Your body is made up of mostly water. According to the four component model, a person's body breaks down into water, protein, minerals, and fat. Nobody can have zero percent body fat. 

So why is all of this important?

It's important because there's more to your body than just losing or gaining weight.

How does your metabolism affect aging?

There is a great deal of conflicting information regarding metabolism, especially when it comes to delaying the effects of aging.

Metabolism is measured using your Base Metabolic Rate (BMR), which the amount of energy (calories) it takes to maintain your body at rest and enable you to live.

Simply, someone with a higher BMR will burn more calories during their day than someone with a lower BMR.