Metabolism does not slow in middle age

An international team led by researchers at Duke University pooled energy expenditure measurements, taken with the gold-standard doubly labeled water method, from 6,421 people ranging from eight days old to 95 years old across 29 countries. They wanted to map how metabolism actually changes across a human life.

Daily energy expenditure, adjusted for body size, stayed remarkably flat from age 20 to 60, neither rising nor falling in any meaningful way across those four decades. Metabolism changed mainly at the edges of life: it peaked near age one, eased down to adult levels by 20, and declined gradually only after 60.

The finding means that typical midlife weight gain cannot be blamed on a slowing metabolic rate, since the data showed none happening. It points instead toward other factors, such as diet and activity. The same dataset showed that, adjusted for the mother's added body mass, energy use stayed at normal adult levels through pregnancy.

Forty flat years, no slowdown.