Answer:
It's basically the percentage of body fat, muscle and bone. You can change it by exercising a lot (cardiovascular in particular), eating less calories (dieting) or just eating more healthy things/ more foods with protein.
Explanation:
I had a question like this on a health/pe test last week
depending what someone wants: are they trying to lose weight, gain weight, gain muscle.
also height, gender, current weight
The pineal gland, also known as the pineal body, is responsible for releasing melatonin. The pineal gland is a "small endocrine gland in the vertebrate brain."
Hope this helps! The quoted part came from Wikipedia.
That condition is called Bulimia.