Ask Monica: where's the missing fat?

Q. I use NutritionData to analyze the fat content of my diet, and noticed that the amounts of unsaturated, monounsaturated, and polyunsaturated fat don't always add up to the amount given for total fat.  One tablespoon of butter, for instance, has 7.2 g saturated fat, 2.9 g monounsaturated fat, 0.4 g polyunsaturated fat, and 11.4 g total fat. The individual components add up to 10.5, not 11.4.  Am I missing something here?  Shouldn’t the total match the sum of the parts?

A. That's a great question, and one I bet others have wondered about as well.  There are two reasons why the amount of individual fatty acids don't always add up to the amount of total fat in a food. First, the total fat and the individual fatty acid content of foods are determined using different analytical methods, and that accounts for some of the discrepancy.  Second, the total fat content includes some lipid fractions, such as sterols, that aren't listed separately but don't belong in the other categories. 

My suggestion is to use the total fat content (the higher number) as a guide to the amount and percentage of calories you are getting from fat (as opposed to carbohydrate and protein), and the breakdown of monounsaturated, polyunsaturated, and saturated fatty acids as a guide to the percentage of fats that come from each category. Any discrepancies should be minor and inconsequential in terms of your health.

You didn’t ask, but I’ll offer my general recommendation that monounsaturated fats make up the largest part of your fat intake. Olive oil, avocados, and nuts are all high in monounsaturated fats. Use ND’s Nutrient Search Tool to find others.