Is a Calorie a Calorie (1)?

Is a Calorie a Calorie?

By MARK BITTMAN

I was looking forward to “Why Calories Count,” the new book by Marion Nestle and Malden Nesheim. I figured gaining an advanced education in calories might allow me to better understand diet and weight gain. These two are not faddists but clear thinkers: actual scientists. But of course there is more to weight gain than the calorie.

This was obvious from the moment I asked Ms. Nestle a key question: “Is a calorie a calorie?” This sounds simple, and if the answer is “yes,” all you do is take in fewer calories than you expend and you’ll lose weight. It need go no further than that.

It might help to first define a calorie, and that’s easy: it’s a measure of the energy derived from a food source. A gram of fat has been determined to have nine calories and a gram of protein or carbohydrate four calories; so for any given measure, fat has more than twice as many calories as protein or carbs. Those numbers are not perfectly accurate, but they’re good enough.

A food isn’t a food — they’re all different — but since a calorie is just a measurement of energy, how can it vary? When I asked my question, Nestle’s answer was confounding: “Yes and no,” she said, adding, “It’s Talmudic.” Because calories change as they enter the body, the nine grams for fat and four for everything else turn out to be not very accurate measures at all; besides, foods are only rarely one thing or another.

Here’s what is true, she said: “The studies that have measured calorie intake, that have put people on calorie-reduced diets and measured what happened, show no difference in weight loss based on composition of the diet.” When people are essentially incarcerated, when all intake is weighed and measured, they will lose weight if the calories in their diets are reduced — regardless of the composition of the diet.

“That’s why we hear a calorie is a calorie,” she said. “But no one lives under experimental conditions, and foods are complicated mixtures: fiber makes a difference and form makes a difference.” (Fiber is special because it’s not digested or digested incompletely. Most of its calories don’t get into the body, which is one reason why fruits and vegetables, which are high in fiber, help with weight loss.)

The “calorie is a calorie” argument is widely used by the processed food industry to explain that weight loss isn’t really about what you eat but about how many calories you eat. But if it were just about calories, you could eat only sugar and be fine. In fact, you’d die: sugar lacks essential nutrients.

That’s an obvious case. But although a calorie may be a calorie when people talk about weight loss and nothing else, there are other factors involved. And once you get past my perhaps lame “Is a calorie a calorie” question, you can begin to see something approaching the truth. For one thing, says Nestle: “There are dozens of factors involved in weight regulation. It’s hard to lose weight, because the body is set up to defend fat, so you don’t starve to death; the body doesn’t work as well to tell people to stop eating as when to tell them when to start.”