The number of daily meals, but not the timing between first and last daily meals, was significantly associated with weight changes over a 6-year period, in a prospective study of more than 500 adults.
Some studies suggest that timing food intake – through time-restricted eating or intermittent fasting – can promote weight loss, but these strategies have yielded similar weight loss to eating throughout the day in randomized trials, and population-based studies of meal intervals and weight changes are needed, Di Zhao, PhD, of Johns Hopkins University, Baltimore, and colleagues wrote.
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“Obesity is an epidemic,” corresponding author Wendy Bennett, MD, also of Johns Hopkins University, said in an interview. “We are interested in identifying ways to prevent weight gain over time and reduce obesity risk, since telling people to ‘just eat less’ doesn’t always work.”
In a study published in the Journal of the American Heart Association, the researchers recruited 1,017 adults who were patients at one of three health systems; of these, complete data were available for 547 individuals.
The participants downloaded an app called Daily24 to record the timing of their meals and sleep for at least 1 day. The researchers used electronic medical records to obtain information on weight and comorbidities of the participants for up to 10 years before study enrollment through 10 months after enrollment.
The mean age of the participants was 51.1 years, 78% were women, and 78% were White; the mean body mass index was 30.8 kg/m2.
The mean interval from first to last meal was 11.5 hours, and this was not associated with change in weight. The mean times from waking up to the first meal and the time from the last meal to sleeping were 1.6 hours and 4.0 hours, respectively, and these were not associated with weight changes over the follow-up period, the researchers wrote. Sleep duration (mean of 7.5 hours) also was not associated with weight change over time.
However, the total daily number of large and medium-sized meals was associated with weight gain over time, while those who reported more smaller meals showed weight loss. A daily increase of one large, medium, or small meal was associated with an average annual weight change of 0.69 kg, 0.97 kg, and –0.30 kg, respectively.
Benefits of time-restricted eating remain unclear
“Animal studies have shown benefits for time restricted feeding, but there are still questions about whether or not it helps prevent weight gain or promotes weight loss in humans,” Dr. Bennett said in an interview.
As for the current study findings, “we were not surprised; humans are more complicated than animals, and we have complicated behaviors, especially with eating,” she said.
“We showed that windows of eating (eating for longer periods of time or less in a day) was not associated with weight change over time among patients from three health systems,” said Dr. Bennett. “The main implication is that restricting your window of eating, such as eating over less time, or having more fasting time, may not reduce weight gain over time, while eating fewer large meals is associated with less weight gain over time.”
The findings were limited by several factors including the exclusion of many younger and less educated individuals, the short follow-up period, and lack of information on weight loss intention at baseline, the researchers noted. Other limitations included the inability to evaluate time-restricted eating or fasting, and the inclusion of individuals currently seeking care, which may limit generalizability.
However, the results were strengthened by the repeated measures of weight, detailed information on obesity risk factors, and real-time assessment of eating behaviors. The results do not support time-restricted eating as a long-term weight-loss strategy, and more studies are needed with a longer follow-up period, the researchers concluded.
However, there may be a role for time restricted eating as a method of total calorie control, Dr. Bennett said.
“Other studies do show that people might be able to use time-restricted eating or intermittent fasting to help them reduce their caloric intake and thus lose weight, so it can still be a helpful weight loss tool for some people who can adhere to it,” she said.
The study was supported by a grant from the American Heart Association to Johns Hopkins University. Dr. Bennett had no financial conflicts to disclose.