Low 24-hour core body temperature as a thrifty metabolic trait driving catch-up fat during weight regain after caloric restriction.

When a person eats significantly fewer calories for a long time, their body burns fewer calories at rest and loses muscle tissue; if they then return to normal eating without adjusting calorie intake downward, they gain fat.

After recovering from severe food restriction, rats have lower core body temperature than rats that were never restricted, even when both groups eat the same amount and move the same amount. This shows that the drop in energy use comes from internal metabolic changes, not reduced physical activity.

In male Sprague-Dawley rats recovering from food restriction, a consistent drop in core body temperature by 0.27°C is linked to greater fat regain compared to lean mass, even when activity levels and room temperature are held constant, indicating that a lower internal temperature setting may increase metabolic efficiency during weight recovery.

When rats lose weight through food restriction and then regain it, their body temperature stays lower than normal even in a warm environment, showing that this change is not caused by cold exposure but by a central metabolic adjustment.

In rats that regain weight after a period of severe food restriction, body temperature remains low even though the molecular mechanism in fat tissue responsible for heat production returns to normal levels.

After periods of severe food restriction, rats regain fat instead of muscle, and this is linked to a 10–13% drop in total energy use, partly due to lower body temperature that reduces the energy needed to maintain warmth by 25–30%.