Calories are the energy required by the body to maintain metabolic reactions. In the 20s the required calories by the body start decreasing. Thus, option b is correct.
What are calories?
In nutrition, calories are defined by the energy provided by the food components carbohydrates, fats, vitamins, fibers, proteins, etc. The energy is provided in the body by the breakdown of the food substances.
The metabolic rate of the body starts decreasing with age which results in a decrease in calories. As the age increases the metabolism slows down and is especially seen around the 20s.
The metabolic rate is very high in the first 20 years of life but decreases as the age increases resulting in low energy leading to tiredness and fatigue.
Therefore, option b. the calories begins decreasing around 20s is correct.
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