In the calorimeter it was found that the carbohydrates and fats burned to the same end products, namely, carbon dioxide and water, while the proteins, upon oxidation, produced carbon dioxide, water and nitrogen gas. In the body it was found that the carbohydrates and the fats acted in exactly the same manner as in the calorimeter, producing the same end products. But this was not the case with the proteins; the oxidation process of this chemical combination was found to be not nearly so complete within the body as in the calorimeter, and instead of the free nitrogen as produced in the apparatus there were urea and other nitrogenous substances eliminated which, while combustible, represented a less complete oxidation of the proteins. The following table represents the amount of heat produced as the result of a complete oxidation of the foodstuffs in the calorimeter. TABLE[16] ================================================== Carbohydrates 4.1 cal. per gram Fats 9.45 cal. per gram Protein (nitrogen x 6.25) 5.65 cal. per gram ================================================== The loss of potential energy due to the incomplete oxidation of the proteins in the body is approximately 1.3 calories to each gram of protein in food; consequently in calculating the fuel value of protein foods, due allowance must be made for these losses. Allowance must also be made for the incomplete digestion, or losses occurring in the digestion, of the foodstuffs. These losses, as well as the approximate amount of each constituent absorbed, are represented in the following table.[17] ===========================+===========+=============== | _Lost_ | _Absorbed_ ---------------------------+-----------+--------------- Carbohydrates |2 per cent.| 98 per cent. Fats |5 per cent.| 95 per cent. Proteins |8 per cent.| 92 per cent. ===========================+===========+=============== The physiological fuel factors of food, or the amount of heat produced as the result of combustion of 1 gram of organic food material after the above-mentioned losses have been accounted for, may be obtained as follows.[18] ================================================= Carbohydrates 4.1 x 98% = 4 cal. per gram Fats 9.45 x 95% = 9 cal. per gram Proteins 4.35 x 92% = 4 cal. per gram ================================================= EFFECT OF HEAT AND COLD UPON THE FOODSTUFFS In primeval days, when man led a more natural life, his very existence depended upon his ability to wrest from the earth his 4--9--4; these, then, constitute what are known as the "physiological fuel factors" of carbohydrates, fats, and proteins respectively.