtable: fast food and the American diet [overview article; ungraded] ↩
There aren’t any high-quality studies showing that a low-carb or ketogenic diet with adequate calories can cause hypothyroidism, a condition reflected by elevated levels of thyroid stimulating hormone (TSH) and low levels of T4 hormone.
In a study of overweight diabetic men without hypothyroidism who consumed less than 20 grams of carbs per day for 16 weeks, TSH levels remained the same or decreased slightly by the end of the study.
Nutrition & Metabolism 2005: A low-carbohydrate, ketogenic diet to treat type 2 diabetes [non-controlled study; weak evidence]
↩It’s important to note that TSH and T4 levels remain normal, and people with isolated decreases in T3 don’t actually appear to have signs or symptoms of hypothyroidism.
Metabolism 1980: The role of dietary fat in peripheral thyroid hormone metabolism [nonrandomized study with only 4 participants, weak evidence]
Clinical Endocrinology 2001: Isocaloric carbohydrate deprivation induces protein catabolism despite a low T3-syndrome in healthy men [nonrandomized study, weak evidence]
↩Anecdotal stories, i.e. very weak evidence. ↩
A 2018 review of 12 randomized controlled trials in people with type 2 diabetes concluded that low-carbohydrate diets do not jeopardize kidney function.
Diabetes Metabolism Research and Reviews 2018: Effect of low-carbohydrate diet on markers of renal function in patients with type 2 diabetes: a meta-analysis [strong evidence] ↩
Keeping protein intake moderate and eating enough fat for enjoyment are the hallmarks of a LCHF diet.
Diabetes Therapy 2018: Effectiveness and safety of a novel care model for the management of type 2 diabetes at 1 year: an open-label, non-randomized, controlled study [weak evidence]
Applied Physiology, Nutrition and Metabolism 2017: A 12-week low-carbohydrate, high-fat diet improves metabolic health outcomes over a control diet in a randomised controlled trial with overweight defence force personnel [moderate evidence]
↩Journal of Nutrition & Metabolism 2016: A high protein diet has no harmful effects: a one-year crossover study in resistance-trained males [randomized cross-over trial; moderate evidence]
Journal of Exercise Physiology 2018: Case reports on well-trained bodybuilders: two years on a high protein diet [very weak evidence]
Nutrition & Metabolism 2005: Dietary protein intake and renal function [overview article; ungraded] ↩
There’s some evidence that this can slow progression of the disease:
American Journal of Kidney Disease 1996: Effects of dietary protein restriction on the progression of advanced renal disease in the Modification of Diet in Renal Disease Study [secondary analysis of randomized controlled trial; weak evidence]
↩A 2018 comprehensive review of 12 RCTs found no evidence that low-carbohydrate diets are harmful for kidney health in people with type 2 diabetes.
Diabetes Metabolism Research and Reviews 2018: Effect of low-carbohydrate diet on markers of renal function in patients with type 2 diabetes: a meta-analysis [strong evidence]
Furthermore, clinicians have reported improvements in renal function in their diabetic patients who follow carb-restricted diets, as documented in this case report:
Nutrition & Metabolism 2006: A low-carbohydrate diet may prevent end-stage renal failure in type 2 diabetes. A case report [very weak evidence] ↩
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 [moderate evidence] ↩
This is mainly based on anecdotal evidence from people in nutritional ketosis. [very weak evidence] ↩
This study, which included exercise, showed similar mental health improvements on two different diets, one of which was a very low-carb diet:
Journal of Internal Medicine 2016: Long-term effects of very low-carbohydrate and high-carbohydrate weight-loss diets on psychological health in obese adults with type 2 diabetes: randomized controlled trial [moderate evidence]
In an earlier study comparing a ketogenic diet to a low-fat diet without an exercise component, the ketogenic diet group reported a greater reduction in depression and fatigue than the low-fat diet group, although both groups experienced overall improvement in these and other symptoms:
Obesity (Silver Spring) 2007: The effects of a low-carbohydrate ketogenic diet and a low-fat diet on mood, hunger, and other self-reported symptoms [randomized controlled trial; moderate evidence]
↩Frontiers in Psychiatry 2018: Sugar addiction: from evolution to revolution [overview article; ungraded] ↩
This is based on consistent clinical experience of low-carb practitioners. [weak evidence] ↩
In a two-week study, overweight adults who consumed a ketogenic diet reported greater fatigue during exercise than those who ate a moderate-carb diet.
