Sugar calories are calories derived from sugars. The two main dietary sugar molecules are fructose and glucose, each of which contain 4 calories per gram. The human body processes each of these types of sugar in a different way.
Sugar calories are essentially the same as carbohydrate calories, because carbohydrates are broken down into sugars during digestion. Different types of food may be easier or more difficult for the body to process. The thermic effect of a food is defined as the amount of calories that the body burns in digesting it. Carbohydrates, including sugars, are much easier for the body to digest than proteins, meaning that sugars leave a higher amount of calories available to be stored as fat.
The sugar molecule glucose is found in most foods that contain carbohydrates, such as potatoes, wheat flour, rice and starchy legumes. Glucose is metabolized easily by the body's tissues, and contributes to feelings of satiety. A food does not have to taste sweet to contain glucose.
Fructose is found in higher concentrations in refined sugar and foods that contain it, such as candy, chocolate and soda. This type of sugar must be processed by the liver. While it has the same amount of calories as glucose, consuming large quantities of fructose may lead to insulin resistance, reduced satiety and excess abdominal fat.