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
Some people base what they eat on how it tastes. Many people believe that if it tastes good why not? And also because many people are uneducated when it comes to food and health.
