Companies that make food products are allowed to decide what the serving size on their product should be. This serving size is often based on how much an average person would eat.

For instance, a Nutrition Facts label on a package of bread might list one serving as two slices of bread with 110 calories and 19 grams of carbohydrate. However, one serving from the starch group is defined by the American Dietetic Association and the American Diabetes Association as one slice of bread with about 80 calories and 15 grams of carbohydrate. Serving sizes on Nutrition Facts labels vary depending on the product and the company that makes it. For this reason, it is always important to look at the serving size and calories on the Nutrition Facts labels.