Question

why is carbohydrate main source of energy

Answer 1

Carbohydrates as a source of energy.  Carbohydrates are the main energy source of the human diet. The metabolic disposal of dietary carbohydrates is direct oxidation in various tissues, glycogen synthesis (in liver and muscles), and hepatic de novo lipogenesis.

Answer 2

the metabolic disposal of dietary carbohydrates is direct oxidation in various tissue ,(in lever and muscles ) . so this is main source of human diet .
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