Does eating late at night cause weight gain?

Eating late at night does not cause weight gain, although night-time eating is positively correlated with weight gain. People who eat late at night are much more likely to consume foods that are high in both calories and fat as compared to meals eaten earlier in the day.^1–5 Although People require energy to keep themselves awake later at night, many studies indicate that individuals over-compensate for this by ingesting more calories than are needed. A research study by Baron et al. suggests that there is an association between eating after 8 pm and higher total calorie intake. People in this study who ate after 8 pm consumed a total of 2153 ± 524 kcal compared with people who did not eat after 8 pm who consumed a total of 1905 ± 526 kcal.⁶ This contributes to an overall increase in the number of calories consumed in a day and causes weight gain.^1–7

Another research study by Baron et al. further illustrates this concept.⁷ The authors conducted a study with a sample of 52 females, 56% of which were normal sleepers (sleep midpoint is before 5:30 am) and 44% of which were late sleepers (sleep midpoint is at or after 5:30 am). The authors found that later sleep timing was correlated with more calories consumed after 8 pm and fewer servings of fruits and vegetables. Late sleepers consumed on average 248 more calories per day than normal sleepers, with the bulk of the extra calories being consumed late at night after 8 pm. This difference in caloric intake between normal and late-night sleepers is not statistically significant. However, it does suggest an increase in weight of approximately two pounds per month for late sleepers if this were to continue over time without greater energy expenditure.

Many individuals believe that eating late at night causes weight gain due to insufficient time available to expend energy and digest food, however, scientists dispute this claim. Several studies indicate that total calories consumed rather than the time of day the food is eaten are what directly causes weight gain.^3,6,8,9 Another study evaluated the relationship between night-time eating and body weight status and found no evidence that the two were associated.¹⁰

Research also suggests that sleep loss contributes to weight gain.³ One study randomized 225 healthy adults into either a control group or a sleep-restricted group with 10 to 12 hours of sleep initially followed by 4 hours of sleep each night for a period of 12, 14, or 18 days. Participants were monitored in a laboratory setting daily. Sleep-restricted subjects were observed to significantly gain weight as compared to the control subjects who had no significant weight gain. Much of the weight gain exhibited by the sleep-restricted subjects can be attributed to the eating choices made during the extended interval of time in which they were awake. These subjects chose to ingest more grams of protein, fats, and carbohydrates with fat consumption being significantly higher as the number of days of sleep restriction progressed. The variance between baseline and sleep-restricted subjects regarding the number of grams of each nutrient consumed is as follows:

• protein: F (6, 180) = 5.74, p<0.001
• carbohydrates: F (6, 180) = 6.78, p<0.001)
• fat: F (6, 180) = 4.70, p<0.001)

Furthermore, the sleep-restricted subjects also ingested a greater number of meals as compared to the control group since many of these subjects chose to eat during the extended time in which they were awake in addition to eating other meals throughout the day.³ People at baseline consumed 3.8 ± 0.9 meals whereas the number of meals consumed during the second day following sleep restriction was 5.3 ± 1.7. The authors suggest that this increase in calorie intake in the evenings combined with greater fat consumption brought about the weight gain observed in sleep-restricted subjects.^1–5,8,9,11

The poor eating choices exhibited by many people who eat late at night may also be reflective of the environment in which these people live. Studies have demonstrated that poor dietary choices are often a result of the food options that are conveniently available.^12–14 Many people who eat late at night are limited to eating fast food and few fruits and vegetables as this is the only option conveniently available to them. These foods are typically high in fat and lead to weight gain and even obesity for those people who chronically sleep late and engage in these dietary behaviors. In addition to the environment, genetics can also play a role in weight gain among night-time eaters via circadian genes.^6,15–17

There is also some evidence that suggests that the timing of food intake is associated with total calorie intake as well as the timing of sleep.⁶ For example, evening macronutrient intake was analyzed in people who were average or late sleepers and results suggested that macronutrients such as proteins and carbohydrates that were consumed after 8 pm were positively correlated with weight gain and a higher body mass index (BMI).^6,7 Carbohydrates consumed after 8 pm in average sleepers were 188 kcal whereas carbohydrates consumed after 8 pm in late-night sleepers were 348 kcal, both of which contribute to an overall higher total caloric intake.⁶ These authors’ findings suggest that rather than the timing of sleeping specifically, the timing of eating in the evenings and before sleeping has a greater effect on total caloric intake and thereby weight gain.

^References

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