YOGA is for the Mind. Once the Mind becomes balanced, the incidental benefit is that our body becomes Healthy, Good looking & Free from Diseases.
Maharshi Patanjali says:-
"yogaś-chitta-vr̥itti-nirodhaḥ" =
When you are in a state of yoga, all misconceptions (vrittis) that can exist in the mutable aspect of human beings (chitta) disappear.