The Cost of Prediction

That’s what homeostasis implies — a system that detects deviation and corrects it. Temperature drops, heating kicks in. Blood sugar falls, hunger rises. Neat, reactive, and not quite right.

In 1988, Peter Sterling and Joseph Eyer proposed a more accurate model: allostasis, “stability through change.” Your body doesn’t defend fixed set points. It predicts what’s coming and adjusts in advance. Cortisol begins surging thirty minutes before you wake — not because anything’s wrong, but because your brain knows that standing up is about to become a cardiovascular problem. Insulin releases at the smell of food, before a single molecule of glucose hits your blood.

The brain runs everything, constantly forecasting demand and pre-tuning physiology to meet it. There’s no “correct” blood pressure — only the right one for what’s about to happen.

This matters because prediction has a price. Bruce McEwen called it allostatic load: the cumulative wear from a system that never stops anticipating. When the forecasts are chronically dire — poverty, discrimination, unrelenting work stress — the prediction machinery itself degrades. The hippocampus shrinks. The immune system misfires. The body ages faster than the calendar says it should.

Homeostasis says disease happens when the body can’t maintain balance. Allostasis says disease happens when the cost of maintaining it gets too high.