Because it may affect your sleep, and what does poor sleep have to do with it? Hormones are secreted, and hormones control the metabolism of the human body. Generally, people with low hormone levels have low basal metabolism and are prone to gain weight.
You know, many hormones begin to secrete two hours after sleep, and generally reach the peak at around 12. If you often can't sleep well, you will get fat easily.
In fact, this is also in line with the theory of traditional Chinese medicine. Staying up late often makes your body "wet", which can easily lead to obesity.
This seems different from the usual concept. It is wrong to think that staying up late will make people thin.