From all you hear, you'd think fat and calories are really bad for you. It's true that many people are eating more fat and calories than they need. But we all require a certain amount of fat and calories in our diets to fuel our growth and activities — everything from solving a math problem to racing up and down the soccer field. So what's the truth on fat and calories?

Fats, or lipids, are nutrients in food that the body uses to build nerve tissue (like the brain) and hormones. The body also uses fat as fuel. If fats that a person has eaten aren't burned as energy or used as building blocks, they are stored by the body in fat cells. This is the body's way of thinking ahead: By saving fat for future use, it plans for times when food might be scarce.

A calorie is a unit of energy that measures how much energy food provides to the body. The body needs calories to function properly.


Calories

Food labels list calories by the amount in each serving size. Serving sizes differ from one food to the next, so to figure out how many calories you're eating, you'll need to do three things:

1) Look at the serving size.
2) See how many calories there are in one serving.
3) Multiply the number of calories by the number of servings you're going to eat.

For example, a bag of cookies may list three cookies as a serving size. But if you eat six cookies, you are really eating two servings, not one. To figure out how many calories those two servings contain, you must double the calories in one serving.

The calories in food come from carbohydrates, proteins, and fats. A gram of carbohydrate contains 4 calories. A gram of protein also contains 4 calories. A gram of fat, though, contains 9 calories — more than twice the amount of the other two.

That's why one food with the same serving size as another may have far more calories. A high-fat food has many more calories than a food that's low in fat and higher in protein or carbohydrates.

Fat

When it comes to fat, labels can say many things. Low fat, reduced fat, light (or lite), and fat free are common terms you're sure to see on food packages. The U.S. government has strict rules about the use of these phrases: By law, fat-free foods can contain no more than 0.5 grams of fat per serving. Low-fat foods may contain 3 grams of fat or less per serving. Foods marked reduced fat and light (lite) are a little trickier, and you may need to do some supermarket sleuthing.

For instance, a ½-cup serving of vanilla ice cream contains:

- 178 total calories
- 2 grams of protein
(2 grams times 4 calories = 8 calories from protein)
- 12 grams of fat
(12 grams times 9 calories = 108 calories, or 61%, from fat)
- 15.5 grams of carbohydrate
(15.5 grams times 4 calories = 62 calories from carbohydrate)

Compare this with the same serving size (½ cup) of cooked carrots:

- 36 total calories
- 1 gram of protein
(1 gram times 4 calories = 4 calories from protein)
- 0 grams of fat
(0 grams times 0 calories = 0 calories from fat)
- 8 grams of carbohydrate
(8 grams times 4 calories = 32 calories from carbohydrate)

So fat makes quite a difference when it comes to total calories in a food.

Maintaining a healthy weight means choosing a variety of foods that are low in fat (especially saturated and trans fats) and added sugars. Think about substitutes for foods that have a lot of sugar, fat, or calories. For example, you may want to drink water or skim milk instead of soft drinks, or choose mustard instead of mayonnaise on your sandwich.

Being aware of the amount of fat and calories you eat makes sense, as long as you eat a balanced diet. Establishing sensible eating habits, choosing foods wisely, and exercising regularly are the keys to long-term good health.