POOLS AND STORAGE
Humans being heterotrophic
organism depend on other organism for their food and nutrition. Proteins, fats and carbohydrates constitute the old
“nutritional trinity” which despite the recent emphasis on trace
nutrients, are still the most important components of the diet. One must take
the required quantities of the indispensable amino acids, and essential fatty
acids and sufficient additional nitrogen to provide for the dispensable amino
acids, typical diet contains primarily carbohydrate, ample or excess nitrogen
but often insufficient amounts of certain essential amino acids, and extremely
variable quantities of fat. A calorie of energy in fat is essentially
equivalent in the body to a calorie in carbohydrate, although there may be
differences in the metabolites which accumulate in the body. A calorie from
protein, when corrected for the fact that the amino acids are not completely
oxidized in the body (i.e., urea is excreted), is also essentially equivalent.
The various nutrients are supplied in proportions to provide the body with
absorbed nutrients which just meet the metabolic needs of the body. These bio molecules are
broken down into free fatty acids and glycerol, glucose and amino acids
respectively to give energy.
Glucose is the main source of
energy for major metabolic pathways. Our brain depends mainly on glucose for
its activity. Only 30% of the food intake is used as depositories as fat or
glycogen whereas 70% of it is used in metabolic pathways. When excess
carbohydrate is taken than required in the body, then these glucose molecules
are stored in the form of fat by lipogenesis in adipose tissue or as glycogen
by glycogenesis in liver.
Fats on the other hand release a
large amount of energy as compared to carbohydrates. These upon breakdown by
lipolysis give rise to free fatty acids which are used in tissues for various
Proteins are building blocks of
our body. The proteins taken in the diet are broken down in free amino acids in
the body. These amino acids are then utilized to produce different proteins of
the body. During extreme starvation these amino acids also serve as source of
glucose through gluconeogenesis.