You can't go anywhere without being confronted by calories. Restaurants now print calorie counts on menus. You go to the supermarket and there they are, stamped on every box and bottle. You hop on the treadmill and watch your "calories burned" click upward.
But just what are calories? The more calories we take in, the more flab we add—and if we cut back on them, then flab starts to recede too, right? After all, at face value, calories seem to be the factor by which all foods should be judged. But if that were true, 500 calories of parsnips would equal 500 calories of Double Stuf Oreos.
Not quite. There's nothing simple about calories. Learn the distinctions and lose the lard.
Myth #1: Calories Fuel Our Bodies
Actually, they don't
A calorie is simply a unit of measurement for heat; in the early 19th century, it was used to explain the theory of heat conservation and steam engines. The term entered the food world around 1890, when the USDA appropriated it for a report on nutrition. Specifically, a calorie was defined as the unit of heat required to raise 1 gram of water 1 degree Celsius.
To apply this concept to foods like sandwiches, scientists used to set food on fire (really!) and then gauge how well the flaming sample warmed a water bath. The warmer the water, the more calories the food contained. (Today, a food's calorie count is estimated from its carbohydrate, protein, and fat content.) In the calorie's leap to nutrition, its definition evolved. The calorie we now see cited on nutrition labels is the amount of heat required to raise 1 kilogram of water by 1 degree Celsius.
Here's the problem: Your body isn't a steam engine. Instead of heat, it runs on chemical energy, fueled by the oxidation of carbohydrates, fat, and protein that occurs in your cells' mitochondria. "You could say mitochondria are like small power plants," says Maciej Buchowski, Ph.D., a research professor of medicine at Vanderbilt University medical center. "Instead of one central plant, you have several billion, so it's more efficient."
Track carbohydrates, fats, and protein—not just calories—when you're evaluating foods.
Myth #2: All Calories Are Created Equal
Our fuel comes from three sources: protein, carbohydrates, and fat. "They're handled by the body differently," says Alan Aragon, M.S., a Men's Health nutrition advisor. So that old "calories in, calories out" formula can be misleading, he says. "Carbohydrates, protein, and fat have different effects on the equation."
Example: For every 100 carbohydrate calories you consume, your body expends fuve to 10 in digestion. With fats, you expend slightly less (although thin people seem to break down more fat than heavy people do). The calorie-burn champion is protein: For every 100 protein calories you consume, your body needs 20 to 30 for digestion, Buchowski says. Carbohydrates and fat give up their calories easily: They're built to supply quick energy. In effect, carbs and fat yield more usable energy than protein does.
If you want to lose weight, make protein a priority at every meal. Adding them to snacks—especially before you exercise—can help too.
Myth #3: A Calorie Ingested is a Calorie Digested
It's not that simple
Just because the food is swallowed doesn't mean it will be digested. It passes through your stomach and then reaches your small intestine, which slurps up all the nutrients it can through its spongy walls. But 5 to 10 percent of calories slide through unabsorbed. Fat digestion is relatively efficient—fat easily enters your intestinal walls. As for protein, animal sources are more digestible than plant sources, so a top sirloin's protein will be better absorbed than tofu's.