The serving size on the back of a package is not an amount anyone has recommended for you. It describes what people typically eat, and every number below it is worked out for that amount. Once you know that, the panel is arithmetic you can do in the aisle.
What a serving size is, and who decided it
By law, serving sizes are based on the amount of food people typically eat, not on how much they should eat, and a serving size is not a recommendation of how much to eat or drink. It is shown as a household measure that suits the food, such as a cup, a tablespoon, a piece, a slice or a jar, followed by the metric amount in grams.
One package can hold more than one serving. Some carry a second column giving the calories and nutrients for the whole package, which is what you get if you eat or drink all of it at once, but many labels give the figures for one serving only. That makes the serving size the first line to read before you decide how much to eat.
Serving sizes are standardized to make it easier to compare similar foods. The word that matters is similar: two different foods can have very different serving sizes, which may be exactly the problem in your hands right now.
The numbers that apply when you eat half a serving
Everything on the panel scales with the amount. Eat two servings and every calorie and nutrient figure doubles, percentages included, as a sample label for a frozen lasagna with a 1-cup serving shows line by line. The rule runs the other way too: half a serving is half of every number. The last column halves each amount and works its percentage out again from the halved amount, because the printed percentages are rounded and do not always scale exactly; the fiber line's 14% doubles to 29% on the printed label:
| Line on the sample label | 1 cup, as printed | 2 cups, as printed | Half a cup, worked out |
|---|---|---|---|
| Calories | 280 | 560 | 140 |
| Total fat | 9g, 12% | 18g, 24% | 4.5g, 6% |
| Sodium | 850mg, 37% | 1700mg, 74% | 425mg, about 18% |
| Dietary fiber | 4g, 14% | 8g, 29% | 2g, 7% |
| Protein | 15g | 30g | 7.5g |
| Calcium | 320mg, 25% | 640mg, 50% | 160mg, about 12% |
Calories are a measure of how much energy you get from one serving. The sample lasagna's package holds 4 servings, so eating all of it means 1,120 calories rather than the 280 at the top of the panel. Juice works the same way: drink a whole bottle that holds two servings and you get twice the sugar on the label. The number of servings you eat sets the calories you actually get. Whether you eat half, a third or a little more than one serving, multiply every line by the same fraction, and weigh what you eat once or twice against the grams beside the serving size to find that fraction instead of guessing.
If you are eating far less than you used to because your appetite has gone, start by writing down one day of eating, and tell your doctor about certain signs that can come with a low appetite (see No appetite at all? Start by writing down one day of eating).
What the percentage column is for
The percentage shows how much a nutrient in one serving contributes to a total day's diet, and it can help you tell whether a serving is high or low in that nutrient. As a general guide, 5% or less per serving is low and 20% or more is high. On the sample label, the lasagna's 37% for sodium is high, and so is its 25% for calcium, one of the nutrients to get more of.
Those percentages are worked out for a reference day. Experts recommend a certain amount of different nutrients daily, and for most lines on the panel those amounts, the Daily Values, are reference amounts to consume or not to exceed each day. They assume 2,000 calories a day, a general figure for nutrition advice, as the footnote at the bottom of the panel says. Your own calorie needs may be higher or lower depending on your age, sex, height, weight and how active you are. So a percentage tells you how much of a Daily Value one serving holds. It is not a share of your own day, and your doctor can tell you whether those Daily Values suit you.
Which way you want a percentage to go depends on the nutrient. Saturated fat, sodium and added sugars are nutrients Americans generally eat too much of: too much saturated fat and sodium is associated with a higher risk of conditions such as cardiovascular disease and high blood pressure, and too much added sugar can make it hard to meet nutrient needs within calorie limits. Dietary fiber, vitamin D, calcium, iron and potassium are nutrients Americans generally do not get enough of.
A few lines carry no percentage. Trans fat and total sugars never show one, and protein shows one only in specific situations, such as when the package claims to be high in protein. For those lines, compare the grams.
The column works across a day as well as across packages. When a food you like is high in a nutrient you want less of, or low in one you want more of, you can balance it with foods that are low, or high, in that nutrient at other times of the day.
Total sugars and added sugars
Two sugar lines sit on the panel, and they count different things. Total sugars covers the sugar naturally present in foods such as milk and fruit as well as any added sugar, and it carries no percentage, because no recommendation has been set for the total amount to eat in a day. Added sugars include sugar added during processing, such as sucrose or dextrose, sweeteners sold as foods, such as table sugar, sugar from syrups and honey, and sugar from concentrated fruit or vegetable juice.
When the panel reads "includes" before the added sugars figure, those grams are already counted inside total sugars, so do not add the two together. If you are eating less than you used to, the added sugars line is worth watching: eating a lot of calories from added sugar can make it hard to get the nutrients you need while staying within your calories.
Comparing two packages when the servings differ
Percentages make comparing foods easy, as long as the serving sizes are the same. When they are not, the two panels describe different amounts of food, so set them to the same amount first. In the aisle:
- Find the grams beside each serving size.
- Pick one amount for both, such as the smaller of the two servings, or the amount you would actually eat.
- Scale each panel's line for the nutrient you care about to that amount, the same way the lasagna was halved above.
- Compare the two results, then check which way you want that nutrient to go.
Front-of-pack words such as "light", "low" and "reduced" can be checked the same way: compare the percentages for the nutrient the claim is about, and there is no need to memorize what each word means. Once the two amounts match, the panel answers the question the front of the pack raises.
