Flavonols (quercetin)
Polyphenols
The most widespread polyphenol in the diet, and the most studied of the pale yellows.
Capers are by far the richest gram for gram, ahead of onion.
Effects and benefits
The most widespread polyphenol in the diet, in onion, kale, apple and tea. The one in onion reaches the blood best; as a high-dose supplement, quercetin lowered blood pressure by a few points in trials.
Quercetin is a color before it is a nutrient: a pale yellow pigment that protects leaves and skins from the sun. In onion, most of it sits in the outer layers, just under the dry skin.
It is not absorbed the same way depending on its source: in onion, it is bound to glucose, which opens a gut transporter to it; in apple or tea, bound to another sugar, much less gets through (Hollman et al., 1997).
A meta-analysis of trials found a drop in blood pressure of a few points with at least 500 mg of quercetin a day as a supplement (Serban et al., 2016). Food provides more like 10 to 30 mg. What is not absorbed reaches the colon, where bacteria cut it into small phenolic acids.
Sources: Hollman et al., FEBS Lett, 1997 · Serban et al., JAHA, 2016
Where to find it (22)
- Apple
- Arugula
- Blackcurrant
- Broccoli
- Buckwheat
- Capers
- Carrot tops
- Chives
- Cranberry
- Dill
- Fennel fronds
- Galangal
- Goji berry
- Kale
- Lingonberry
- Lovage
- Onion
- Radish greens
- Scallion
- Shallot
- Tea (black, green, oolong)
- Turnip greens