Intermittent fasting doesn’t influence weight, Johns Hopkins study suggests

Scientists say portion size plays a greater role in putting on or shedding pounds, while time-restricted eating ineffective

BALTIMORE — Intermittent fasting is a popular dietary routine followed by many to maintain a healthy weight, but it may not be as effective at shedding the pounds as believed, according to new research. Researchers at Johns Hopkins University say a traditional diet consisting of fewer large meals and smaller portions is the best way to lose weight.

The findings are based on almost 550 adults tracked for an average of six years. Senior author Dr. Wendy Bennett, an associate professor of medicine at Hopkins’ School of Medicine, reports that meal timing did not influence weight change in the participants.

Time-restricted eating has become fashionable in recent years. Proponents include Gisele Bundchen, Jennifer Aniston, Kourtney Kardashian and Scarlett Johansson. The diet recommends eating only during certain hours of the day, such as between 10 a.m. and 6 p.m., and then fasting during the off hours. Previous studies have pointed to numerous benefits, including a reduced risk of inflammation, diabetes, Alzheimer’s disease, and even the potential for a longer lifespan. Most recently, however, another study suggests intermittent fasting could also lead to an earlier death.

But study authors conclude that there simply was no link between eating meals in a specific window and one’s weight. That held true across the set of participants no matter their weight or body size.

“Although experimental studies have suggested that time‐restricted eating could improve circadian rhythms and play a role in metabolic regulation, our study did not detect an association in a population with a wide range of body weights,” the authors write.

Instead, the total daily number of large and medium meals of more or less than 1,000 calories respectively were each linked to putting on pounds. Fewer small meals of less than 500 calories reduced the risk of obesity. The average time from first to last meal was 11.5 hours with breakfast, 1.6 hours after waking up, and dinner four hours before going to bed. Average sleep duration was 7.5 hours.

Scientists analyzed electronic health records from three health systems in Maryland and Pennsylvania for the study. They created a smartphone app for patients to log sleeping, eating and wake up time in real time over six months. Emails, text messages and notifications prompted use as much as possible during the first month and again during regular “power weeks.”

The average age of the participants was 51 and average (BMI) was 30.8, which is considered obese. Most (80 percent) were white, women, and well-educated. The authors note that their findings are observational so could not prove direct cause and effect. They call for further trials including a more diverse population.

“In this clinically based prospective cohort, the number of large and medium meals was positively associated with weight change, while number of small meals was inversely associated with weight change,” their paper concludes. “The distribution of energy intake earlier during the day appeared to be associated with less weight increase after enrollment. Duration from first to last meal, as well as other meal patterns, did not show a clear association with weight trajectory. Our findings did not support the use of time‐restricted eating as a strategy for long‐term weight loss. Further large‐scale studies with long follow‐up time are needed to better characterize the association for time of eating with weight change.”

According to the American Heart Association, four in 10 adults in the U.S. are obese. Current diet and lifestyle recommendations to reduce cardiovascular disease risk include limiting overall calorie intake, eating healthy foods and increasing physical activity.

It does not offer clear preference for frequent small meals or intermittent fasting, noting irregular patterns of total caloric intake appear to be less favorable for the maintenance of body weight and optimal cardiovascular health. Altering meal frequency may not be useful for decreasing body weight or improving traditional cardiometabolic risk factors, it says.

The study is published in The Journal of the American Heart Association.

South West News Service writer Mark Waghorn contributed to this report.