August 18, 2020
Eating before bed and weight gain: will eating before bed hurt your sleep or make you gain weight?
Eating before bed may comfort your soul, but your body may not be happy about it. There is mounting evidence linking those late-night calories to metabolic changes, weight gain, and obesity. There are several theories behind this. Sleep, together with the circadian rhythm, or natural body clock, slows down your digestive tract and winds your metabolism down each night. As a result, your pre-bed ice cream will be subject to incomplete digestion. This could leave complex molecules like fats and sugars intact and circulating, which may contribute to metabolic disorders.
The objective of this work is to examine the impact of late dinner on nocturnal metabolism in healthy volunteers.
Source: Metabolic Effects of Late Dinner in Healthy Volunteers—A Randomized Crossover Clinical Trial
Researchers at Johns Hopkins set out to study the mechanisms of a late dinner and sleep. 10 men and 10 women were recruited to stay overnight in a lab. Every participant was given breakfast and lunch at 8 am and 1 pm respectively; half the participants ate dinner at 6 pm and the other half at 10 pm. These meals were adjusted by weight to account for each person's metabolic demands. Participants were urged to sleep at 11 pm, regardless of mealtime.
Biochemical markers of metabolism such as glucose, insulin, and cortisol levels were determined through IV monitoring, while fat breakdown was determined with its own assay. Brain and breath monitoring technology documented any changes in sleep quality between the two study groups.
A late dinner induces nocturnal glucose intolerance, and reduces fatty acid oxidation and mobilization, particularly in earlier sleepers. These effects might promote obesity if they recur chronically.
Health differences were stark after just one night of monitoring. Those who ate a late dinner had significantly higher blood sugar over the course of the entire study period, even away from mealtime. This coincided with a higher insulin spike after these participants' late dinner. Triglycerides, or fats as they are available in the body, also generally spike after large meals and then subsided. This is exactly what happened for the early dinner crowd; however, the late dinner group saw this spike last for longer, with elevated free fatty acid levels maintained until waking hours the next morning. Perhaps alarmingly, rates of fatty acid breakdown, indicating your body's ability to digest and excrete these extra fats, was 10% lower by the morning after eating a late dinner compared to an early one. This group also reported higher stress levels.
Our hyper-productive society often demands a lifestyle of late dinners, high stress, and limited sleep. If such discrete metabolic changes can happen overnight as in the study, living this way could contribute to weight gain and other health concerns long-term. However, in such a small study, important population-level variations in metabolism and lifestyle may have been neglected. Overall, eating early is not a replacement for a good diet and adequate sleep; however, when combined, your body may have the tools it needs to prosper.
While it is pretty clear that eating close to bedtime alters your metabolism, how does it affect your sleep? Sleep quality can influence body mass, sugar levels, cholesterol, and other important bodily functions. While most studies examine the effect of sleep on weight gain, very few studies have looked at the effect of food on sleep quality as a proxy for this very weight gain.
To tease apart this cycle, researchers in Sao Paolo set up a study to test how food before bed affected sleep quality. 52 participants were monitored overnight by polysomnography (PSG), which tracks changes in their brains over the course of sleep while monitoring breathing, oxygen intake, and other metrics. Diets were evaluated with an extremely detailed self-reported survey. The effect of total calories, fat and protein intake, and meal times were analyzed against the quality and phases of sleep.
Eating fats close to bedtime was statistically associated with less time spent asleep in total (β=-.17, p=0.004). Fragmented sleep (β=0.55, p= 0.01) and time-delayed before REM sleep (β=1.25, p=0.001) were increased with higher fat consumption.
Source: Relationship between food intake and sleep pattern in healthy individuals
For both men and women, fat consumption significantly overlapped with a lower time spent asleep. These interruptions coincided with a high rate of waking up during the night. Since it takes time to enter a deep sleep state, this fragmentation reduced participants' beneficial sleep time. The most striking correlation with high fats was a delay in REM phases, which occurred significantly later than normal after falling asleep. REM phases are the mentally active stage of sleep most associated with dreaming and are thought to aid in memory retention.
Eating fatty foods before bed was correlated with an increase of the N2 phase (β=.13, p=0.03) and a decrease of the REM phase (β=-.12, p=0.002).
The REM phase was not only delayed with late-night consumption of fatty food. Participants also spent significantly less time in that phase overall. Meanwhile, both sexes saw a significant increase in time spent in the N2 phase of sleep, which is the transition phase right before the deep sleep phase.
Different correlations were observed between sleep and dietary variables according to gender. The correlation between dietary and sleep variables in men indicated a negative relationship between nocturnal fat intake and the sleep latency, including REM sleep. The percentage of nocturnal fat intake correlated with sleep efficiency, sleep latency, REM latency, stage 2 sleep, REM sleep, and wake after sleep onset (WASO) in women. The percentage of nocturnal caloric intake correlated with sleep latency and efficiency in women.
Women were more likely than men to wake up at night after falling asleep if they ate more calories before bed. In addition, women were more likely to experience insomnia, or inability to fall asleep after shutting the lights off and laying down, after eating late at night. Men saw no significant increase in these behaviors regardless of when they ate at night. This study suggests that eating before bed is associated with several negative markers of sleep patterns in healthy adults, especially in women.
It appears that an unhealthy meal soon before bed can trigger sleep issues as well as weight and health problems. Problems with sleep can in themselves exacerbate and drive the very weight problems pushed by late eating. While sex differences in sleep disorders have been established, the role of food is not fully explored. Those who eat fatty late-night meals have been shown to have pre-diabetic metabolic markers as well as a higher fat percentage and BMI. As established in the first study above, food before bed does not always affect sleep patterns and has its own biochemical effects. Further studies with more patients and longer follow-up times will be necessary to better understand the interplay between sleep, food, and weight gain.