Healthnotes Newswire (November 18, 2004)—A new study indicates that some onion varieties may contain more health-promoting substances than others, reports the Journal of Agricultural and Food Chemistry (2004;52:6787–93). The study evaluated the antioxidant properties of shallots and ten other types of onions, as well as their ability to inhibit cancer cell growth in the test tube.

By Kimberly Beauchamp, ND

Flavonoids are one group of phenolic compounds (substances found in a wide variety of plants) that are well known for their antioxidant properties. Antioxidants protect cells in the body from damage caused by free radicals, which are unstable compounds formed during a chemical reaction with oxygen. Consuming flavonoids is associated with a reduced risk of heart disease, cancer, and diabetes. These substances have also been shown to have antibacterial, antiviral, anti-inflammatory, and anti-allergic actions. Onions are a particularly rich dietary source of flavonoids.

Perhaps the best-known flavonoid found in onions is quercetin. Yellow onions tend to have the highest concentration of quercetin; pink and white onion varieties have the lowest. Relatively little is known about the levels of flavonoids in different onions and their associated antioxidant and anticancer properties. The new study evaluated a number of different onion varieties: shallots, Western Yellow, New York Bold, Northern Red, Empire Sweet, Western White, Peruvian Sweet, Mexico, Texas 1015, Imperial Valley Sweet, and Vidalia. Each onion was analyzed for its phenolic content, flavonoid content, antioxidant activity, and anticancer properties (measured as the ability of the onion extract to inhibit liver and colon cancer cell growth).

Shallots had the highest phenolic content of the varieties tested, with six times more phenolics than the lowest-ranked onion, the Vidalia. Shallots also had the greatest antioxidant activity among the varieties tested. Western Yellow onions had 11 times more flavonoids than the Western White, the onion lowest in flavonoids. The Western Yellow onion, shallots, and New York Bold onions had the greatest effect against liver cancer cell growth. New York Bold and Western Yellow onions were most effective against colon cancer cell growth.

Those onions with higher phenolic and flavonoid contents tended to have higher antioxidant and anticancer activities. Overall, shallots, Western Yellow, New York Bold, and Northern Red onions had the highest total levels of flavonoids and phenolics of all the onions sampled—and they also have a strong, pungent flavor. In contrast, the Vidalia onion, which consistently had the lowest levels of flavonoids and phenolics, and was associated with the lowest antioxidant and anticancer activities, is a sweet and mild variety that lacks the strong smell of the more potent onions.

The findings of this study suggest that many of the onions that are more pungent and stronger in flavor may actually have more health-promoting properties than the milder varieties. This could have important implications for consumers and growers of onions.

Kimberly Beauchamp, ND, received her bachelor’s degree from the University of Rhode Island and her Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. She is a co-founder and practicing physician at South County Naturopaths, Inc., in Wakefield, RI. Dr. Beauchamp teaches holistic medicine classes and provides consultations focusing on detoxification and whole-foods nutrition.

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