hormones
Cortisol
A glucocorticoid hormone released by the adrenals during stress that, when chronically elevated, promotes central fat storage.
Cortisol follows a daily rhythm (high in the morning, low at night) and is essential for survival. The problem is chronic elevation from poor sleep, under-eating, over-training, and psychological stress — which promotes visceral fat storage, raises hunger, and suppresses thyroid output. Stress-management, 7–9 hours of sleep, and avoiding extreme deficits are the most evidence-backed ways to normalise it.