Cancer. Some 45 percent of colon cancers, 38 percent of breast cancers, and 69 percent of esophageal cancers would never occur if Americans ate better, weighed less, and exercised more, estimates the American Institute for Cancer Research. The organization recommends limiting red meat to 18 (cooked) ounces per week and loading up on plant-based foods, which are high in the phytochemicals and antioxidants known to inhibit cancer cell growth in lab animals. Those with the deepest colors—like purple grapes, blueberries, and leafy green vegetables—tend to have the most beneficial compounds. One study, for example, showed that eating foods such as broccoli and kale that have lots of sulforaphane, an antioxidant, suppresses a bacterium linked to stomach cancer.
Updated on 5/22/12: This story was originally published on December 14, 2009. It has been updated.