Why don t the individual fatty acids or the fatty acid classes add up to the total lipid (fat)?
The fatty acids are reported as grams of fatty acid per 100 grams of food. They may not add up to the total lipid value provided in a database because the fat value may include some non-fatty acid material, such as, glycerol, phosphate, sugar or sterol. In the case of vegetable oils that are 100% triglyceride, 95.6% is fatty acid and the remaining 4.4% is glycerol. For other fats, the percent of fatty acid will be even lower. Lipid conversion factors for specific fats define the amount of fatty acid (in grams) per gram of fat. The factor is 0.956 for triglycerides and lower for other fats. The factors used in each section of Agriculture Handbook No. 8 were published in an appendix table. In addition, the individual fatty acids may not add up to their respective total fatty acid classes (saturated, monounsaturated, and polyunsaturated) and in turn, the sum of the total for each class may not add up to the value for total lipid.
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