The below mentioned article provides a short note on Specific Dynamic Action (SDA).
Definition Specific Dynamic Action (SDA):
It is defined as the extra heat production over and above the caloric value of a given amount of food when used by the body.
An amount of protein which contains 100 kcal (25 gm.) when metabolized in the body, the heat production is not 100 kcal but 130 kcal. This extra 30 kcal is the product of the SDA of protein. Similarly, in the body, a 100 kcal portion of fat produces 113 kcal, and a 100 kcal portion of carbohydrate produces 105 kcal. This extra heat is due to the activity of tissues metabolizing these foodstuffs.
When these above foods are taken in a mixed diet, the SDA is not the total of the SDA of each foodstuff when fed separately. According to Forbes, when the glucose and protein are combined, the SDA is 12.5% less than the sum of their individual effects.
The SDA is 22% less when lard, glucose, and protein are combined, the SDA is 35% less in case of glucose-lard combination, and 54% less in case of protein-lard mixture than the sum of their individual SDA. The high SDA of protein can be reduced depending on the quantities of other foodstuffs in the diet.
It has been found in Forbes’s data that fat (lard) has much influence on SDA than does any other nutrient, i.e., fat decreases the SDA more than any other nutrient. When different amino acids are fed, alanine, glycine, and phenylalanine are found to produce high SDA.
According to Krebs, the high SDA is due to two main factors:
1. The energy required for deamination of amino acids which is again derived by the oxidation of other metabolites.
2. The energy required for the synthesis of urea which is obtained by the oxidation of other metabolites present in tissues.
There is evidence also that the increment is greater during the process of lipogenesis from glucose than during its oxidation to CO2 and H2O.
The SDA of carbohydrate is to represent the energy liberated in excess of that required for the conversion of glucose to glycogen.
The SDA of fat is due to the increased concentration of fat in the tissue fluids and to its more rapid oxidation.
The glands of internal secretion have no direct influence upon the SDA of protein. Thyroidectomy in animals reduces the SDA of carbohydrate and fat.
A diet very rich in protein is unfavorable to heavy muscular work. The SDA of protein is an important factor in the regulation of body temperature. With fat and carbohydrate, the extra heat is accelerated in the performance of work. When new tissue is formed, protein does not exert its usual SDA.