mechanism of lipoprotein lipase

The job of determining how fuels (glucose and fatty acids) will be used, whether we will store them as fat or burn them for energy, is carried out primarily by the hormone insulin in concert with an enzyme known technically as lipoprotein lipase - LPL, for short. (Sex hormones also interact with LPL, which is why men and women fatten differently.)

In the Eighties, biochemists and physiologists worked out how LPL responds to exercise. They found that during a workout, LPL activity increases in muscle tissue, and so our muscle cells suck up fatty acids to use for fuel. Then, when we're done exercising, LPL activity in the muscle tissue tapers off and LPL activity in our fat tissue spikes, pulling calories into fat cells. This works to return to the fat cells any fat they might have had to surrender - homeostasis, in other words. The more rigorous the exercise, and the more fat lost from our fat tissue, the greater the subsequent increase in LPL activity in the fat cells. Thus, post-workout, we get hungry: our fat tissue is devoting itself to restoring calories as fat, depriving other tissues and organs of the fuel they need and triggering a compensatory impulse to eat. The feeling of hunger is the brain's way of trying to satisfy the demands of the body. Just as sweating makes us thirsty, burning off calories makes us hungry.