Journal of the American Dietetic Society 2007: Blood ketones are directly related to fatigue and perceived effort during exercise in overweight adults adhering to low-carbohydrate diets for weight loss: a pilot study [randomized controlled trial; moderate evidence]
However, such studies have been criticized for not allowing enough time for proper keto-adaptation prior to testing exercise capacity. ↩
According to ketogenic researcher Dr. Steve Phinney, although it takes only a few days to get into nutritional ketosis, it can take 3 to 4 weeks to become fully keto-adapted, regardless of body weight, composition, or fitness.
Nutrition & Metabolism 2004: Ketogenic diets and physical performance [overview article; ungraded]
↩Metabolism 2016: Metabolic characteristics of keto-adapted ultra-endurance runners [nonrandomized study; weak evidence] ↩
You can read our article on the topic here. ↩
Journal of Strength and Conditioning Research 2018: A low-carbohydrate ketogenic diet reduces body mass without compromising performance in powerlifting and Olympic weightlifting athletes [randomized controlled trial; moderate evidence] ↩
Journal of the International Society of Sports Nutrition 2018: Efficacy of ketogenic diet on body composition during resistance training in trained men: a randomized controlled trial [moderate evidence]
Journal of Strength and Conditioning Research 2017: The effects of ketogenic dieting on body composition, strength, power, and hormonal profiles in resistance training males [randomized controlled trial; moderate evidence] ↩
At this time, it’s unclear how performance during high-intensity sports like soccer and basketball would be affected by eating LCHF long term.
Journal of Human Kinetics 2017: Low-carbohydrate-high-fat diet: can it help exercise performance? [overview article; ungraded] ↩
The gut microbiome is the entire collection of bacteria and other organisms living in your digestive tract. ↩
For instance, in a 2018 review of studies looking at the effects of different types and amounts of fat on gut health, results from most observational studies found weak associations between self-reported high fat intake, gut bacteria imbalances, and metabolic dysfunction (e.g. insulin resistance).
However, the controlled trials (higher-quality evidence) found that fat intake didn’t have a significant effect on gut bacteria or metabolic health:
Clinical Nutrition 2018: Dietary fat, the gut microbiota, and metabolic health: a systematic review conducted within the MyNewGut project [systematic review of RCTs and observational studies; moderate evidence]
↩Nutrients 2019: The impact of low-FODMAPs, gluten-free, and ketogenic diets on gut microbiota modulation in pathological conditions [overview article; ungraded]
Frontiers in Microbiology 2017: Reduced mass and diversity of the colonic microbiome in patients with multiple sclerosis and their improvement with ketogenic diet [non-randomized study; weak evidence]
World Journal of Gastroenterology 2017: Ketogenic diet poses a significant effect on imbalanced gut microbiota in infants with refractory epilepsy [non-randomized study; weak evidence]
Some of the changes may be uniquely beneficial, such as having an anti-inflammatory effect.
Cell 2020: Ketogenic Diets Alter the Gut Microbiome Resulting in Decreased Intestinal Th17 Cells [animal and human mechanistic study; very weak evidence]
↩In a 6-month study where overweight or obese people ate fewer than 25 grams of total carbs per day, 68% of the study participants reported that they became constipated at some point during the study.
American Journal of Medicine 2002: Effect of 6-month adherence to a very low carbohydrate diet program [non-controlled study; weak evidence] ↩
This is mainly based on the consistent experience of experienced clinicians. [weak evidence] ↩
Between three times a day to three times a week is considered a very normal range for bowel movements.
This includes diets in which very few carbs are consumed, e.g. ketogenic diets.
