Flavonols are phytochemicals belonging to the flavonoid class. Abundant in the flesh of fruits and vegetables, their colour is influenced by exposure to UV light. Flavonols represent one of the largest groups of flavonoids, but their concentration in foods is not fixed. Factors such as plant type, season, ripeness, processing, and preparation can all affect the amount of flavonols found in food.
Flavonols usually appear as a vivid shade of yellow. Brilliant colouration indicates a higher density of flavonols.
Dozens of flavonols exist, but the most common types include:
Capers, cranberries, onions, white currants
Spinach, kale, chives, green beans
Broccoli, oregano, fennel, red wine
Almonds, tarragon, pears, nopal
Flavonol-rich diets have been linked to favourable outcomes in several studies. Research is ongoing, but the influence of flavonols could extend to weight management, cardiovascular disease prevention, and cancer prevention.
A 2016 study in the BMJ observed flavonoid intake among men and women for up to 24 years. Once lifestyle factors were accounted for (diet, smoking, and physical activity), results showed that “higher intake of foods rich in flavonols, flavan-3-ols, anthocyanins, and flavonoid polymers may contribute to weight maintenance in adulthood” (Bertoia et al., 2016).
The British Journal of Cancer found that women in Greece with a flavonoid-rich diet had an “inverse association” with breast cancer. Eight hundred twenty women took part in the case–control study, with researchers concluding, “there was no association of breast cancer with flavanones, flavan-3-ols, flavonols, anthocyanidins or isoflavones” (Peterson et al., 2003).
In 2002, the American Journal of Clinical Nutrition found that several flavonols might reduce the risk of chronic diseases. Quercetin was associated with “lower mortality from ischemic heart disease” and “lower lung cancer incidence”. Kaempferol intake reduced the “incidence of cerebrovascular disease”, while diets rich in myricetin had “ a lower prostate cancer risk” (Knekt et al., 2002).
Flavonoid intake over a ten year period is believed to positively influence cognitive decline. The American Journal of Epidemiology found that subjects with a higher intake of flavonoids had “better cognitive performance at baseline” and a “better evolution of the performance over time”. When accounting for lifestyle impacts, the researchers still found the gradient to persist (Letenneur, Proust-Lima, Le Gouge, Dartigues, & Barberger-Gateau, 2007).
Although most studies indicate flavonols are well tolerated, some side effects have been observed in excessive flavonoid intake. In 2000, a report by Free Radical Biology & Medicine noted that higher doses of flavonoids might act as mutagens, pro-oxidants, and inhibit enzymes such as cytochrome P450. Their advice was to avoid ingesting flavonols at “levels above that which would be obtained from a typical vegetarian diet”.