Healing Kitchen

Eat Your Apples, Onions & Grapefruit
Flavonoids are polyphenolic compounds that appear widely in plant-based foods. Acting as antioxidants, flavonoids are currently under review for their potential to function as disease fighting agents. Thousands of flavonoids (more than 4,000) have been identified. The significance of flavonoids was evidenced recently in a study published in the Journal of the National Cancer Institute, which reported a compelling correlation between high intake of dietary flavonoids and the reduced risk of lung cancer. The specific food sources of the flavonoids that appear to be the best for lung protection are onions, apples and white grapefruit.

A population-based, case control study was conducted in Hawaii on 582 patients with lung cancer and 582 control subjects. Both groups were between 26 and 79 years of age. An in-person interview was conducted with each participant to assess smoking history and intake of 242 food items for both study groups. To eliminate confounding factors, researchers sifted out those who took beta-carotene supplements, since a number of disturbing studies have shown that beta-carotene supplements may have either no effect or an adverse affect upon those who are at risk for developing lung cancer. After adjusting for intakes of saturated fat and beta-carotene as well as smoking, the researchers found an inverse association between lung cancer risk and the primary food sources of two flavonoids in particular: quercetin from onions and apples, and naringin, which is present in greater amounts in white grapefruit than pink or red grapefruit.

The ability of particular dietary flavonoids to decrease stimulation of carcinogens could be an important mechanism by which these particular foods may be protective against cancer. The researchers hypothesize that quercetin and naringin inhibit cytochrome P450 enzymes (CYP1A1 and CYP3A4) that assist in the bioactivation of carcinogens. The potential chemopreventive effect of quercetin and naringin possibly results from their antioxidant activity and their capacity to eliminate free radicals. It is also possible that the synergistic interplay between a host of microconstituents in foods such as onion, apples and grapefruit could create a potent formula for optimal health.

An earlier study by other scientists conducted in Finland on dietary flavonoids and lung cancer, reinforces the conjecture that flavonoids may harbor significant anticancer properties. In that study, researchers discovered that out of approximately 10,000 men and women who participated, the group with the highest flavonoid intake had a 46% lower risk of developing lung cancer. The flavonoids in the Finnish study that came out on top were apples and onions, respectively. Further studies on flavonoids suggest that the use of certain plant foods may demonstrate highly protective effects against lung cancer.

The extent of absorption of dietary flavonoids is a significant issue when studying their health effects. Absorption studies have shown that quercetin in onions is better and more efficiently absorbed than from other foods, making its bioactivity more potent because it resides in the blood for a longer period of time. The absorption of quercetin from onions has been shown to be fourfold greater than that from apples or tea. While few humans studies have been conducted on bioavailability of flavonoids, the human studies that have been done have shown that onions, apples and white grapefruit may prove to play an important role in the suppression of cancerous tumors.

Author: Maureen Mulhern-White
Date Published: 03/27/2000
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