New research challenges intermittent fasting as an effective long-term weight loss tool

Your weight is affected by how many meals you eat rather than when you eat them, according to research published in the Journal of American Heart Association. The study analyzed the electronic health records of about 550 adults who were followed for six years and found that eating less overall and fewer large meals may be a more effective weight management strategy than restricting meals to a narrow time window, such as intermittent fasting. Over the course of the six years, the time interval from first to last meal was, overall, not associated with weight change among study participants.

According to the senior study author Wendy L. Bennett, M.D., M.P.H., an associate professor of medicine at Johns Hopkins University School of Medicine in Baltimore, the research shows that eating smaller meals was associated with less weight gain over time. Bennett also says animal studies and some smaller human studies have shown weight loss benefits of time-restricted feeding, but key questions remain. “Humans are more complicated than animals and we have complicated behaviors, especially with eating,” she says.

“While some small experimental studies have shown that time-restricted feeding —limiting the time when people can eat — may result in short-term weight loss, there were few population-based studies to evaluate the association between meal intervals and weight changes over time,” says Di Zhao, Ph.D., an associate scientist at Johns Hopkins University’s School of Public Health, another author on the study. 

Intermittent fasting might also have risks, Bennett says, like loss of muscle in addition to fat. “Fasting diets may be helpful tools for short-term weight loss, most likely because they help us reduce caloric intake,” says Bennett. “Because of possible risks and because the weight loss is often not sustained, it is important to discuss the diet approach with a medical provider.”

Linda Van Horn, Ph.D., R.D.N., Chief of the Nutrition Division in the Department of Preventive Medicine at the Northwestern University Feinberg School of Medicine in Chicago, who was not involved with this study, says, “Women are often attracted by publicity surrounding the latest fad diets, weight loss techniques and eating behaviors. [Research shows that] more women have attempted intermittent fasting than men. Reports like this and the guidance provided on the American Heart Association website are trusted resources that can facilitate truth versus hype.”

The majority of the participants in the study were white women, which means these findings are most applicable to that group. In addition, “Diet quality — more veggies, fiber and lean protein — was not evaluated in this study,” says Bennett, “but in other research has been shown to be important for maintaining a healthy weight.”

Bennett says, “Our study was not an intervention – it was not designed to evaluate the effect of intermittent fasting on weight loss. Rather, we used an app to collect information about the timing of eating and sleeping over about 6 months, and then looked at the association of the timing of meals with weight change before and after study enrollment.”

The study information was self-reported by participants. Van Horn says, “There is no way to guarantee that every person was meticulously accurate regarding documentation of these dietary details.”

Zhao says that large-scale, randomized controlled trials or cohort studies with a long follow-up time and valid measurement tools to collect eating behaviors from participants would be most helpful. According to Van Horn, it could be useful for future research to specify for whom intermittent fasting is more likely to be effective versus those who would benefit from other approaches.

“It seems the intermittent fasting craze is leveling off and the realities identified in this paper are being understood,” says Van Horn. “Children and adolescents need healthy dietary patterns and eating frequency to meet all of their nutrient needs. This fasting approach is clearly inappropriate for this vulnerable population.”

When it comes to healthy weight management, Bennett says, “It is most important to not diet or have weight cycling but maintain a healthy diet long term to prevent weight creep.”