Body Weight Set Point

The set point model holds that body weight is a regulated variable, defended by a feedback loop with leptin as the main afferent signal and hypothalamic circuits as the controller. Push weight down and the loop responds: leptin falls, ghrelin rises, satiety signalling weakens, and energy expenditure drops by more than the loss of tissue mass alone predicts. The rival settling point model keeps the physiology but drops the reference value: weight settles wherever intake and expenditure balance in a given environment.

The supporting human data are old and consistent. Leibel and colleagues showed that a ten percent reduction in body weight lowered total energy expenditure well beyond what the smaller body predicts. Sumithran and colleagues reported in 2011 that appetite hormones and hunger ratings remained shifted toward weight regain a full year after a ten-week very-low-energy diet. Six-year follow-up of Biggest Loser contestants found persistent suppression of resting metabolic rate alongside substantial regain.

For drug trials this is the background every result should be read against. Weight loss that persists only while a drug is given is what a defended-weight model predicts, which is why withdrawal extensions matter more than the headline figure. When semaglutide was stopped after the STEP 1 treatment period, participants regained roughly two thirds of the lost weight over the following year, with cardiometabolic markers tracking back with it.

The term gets stretched in both directions. Advocates use it to argue that behavioural change is futile, which the same data do not support; marketers use it to claim a compound resets the set point downward, for which there is no human evidence. Set point is also used where settling point is meant, and the two predict different things when the environment, rather than the person, changes.