Serving size. The serving size is the portion size for which all of the nutrition information on the food label is based. In the past, serving sizes on labels were determined by individual manufacturers, and they varied a great deal. Today, serving sizes are standardized, and all manufacturers are required to use the same standard portion sizes. Standard serving sizes are based on amounts people typically eat in a single sitting, and they must be provided in both common household measures, such as cups, tablespoons, or slices, and as a weight in grams (g) or volume in milliliters (ml).
If you look at these sample food labels for pizza, you can see that the serving size for the vegetarian pizza is 1 pizza (170 g), while the serving size for the meat pizza is 2 slices (154 g). Even though the pizzas themselves are different sizes, because the nutrition values are calculated for a similar amount of pizza, you can easily compare the fat, calories, and other nutrients in the two products.
Not all foods fit neatly into standard serving size categories, however, so the FDA allows manufacturers to adjust serving sizes and to round off values based on specific guidelines. This means that if you need very precise nutrition information about foods, it is most accurate to weigh foods on a food scale yourself.
A common mistake people make when reading food labels is to confuse the weight of the entire serving of food for the amount of carbohydrate in the food. For example, the total weight of the vegetarian pizza is listed as 170 grams, but only 47 grams are carbohydrate. If you want to know how much carbohydrate is in a serving of a food, be sure to look for “Total Carbohydrate” on the label.
Another common mistake is to assume that the nutrition information listed on the label is for the entire package of food. Sometimes, it is, but often, it is not. To find out how many portions of food a package contains, look at the “Servings Per Container.” If this number is 1, the nutrition information provided is for the whole package, but if this number is greater than 1 and you intend to eat the entire package, you must multiply the amount of fat, cholesterol, sodium, etc., by the number of servings per container to find out how much of these nutrients you will be consuming.
For example, the “Serving Size” for the meat pizza on the sample label is 1/4 pizza, 2 slices (154 g). If you were going to eat the whole pizza, you would be eating four servings, so to figure out the amount of nutrients in your actual serving, you would multiply the nutrition information provided by 4. In this case, one serving has 510 calories and 43 grams of carbohydrate. If you were to eat the entire package, you would be consuming 2,040 calories (4 x 510) and 172 grams of carbohydrate (4 x 43 grams).
Percent Daily Value (%DV). Major nutrients on food labels, such as fat, cholesterol, sodium, carbohydrate, and protein, must be listed as a quantity, in grams or milligrams, and as a percent Daily Value. Percent Daily Values are reference values designed to help people see how a food fits into their overall diet. For example, the amount of fat in one serving of the vegetarian pizza is 9 grams, and the %DV is 14%. This means that one serving of this food provides about one-seventh of a typical person’s recommended maximum daily fat intake, and seven servings would provide 100%. One serving of the meat pizza has 26 grams of fat and provides 40% of a typical person’s daily fat intake, so just 2 1/2 servings would supply an entire day’s recommended maximum fat intake.
The percent Daily Value also provides context for interpreting the quantities of nutrients in a food. For example, you could mistakenly think the meat pizza is a low-fat food, because 26 grams is a relatively small number, but when you look at the %DV, you see that it is actually a high-fat food, since one serving provides 40% of your day’s fat intake. Alternatively, you might think that the vegetarian pizza is a high-sodium food because it has 360 milligrams of sodium, a fairly large number, but when you look at the %DV, you see that one serving provides only 15% of the average person’s recommended daily maximum.