Adelle Davis once said, “Eat breakfast like a king, lunch like a prince, and dinner like a pauper.” Eating at night has long been associated with weight gain, but the reasons are continuously debated. Does it have to do with changes in metabolism, hormones, sleep quality, or additional calories? Some nutrition professionals teach that calories at night are the same as calories during the day—that it is all about total calories consumed versus calories burned. Could there be more to it?

Is It All about Breakfast?

One study found that calorie restriction can lead to weight loss at any time of the day. However, morning meals tend to be more satiating and can lead to lower overall calorie intake throughout the day, compared to late night meals or snacks, which can lack satiating value1. Another study found that eating dinner less than three hours before bed was associated with a higher BMI, and that skipping breakfast may cause increased waist circumference and BMI2. These studies would suggest that the weight gain is likely due to overeating at night after restrictions during the day. However, consuming calories at night versus the day may not be equal. In a study by Hibi et al, young female participants were given a snack either during the day or late at night for 13 days. Late night snacking increased both total and LDL cholesterol. It also reduced fat oxidation, suggesting that eating at night changes fat metabolism and increases the risk of obesity3. This research would indicate that calories should be mostly consumed during the day, especially at breakfast.

Or Is It All about Sleep?

Other researchers have found that eating at night leads to poor sleep quality4, and that sleep has a big impact on late night snacking and weight gain. Chronic sleep deprivation or late bedtimes in adults can lead to weight gain, because adults tend to eat extra calories during late night hours5. This would imply that the longer you are awake, the more likely it is that you will eat again. However, circadian regulation and nighttime light exposure may also impact weight gain. In a study with rats, it was found that low levels of light at night changed metabolic signals and timing of food intake, which lead to excess weight gain, despite equal levels of caloric intake and daily activity6. This change in metabolism may not just be in rats. Other studies have discovered that light levels and sleep deprivation effect melatonin, leptin, and ghrelin levels, which can lead to increased food intake and decreased activity7,8. This increase in calories may also be compounded not only by hormone changes, but also by brain activation. Sleep deprivation in the obese has been shown to lead to increased activation in the reward centers of the brain in response to unhealthy foods, further compounding the problem9.

Do All Studies Agree?

It appears that eating at night may lead to poor sleep and negative metabolic changes. However, most of the studies in this area are small, have specific populations, or are animal studies. Other research has discovered that these negative effects were not consistently seen when the late night consumption was small and energy dense. In fact, in some populations, late night snacking (when composed of healthy foods) can actually help with exercise training and muscle gain10,indicating that for some of the population, this behavior may be beneficial.

Overall, more research is needed on the effects of eating at night. For now, remember to eat a healthy breakfast, get adequate sleep (7-9 hours), and engage in physical activity. Avoid eating extra food and sweets at night. If eating at night, make sure foods fit within total daily calorie goals and avoid high sugar foods and empty calories.

Megan Ostler MS, RD
iFit Dietitian