The Nutrition Facts label carries most of what you need to judge how a packaged food will affect your blood sugar. This article walks through the label in the order that matters most for carbohydrates.

Start with the serving size

Every number on the label refers to one serving, shown at the top along with the number of servings in the package. A bag of chips or a bottle of juice that looks like a single portion often holds two or more servings. If you eat the whole package, multiply every number on the label by the number of servings.

Total carbohydrate

Total carbohydrate is the most useful single number for blood sugar. It includes starch, fiber, natural sugars and added sugars together. Many diabetes education programs count carbohydrate in units of 15 grams, often called one carb choice, so a food with 30 grams of total carbohydrate per serving counts as two choices.

How many grams to eat at a meal depends on your body size, activity and medication. A common starting range in diabetes education is 45 to 60 grams per meal for many adults, adjusted with a dietitian or doctor based on your blood sugar readings.

Dietary fiber

Fiber is listed under total carbohydrate. Fiber is not broken down into glucose, so it does not raise blood sugar the way starch and sugar do, and it slows the digestion of the rest of the meal. Foods with 3 grams of fiber or more per serving are considered a good source, and 5 grams or more an excellent one.

Some packages advertise net carbs, which is total carbohydrate minus fiber and sometimes minus sugar alcohols. The FDA does not define net carbs, so the way it is calculated varies between brands. Using total carbohydrate keeps your counting consistent.

Total sugars and added sugars

Total sugars includes the sugar found naturally in milk and fruit as well as sugar added during processing. Added sugars is listed separately below it. The FDA's daily value for added sugars is 50 grams on a 2,000-calorie diet, and the American Heart Association suggests lower limits of about 25 grams a day for most women and 36 grams for most men.

Sugar is part of total carbohydrate, so you do not add it again when counting. A food can be low in sugar and still high in carbohydrate if most of it is starch, as with crackers, bread and many snack foods.

Sugar-free and no sugar added

A food labeled sugar-free can still contain a lot of carbohydrate from flour or starch. No sugar added means no sugar was put in during processing, but the food may still be high in natural sugar, as with fruit juice. Sugar alcohols such as sorbitol, maltitol and erythritol are partly absorbed and can raise blood sugar a little, and in larger amounts some of them cause bloating or diarrhea.

The ingredient list

Ingredients are listed in order of weight, from most to least. If sugar, corn syrup, honey, dextrose or another sweetener appears among the first three ingredients, the product is high in sugar. For bread and cereal, look for a whole grain, such as whole wheat or oats, listed first.

A quick routine at the store

• Check the serving size and how many servings you will actually eat.
• Read total carbohydrate and work out how many 15-gram choices that is.
• Look for at least 3 grams of fiber in grain products.
• Compare added sugars between two similar products and pick the lower one.