Facebook Twitter

Intermittent fasting may not be best for weight loss: study

The American Heart Association research suggests that reducing calories is still the better option to lose weight

SHARE Intermittent fasting may not be best for weight loss: study
A waist is measured during an obesity prevention study.

In this Jan. 20, 2010, file photo, a waist is measured during an obesity prevention study at Rush University Medical Center in Chicago. Intermittent fasting has become increasingly popular, but a new study says that eating fewer calories is a more effective path to losing weight.

M. Spencer Green, Associated Press

Intermittent fasting has become increasingly popular, but a new study says that an old standby — eating fewer calories — is a more effective path to losing weight.

According to a new study in the Journal of the American Heart Association released Wednesday, “The frequency and size of meals was a stronger determinant of weight loss or gain than the time between first and last meal.” The authors said their research “did not support the use of time-restricted eating as a strategy for long-term weight loss in a general medical population.”

Intermittent fasting refers to “time-restricted eating patterns” and they’re popular, the study’s lead author, Dr. Wendy L. Bennett, an associate professor of medicine at Johns Hopkins University School of Medicine, said in a news release about the research. She said that rigorous research has not shown if limiting the “eating window” during the day helps control weight.

The new research isn’t the first to diss intermittent fasting as a weight-loss strategy. A study from China published in 2022 in the New England Journal of Medicine had similar findings, as the Deseret News reported.

And a 2020 study in JAMA Internal Medicine suggested intermittent fasting may lead to muscle loss rather than fat loss.

Study nuts and bolts

The new study followed close to 550 adults in Maryland and Pennsylvania for six years to see if limiting the eating window during a day would lead to weight loss. Participants were enrolled from three health systems — Johns Hopkins Health System, Geisinger Health System and the University of Pittsburgh Medical Center — their electronic health records linked to the study. All of them had at least one weight and height measurement taken within two years of the enrollment period, which was in 2019.

The time interval between a day’s first and last meal didn’t impact weight loss, the researchers said.

Among participants, the average age was 51 and the average body mass was 30.8, which categorized them as obese. The average follow-up time for weight recorded in the health record was just over six years.

Data reporting relied in part on a mobile app the researchers called Daily24, where participants reported what time they slept, ate and awakened in real time each day. “Emails, text messages and in-app notifications encouraged participants to use the app as much as possible during the first month and again during ‘power weeks’ — one week a month for the six-month intervention portion of the study.”

The researchers calculated the time from the first to the last meal each participant consumed on a daily basis, how long people waited to eat after waking up and how long after that last meal before each fell asleep.

The study showed:

  • Meal timing was not linked to weight change in the six-year follow-up period.
  • The daily number of large meals (more than 1,000 calories) and medium-sized meals (500 to 1,000 calories) was linked to increased weight, while small meals (under 500 calories) were linked to weight loss.
  • The study did not find an association between meal timing and weight change “in a population with a wide range of body weight,” the Heart Association reported.

Even the study’s finding that meal frequency and the number of calories consumed were stronger risk factors for weight change compared to meal timing did not allow direct cause and effect to be shown, study lead author Di Zhao, an associate scientist in cardiovascular and clinical epidemiology at Johns Hopkins Bloomberg School of Public Health, said.

The authors noted a need for more research, including on a more diverse population. This study included primarily well-educated white women in a single region of the country. The researchers also said they couldn’t tell if people were trying to lose weight before they joined the study and if existing health conditions made a difference.

Healthier lifestyle

In 2022, the American Heart Association reported that 40% of U.S. adults are obese. The group’s recommendations for heart disease prevention include limiting calorie intake, eating healthy foods and getting more exercise.

“The 2017 American Heart Association scientific statement: Meal Timing and Frequency: Implications for Cardiovascular Disease Prevention did not offer clear preference for frequent small meals or intermittent fasting. It noted that irregular patterns of total caloric intake appear to be less favorable for the maintenance of body weight and optimal cardiovascular health. And, altering meal frequency may not be useful for decreasing body weight or improving traditional cardiometabolic risk factors,” according to the association.

“However, it should be noted that healthy, sustainable weight loss should be part of an individualized plan, and that these study findings are not universally applicable,” as ABC News reported.

“The decision to lower calories or try intermittent fasting should really be individualized to the person. [Some] people find intermittent fasting easier to lower their calories and others find they just get too hungry when they fast and then they eat too much during their non-fasting time,” Liz Weinandy, a registered dietitian at the Ohio State University Medical Center and instructor of practice at OSU in Columbus, Ohio, told ABC News.

She said those trying to maintain or reach a healthy weight should focus on a balanced diet, and should not exclude “a specific food group or macronutrient. Those diets do not work long term and if they do work, they are generally not healthy.”