Abstract: The role that meal pattern plays in weight regulation is a popular topic of scientific and common debate. The goal of this study was to evaluate the relationship between meal timing with caloric intake and body mass index (BMI). We hypothesized that late meal timing and eating closer to sleep onset time would be associated with greater energy intake and higher BMI. Participants included 59 individuals recruited from the community. Rest/activity patterns were assessed using 7 days of wrist actigraphy, and caloric intake was evaluated using 7 days of diet logs. Results demonstrated that the timing of meals was associated with overall energy intake but not with BMI. In multivariate analyses controlling for age, sex, sleep duration, and timing, eating more frequently, later timing of the last meal, and a shorter duration between last meal and sleep onset predicted higher total caloric intake. In a mediational model, eating frequency explained the relationship between eating closer to sleep onset and total caloric intake. Results suggest that later relative timing of meals, particularly eating close to sleep, could lead to weight gain due to a greater number of eating occasions and higher total daily caloric intake. These findings have important implications for the development of novel, time-based interventions for weight management.
Alex’s Notes: When it comes to meal timing, there is definitely some interesting animal studies out there. One such study found that mice fed a high-fat diet during the light phase (normal rest period), compared to mice fed only during the dark phase (normal active period). Similarly, when mice were kept in constant light (this would be like us staying in complete darkness), they gained more weight compared to mice who maintained a light/dark cycle; however, when feeding was restricted to the normal feeding time (biological night), the effects of the constant light were no longer observed. Finally, a third study that restricted the feeding period to eight hours found that these mice were protected against the metabolic onslaught of an obesogenic diet.
But humans are not mice, and while the above appears to make sense, especially when considered through an evolutionary lens and in conjunction with other studies done on circadian rhythms, few studies have looked at the effects of meal timing within humans. It has been demonstrated, for example, that eating after 8pm was associated with a greater BMI, even after controlling for sleep timing and duration. The current study sought to evaluate the relationship between the timing of meals with caloric intake and BMI.
To do so, the researchers provided seven days’ worth of diet logs, sleep logs, and wrist actigraph (to be worn for seven days and provide a more objective measurement of sleep) to 59 participants. These assessments were conducted almost exclusively through the mail and telephone, so self-reporting bias is bound to be high. It should be noted that approximately 30% of participants who complete any type of dietary assessment tend to underreport via forgetfulness, inaccurate measurements, and underreporting. Moreover, even the participants BMI had to be self-reported, and respondents tend to overestimate BMI at the lower range and underestimate BMI at the higher range.
Nonetheless, the average age of the subjects was 32-years and the average BMI was 24 kg/m2. Amazingly, the average sleep-start time was 1:17am with sleep duration of just over six hours. This put the sleep-wake time around 8:30am, and breakfast soon followed at 9:37am. Lunch was around 1:30pm and dinner was consumed around 7:10pm, with a final “last meal” being eaten around 9pm. The eating frequency ranged from 2-9 meals, with an average of 4.5 per day.
Eating frequency, time of the last meal, the duration between lunch and dinner, the duration between dinner and the last meal were significantly positively associated with daily caloric intake, while the duration between sleep onset and the last meal had a significant inverse association. After controlling for age, sex, sleep duration, and sleep timing, the significant associations remained for all except the duration between lunch and dinner. However, when both eating frequency and duration between the last meal and sleep onset were entered into the same model, only eating frequency remained significant.
So what does this mean?
The study demonstrates that with some demographic and sleep variables taken out of the picture, eating later at night, eating a last meal closer to sleep onset, and eating more frequently were associated with greater caloric intake throughout the day.
Interestingly, there was no association between eating earlier in the day and overall caloric intake or BMI, with 85% of the subjects consuming breakfast within an hour and a half of waking up. Conversely, when it came to the timing of the last meal and how closely sleep followed, the participants were all over the board. The average last meal was indeed around 9pm, but ranged from 5pm to 2:11am, and the timing between it and sleep onset ranged from 52 minutes to nine hours. Coming back to circadian rhythms, it does appear that the subjects may well be eating the first meal at a more biologically appropriate time relative to later in the day. For what it is worth, I routinely wake up around 5:30-6am and just drink coffee until 9am where I will eat breakfast. My last meal is dinner and ends around 7pm with sleep onset being between 9:30-10pm.
Anyways, the study also found that eating frequency explained the relationship between eating close to sleep onset and higher caloric intake, perhaps because eating later provided more opportunities to eat throughout the day, which brings up the question of how many meals we should be eating. I’m not even going to begin to get into that one, although I will say that eating nine meals (or snacks) like some of the current study’s subjects did is not going to be ideal for most people. Personally, I believe that 2-4 meals depending on the person in question work best. It should be noted, however, that when taken in conjunction with the previously mentioned mouse studies, there may also exist the possibility that eating relatively late at night may have effects on metabolism through messing with our circadian rhythm. Although, BMI was not associated with meal timing variables (could be self-reporting error).
The results only show an association between eating later at night, eating a last meal closer to sleep onset, and eating more frequently and total daily caloric intake, so causality cannot be determined. Moreover, in persons who track calorie and/or food intake, these results would likely not apply to them. That said, in the layman who is trying to simply lose weight without much effort, a reasonable first step would be to eat the last meal of the day sooner and allow more time between it and sleep. Simply be reducing the feeding window the person may eat less frequently and thus consume fewer calories. Depending on the eating habits, a second possible step would then be to reduce the number of meals within this timeframe, which would again possibly reduce caloric intake through fewer feeding and depending on dietary habits, also possibly eliminate “junk” or “snack” foods.