Rubber (yr) observed that carbohydrates, fats and proteins fed to a fasting dog, stimulated the energy metabolism over the basal level to varying extents. For example, he found that in a fasting dog requiring 400 Kcal, feeding of 100 g of carbohydrates produces 425 Kcal, 44.4 g of fat produces 416 Kcal and 100 g of protein produces 520 Kcal of heat. The extra heat produced is obtained by the oxidation of the tissue constituents and the animal will be in negative energy balance. This stimulating effect of carbohydrates, fats and proteins on energy metabolism is called Specific Dynamic Action (S.D.A.).
The S.D.A. of proteins is the highest (about 30 per cent) while that of carbohydrates and fats are only 6 percent and 4 per cent respectively. The S.D.A. of a mixed diet containing 62.5 g carbohydrates, 10 g fat and 10 g protein is about 8 percent. A considerable amount of work has been carried out by Lusk (yr) and several other workers on the causes of the high S.D.A. of proteins. Two main factors responsible for the high S.D.A. of proteins are
The energy required for deamination of amino acids which again is derived by the oxidation of other metabolites and
The energy required for the synthesis of urea which is obtained by the oxidation of other metabolites present in the tissues.
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