Sleep and fat loss

Same diet, 5.5 h vs 8.5 h sleep: 55% less fat lost. Sleep is a fat-loss tool.

Galpin: it is categorically simple to lose fat — a calorie deficit — and practically hard. What people miss is that sleep decides what you lose. In the landmark crossover trial, dieters sleeping 5.5 h lost 55% less fat and 60% more lean mass than the same people sleeping 8.5 h, on identical calories, and were hungrier.

Mechanisms: two nights of short sleep raise ghrelin, drop leptin and increase appetite ~24% (especially for calorie-dense carbs); four nights make fat cells ~30% less insulin-sensitive; five nights of restriction reduce muscle protein synthesis ~18%. Sleep-restricted people gain about a kilo in five days, mostly from late-night eating.

The flip side is remarkable: extending sleep by ~1.2 h in a real-life RCT cut intake by ~270 kcal/day with no dietary advice at all. Short sleepers have ~55% higher odds of obesity, and each hour of social jet lag adds ~33% odds of being overweight.

SleepShred tracks weight/waist and pairs weekly weight change with weekly average sleep, so you can see whether your bad weeks are sleep-short weeks.

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Educational summary of published research, not medical advice. Screening scores are not diagnoses. If a score is elevated or you feel unwell, talk to a clinician.