BODYPOOLS AND STORAGEHumans being heterotrophicorganism depend on other organism for their food and nutrition. Proteins, fats and carbohydrates constitute the mostimportant components of diet, despite of many trace nutrients. One must takethe required quantities of the essential amino acids, and fatty acids andsufficient additional nitrogen to provide for the amino acids. A calorie of energy in fat is essentiallyequivalent in the body to a calorie in carbohydrate but there may bedifferences in the metabolites which accumulate in the body. The variousnutrients are supplied in proportions to provide the body with absorbednutrients 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. Thusthere is an interrelationship between carbohydrates, fats and protein. For egcarbohydrates can supply the carbon chains for synthesis of many of the aminoacids. The carbohydrate pool storage is rapidly “depleted” as the supplythe energy requirement of the body increases (fasting). Tissue often provides arather large storage pool of energy as triglyceride, which is utilized when thecarbohydrate reserve is low. The protein pool is invariably large and the liverprotein pool turns over with a half-life of about a week and can provide forthe energy needs of the body. Thusmetabolism is a highly inter related with many intermediary metabolites.