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Bond Energies and Food Calories 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.


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