Study details

For the study, researchers recruited 165 people with body mass indexes (BMIs) ranging from 27 to 46 between January 2018 and April 2021.

The participants were divided into two groups. The first group was told to fast intermittently by reducing their caloric intake by 80% on three nonconsecutive days each week. The second group was told to reduce their daily caloric intake by around 34%.

Participants in the intermittent fasting group were told they could eat whatever they wanted on the four non-fast days but were encouraged to opt for healthy choices and portion sizes. All participants also took part in a comprehensive lifestyle program focused on changing behavior, setting an exercise goal of 300 minutes of moderate-intensive aerobic physical activity each week, attending frequent group meetings led by dietitians, and receiving personalized support.

The researchers found that over the course of a year, participants in the intermittent fasting group lost almost 17 pounds, roughly 60% more than those in the daily caloric reduction group. In total, the intermittent fasting group saw a 7.6% reduction in body weight by month 12, compared to 5% in the daily caloric reduction group.

Discussion

Danielle Ostendorf, a co-author of the study and assistant professor at the University of Knoxville, and Victoria Catenacci, lead author of the study and associate professor of medicine at the University of Colorado, said the findings were "very exciting" but not necessarily surprising, since intermittent fasting may be easier for some people to stick with than daily caloric reduction.

"We know the best dietary weight-loss strategy is going to be the one that people feel they can adhere to over time, so this study provides an additional evidence-based dietary weight-loss strategy for people to consider," the authors said. "The 4:3 [intermittent fasting] strategy didn't work for everyone in that group, and we don't think this is a magic bullet for producing weight loss in everyone. However, given that it was on average more effective than [daily caloric reduction], we think patients can be encouraged to give it a try and see if it is something that works for them."

Ostendorf and Catenacci added that "fasting 3 days a week might be sort of [the] sweet spot for an [intermittent fasting] paradigm," as intermittent fasting diets with more fasting days could be "too rigid and difficult to adhere to" for some, but too few fasting days might not produce enough of a caloric deficit during the week.

The authors also emphasized the importance of additional support.

"Our participants met with a registered dietitian weekly for 3 months, and every other week for 9 months and focused on healthy eating behaviors and portion sizes in addition to the 4:3 [intermittent fasting] paradigm," Ostendorf and Catenacci said. "Thus, if a physician just told a patient to try 4:3 [intermittent fasting] but didn't direct them to a behavioral support program, they may not be as successful."

Amy Rothberg, an endocrinologist and director of the University of Michigan Weight Management Program, said she supports patients trying new diets provided they still balance healthy foods. "If that's something that they think they can do, I'm all for it," she said.

"If you don't want to count calories, track and log your food intake," intermittent fasting "may be beneficial for some people," Rothberg added. Still, she emphasized that people should choose diets they can stick with long-term.

"There's no superior dietary approach," she said. "So you need to find an approach that is tailored to that individual."