A new study published in the Journal of the American Heart Association has found that the frequency and size of meals is a stronger determinant of weight loss or gain than the time between the first and last meal. This is a blow to the idea of intermittent fasting, which has grown in popularity in recent years. The study evaluated the association between time from the first meal to last meal with weight change. Nearly 550 adults from three health systems in Maryland and Pennsylvania were enrolled in the study. Participants had at least one weight and height measurement registered in the two years prior to the study’s enrollment period (Feb.-July 2019).
Key Findings
- The frequency and size of meals is a stronger determinant of weight loss or gain than the time between the first and last meal.
- The total daily number of large meals and medium meals were each associated with increased weight over the six-year follow up, while fewer small meals was associated with decreasing weight.
- The study did not detect an association between meal timing and weight change in a population with a wide range of body weight.
Recommendations
- Focus on eating smaller, more frequent meals throughout the day.
- Avoid eating large meals or medium meals.
- Talk to your doctor or a registered dietitian about the best way to manage your weight.
The research team created a mobile application, Daily24, for participants to catalog sleeping, eating and wake up time for each 24-hour window in real time. 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 per month for the six-month intervention portion of the study.
Based on the timing of sleeping and eating each day recorded in the mobile app, researchers were able to measure the time from the first meal to the last meal each day, the time lapse from waking to first meal, and the interval from the last meal to sleep. They calculated an average for all data from completed days for each participant.
The data analysis found that meal timing was not associated with weight change during the six-year follow-up period. This includes the interval from first to last meal, from waking up to eating a first meal, from eating the last meal to going to sleep and total sleep duration. Total daily number of large meals (estimated at more than 1,000 calories) and medium meals (estimated at 500-1,000 calories) were each associated with increased weight over the six-year follow up, while fewer small meals (estimated at less than 500 calories) was associated with decreasing weight.
“This study suggests that the number and size of meals consumed plays a more significant role in weight loss or gain than the time between the first and last meal. “
The study also did not detect an association between meal timing and weight change in a population with a wide range of body weight. Even though prior studies have suggested that intermittent fasting may improve the body’s rhythms and regulate metabolism, this study in a large group with a wide range of body weights did not detect this link.
Large-scale, rigorous clinical trials of intermittent fasting on long-term weight change are extremely difficult to conduct; however, even short-term intervention studies may be valuable to help guide future recommendations.
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