Intermittent fasting may not be as helpful for losing weight as once thought, study finds

By Madeline Holcombe, CNN

Are snacks before bed your vice? Or do you prefer to wait a few hours after you wake up to eat?

The timing of meals may not have as big an impact on weight as once thought, according to a new study.

The study tracked the portion sizes and eating times of 547 people, in addition to data on their health and weight, over the course of six years. The data showed no association between an interval of the day in which people had their meals and their weight, according to the study published Wednesday in the Journal of the American Heart Association.

Restricting eating times, as seen in diet trends such as intermittent fasting, has been a popular method to try to lose weight in recent years.

But the researchers found no association between restricting eating times and weight loss, said principal investigator of the study Dr. Wendy Bennett, an associate professor of medicine in the division of general internal medicine at Johns Hopkins School of Medicine. That included how long people ate after waking up, how long their window of eating was throughout the day and how close to going to bed they ate, she noted.

Instead, smaller meals were associated with weight loss, she said.

“Based on other studies that have come out, including ours, we are starting to think that timing of meals through the day most likely doesn’t immediately result in weight loss,” Bennett said, adding the caveat that for some people, timing meals may be a useful tool in tracking nutrition.

Study limitations

The results of this study should be taken with a grain of salt, experts cautioned.

There were few racial and ethnic minorities among the participants, noted Dr. Fatima Cody Stanford, associate professor of medicine at Harvard Medical School. There are also many social determinants of health, such as stress and people’s environment, that could be added to the data, Stanford added.

Those factors could be important for getting a better look at the effects of meal timing, added Alice Lichtenstein, professor of nutrition science and policy at Tufts University.

“I suspect that if they looked more closely at the data, that there would be subgroups (where timing of meals) may have had a significant effect,” Lichtenstein said.

This study was observational, Bennett noted, meaning that they looked at existing patterns for the study instead of making changes to a randomized group. Further work on this topic is underway, she added.

Quality over quantity

The big takeaways are that there is no one strategy that works for all people when it comes to nutrition, and that quality of the food counts, Lichtenstein said.

“If you make some effort to consume a healthy diet, you make some effort to be physically active, you’re less likely to have diabetes, chronic kidney disease, obstructive pulmonary disease and hypertension,” Lichtenstein said.

It’s the boring stuff no one wants to hear, she added, but there is no getting around eating fruits and vegetables and getting physical activity when it comes to weight management.

For some people, trying intermittent fasting or restricting eating intervals can be a helpful way to take note of personal tendencies, but many people can’t sustain it for enough time to see long-term change — or keep off any weight they lose, Lichtenstein added.

Stanford, who is an obesity medicine physician at Boston’s Massachusetts General Hospital Weight Center, doesn’t like to focus too strongly on either calorie restriction or intermittent fasting, she said. Instead, she wants her clients to look at the nutritional value of the food they are eating.

To the body, 100 calories of gummy bears is not the same as 100 calories of oatmeal with fruit and nuts, she added.

But different approaches work better in different lifestyles, and everyone should work with their own doctor and their own body without stress and shame, Stanford said.

If a nutrition strategy works for someone else, she said, “it just means someone’s body responded and the other one didn’t. It doesn’t mean you’re flawed. It just means that’s just not what your body needed.”

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CNN’s Jen Christensen contributed to this report. Correction: A previous version of this story incorrectly stated Dr. Fatima Cody Stanford’s last name.