Evidence based

By Dr. Bret Scher, MD, medical review by Dr. Michael Tamber, MD Evidence based

Intermittent fasting for healthy weight loss

Intermittent fasting — introducing relatively brief but regular fasts into your eating routine — is a popular approach for weight loss and improving metabolic health. If you’re not familiar with it, you can read all about it in our beginners guide linked above.

Studies demonstrate that intermittent fasting can help people with weight loss, but there’s some controversy about whether it helps with healthy weight loss. We explain more about this distinction in our detailed guides about healthy weight loss and how to measure it. In brief, healthy weight loss involves improving metabolic health while losing mostly fat mass with minimal loss of lean muscle mass. 

See below for our top tips regarding the use of intermittent fasting for healthy weight loss. After that, read on as we examine the evidence supporting intermittent fasting for weight loss and explore whether it has been found to facilitate healthy weight loss.

Key takeaways

Skip it to lose it. Intermittent fasting — or even just skipping one meal per day — can help with weight loss. Here’s how

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Focus on health. Not all weight loss is healthy. Intermittent fasting may or may not help with healthy weight loss.Here’s the difference

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6 tips for success. If you follow our top tips for success, you have a better chance of achieving healthy weight loss with intermittent fasting. Here’s how

6 tips for intermittent fasting for healthy weight loss

Are there ways to use intermittent fasting to make sure you lose weight in a healthy way?

Yes! Here are our top tips:¹

1. Don’t fast for more than 24 hours at a time without professional supervision, especially if you take blood sugar lowering medications.
2. Start with eating at least two meals per day, targeting a 14 to 18 hour fasting window.
3. Eat an adequate-protein or high-protein diet to help maintain lean muscle mass. 
4. Add a snack on your fasting days if needed to meet your protein goals.
5. Add resistance training to your weekly exercise routine. 
6. Eat until you feel satisfied — you don’t need to overeat during your eating window to “make up” for lost calories.

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Intermittent fasting for weight loss

Social channels are filled with reports of significant weight loss using intermittent fasting. Studies show efficacy, too, but the reported weight loss is frequently much smaller.

One difficulty with assessing the scientific support for intermittent fasting for weight loss involves comparing different fasting protocols. For instance, some studies evaluate time-restricted eating with daily fasting windows ranging from 14 to 20 hours. Others investigate alternate-day fasting, while others focus on severe caloric restriction to mimic fasting physiology.

Another issue is factoring in the baseline diet followed by study subjects. Are many of them eating a high-carb standard Western diet? Or are they eating a low-carb, high-protein diet? The difference may matter as those eating low carb and/or high protein may find fasting easier, and thereby stick with it longer to see greater healthy weight loss benefits.

Despite the discrepancies, most fasting interventions show benefits for weight loss. (Keep reading for a few exceptions.)

One meta-analysis of randomized controlled trials (RCTs) looking at time-restricted eating (at least a 16-hour fasting window and no more than 8 hours eating each day) found an average weight loss of 4.4 pounds (2.0 kilos) in up to 12 months.² While the absolute weight loss may not be much, that’s still pretty impressive considering that participants didn’t change what they ate. They only changed when they ate.

Other meta-analyses of intermittent fasting or severe calorie restriction (less than 800 calories per day) found greater weight loss — around 8.8 pounds (4.0 kilos) in up to 12 months — compared to a control group, and equivalent weight loss compared to continuous calorie restriction.³

So it’s safe to say that intermittent fasting has the potential to help people lose a little weight.

Intermittent fasting for healthy weight loss

As we’ve said, not all weight loss is the same. It’s essential to make sure you’re losing weight in a healthy way. Can intermittent fasting help with healthy weight loss?

Here, the data are conflicting.

On one hand, intermittent fasting can help improve metabolic health by reducing blood sugar and blood pressure while also improving blood lipid levels.⁴

On the other hand, three trials suggested that intermittent fasting may not lead to greater weight loss than usual care, or — even worse — may lead to greater loss of lean muscle mass than usual care or continuous calorie restriction.⁵

A healthy weight loss intervention also should be relatively easy to comply with and maintain long-term. Fortunately, intermittent fasting may fit that criteria.

One study reported that working adults found time-restricted eating with an eight-hour eating window easy to comply with and maintain for three months.⁶

That fits with frequent clinical experience suggesting many people easily adapt to time-restricted eating, especially when they follow a low-carb or high-protein diet that helps improve satiety and reduce appetite.⁷

So, in terms of convenience and ease in your approach to healthy weight loss, intermittent fasting seems to be a winner.

Fasting for healthy weight loss – the wrap up

Intermittent fasting can play a role in your healthy weight loss lifestyle. 

But remember, fasting is not a “magic bullet.” The rest of your diet and lifestyle still matter. 

Also, remember our six tips for healthy weight loss with intermittent fasting:

1. Start with shorter fasts, especially if you take blood sugar lowering medications. You can always increase your fasting time later as you gain experience with it.
2. Start with eating at least two meals per day, targeting a 14 to 18 hour fasting window to ensure you aren’t feeling too deprived or excessively hungry.
3. Eat an adequate-protein or high-protein diet to help maintain lean muscle mass.  This is a key component of healthy weight loss!
4. If you need help meeting your protein goals, feel free to add a high-protein snack on your fasting days.
5. It isn’t all about food. Add resistance training to your weekly exercise routine to maintain lean mass. 
6. You don’t need to overeat during your eating window to “make up” for lost calories. Eat until you feel satisfied and then stop.

If you follow these tips, there’s a good chance that intermittent fasting can help you lose weight in a healthy way.