Nighttime eating, particularly before bed, has received considerable attention. Limiting and/or avoiding food before nighttime sleep has been proposed as both a weight loss strategy and approach to improve health and body composition. Indeed, negative outcomes have been demonstrated in response to large mixed meals in populations that consume a majority of their daily food intake during the night.
However, data is beginning to mount to suggest that negative outcomes may not be consistent when the food choice is small, nutrient-dense, low energy foods and/or single macronutrients rather than large mixed-meals. From this perspective, it appears that a bedtime supply of nutrients can promote positive physiological changes in healthy populations.
In addition, when nighttime feeding is combined with exercise training, any adverse effects appear to be eliminated in obese populations. Lastly, in Type I diabetics and those with glycogen storage disease, eating before bed is essential for survival. Nevertheless, nighttime consumption of small (~150 kcals) single nutrients or mixed-meals does not appear to be harmful and may be beneficial for muscle protein synthesis and cardiometabolic health. Future research is warranted to elucidate potential applications of nighttime feeding alone and in combination with exercise in various populations of health and disease
Nighttime eating, particularly before bed, is a topic that has received considerable media attention in recent years. Over the past decades it was thought that health and weight conscious individuals should limit and/or avoid food in the hours close to nighttime sleep because it would negatively impact health and body composition.
Ultimately, this may increase the risks for cardiometabolic diseases such as obesity and diabetes. However, recent studies investigating the impact of pre-sleep nutrient intake have reported positive physiological outcomes in various populations. This review will examine the factors that have contributed to previous opinions on the health impact of nighttime eating and explore new evidence suggesting that our understanding of nighttime eating may need to be modified based on the content and quantity of the food consumed during this time.
2 Effect of Nighttime Eating: An Old Perspective
The arguments in favor of limiting and/or avoiding food intake late in the night are supported by data demonstrating diurnal variations in glucose tolerance , gastric emptying , resting energy expenditure . Moreover, in healthy normal weight men, it has been demonstrated that the postprandial metabolic response to identical meals changes throughout the day [4,5]. For instance, when identical meals (~544 kcals; 15% protein, 35% fat, 50% carbohydrate) are consumed either in the morning, afternoon, or night, the thermic response to that meal appears to be the lowest with nighttime intake . Similarly, studies in free-living healthy adults have shown that meal satiety also varies with time of day and that food intake during the night is less satiating and leads to greater daily caloric intake compared to food consumed in the morning hours [6,7]. Collectively, these studies demonstrate that the fate of ingested nutrients changes throughout the day and that nighttime intake, when compared to daytime intake, may lead to over-eating and weight gain with potential metabolic consequences. In light of this, it has been suggested that food consumed at night, prior to sleep, may have adverse effects on health.
While data from animal studies appear to support this concept [8,9], not all studies concur . In human trials, populations of shift workers , those with the Night Eating Syndrome (NES; consume a large percentage of total daily calories after dinner) , and epidemiological data [13,14,15,16,17] suggest that consuming a majority of daily nutrients in the evening may have adverse health consequences (see the following references for thorough reviews on shiftwork [11,18] and NES )). Briefly, regarding shiftwork (characterized by irregular work hours to provide service throughout a 24 h day), available data suggest that shiftwork, but more so night shiftwork, is a risk factor for negative health outcomes [11,18]. For example, it has been shown that night shift workers tend to have a higher prevalence of overweightness, abdominal obesity , elevated triglycerides, dyslipidemia, impaired glucose tolerance [21,22,23,24,25], and decreased kidney function  compared to day workers. In a study of simulated night shiftwork in normal weight women, reductions in both total daily energy expenditure and the thermic effect of dinner were highlighted as contributing mechanisms for weight gain, obesity and impaired health as a result of shiftwork . Thus, these data demonstrate an increased cardiometabolic risk with night shiftwork.
