Last week I addressed questions from a reader in Oregon on the subject of calories. A recent step on my own scale reminded me to pay a little more attention to his follow-up questions:
"Our nominal diet is supposed to be about 2,000 (US) calories per day, enough to keep a reasonably active adult going but hopefully not putting on weight. How did 'they' come up with this number?"
_ Phil, Oregon
Dear Phil: "They" are committees of nutrition experts in Canada and the US Food and Nutrition Board Institute of Medicine. These committees periodically review current nutrition research to establish Dietary Reference Intakes (DRI) for nutrients and calories.
The 2,000 calorie per day guideline was established when the U.S. Food and Drug Administration (FDA) needed to come up with one general value for calories that is reasonable for adults and children over the age of 4. This is the Daily Value (DV) that you see on food labels. So the 2,000 calories a day is used as a general guide for nutrition advice.
Obviously our calorie needs go up or down from there depending on our age (we require fewer calories as get older), sex (men tend to require more calories than women), height (your 6-foot-4-inch uncle needs more calories than his 5-foot-2-inch wife) and weight (a Prius requires more fuel than a F-250 pick-up truck). And don't forget activity level. A marathon runner who suddenly becomes a couch potato needs way fewer calories, regardless of his or her age, sex, height or weight.
Here's a cool resource to help you calculate your actual calorie needs: https://www.choosemyplate.gov/resources/MyPlatePlan .
Last question: "In the U.S., our nutrition labels tell us the number of calories. But in fact a U.S. "calorie" is actually a kilocalorie per the scientific definition of a calorie, the amount of energy needed to heat a gram of water by one degree centigrade. In Europe, the labels correctly show as kilocalories. Are Americans assumed to be too fragile to know that we are taking in kilocalories with each bite?"
I'm not qualified to know who assumes what about Americans. In nutrition circles, though, we still refer to a patient's calories needs in kilocalories (kcals). According to the current Dietary Guidelines for Americans, "a kilocalorie is the amount of energy (heat) required to raise the temperature of 1 kilogram of water 1 degree centigrade. If not specified explicitly, references to "calories" refer to "kilocalories."
And remember calories only come from fat, protein, carbohydrates (sugars and starches) and alcohol. If my weight is creeping up, I need to cut back on one or more of these calorie sources.
