Research has also linked high consumption of quercetin with catching fewer colds, says University of South Carolina researcher J. Mark Davis, PhD. His virus-avoiding strategy (besides steering clear of those who are sick and being vigilant about hand washing) includes loading up on quercetin-rich foods. Best of all, he says, are red onions, which have quadruple the quercetin of most other produce. Eat them raw or cooked, though cooking foods with quercetin may make the antioxidant more easily absorbed.