Control

The brain controls everything and the body exists in a perfectly symbiotic state with the brain. Many thoughts are about survival of the brain: to feed the brain properly and to feed the body well.

If the brain dies then so does the body. Or the other way around. The one without the other will fail.

In a normally functioning body, I believe that many age related mental problems can be related to poor diet. And that the brain should be treated in the same way as a muscle:

'if you don’t use it, you lose it'