BODYPOOLS AND STORAGEHumans being heterotrophicorganism depend on other organism for their food and nutrition. Proteins, fats and carbohydrates constitute the old”nutritional trinity” which despite the recent emphasis on tracenutrients, are still the most important components of the diet. One must takethe required quantities of the indispensable amino acids, and essential fattyacids and sufficient additional nitrogen to provide for the dispensable aminoacids, typical diet contains primarily carbohydrate, ample or excess nitrogenbut often insufficient amounts of certain essential amino acids, and extremelyvariable quantities of fat. A calorie of energy in fat is essentiallyequivalent in the body to a calorie in carbohydrate, although there may bedifferences in the metabolites which accumulate in the body. A calorie fromprotein, when corrected for the fact that the amino acids are not completelyoxidized in the body (i.
e., urea is excreted), is also essentially equivalent.The various nutrients are supplied in proportions to provide the body withabsorbed nutrients which just meet the metabolic needs of the body. These bio molecules arebroken down into free fatty acids and glycerol, glucose and amino acidsrespectively to give energy. Glucose is the main source ofenergy for major metabolic pathways.
Our brain depends mainly on glucose forits activity. Only 30% of the food intake is used as depositories as fat orglycogen whereas 70% of it is used in metabolic pathways. When excesscarbohydrate is taken than required in the body, then these glucose moleculesare stored in the form of fat by lipogenesis in adipose tissue or as glycogenby glycogenesis in liver. Fats on the other hand release alarge amount of energy as compared to carbohydrates. These upon breakdown bylipolysis give rise to free fatty acids which are used in tissues for variousmetabolic pathways. Proteins are building blocks ofour body.
The proteins taken in the diet are broken down in free amino acids inthe body. These amino acids are then utilized to produce different proteins ofthe body. During extreme starvation these amino acids also serve as source ofglucose through gluconeogenesis.