A small direct effect is real. Hold total calories fixed and shift only the clock, and early eaters lose about one to three more kilograms over a weight-loss stretch ^{1 2}. Your body burns about half as many calories digesting dinner as it does breakfast ³, and the same meal spikes blood sugar roughly 17% higher in the evening ⁴. Move eating earlier and, in prediabetes, insulin sensitivity and blood pressure improve with no weight loss at all ⁵.

The bigger effect runs through sleep. A heavy late meal loosens the valve at the top of the stomach and floods the next hours with reflux you barely wake for ⁶. Short, fragmented sleep then raises the hunger hormone ghrelin and drops the fullness hormone leptin, so tomorrow's appetite drifts up by several hundred calories ⁷. The pizza is fattening because you sleep worse and eat more the next day.

Shrinking your window late does little. A noon-to-8pm eating window with matched calories barely moves weight ⁸, and a year-long trial found the same loss with or without a late time-restricted window ⁹. Skipping meals only helps if it pulls eating earlier.

Two levers, and the first one is most of the win.

Sleep shifts first, in nights. Reflux fades, the 3am wake-up mostly stops, and mornings start with real appetite instead of fog. Within a fortnight the hunger hormones recalibrate with the sleep they are no longer losing ⁷, and the afternoon coffee drops a cup. Across months the weight benefit accrues at the modest rate trials actually saw, a kilo or two, more with calorie attention ¹. Postprandial blood sugar and fasting insulin trend down ⁵.