The period of transition between childhood and adulthood is known as .

Adolescence

Teens will need food to eat and for their body growth
Food eaten and digested in the body are converted into calories. Food when broken down inside the body turns into usable sugar, called glucose. Glucose is a key component in determining caloric values in food. When you digest food, the nutrients that they provide are calculated in the form of calories. This is what you usually see in the food labels that are printed outside of wrappers in food you buy from the supermarkets. 

On average a person should consume between 1,500-2,000 calories per day in order to maintain proper bodily functions. Excessive amounts of caloric intake and less exercise may lead to obesity and other health related diseases.