Body weight is a function of three things: metabolism, caloric intake, and caloric expenditure. There is little that one can do about the first of these, but the second and third are well within one’s control. I like my weight where it is (154 pounds). To stay there, I must expend as many calories as I take in (or, conversely, take in no more calories than I expend). Yesterday’s 6.6-mile run, for example, burned off 726 calories, which allowed me to eat a piece of cake in addition to my regular food. If I began taking in more calories than I expended, I’d gain weight. Today, I thought of an analogy. If you spend more money than you earn, you go into debt. Many people are deep in debt to credit-card companies. They lack discipline. Many people are obese. They lack discipline. In both cases, the trick is to live within one’s means. If you want to spend more, earn more. If you want to eat more, exercise more. Then again, maybe you don’t mind being in debt (which means paying interest) or overweight (which means risking various diseases). That’s fine. Each of us must make choices. There ain’t no such thing as a free lunch.

Addendum: Here is the Caloric Needs Calculator that I use.

Addendum 2: Here is a New York Times story about obese football players.