Whole grains add two kinds of fiber to your diet. Soluble fiber lowers blood cholesterol levels. Insoluble fiber keeps the food you eat -- both the healthy kind and nutritionally shady indulgences -- moving through your body at a steady clip.
Preventing digestive traffic jams reduces strain on your intestines and lowers your risk of getting diverticulitis (the formation of swollen pouches in your digestive system). Slow moving food is uncomfortable, and it gives the bad guys -- harmful bacteria and cancer cells -- way too much time to develop in your intestines.
Whole grains, along with water, make you feel full, so it's easier to avoid overeating and gaining weight. Excessive weight adds to your risk of developing diabetes, elevated cholesterol levels and heart disease.