Calories are units that measure energy. Calories come from four sources: carbohydrates, fat, protein, and alcohol. Fat is a high calorie food. There is 9 calories in each gram of fat. Fat contains more than twice the number of calories in protein or carbohydrates. Fat-free foods are not necessarily low in calories. Many fat-free sweet products are high in sugar, and therefore high in calories.

1 gram of protein = 4 calories

1 gram of carbohydrates = 4 calories

1 gram of alcohol = 7 calories

1 gram of fat = 9 calories

Sources: www.annecollins.com