I was fascinated by [this recent column](http://www.nytimes.com/2008/08/05/health/05brod.html) about the health benefits of coffee, even though I rarely drink coffee. No, the part that grabbed me was this:

> Although caffeine speeds up metabolism, with 100 milligrams [about one cup of coffee] burning an extra 75 to 100 calories a day, no long-term benefit to weight control has been demonstrated.

Upon reading this, I reached for the back of my envelope. (I used to have one of those calculator watches, but the back of an envelope works just as well, don’t you find?) Burning an extra 75 calories per day, all other things being equal, should translate to an annual weight loss of 8 pounds.

But the actual weight loss experienced by people who start drinking coffee (or who switch from decaf to caf) is: 0 pounds. What’s going on?

The simplest explanation is probably correct: drink coffee and you’ll burn more calories. Burning more calories makes you feel hungry. Feeling hungry causes you to eat more.

Just look at what happens when people switch from regular soda to diet. It’s easy to consume several hundred calories of Coca-Cola per day. Switch that out for diet (approximately zero calories) and you should see swift and sustained weight loss.

Of course, diet sodas don’t make people lose weight, any more than coffee does. You switch from regular to diet, you get hungrier. I’m sure the same is true for baked Lays, Olestra, skim milk, stevia, eating off smaller plates, and so on.

Is this an oversimplification? You bet. I doubt our bodies treat every calorie the same. But so much of what’s written about diet and weight seems to assume the body is so stupid it doesn’t know what calories are at all, and our brains will just shrug at Diet Coke and say, “Seems the same to me.”