Updated November 02, 2014.

Fats are confusing, right? I mean when you look at a Nutrition Facts food label or the info on a calorie-counting or nutrition website, you'll see both total fat and all the different types of fats, but sometimes the numbers don't add up.

For example, when you search for an item such as avocados, you might look at the nutrition information and see the total fat grams is more than the sum of the three individual fatty acids (saturated fats, polyunsaturated fats and monounsaturated fatty acids).

Doesn't seem right, does it? 

Don't worry, while the total fats section of the nutrition charts may appear to be off, they're correct. The disparity isn't due to math errors (although rounding up or down may cause slight differences); the major reason is that there are other types of fatty substances present. These substances (phospholipids, glycerol and sterols) are included in the total fat, but they're not considered to be part any of the three fatty acid groups.

You won't find the phospholipids or glycerols listed in the nutrition information charts, even though they are important for fat structure and function. However, you will find the sterols. The best-known sterol is cholesterol, which is found in animals as well as the phytosterols (beta-sitosterol, stigmasterol and campesterol), which are found in plants.

Where Does the Nutrition Information Come From?

The United States Department of Agriculture (USDA) provides a database of nutrition information for the foods we eat. It's called the USDA National Nutrient Database for Standard Reference.

 Many diet and healthy living sites, such as Calorie Count, use this information as the basis for creating their own calorie and nutrition databases.

The USDA breaks down the macronutrients (fats, carbohydrates and proteins) into their various components and lists the amounts of each component as well as the total for each macronutrient. It also has the vitamins, minerals, fiber and water content. 

It's easy to use -- so you can use the USDA site to do your own searches if you'd like. You can choose from a number of different serving sizes or go with a standard 100 gram serving for any food.

<sub>Sources:

Gropper SS, Smith JL, Groff JL. "Advanced Nutrition and Human Metabolism." Fourth Edition. Belmont, CA. Wadsworth Pub Co. 2005.

United States Department of Agriculture. "USDA Nutrient Database: Frequently Asked Questions." Accessed July 13, 2010. http://www.ars.usda.gov/Main/docs.htm?docid=6233#fattyacid.

Unite States Food and Drug Administration. "How to Understand and Use the Nutrition Facts Label." Accessed October 29, 2014. http://www.fda.gov/Food/IngredientsPackagingLabeling/LabelingNutrition/ucm274593.htm.</sub>