When is a calorie not just a calorie?

by Mary C. Weaver, CSCS on December 23, 2012

some calories are more equal than others

We’re only human, so we love solutions that sound simple. Like “Carbohydrates make you fat, so just stop eating them and you’ll shed your fat effortlessly.” That’s been a popular myth for years now.

Before the carbohydrate myth came the fat myth: “If you eat fat, you’ll get fat—so just slash all the fat from your diet.” Like the myth about carbs, this one is a terrific recipe for feeling bad and even looking bad, since you need good fat for healthy skin and hair (and a whole lot more).

Both of those wrong-headed, simplistic solutions suggest that calories don’t count—just the kinds of food we eat.


No matter what food plan you follow to burn fat, the whole point is to create a caloric deficit. If you’re losing fat on a low-carb diet, it’s because you’re consuming fewer calories than your body needs.

Same thing for a low-fat diet, an all-turnip diet, a Twinkie diet, or a grapefruit diet. Create a caloric deficit, and you will burn fat. Admittedly, some diets also build health . . . and eating mostly turnips, Twinkies, or grapefruit won’t.

But there is one secret weapon low-carb diets have if they are also high-protein diets: the thermic effect of food.

Some calories are more equal than others

As I’ve explained elsewhere on this site, every bodily process has an energy cost. We burn calories breathing, sleeping, digesting food, circulating blood, and so on.

The energy cost of breaking down what we eat is called the “thermic effect of food.” And it turns out that digesting protein costs much, much more than breaking down fats or carbohydrates. Here are the facts:

  • digesting fat requires 2 to 3 percent of calories
  • digesting carbs takes 6 to 8 percent
  • digesting protein requires 25 to 30 percent.

In real terms, that means if you eat 100 calories of fat, about 97 to 98 calories are available for use by the body—to be burned as fuel or deposited as fat.

When you eat 100 calories of carbs, 92 to 94 calories are available.

But when you consume 100 calories of protein, only 70 to 75 calories can be used to build or repair tissues, burned as energy, or converted into fat and stored as excess energy.

You can see the implications.

Calories definitely count—but some count more than others.

Is low-carb the answer?

Does this mean I recommend low-carb plans? Not at all. Some people seem to thrive on them, and that’s just fine. But your body is a machine whose preferred fuel is carbohydrate: blood sugar and stored glycogen in your muscles and liver.

Anyone who exercises regularly needs carbohydrates to feel and perform her best. If you don’t believe me, try a week without grains, potatoes, beans, fruits, and other starchy and sugary carbs. Exercise normally. Take notes on your energy level, especially after three or four days of working out but not eating a significant amount of carbohydrates.

Now restore the carbs for a week and see how you feel.

A healthy diet is a mix of carbs, protein, and fats. Of course, your ideal proportions of those nutrients may be different from mine.

I like a ratio of around 50 percent calories from carbohydrate, 25 percent from protein, and 25 percent from fat. Depending on your physiology and your exercise program, you may well benefit from greater or smaller percentages of these macronutrients.

But when you’re making dinner decisions and choosing between, say, a skinless grilled chicken breast, brown rice, and broccoli (an excellent mix of lean protein, whole grain, and veg) or pizza (scrumptious but higher in fat and carbs and lower in protein), remember the hidden calorie-burning benefit of digesting that lovely protein.

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