Endocrine 2017: Acid–base safety during the course of a very low-calorie-ketogenic diet [non-randomized study; weak evidence]
Nutrients 2018: Chronic ketogenic low carbohydrate high fat diet has minimal effects on acid-base status in elite athletes [non-randomized study; weak evidence]
↩Computational and Structural Biotechnology Journal 2019: High versus low dietary protein intake and bone health in older adults: a systematic review and meta-analysis [meta-analysis of randomized controlled trials; strong evidence]
Current Opinion in Lipidology 2011: Dietary protein and skeletal health: a review of recent human research [overview article; ungraded] ↩
The American Journal of Clinical Nutrition 2017: Dietary protein and bone health: a systematic review and meta-analysis from the National Osteoporosis Foundation [meta-analysis of RCTs and observational studies; moderate evidence] ↩
Here are three examples:
- Nutrition 2016: Long-term effects of a very-low-carbohydrate weight-loss diet and an isocaloric low-fat diet on bone health in obese adults [randomized controlled trial; moderate evidence]
- Annals of Internal Medicine 2010: Weight and metabolic outcomes after 2 years on a low-carbohydrate versus low-fat diet: a randomized trial [moderate evidence]
- The Journal of Pediatrics 2010: Efficacy and safety of a high protein, low carbohydrate diet for weight loss in severely obese adolescents [randomized controlled trial; moderate evidence]
In medical terms it’s called telogen effluvium. It typically occurs 3-6 months after a big dietary change or any other kind of stressful experience for the body. ↩
Journal of the American Medical Association 1976: Alopecia in crash dieters [consistent case reports; weak evidence]
The association of hair loss with low carb is based on reports from people who’ve experienced hair loss after beginning a low-carb or ketogenic diet, rather than published research. [very weak evidence] ↩
This is the safe, effective and sustainable way to follow a low-carb diet.
Diabetes Therapy 2018: Effectiveness and safety of a novel care model for the management of type 2 diabetes at 1 year: an open-label, non-randomized, controlled study [weak evidence]
Applied Physiology, Nutrition and Metabolism 2017: A 12-week low-carbohydrate, high-fat diet improves metabolic health outcomes over a control diet in a randomised controlled trial with overweight defence force personnel [moderate evidence]
↩Diabetes Research and Clinical Practice 2017: Effects of SGLT-2 inhibitors on diabetic ketoacidosis: a meta-analysis of randomised controlled trials [strong evidence] ↩
Lakartidningen 2018: Life-threatening ketoacidosis in patients with type 2 diabetes on LCHF diet [case reports; very weak evidence] ↩
Case Reports in Nephrology: Ketogenic diet-induced severe ketoacidosis in a lactating woman: a case report and review of the literature [very weak evidence] ↩
In rare cases, being in ketosis can be dangerous for certain people; for instance, those who are deficient in certain enzymes needed to use ketones effectively. Although disorders like this are typically diagnosed in childhood, one condition (porphyria, a blood disorder) can happen at any time. Other conditions require consulting with a doctor to ensure that being in ketosis is safe.
Journal of Nutrition and Metabolism 2018: Nutritional ketosis and mitohormesis: potential implications for mitochondrial function and human health [overview article; ungraded] ↩
Several studies have shown that diets leading to nutritional ketosis often accelerate fat loss, among other benefits.
British Journal of Nutrition 2013: Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials [strong evidence]
Diabetes and Metabolic Syndrome 2017: Induced and controlled dietary ketosis as a regulator of obesity and metabolic syndrome pathologies [randomized controlled trial; moderate evidence]
Journal of the International Society of Sports Nutrition 2014: The effects of ketogenic dieting on skeletal muscle and fat mass [abstract of RCT; weak evidence] ↩
For instance, a grain-free, very-low-carb diet was shown to be much more effective for weight loss and decreasing blood sugar in overweight people with type 2 diabetes compared to a low-glycemic-index (low-GI) diet that included whole grains:
Nutrition & 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 controlled trial; moderate evidence] ↩
Cochrane Reviews 2017: Whole grain cereals for the primary or secondary prevention of cardiovascular disease [systematic review of RCTs; strong evidence] ↩