Magnesium may be key in preventing colon cancer in men, according to recent research published in the Journal of Nutrition. The eight-year study of nearly 90,000 people showed that taking at least 327 mg magnesium daily reduced men’s colon cancer risk by 52 percent. Get magnesium through dietary sources, including green vegetables, nuts, peas, beans, soy products, and whole grains, as well as supplements.