Heats of combustion of chemically different lipids

The caloric content of foods listed in food composition tables, such as the USDA Agriculture Handbook No. 8, is calculated by multiplying the gram amount of the protein, fat, and carbohydrate in the food by specific caloric factors derived around the turn of the century by Atwater and co-workers. To evaluate the accuracy of these specific caloric factors, we determined the heats of combustion of vegetable oils as purchased; of lipids extracted from red meats, chicken, fish, egg yolk, and cereal grains; and of the residue (protein) left after lipid extraction of the meats. These heats of combustion were converted to available energy values by the method of Atwater . The specific caloric factors used to calculate the caloric content of foods in Agriculture Handbook No. 8 and other tables of food composition may exaggerate the calories contributed by the lipids in some foods. When the food lipid was mainly triglyceride, the available energy values calculated in this study were within 2% of the specific factors used in Agriculture Handbook No. 8. However, when the food lipid had a high content of phospholipid, our calculated available energy values were lower than the specific factors used currently. The energy content of the fat-free residue (protein) of meat, poultry, and fish was also less than that currently used for those foods in food composition tables.