Energy from food is measured in calories. More specifically, 1 calorie is the amount of energy it takes to heat 1 gram of water by 1 degree centigrade. Typically, calorie counts on food labels refer to kilocalories, which are technically 1,000 calories; however, the term "calorie" has replaced the term "kilocalorie" in popular vernacular. Because of this, the two are often used interchangeably. Your body burns calories to fuel involuntary functions such as breathing and pumping blood, as well as for physical activities such as speaking, typing and exercising.
Carbohydrates are made of sugar molecules, and your body converts most carbs into glucose for energy. Some carbohydrates, such as table sugar and fructose, are considered "simple" carbs, because your body processes them more rapidly than starch, which is a "complex" carb. That's why sweet foods provide a quick energy boost -- often followed by a crash -- while energy from breads, cereals and beans lasts longer. Fiber is also a complex carbohydrate, but your body can't break it down into glucose; thus, fiber is considered a calorie-free carb. Your body needs fiber for healthy digestion and other nutritional benefits.
Carbs, Calories and Weight
Although certain fad diets promote cutting carbs to slim down, it's calorie intake that truly matters for weight management. Eating more calories than you burn causes weight gain, while eating fewer calories than you burn leads to weight loss. You get calories from carbs and protein, each of which contains 4 calories per gram, as well as fat, which contains 9 calories per gram.
Most moderately active women burn 1,800 to 2,200 calories per day, and most moderately active men burn 2,200 to 2,800 calories per day. Exercising helps you burn more calories, and larger people -- as well as those with more muscle mass -- naturally burn more calories throughout the day. The 2010 Dietary Guidelines for Americans recommends that adults get 45 to 65 percent of calories from carbs, 10 to 35 percent of calories from protein and 20 to 35 percent of calories from fat. To get more fiber and other important nutrients, choose whole carbohydrate sources such as fruits, vegetables, legumes, oatmeal, whole-wheat products and brown rice.