What drives people to overeat?
Balancing food intake and energy expenditure is a complex process that involves two systems in the brain: a need-based system that triggers hunger when the body requires energy, and a reward-based system that triggers the desire to eat. The two sites are close to each other anatomically and work like parts of a machine.
The need-based system involves metabolism. It’s the part that monitors calories and receives signals from the body — for example, shifting levels of glucose or the hormones insulin and leptin — that tell you you’ve eaten enough and it’s time to stop. If you’re genetically prone to becoming obese, you may not be very sensitive to those signals, and you’ll eat more before stopping than someone who is not obesity-prone.
Everyone’s system strives to maintain a constant weight, or set point. The set point can be shifted upward, but only over time. If you overeat during a single meal — say, a big Thanksgiving dinner — your body goes into overdrive to try to get rid of those excess calories. But if you gain weight gradually, your body eventually will become accustomed to a higher weight and work to maintain it.
