Make no mistake the body needs fat. It is the most concentrated source of stored energy and necessary for making hormones, such as testosterone and estrogen, and it controls body temperature and a host of other important functions. Carbohydrates Glucose is still the body's first choice of energy, but, if you run out of it, your body will begin to break down stored fat. All carbohydrates are broken down into glucose, except fiber. It is the fuel for every cell in your body and the only fuel used by the brain.
Animal products contain no carbohydrates at all.
Your body has to work harder to break down complex carbohydrates into glucose, thereby providing a steady stream of energy. In addition, complex carbohydrates generally contain more vitamins and minerals than their simple sugar counterparts. Complex carbohydrates are also a wonderful source of dietary fiber. Because human digestive enzymes cannot break down the bonds that hold fiber together, fiber provides no nutritional value or calories to your diet. However, far from unimportant, fiber absorbs large amounts of water, moving solid materials through the digestive tract, preventing constipation and possibly some types of colon cancer.