For how we live.
Short sleep is tied to obesity, and experiments suggest the link is partly causal. Adults told to sleep longer ate about 270 fewer calories a day; dieters who slept less lost far less of their weight as fat.
Losing weight lowers resting metabolism and keeps it low — Biggest Loser contestants ran hundreds of calories below baseline six years on. But that brake slows loss; it does not store fat.
The advice to lose weight slowly assumes fast loss is regained faster. Two randomised trials found the rate barely affects long-term regain — though rapid loss can cost more lean mass and carries its own risks.
Lying down soon after a meal will not harm most healthy people, but it is not neutral. It reliably worsens acid reflux, and habitually eating late shifts the body's metabolism in a direction tied to weight gain.
Chronic stress is linked to weight gain, and cortisol is one plausible route. But the measured associations are modest, and cortisol is a contributor, not the master switch that supplement marketing implies.
An unplanned cheat day can erase a week's calorie deficit and has no trial support. Structured diet breaks are different — one trial found they improved weight loss, though another found no body-composition edge.
Intensive family-based behavioural programmes produce small, real cuts in children's BMI; the newer weight-loss drugs produce much larger ones, but the weight returns when they stop.
A tightly controlled crossover trial found late eating increased hunger, cut waking energy expenditure and shifted fat-tissue gene expression. The population data show a 17% higher odds of obesity.
Two WHO bodies reported on the same day in July 2023 and reached findings that sound contradictory. Both were right, because they were answering different questions.
Pooling 13 randomised trials, people assigned to eat breakfast ended up 0.44 kg heavier and ate 260 more calories a day than people assigned to skip it. The trials were small, short and mostly low quality.