Evidence Base

The studies behind every answer.

Original papers. Full analysis. Every finding linked to its DOI so you can check our work.

The Scale Lied: Same Diet, Opposite Results Researchers put the same people on the same calorie-restricted diet twice. Both times the scale dropped by 3 kg. But one group lost fat while the other lost muscle, and sleep was the only thing that changed. Nedeltcheva et al. · 2010 · Annals of Internal Medicine · n=10
Your Protein Shake Couldn't Fix What Sleep Broke Researchers fed the same protein meals to the same people after sleeping and after staying up all night. The sleep-deprived group built 18% less muscle — not because the food was wrong, but because the muscle couldn't use it. Lamon et al. · 2021 · Physiological Reports · n=13
The Night Your Brain Ordered an Extra Meal A meta-analysis of eleven studies found that sleep-deprived people eat a specific, measurable calorie surplus — and the explanation most health content gives for why is the wrong one. HK et al. · 2017 · European Journal of Clinical Nutrition · n=496
What Five-Hour Nights Actually Do to Testosterone Researchers found one week of five-hour nights crashed testosterone by 10–15% in young men. Then later studies couldn't replicate it. The honest answer requires both findings. Leproult et al. · 2011 · JAMA · n=10
Your Body Fat Readings Looked Normal. The CT Scanner Disagreed. Researchers restricted sleep to four hours and measured body composition two ways. Standard tools saw nothing. CT imaging found 11% more fat wrapping the organs — and recovery sleep didn't reverse it. Covassin et al. · 2022 · Journal of the American College of Cardiology · n=12
Your Strength Survives a Bad Night. Your Accuracy Doesn't. 77 studies measured exactly what short sleep costs every kind of workout — and the gap between what breaks and what holds is bigger than anyone admits. Craven et al. · 2022 · Sports Medicine · n=959
They Slept In All Weekend. It Fixed 9%. A controlled lab study found weekend catch-up sleep barely dented the week's sleep debt — and the group that tried to recover ended up with worse insulin sensitivity than the group that never caught up. Depner et al. · 2019 · Current Biology · n=36
23 Studies Just Cleared Your Evening Workout The largest meta-analysis ever conducted on evening exercise and sleep found zero significant harm, with one specific, easy-to-avoid exception. Stutz et al. · 2019 · Sports Medicine · n=275