To extract the oils, they are pressed in mechanical processes which creates friction as well as therefore heat, thereby increasing oxidation. However, done under the right conditions, the integrity a number of oils can be maintained. Oils termed 'cold-pressed' are complied at temperatures that prevent damage. After pressing, these delicate oils should be stored outside of the light, moisture and heat. This is why you will notice good quality oils residing in dark glass bottles.
For example if in order to eating enough calories that permit you to nourish your present body anyone build up new groups of muscles. Those calories a person eat go to feed the new muscles and formulate a calorie deficit in your body.