There are basically two ways to get nutrition information for foods. Most packaged foods are sold with nutrition labels that spell out the nutritive values of the food for a standard serving. If the food does not come with a nutrition label, as with fresh foods or bulk foods, you will have to look up the item in a book, on a website or in a database, such as the USDA National Nutrient Database. These sources will list the nutritional value for one or more standard serving sizes. Once you have that information, either from the package or another source, you will have to do some math to determine exactly what nutrients you are taking in, depending on the amount of the food you actually eat. Let's consider an example of this process using a simple breakfast favorite---a spinach omelet. We'll go through the process of calculating the calories and the amount of protein, carbohydrates and fat in the omelet, along with the fiber content.
Step 1
Gather the ingredient list for whatever you are eating. In many cases, this will only be one thing, like an apple, but sometimes it will be several things. In the case of our spinach omelet, our ingredient list contains: 2 large eggs, 2 tsp. of butter, and a cup of chopped raw spinach.
Step 2
Figure the calories contained in your food. Since this omelet is being made at home from scratch, we'll use the USDA Nutrient Database to find our nutritional values. Looking up these items in the database tells us that large, whole fresh eggs have 72 calories apiece; butter has 102 calories per tablespoon; and chopped spinach has seven calories per cup. To get your calorie total, multiply those numbers by the portion of the given serving size you will be consuming and add them up.
For example, two eggs x 72 calories each = 144 for the eggs. One tablespoon has three teaspoons in it, so 2 tsp. of butter has 2/3 x 102 = 68 calories. One cup of spinach gives an additional seven calories. Thus, the two-egg spinach omelet has a total of 144 + 68 + 7 = 219 calories.
Step 3
Determine the amount of protein in your food. This process is similar to the calorie process, except it uses grams of protein instead of calories. The database provides the following protein gram counts for one large egg, 1 tbsp. of butter and 1 cup of spinach: 6.3, 0.1 and 0.9. To convert those to the amounts used in our omelet, just multiply by the same factors above. Two eggs have 2 x 6.3 = 12.6 grams of protein; 2 tsp. of butter have 2/3 x 0.1 = 0.07 grams of protein, and a cup of spinach, 0.9. The total protein for this food item is 12.6 + 0.07 + 0.9 = 13.6 grams.
Step 4
Find the amount of carbohydrate contained in your food. Checking the USDA database for our omelet ingredients shows that spinach omelets have very little carbohydrate. Butter has none; eggs have only 0.4 grams each; and a cup of spinach has 1.1 grams. Again, multiplying by the quantities in our omelet, that gives: 2 x 0.4 + 1.1 = 1.9 grams of carbohydrate in the whole omelet.
You would use a similar process to computer the fiber content. Neither butter nor eggs have any fiber, so the fiber count for our spinach omelet would just be that of the one cup of spinach, 0.7 grams.
Step 5
Calculate the fat grams in your meal. One large egg contains five grams of fat, while a tablespoon of butter has 11.5. Spinach has only 0.1 grams of fat in a cup. The total fat then for the spinach omelet would be 2 x 5 + 2/3 x 11.5 + 0.1 = 17.8 grams.
Tips and Warnings
- The trickiest part of all this is matching the serving sizes on your labels or database entries to the amount you actually eat. The USDA Nutrient Database can be helpful in this regard, because it will list different serving sizes for every food, so you are more likely to find something that does not require a lot of complicated measurement conversions.
- When you are eating out, be aware that serving sizes in restaurants are frequently larger than serving sizes used at home, so trying to estimate values in this situation can be difficult. Ask your server if the restaurant has its nutritional information available as a handout or online, as more and more of them do. In fact, several of the most popular fast food restaurants are now included in the USDA database.
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