Hacker News Reader

The point is that it is difficult for people to follow the diet consistently.

Or, you put in less energy and consequently lower your metabolism and move less and feel more tired to compensate while your reserves don't change, or even increase, or the difference could be made up by destruction of muscle or organs rather than fat.

If it was as you suggest, you could eat nothing and not starve as long as you have fat reserves.

Actually the body goes in to starvation mode and starts destroying muscle to lower energy consumption not to mention the fact that going on a diet lowers blood sugar so you feel tired and stop consuming as much energy.