Similarly, NES is associated with obesity in some studies [16,28,29]. It is unclear, however, as to whether obesity is a consequence or cause of NES. Compared to those who do not eat late at night, individuals with NES consume a larger portion of their total calories at night (≥50% after dinner) and have higher overall daily and evening caloric intake in some [30,31], but not all cases [32,33,34]. Likewise, those with NES have higher 24 h respiratory quotient indicative of greater carbohydrate oxidation and less fat oxidation  compared to those without NES. In addition, those with NES consume double the amount of carbohydrate and protein and four times the fat  in daily meals compared to those without NES. It is practical to assume that these behaviors would predispose night eaters to weight gain, particularly if food is consumed in chronic excess . However, not all studies report differences in daily caloric intake between night eaters and controls [32,33,34] and, it is interesting to note that NES is also present in normal-weight/non-obese individuals [12,30,31,37,38]. The possibility of the non-obese night eaters engaging in compensatory weight maintenance behaviors (e.g., exercise) cannot be ignored  as this would be a plausible explanation for any weight-related differences observed. It is also possible that NES may be a precursor to obesity as one study found that the only difference in NES characteristics between obese and non-obese adults was that the non-obese night eaters were significantly younger  suggesting that in the long-term, NES may lead to obesity. Others have found that night eating impairs weight loss attempts  and is only associated with weight gain in already-obese individuals .
These data from shift workers and NES populations provide some evidence to suggest that consuming the majority of daily nutrients late in the evening may have health consequences. However, this concept cannot be fully understood without considering, the influence of sleep, or lack thereof. An inverse relationship exists between sleep duration and body mass index with a greater likelihood of obesity in those reporting less than 7–9 h of sleep each night . Indeed, both shift workers  and individuals with NES  report higher levels of subjective sleep disturbances (short sleep, reduced sleep quality, difficulty falling asleep) compared to their respective counterparts. Sleep duration plays a significant role in human behavior  and, while speculative, when the duration of sleep is short it is likely that there are just more opportunities (awake hours) to eat and, in the long term, promote unfavorable body composition changes.
Indeed, some epidemiological data suggests that consuming a higher proportion of calories later in the day, as opposed to earlier in the day, is associated weight gain [13,14,15,16,17]. However, not all studies agree [12,36,38,43]. It is important to note that several inconsistencies exist in the research examining the effect of late evening caloric intake and body weight. Some of these discrepancies include, but are not limited to: (1) differences in the calories consumed within a specified time frame (i.e., intake after 5 pm  vs. 8 pm , (2) whether it constitutes a portion of the dinner meal  or solely post-dinner intake, and (3) whether the individual wakes up from sleep to eat . Despite these inconsistencies it is evident that consuming large quantities of food (binge eating) in the late evening may have adverse health implications
3 Effect of Nighttime Eating: A New Perspective
As demonstrated above, consuming large meals or the majority of daily nutrients late in the evening may increase susceptibility to obesity and other cardiometabolic diseases. While this may hold true when large quantities of food intake occurs at night, data is beginning to mount to suggest that this finding is not consistent if the food choice is altered to favor small, nutrient-dense, low energy foods and/or single macronutrients (<200 kcals) [45,46,47,48,49,50]. In fact, recent studies have examined the impact of low-energy nutrient intake that occurs in close proximity to sleep and reported positive findings [45,46,47,48,49,50]. Conversely, one study  compared the impact of a 200 calorie snack (carbohydrate, 20.6 ± 2.6 g; protein, 2.6 ± 1.1 g; fat 11.0 ± 1.0 g) consumed in the daytime (1000 h) or nighttime (2300 h) for 13 days in healthy, normal weight women (n = 11, age, 23 ± 1 years, BMI 20.6 ± 2.6 kg/m2). It was reported that despite no difference in nutrient composition or calorie intake for each 13 day period, the nighttime eating resulted in small decreases in 24 h fat oxidation and small increases in total cholesterol . The short duration of this study does not allow for conclusions to be drawn with regard to body composition changes, however, body weight was unchanged. Nevertheless, as there is typically a long duration between eating dinner, sleep, and the next main meal (i.e., breakfast the following morning), the overnight period may represent a 6–8 h window of opportunity to potentially optimize health, metabolism and overall human performance. Fortunately, short-term preliminary studies have provided insight to the potential benefits of pre-sleep nutrient intake and its relevance to healthy, active young [47,52] and older individuals  and diseased populations [46,48,49,50,53,54]