Why a bad night's sleep makes you raid the fridge

It feels like a lack of willpower, but reaching for snacks after a short night is largely hormonal. Two hormones govern hunger: leptin, which signals fullness, and ghrelin, which signals hunger. When you cut sleep short, leptin drops and ghrelin rises — so your body simultaneously feels less satisfied and more hungry, even when you've eaten enough.

The cravings aren't random, either. Sleep-deprived people tend to reach for calorie-dense, sugary, and salty foods rather than vegetables. Research also points to heightened activity in the brain's reward regions and blunted signaling in areas handling impulse control, which makes tempting food harder to resist.

There's a slower effect too: chronically short sleep is linked to reduced insulin sensitivity, meaning the body handles blood sugar less efficiently. Over time, this combination of extra hunger, poorer food choices, and altered glucose handling is one reason short sleep is associated with weight gain and metabolic problems — not because tired people are lazy, but because their internal appetite signals are genuinely miscalibrated.