A defended range, not a fixed number
Set point theory proposes that the body regulates weight around a preferred range rather than a single value, using feedback loops involving hormones such as leptin and appetite and metabolic responses. When weight drops below the range, hunger and energy conservation tend to rise; when it climbs above, those signals can ease. The result feels like a thermostat resisting change in either direction.
The evidence is better described as a defended range with some flexibility than a rigid setpoint, and the strength of the defense varies between people.
Why crash diets snap back
Short-term aggressive dieting often triggers the body's defenses (increased appetite, reduced spontaneous movement, modest metabolic slowdown), which can drive regain once the diet ends. Sustained habit change appears more able to shift the defended range over time, which is one reason gradual approaches tend to hold better than rapid ones.
How much the range can move, and how quickly, remains debated and is individual. This is general educational information, not medical advice.