The truth is that your body is NOT yours to treat as you wish. Your body belongs to G-d, Who gave it to you to care for, as a vehicle to carry your soul through life. Just as you would not harm another person, just as you would not harm anything that G-d has created, you should not harm your own body. It is your duty to eat well, to rest, to stay in shape, and to treat your body with respect in every way. The body is a vehicle for the soul.
Good health is a sound soul in a sound body.
Modern medicine has begun to discover the dramatic effect that a person's spirit can have on the healing process. Just as the body is nourished by certain foods, the soul needs spiritual nourishment. This nourishment includes an awareness of one's mission in life and an awareness of G-d, Who has empowered us with the abilities to fulfill that mission. It is important to see that every aspect of your physical fitness has a spiritual component. When you eat, you should acknowledge that the food is not meant for simple indulgence, but to generate the vitality necessary to lead a meaningful life.