Foods are considered to be the preferred way of boosting antioxidant levels because they're thought to contain a wide array of antioxidant substances. Many of  them, such as blackberries, are also high in vitamins, minerals and fiber.

A university study by Halvorsen et al (2006) analyzed the antioxidant content of commonly consumed foods. Researchers tested over 100 foods. Blackberries ranked the highest in per-serving cancer-fighting levels of antioxidents. Here is a ranked list of the top 10 fruits, vegetables and nuts:

1. Blackberries
2. Walnuts
3. Strawberries
4. Artichokes, prepared
5. Cranberries
6. Coffee
7. Raspberries
8. Pecans
9. Blueberries
10. Cloves, ground