You're going to want to read the label from top to bottom.
Serving Size and Calories
The first thing you will see at the top tells you the serving size and the amount of calories. It will say "Serving Size {x} " where x is the amount of whatever measurement is used. It may also give the amount of another measurement (usually grams) and sometimes even amount of how many of the product is one serving size (chip bags usually do this). Using the amount of servings that you eat, you can use simple math to determine how much of each nutrient/vitamin you have, this also includes the daily value percentage.
Under the serving size, there will be the amount of calories and the amount of calories from fat. The calories shown are the calories per serving, so if you eat two servings, then you can double the amount of calories. You can compare the calories that you eat to the daily amount you are supposed to have.
General rules for calories (based on a 2000 calorie diet)
- 40 calories or less - low
- Around 100 calories - moderate
- 400 calories or more - high
Calories from fat are just the amount of calories that come from fat in the product. Calories are important because eating too many calories is linked to obesity.
Nutrients
The next section (under calories) on the food label is about the nutrients in the food. There are two subsections in this section, nutrients to limit and nutrients to get enough of.
Nutrients to Limit
- Total Fat - under it there will also be trans and saturated fat
- Cholesterol
- Sodium
These nutrients have been shown to increased risks some cancers, heart disease, and high blood pressure.
Nutrients to get Enough of
- Dietary Fiber - under Total Carbohydrates
- Vitamins A and C
- Calcium
- Iron
Getting more of these has been shown to reduce the risk of many of the diseases and problems mentioned, but you shouldn't have too many of these.
Other nutrients
- Total Carbohydrates - sugar is under this
- Protein
These foods are neutral-ish, but there are some risks in having too much (over the limit) of these. In fact, too much sugar has been shown to increase the risk of diabetes.1
Reading the numbers
The nutrients to limit usually have both an actual amount and a daily value percentage (%DV) based on a 2000 calories diet. The nutrient to get enough of usually don't.
Guide to %DV
- 5% or less - low
- 20% or more - high; most products won't have anything higher than 20%
If you have something that has 20%DV of vitamin A, then there will 80%DV of vitamin A left. You could eat 4 more products with 20%DV of vitamin A or some other combination that equals 80%DV.
Footnote
There will three columns, one with the daily recommended amount for a 2000 calories diet and one for a 2500 calorie diet. All of the %DV are based on the 2000 calorie diet, but you can easily convert the percentages to the 2500 calorie diet if you have a calculator (or you can do them by hand). The one column I didn't mention is the calories column. If it says "Less than" then you should have less than the amount said in the column of the diet you are on.
Usually "Total Fat", "Sat Fat", "Cholesterol", and "Sodium" will have a "Less than" next to them, so you should have less of these than the amount to the right says. "Total Carbohydrates" and under it "Dietary Fiber" will usually have nothing next to them, so you should get the recommended value to the right.
Reading an ingredient list
This is a bit trickier than reading the actual label, but the ingredients should be put in order of quantity. There isn't any definite way to see the exact amount of each ingredient in the product, though. It is better to rely on the amount of each nutrient instead of trying to guess how much of each ingredient there is. If you just want to know what you are eating, then there are some good tricks.
- Sugar has many names - high-fructose corn syrup or corn syrup, agave nectar, barley malt syrup, dehydrated cane juice
- Sodium does too - salt, sodium benzoate, disodium, monosodium glutamate
- Trans fat - not listed as an ingredient, but it is in hydrogenated oil which is a common ingredient
[1] Is there evidence that eating too much sugar can increase the risk of diabetes?
How to Understand and Use the Nutrition Facts Label
Understanding Ingredients on Food Labels