Quercetin is a plant chemical that naturally occurs in many different fruits and vegetables. Red onions are one of the best sources of quercetin. It has demonstrated both anti-inflammatory, and anti-viral effects. But can it also help improve endurance capacity?
According to the University of South Carolina, Columbia, SC, in The dietary flavonoid quercetin increases VO(2max) and endurance capacity:
Seven days of quercetin feedings were associated with a modest increase in VO2max (3.9% vs. placebo; p < .05) along with a substantial (13.2%) increase in ride time to fatigue (p < .05). These data suggest that as little as 7 days of quercetin supplementation can increase endurance without exercise training in untrained participants. These benefits of quercetin may have important implications for enhancement of athletic and military performance. This apparent increase in fitness without exercise training may have implications beyond that of performance enhancement to health promotion and disease prevention.
Interesting! But this is just one study. Fortunately a meta-analysis(a study that combines the results of several studies) of the effects of quercetin was done by the Georgia Institute of Technology, Atlanta, GA, in Quercetin and endurance exercise capacity: a systematic review and meta-analysis:
On average, quercetin provides a statistically significant benefit in human endurance exercise capacity (VO(2max) and endurance exercise performance), but the effect is between trivial and small. Experimental factors that explain the between-study variation remain to be elucidated.
There does appear to be an effect, but it’s small. More research needs to be done, but I won’t be eating lots of red onions just because of this.