Yo-yo dieting
A cycle of weight loss and regain, often beyond the starting weight, sustained by the metabolic and hormonal adaptations that follow any marked restriction.
Yo-yo dieting describes the pattern of weight loss followed by regain, with each cycle often leaving the weight above where it started. It is not a problem of willpower: it is the predictable consequence of several physiological adaptations.
Three mechanisms combine. Energy expenditure drops by more than weight loss alone would explain, notably through a reduction in spontaneous activity. Muscle mass falls if protein intake is insufficient, which lowers the basal metabolic rate for the long term. Finally, hunger signals change: ghrelin rises and leptin falls.
These adaptations persist long after the diet ends, and this is the most important point. The body does not return to its previous state as soon as you eat normally again: it keeps spending less and asking for more, sometimes for months. Regain is therefore not a lapse, it is a biological response.
The known ways to limit this are a moderate rather than drastic deficit, maintained protein intake, resistance training to preserve muscle, and a stabilisation phase that is genuinely planned. Our guide yo-yo dieting: why diets fail explains these strategies.