Many diets inevitably come with rules not just about what you can eat, but when you can eat. Eating disorder thoughts and even diet culture can promulgate the idea that eating after a certain time is bad for your health and will cause weight gain.
This myth’s foundation is based on the false idea that the metabolism slows when you fall asleep and the undigested calories will be stored as fat. This is physiologically not true. The body stores any unused calories at that time as fat whether you just ate or ate 8 hours before. In addition, a study has shown that the energy cost of sleep is equal to our Basel Metabolic Rate (BMR). This means that we are burning similar amount of calories sleeping as we do while resting during the day. Although our bodies during sleep may feel like they shut down they are still working and consuming energy. The study concluded “data suggest that the use of BMR to estimate overnight energy expenditure would introduce an average overestimate of approximately 5 percent during the actual hours of sleep, but that when applied over 24 h the error becomes negligible” https://pubmed.ncbi.nlm.nih.gov/3378547/ Therefore, the idea that metabolism slows down while we sleep and the body is not working as efficiently as when we are awake is inaccurate.
The body is equipped to metabolize food 24/7, and cannot tell the difference between minutes or hours. Our bodies digest and absorb food whatever time of the day. There is a belief that when eating too late at night the body is unable to digest and absorb nutrients consumed efficiently whereas eating earlier allows the body to “burn” those calories directly. The body is incredibly effective and will utilize whatever calories and nutrients it obtains in a manner that works physiologically. If it needs to use energy for movement that energy can be derived from the meal you just ate or the meal you ate last night. The body doesn’t know what time it is.
To be fair, some evidence exists that nighttime eating can lead to weight gain. However, this is more a function of an individual’s habits vs. what is physiologically happening in the body. There are several studies that show that people who eat before bed are more likely to have higher overall caloric intake and thus increased BMI (https://pubmed.ncbi.nlm.nih.gov/25439026/ , https://pubmed.ncbi.nlm.nih.gov/23036285/). This is likely because people who eat before bed are eating an “extra” meal or snack and thus more calories than they may need. Additionally, at night people tend to eat while watching TV or scrolling on their phones which may contribute to more mindless eating than eating according to hunger and fullness cues. Lastly, people may not actually be eating enough during the day and be very hungry at night. This hunger can cause people to overeat at night and begin a vicious cycle of not eating the next morning from being too full.
The notion that eating at night is unhealthy because your metabolism slows down and stores calories as fat is mistaken. Literature referring to weight gain is mostly linking unhealthy eating patterns and habits that accompany bedtime snacking and eating.
Eating disorder recovery and treatment reccommends structured but flexible meal plans therefore there should be no “hard and fast” rule about timing of meals. Rules can become extremely rigid and not allow for flexibility that naturally occurs in life. For instance, if there is a rule of not eating after 7pm this could impact your social life if a friend wants to make dinner at 8pm. Working and returning home late could also impact your eating if arbitrary eating rules are strictly enforced. These rules tend to get increasingly stricter until they are so limiting that missing meals and snacks becomes a part of the rule.
Given there is no physiological reason to not eat before going to bed AND typically for our eating disorder population, meal and snack times provide recovery maintenance say YES to a later night dinner or bedtime snack more often!