You can find the nutritional information for most foods either on their labels or by using a nutrition database, website or book. The information will be presented as one or more standard serving sizes, so unless you eat exactly that amount, you will have to calculate the nutrition information yourself for the amount that you did eat. Below is an example of how this is done using a family favorite, the classic peanut butter and jelly sandwich. This example will show you how to calculate the calorie content, the fat grams, the protein and carbohydrate content, as well as the fiber.
Step 1
Get the list of ingredients for the food you want to calculate nutritional values for. Sometimes this will be one item, like a banana, but often it will be many things -- for example, the ingredients in a plate of spaghetti and meatballs. For a peanut butter sandwich, this list is two slices of whole wheat bread, 2 tbsp. of peanut butter and 2 tbsp. of strawberry preserves.
Step 2
Compute the number of calories in each item and add them up. For simplicity's sake, this example will use the USDA nutrient database, but you could use any reliable nutrition source, such as the NutritionData.com website. In the USDA database, you will find 70 calories for a 1-ounce slice of wheat bread, 188 calories for 2 tbsp. of peanut butter and 56 calories for 1 tbsp. of preserves. From there, multiply the standard serving sizes by the actual amount in the sandwich. Two slices of bread will be 140 calories, and 2 tbsp. of preserves will equal 112 calories. The peanut butter is already in the right serving size, so the total for the sandwich is 440 calories.
Step 3
Find the amount of protein for your selected food. The procedure for this is just like the calorie calculation. Look up the protein grams for each of the ingredients in the database, then add them up. In this case, you will find that one slice of bread has 3.7 g of protein; 2 tbsp. of peanut butter, 7 g; and 1 tbsp. of preserves, 0.1 g. Multiplying by the serving sizes yields: 2 x 3.7 + 7 + 2 x 0.1 = 14.6 grams of protein in the sandwich.
Step 4
Figure the quantity of carbohydrates in this food. The database gives these values for a slice of bread, 2 tbsp. of peanut butter and 1 tbsp. of jam: 11.7, 7.7 and 13.8 grams of carbohydrates, respectively. Calculating out by the serving sizes makes for 58.7 total grams of carbohydrates.
The portion of fiber would be calculated the same way. Simply look up the fiber grams for each of these foods, then multiply by the serving sizes, and add them up. Here is that computation for bread, peanut butter and preserves: 2 x 1.9 g + 1.8 g + 2 x 0.2 g = 6 g of fiber in a peanut butter and jelly sandwich.
Step 5
Count up the fat grams. One slice of wheat bread has 0.9 grams of fat, and 2 tbsp. of peanut butter have 15.9. There is no fat in fruit preserves, so the total fat grams in this peanut butter and jelly sandwich will be 17.7.
Tips and Warnings
- The hardest part of this process is converting the serving sizes from the nutrition labels or database entries into the serving sizes you use in your meal. The USDA nutrient database offers several different serving sizes for each food, so that can make your calculations a bit easier. When using product labels to do these calculations, however, the serving sizes can be challenging to estimate. For example, if your bag of pretzel sticks tells you that a serving size is 1.7 ounces and each serving is 100 calories, you may have no idea how many pretzel sticks it takes to make up that 100 calories. In that situation, you might just want to calculate the nutritional values for the whole bag, and then estimate what portion of the bag you ate. For example, if the bag has 10 servings, and you ate about a quarter of it, the calculation would be: one bag = 10 x 100 = 1,000 calories, and your serving was 1/4 x 1,000 calories = 250 calories.
- When eating out, you will often find it difficult to estimate serving sizes and have no idea of ingredients, so these calculations can be almost impossible. Always ask if the restaurant provides its nutritional information as a brochure or online, since that is becoming more common. In fact, many fast food restaurants now have their data included in the USDA database.
Things You'll Need
- Ingredients listing
- Calculator
- Product labels
- USDA nutrient database
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