Up to two thirds (66%) of all the energy we metabolise each day comes down to our body composition. That is, the amount of muscle we possess.
Our muscles drive our metabolism.
As adults with every passing decade on this planet we can expect to lose 10 kg's of pure muscle and replace it with up to 20 kg's of body fat. An ever-increasing amount of research suggests this process triggers accelerated aging!
On the other hand, building and maintaining our muscle mass appears to trigger all the responses that keep us young and vital. In fact, building muscle is the closest humans will ever get to the fountain of youth!