The Truth About Calories

They get a bad rap, but your body needs calories. Most are used up by functions like breathing, making your heart beat, talking, and walking. If any are left over, your body stores most of them in the form of fat. But it also stores some in your liver and muscles that can be released quickly into your bloodstream if you need a burst of energy.

Everyone's calorie needs are different, and the 2,000 per day you see listed on nutrition labels is really only right for a small group of fairly active women who aren’t trying to lose weight. To get a better sense of how many calories you probably need each day, visit the Calorie Control Council’s Healthy Weight Calculator.

That’s only a rough estimate based on research of obese women in the 1950s. The number of calories you’d need to cut out of your diet to lose weight depends on several things, including your sex, your age, and how active you are.

It's true that you need to take in fewer calories than you burn off if you want to lose weight. But be careful about going too low. If you cut too many, your body may think food is scarce, click into starvation mode, and burn off calories more slowly. In other words, your body is going to hang onto that small number of them very tightly. 

In one study, people who cut their daily calories by this amount lost an average of about 20 pounds over 2 years -- and slowed down their metabolism. While that might not sound like a good thing, it means their bodies needed fewer calories to carry out basic functions, and that might delay the aging process. 

While some are very low in calories, there’s no evidence that any food is “negative-calorie.” Only about 5% to 10% of all the calories you burn each day are used to digest food and store energy.

Fat has more than twice as many calories per gram (9) as carbs and protein (4 each), but there's no need to shun it completely. You need all those nutrients -- along with vitamins, minerals, and fiber -- for a healthy diet. 

How hard you're pulling weeds and clipping hedges matters, as does your body size, but the message is clear: You don't have to go to the gym to burn calories. Everyday activities can add up.

A small splash of olive oil and vinegar dressing might seem harmless enough, but 2 tablespoons can tack 150 calories onto your meal. Hummus is a close second, at 110 calories per 2 tablespoons, though the protein and fiber in it may help fill you up so you eat less. If your goal is to keep the calorie count low, go with honey mustard. Despite the slightly sweet flavor, 2 tablespoons have only 40 calories, and you probably won’t need that much to add lots of flavor.

Moms-to-be may be "eating for two," but they don't need to double their daily amount. During the second trimester, they should aim for about 340 more calories per day. In the third trimester, when the baby is larger, they might need about 450 additional calories a day. Most of these should come from healthy, nutrient-rich foods like protein, whole grains, and produce.