Last week, federal health officials issued a report saying that Americans got 11 percent of the calories in their diets came from fast food restaurants like McDonald's, Burger King and Pizza Hut. With all the health risks associated with fast food and obesity, this new study could hardly be considered good news.
In addition to making me pass up Little Caesars for a home-cooked meal, this report also left me wondering about calories. I mean, we spend an awful lot of time talking about them, tracking them, avoiding them and, of course, feeling guilty when we consume too many of them. But what, exactly, are calories and what do they have to do with food?
Dr. Prescott prescribes
Most of us associate calories with food, but the calorie is actually a measure of heat energy. You know how your car generates heat — energy — by burning gasoline? Well, our bodies generate energy by burning food, and calories are the way we measure how much “fuel” a particular item on our plate can provide.
A food calorie (technically, a kilocalorie) is the amount of heat required to raise the temperature of one kilogram of water one degree Celsius. To figure out how many calories something possesses, scientists use a device known as a bomb calorimeter. They place a sample inside the device, use a small electric charge — the “bomb” — to ignite it, then see how much the water in a neighboring chamber heats up.
Lots of things that we'd never dream of putting in our mouths possess calories. For example, if our bodies could digest gasoline, a gallon would be worth about 31,000 food calories. That's about the same as 50 Big Macs. But when doctors and nutritionists talk about calories, they mean the ones generated by substances that our bodies actually can use to fuel our muscles and organs.
Of the foods we eat, fat is the richest source of energy, possessing nine calories in each gram. Protein and carbohydrates each have four calories per gram, while soluble fiber has about two calories per gram. For those among us who like a drink now and then, every gram of (undiluted) alcohol holds seven calories.
How does it all add up? While energy needs vary depending on age, body size and activity level, most of us require about 2,000 calories a day to go about our business.
Unlike cars, though, when we put extra fuel into our tanks, it just doesn't spill out onto the ground. Instead, our bodies convert that excess to fat. And it adds up quickly: Every 3,600 calories you pack away means another pound on your belly. Or elsewhere.
The key to keeping weight off is to limit the amount of calories you take in to the amount you burn off. Sounds easy enough, right? Just remind me of that next time I'm staring down a nice rib-eye at Red Prime. I might end up eating my words.
Prescott, a physician and medical researcher, is president of the Oklahoma Medical Research Foundation. Cohen is a marathoner and OMRF's senior vice president and general counsel.