The lipostat: a defended adiposity setpoint

Body fat is regulated, not merely accumulated. Adiposity sits in a defended R19 basin; sustained sub-spinodal over- or underfeeding shifts the defended state only modestly and is actively opposed (leptin-melanocortin) (True). A supra-spinodal chronic drive would cross to a NEW basin -- the obesity setpoint of the next section.

RE2. The lipostat is a defended setpoint with the usual hard edge: modest chronic forcing is opposed, but a large enough sustained drive crosses the spinodal to a new defended adiposity. Mechanism [V]; the adiposity setpoint is [L]; absolute kg/BMI is [O].

Opposed, within limits

Sustained overfeeding and underfeeding both shift the defended state only modestly and are pushed back (True). The lipostat behaves like the thermostat: robust regulation up to a threshold.

The edge is the disease

Crucially, a chronic drive ABOVE the spinodal does not just shift the setpoint -- it crosses to a different basin. That crossing is exactly how obesity is framed in the pathology section: not a failure of will but a defended setpoint that has moved.