A lack of sleep is known to cause weight gain. During adaptation, sleep deprivation accumulates until it is relieved at the end. During this process, unstable appetite or altered metabolism may lead to gaining weight as a side effect.
Gradual weight gain was prominently reported by Youtuber Aeia during her adaptation to and subsequent stay on Uberman, which persisted despite her efforts at controlling this weight gain. This eventually led to her quitting the schedule, as it was negatively affecting her life in other ways. It is therefore hypothesised that even after adapting to Uberman and likely other nap-only schedules, the body remains in a state of sleep debt, causing these metabolic changes to persist. Alternatively, it may also be due to the lack of a stable circadian rhythm on these schedules, which can be mitigated with a dark period.
Losing weight during adaptation is difficult, as the sleep deprivation incurred during adaptation also reduces self-control, making it more difficult to resist overeating. Moreover, the increased time awake in most cases would also contribute to a larger time window to consume food, which can increase food intake.