Research paper
Scheer FAJL, Morris CJ, Shea SA. The internal circadian clock increases hunger and appetite in the evening independent of food intake and other behaviors. Obesity (Silver Spring). 2013;21(3):421-423.
Why we cite it
Isolates endogenous circadian drive on hunger from time since last meal and time since waking, using forced desynchrony — the reference method for separating circadian biology from behaviour, because it distributes all behaviours evenly across the circadian cycle rather than controlling for them statistically.
The scale, which this record did not state until 2026-09-02: 12 healthy non-obese adults (6 male, aged 20–42), across a 13-day laboratory protocol with eucaloric meals and sleep periods balanced across the endogenous cycle. The design is the strength and the sample is the limit, and both are facts about the same study. The circadian rhythm in hunger was large, with the trough at the biological morning (8 AM) and peak at the biological evening (8 PM) — peak-to-trough amplitude 17%, P = 0.004. This is the primary source for the project’s claim that evening eating difficulty is biological, not a character flaw, and that hunger is lowest in the morning despite the longest fast.