The hormones sleep controls
Ghrelin (hunger) rises with short sleep.
Leptin (fullness) falls with short sleep.
Cortisol stays elevated, encouraging visceral fat storage.
Insulin sensitivity drops after just one night under 5 hours.
The Chicago study
In a 2010 trial (Nedeltcheva et al.), dieters sleeping 5.5 hours vs 8.5 hours lost the same total weight — but 55% less fat and 60% more lean mass in the short-sleep group.
Practical target: 7–9 hours, consistent bed and wake times, dark cool room, no screens for 30 minutes before bed.
