If you consider some principles, one can actually burn calories while sleeping … apart from that,
the basal metabolic rate and so on …
the little mysterious compounds called
hormones, some of which even have their own rhythm, and
a lowered glucose level at the right time, as when fasting.
That sounds too “mainsational” … my own made-up word for something mainstream and sensational.
The hypothalamus has its fingers everywhere in the body, including in the circadian rhythm. There, a certain nucleus (I can never remember the name of it!) produces the neurotransmitter histamine and a peptide called orexin. This is a very interesting peptide Orexin itself works through certain receptors on the lateral hypothalamus and leads to increased alertness. Mutations of this receptor are deemed responsible for symptoms of narcolepsy. And best of all, orexin is used as a wake-up drug e.g. for fighter pilots. The interesting thing in this context is that insomnia can lead to an increase in …
… food intake and weight loss at the same time?!
Orexin, however, has an appetite-increasing effect. Strictly speaking, these are two different aspects … appetite and food intake that only seem to be related … and the question is: which of them wins? What I mean by this is that appetite and food intake are also influenced by other completely separate factors via the hypothalamus.