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Human nutrition deals with the digestibility of human beings. Digestibility mainly refers to the breakdown of complex food materials into simpler ones. Assimilation definition deals with the use of those absorbed simpler food materials by the body for different purposes like generation of energy, osmoregulation, and so on. Absorption and assimilation go side by side. Absorption is done in the small intestine, after which the nutrients are transferred to the body cells and tissues through blood vessels where usage of those nutrients or assimilation takes place in the body. Assimilation of food is important as without that intake of nutrition is of no use.
What is Assimilation?
Assimilation is the process of transfer of digested food materials from the small intestine to the cells via blood and the use of those nutrients by the body. After absorption, the simpler food materials are transported all over the body to the body cells. There, by the process of metabolism, catabolism, and anabolism, assimilation of those food elements is done.
Energy production from food
The breakdown of glucose to form ATP comes under cellular respiration and is part of catabolism. This occurs by three processes, first glycolysis and Kreb cycle, and ETS. Glycolysis occurs in the cytoplasm of the cell. Here, one molecule of glucose is hydrolyzed to form 2 molecules of pyruvic acid. This occurs in the presence of different enzymes and their cofactors. All total 2 molecules of ATP are generated in this step. This step is present in both aerobic and anaerobic forms of cellular respiration as it does not need any oxygen. After that, the next step is the Kreb cycle. This is the step that occurs in the matrix of mitochondria. Before entering into this step the pyruvic acid is modified to form acetyl CoA. This acetyl CoA takes part in the kreb cycle along with oxaloacetic acid to form citric acid. This is the second step occurring under the influence of different enzymes and occurs only in the case of aerobic respiration. Here, different energy molecules like ATP, NADPH, GTP, FADH2 are formed. All these steps come under the process of assimilation. All these energy molecules are again hydrolyzed in the inner membrane of mitochondria by the process of ETS.
Calorific value
This refers to the amount of energy generated in calories by the combustion of 1gm of food in a bomb calorimeter in the form of heat. The calorific value of different food items is expressed in the form of kcal per gram or kilojoule per gram. The calorific value of carbohydrates is 4.1kcal per gm whereas those of protein and fat are 5.65 kcal per gm and 9.45 kcal per gram respectively. As these are the sources of energy in our body, assimilation means the breakdown of these food items. Calorific value is different from that of physiological value which deals with the actual amount of energy produced by the combustion of 1 gm of food.
Conclusion
Assimilation deals with the transport of food material by the blood vessels and the usage of those food materials for the production of energy. The breakdown of glucose to form ATP comes under cellular respiration and is part of catabolism. This occurs by three processes, first glycolysis and Kreb cycle, and ETS. Glycolysis occurs in the cytoplasm of the cell. The Kreb cycle occurs in the mitochondrial matrix and the third ETS occurs in the inner membrane of mitochondria in the presence of different enzymes. The calorific value of food mainly deals with the amount of energy produced in the form of heat by the breakdown of 1 gm of food using a bomb calorimeter.
