Three competing models for how body weight stabilizes — and the review’s proposed synthesis is the third.
What the evidence says
- Set point model: Adipose tissue signals fat stores (via leptin) to brain, which compares to target and adjusts hunger/metabolism[1]
- Settling point model: Weight stabilizes based on environmental factors without active defense of specific target[1]
- Dual intervention point model: Upper and lower boundaries where active regulation kicks in, with passive dynamics between them[1]
- What defeats the set point model: it cannot explain the obesity epidemic — if tight biological regulation existed, why do most people in Western countries gain weight across their lives — nor why obese individuals defend an elevated weight rather than returning to a lower target[1]
- What defeats the settling point model: it cannot explain the ~50–70% heritability of BMI, why people differ so much in susceptibility within the same environment, or the powerful hunger signals that follow weight loss. The heritability figure carries the review’s own caveat and the argument leans on it: ”heritability estimates vary according the study design… In general, heritability estimates tend to be higher when derived from twin studies compared with family and adoption studies”, and classic twin studies ”will overestimate h2″ under stated conditions[1]
- The dual intervention point model’s rationale is evolutionary: the lower boundary reflects starvation risk under strong selection, while the upper boundary historically reflected predation risk — a pressure the review argues was removed in humans roughly two million years ago, allowing the upper bound to drift[1]
- Genes may encode the intervention points themselves rather than directly controlling intake or expenditure, which would explain why people resist or gain weight so differently in identical environments[1]
- But the measured genetics are thin, and the review says so: a GWAS of 123,865 individuals of European ancestry identified 32 variants associated with BMI at genome-wide significance, explaining only 1.5% of BMI variance — which the review says ”roughly corresponds to 3% of the genetic variance based on an estimated BMI heritability of 0.5″[1]
- Neither pure model is adequate; gene-by-environment interactions dominate weight regulation[1]
- Set point explains weight regain after dieting; settling point explains environmental contributions[1]