Study: Intermittent Fasting Might Not Be Helpful for Losing Weight After All
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New study finds eating during certain windows has no impact on weight.
Other recent research has not linked intermittent fasting to weight loss.
Experts say intermittent fasting can be a difficult diet to maintain over time.
Intermittent fasting has been a buzzy diet for years, but new research has found that the eating plan may actually not be very helpful for weight loss.
The study, published in the Journal of the American Heart Association, monitored the portion sizes and eating times of nearly 550 people over six months. The researchers learned that there was no link between the intervals when people ate and their weight.
The researchers also looked for possible associations between weight loss and when people ate after they woke up, how long their eating window was during the day, and how close they ate to bedtime—and none of these were linked with weight loss. The only thing that was linked with weight loss was having smaller meals.
“Our findings did not support the use of time-restricted eating as a strategy for long-term weight loss in a general medical population,” the researchers concluded.
Study co-author Wendy Bennett, M.D., assistant professor in the Division of General Internal Medicine at Johns Hopkins Medicine says that, while the study wasn’t designed to look directly at intermittent fasting, “we did look at eating windows and showed that windows of eating—i.e., eating for longer periods of time or less time in a day—was not associated with weight change over time.”
This isn’t the first study that didn’t find an association between certain eating windows and weight loss. So why might intermittent fasting not be the best way to go if you’re looking to lose weight? Here’s the deal.
Why might it be difficult to lose weight over time with intermittent fasting?
Some people have success losing weight on an intermittent fasting diet, but research has shown the eating plan—which is also called time-restricted eating—isn’t usually any better than restricting calories for weight loss.
One study of 139 people with obesity published in the New England Journal of Medicine last year found that intermittent fasting wasn’t more effective at reducing body weight or body fat than restricting calories.
Another meta-analysis of 27 intermittent fasting trials had a similar conclusion. And a small clinical trial of 36 health adults found that people lost more weight on a calorie-restricted diet compared to an intermittent fasting diet.
That doesn’t mean people can’t lose weight with intermittent fasting. “Intermittent fasting can put you in a calorie deficit but, once you’ve lost weight in the form of muscle mass and your metabolism decreases, you have to [do] intermittent fasting harder to get results,” says Gina Keatley, a certified dietitian nutritionist practicing in New York City. “This is a losing game and, in the long term, seems doomed to fail.”
The general messaging around intermittent fasting is also problematic, says Vanessa Rissetto, R.D., the CEO and co-founder of Culina Health. “The messaging for intermittent fasting makes it seem as though in your window of eating you can eat whatever you want without consequence, so the kinds of foods people are taking in might not be in line with weight loss,” she says. If executed correctly, you would lessen the frequency of eating, while eating high-fiber, low-calorie foods and the practice of being in a specific window might just accelerate the process.”
Keri Gans, M.S., R.D., author of The Small Change Diet, says weight loss ultimately comes down to numbers. “Restricting calories for a certain period of time throughout the day doesn’t necessarily negate overeating later,” she says. “What matters at the end of the day is what you ate and how much of it. For some people, restricting calories makes them extremely hungry and they may inadvertently consume too many calories during their window of eating.”
One of the biggest challenges with intermittent fasting is sticking with it, Dr. Bennett says. “If you don’t stick with the behavior change, the weight will come back,” she says. Keatley agrees. “It doesn’t seem to work long-term,” she says. “Having too much of a calorie or protein debt will ultimately result in less muscle mass and a lower metabolic rate, making it easier to gain fat (weight) after the diet is no longer sustainable.”
What is intermittent fasting, again?
Intermittent fasting is an eating plan that focuses on eating and fasting windows. During fasting periods, you’re supposed to avoid food and just have liquids like water, coffee, and tea. During the eating windows, you can technically eat whatever you want.
The exact timing of fasting and eating windows varies, says Jessica Cording, R.D., the author of The Little Book of Game-Changers. One of the more popular forms of intermittent fasting is the 16:8 diet, where you can only eat during eight hours of the day and fast for the other 16, Cording explains. (Most people typically stop eating in the evening and wait to eat again until late morning to sleep during part of their fast.) However, there are also intermittent fasting diets where people eat less than 500 calories for two non-consecutive days a week and whatever they want for the other five days a week.
The best way to approach weight loss
Experts agree that the best way to find the right eating plan for you is to focus on eating healthy foods in a diet you can follow for the long-term. “Focus on adding more satiating foods to your diet, such as those packed with fiber, as opposed to eliminating foods,” Gans advises. “Building your plate with fruits, veggies, and 100% whole grains may help to fill you up and leave less room for non-nutritious foods”.
It’s also crucial to include foods you love, while keeping portion sizes in check. “Deprivation will only make you want them more,” Gans says.
Keeping an eye on how many calories you take in vs. what you burn also matters, Dr. Bennett says. “The cornerstone for effective weight loss is to self-monitor calories, track your weight, and aim to lose weight slowly with sustainable behavior changes,” she says. Then, have a plan to maintain your weight.
If you’re interested in losing weight, Rissetto recommends consulting a professional for help. “Working with a registered dietitian is a good start because they can help you navigate through all that’s out there in the world of weight loss and personalize a plan to you so that you see results while being able to sustain your efforts long term,” she says.
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