When your body burns calories more efficiently, you
a. exercise without fatigue.
b. decrease the amount of muscle mass and increase the amount of body fat.
c. increase the amount of muscle mass and decrease the amount of body fat.
d. lose all your body fat.

When the body is efficient or effect in burning the calories, the body tends to increase the amount of muscle mass and decrease the amount of body fat. The term "burning of calories" is more likely to be related to the word "exercising" which allows a certain person to get rid and lessen the body fats.

Breastfeeding should last for 12 months.