If a persons wants to improve his body structure, then only change of diet will not help, until and unless he changes his thoughts.
When a man makes his thoughts pure, then he no longer desires impure food and starts disliking the food, which is not good for health. This automatically improves his health.
Therefore guard and beautify your mind and it will automatically change your habit and actions is such a way, that you will become a healthy man.
Remember that body acts as per the direction of mind.