Total Meals, Not Timing, Drives Long-term Body Weight Changes
Sustainable habits, calories, and quantity likely matter more than eating schedules or fasting windows, a new study suggests.
How many meals a person eats is more important than when that food’s eaten throughout the day when it comes to long-term changes in body weight, a cohort study suggests.
Among participants recruited from three US health systems, various intervals defining the timing of meals, as well as sleep duration, were not associated with weight change over a mean follow-up of 6.3 years, researchers led by Di Zhao, PhD (Johns Hopkins Bloomberg School of Public Health, Baltimore, MD), report in a study published online recently in the Journal of the American Heart Association.
Each additional meal consumed each day, however, was associated with an average annual weight increase of 0.28 kg (0.62 lbs), a number that was greater when the added meals were considered medium or large in size. Eating an additional small meal per day, on the other hand, was associated with an average annual reduction in weight of 0.37 kg (0.82 lbs).
“We’re still cautious about recommending that changing the timing of eating could result in preventing weight gain over time, or even in weight loss,” senior author Wendy Bennett, MD (Johns Hopkins School of Medicine, Baltimore, MD), told TCTMD. “Likely, the cornerstone of weight loss or weight-gain prevention continues to be reducing how much we eat.”
It’s still worth conducting randomized trials to evaluate whether the timing of meals during the day can affect weight trajectories, she added. She stressed, however, that the current study cannot address the impact of intermittent fasting, which has grown in popularity in recent years as a way to lose weight, because the analyses focused on average eating windows over time and not on specific fasting behaviors on a day-to-day basis.
Timing and Number of Meals
When treating obesity, Bennett said, the usual recommendation is to cut back on how much is eaten, although the impact of how meals are timed throughout the day and aligned with circadian rhythms has been an area of research. “There’s been a lot of interest in seeing if that could facilitate reducing the excess weight gain that we have over time, and also in some people who are trying to lose weight, whether it can result in a slow gradual weight loss,” she explained.
Evidence from experimental, mechanistic, and randomized studies of approaches to changing the timing of food consumption is mixed when it comes to impacts on weight loss and other factors, such as cardiometabolic risk factors. For instance, one recent randomized trial showed that restricting eating to a daily window of 8 hours, on top of caloric restriction, didn’t increase weight loss compared with cutting calories alone in people with obesity, whereas another demonstrated greater weight loss and improved diastolic blood pressure by concentrating eating within an 8-hour window early in the day, but no significant effects on other cardiometabolic risk factors or fat loss.
Thus, there remains some uncertainty about the potential benefits of time-restricted eating. In addition, it’s still unclear whether the number and size of meals eaten throughout the day are important when it comes to long-term changes in body weight.
To address some these questions, the investigators conducted a study in a cohort of adults receiving care at three health systems participating in the PaTH Clinical Research Network (Johns Hopkins Health System, Geisinger Health System, and the University of Pittsburgh Medical Center). Participants downloaded and used a mobile app—called Daily24—during a 6-month period to record the timing and size of meals, as well as sleep duration, for at least 1 day; they also answered a baseline online questionnaire. Information on height, weight, and comorbidities was obtained from electronic health records going back as far as 10 years before baseline and then up to 10 months after the study started to assess long-term changes in body weight.
The study included 547 participants (mean age 51 years; 78% women) with a mean body mass index of 30.8 kg/m2. Comorbidities included hypertension (36.6%), chronic obstructive pulmonary disease (14.6%), diabetes (10.8%), chronic kidney disease (9.9%), and ischemic heart disease (6.9%).
It’s important when people choose what works for them for weight loss that they choose behaviors that are sustainable. Wendy Bennett
The mean time from the first to the last meal of the day was 11.5 hours. There were an average of 1.6 hours between waking up and the first meal and 4.0 hours between the last meal and sleep. Participants reported sleeping for an average of 7.5 hours each night.
None of those figures were significantly associated with changes in body weight over an average of 6.3 years.
The researchers then assessed the relationship between the number of daily meals and weight changes over time. On average, participants reported eating three times a day. In the fully adjusted model, each additional meal consumed was associated with an annual increase in body weight, particularly when the meals were deemed to be of medium or large size, with annual gains of 0.99 kg (2.18 lbs) and 0.56 kg (1.23 lbs), respectively.
“This study makes us think that timing of eating is probably not as important to our weight trajectory, our weight change, over time as how much we’re eating, whether we’re eating more large meals versus smaller meals,” Bennett said. “So it comes back to that calories and quantity probably matter more than timing.”
The next steps would be rigorously designed RCTs to evaluate the impact of various specific eating windows, studies that typically can be performed over short periods of time only, she said.
“Overall, a lot of people struggle with maintaining behaviors that require them to eat during shorter windows of time. They might be able to lose weight in the short term in part because they’re probably also restricting their calories overall when they’re eating in a shorter window, but then most people, if they go back to regular eating patterns, will regain their weight,” Bennett said. “So it’s important when people choose what works for them for weight loss that they choose behaviors that are sustainable, since a lot of times the time restriction can be challenging for people to adhere to.”
Zhao D, Guallar E, Woolf TB, et al. Association of eating and sleeping intervals with weight change over time: the Daily24 cohort. J Am Heart Assoc. 2023;12:e026484.
- This research was funded by the American Heart Association, through a Strategically Funded Research Network Grant to Johns Hopkins University School of Medicine. The authors also acknowledge assistance for clinical data coordination and retrieval from the Core for Clinical Research Data Acquisition, supported in part by the Johns Hopkins Institute for Clinical and Translational Research. The research was conducted, in part, using PCORnet, the National Patient-Centered Clinical Research Network. PCORnet has been developed with funding from the Patient-Centered Outcomes Research Institute (PCORI). The PaTH Clinical Research Network’s participation in PCORnet was funded through PCORI Award.
- Bennett and Zhao report no relevant conflicts of interest.