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Does what you eat affect cancer risk?

Those among us who keep up with all the studies linking diet and cancer are currently eating lots of foods rich in fiber; vitamins A, C and E; and selenium (a mineral). Just to be sure we’ve covered all the bases, many of us also take special supplements that are chock full of these nutrients.

What’s wrong with loading up on nutrients thought to prevent cancer? Two things:

  1. Many nutrients, including those mentioned above, are toxic in high doses. Too much vitamin A can cause liver damage and birth defects. Megadoses of vitamin C can cause diarrhea and kidney stones and can damage vital organs. Too much fiber can interfere with the absorption of zinc, iron and calcium, vital nutrients.
  2. In nutritional studies on humans, there are so many variables that it’s impossible to be certain exactly which nutrient is responsible for any detected effect on cancer risk. By focusing on one nutrient, you may miss out on others that are equally important but have yet to be named as cancer blockers. For example, after all the hoopla about beta-carotene, many of us started munching carrots faster than Bugs Bunny. However, researchers at Harvard University found that diets high in carrots (rich sources of the antioxidant) did not protect against cancer. Instead, they found that tomatoes, which contain almost no beta-carotene, were associated with some protective action.

Best advice

Although there’s disagreement about the exact composition of the best cancer-preventing diet, experts agree on several points.

  • Eat a variety of healthful foods. The greater the variety, the more likely it is that you’ll consume whatever anticancer nutrients there are. If your diet is varied, it’s also less likely that you’ll consume too much of a harmful substance.
  • Eat plenty of a variety of fruits and vegetables. While no one knows for sure which nutrients or combination of nutrients will help you avoid cancer, lots of evidence suggests that fruits and vegetables have what it takes.
  • Keep fat intake to less than 35 percent of calories (30 percent if you’re overweight).
  • Maintain a healthy weight. The link between excess weight and cancer is well established.
  • Limit alcohol consumption. Heavy alcohol consumption has been linked to cancers of the head, neck and lungs. Drinking becomes even riskier when combined with smoking—the combination appears to increase cancer risk many times.