For years, quercetin has been one of those “promising” compounds that appear again and again in nutritional studies: antioxidant, anti-inflammatory, present in common fruits and vegetables. But its real role in health, and especially in cancer prevention, has always been disappointing outside the laboratory. The reason is simple: consuming quercetin does not guarantee that the body knows what to do with it. But let’s take it step by step because that could have changed. Quercetin is a plant flavonoid, a type of polyphenol that plants use as a defense against ultraviolet radiation or pathogens. We ingest it daily, although we are almost never aware of it. Apples have taken much of the fame regarding their content, but they are far from being the main source. Especially high amounts appear in onions (especially red ones), capers, blueberries, grapes, cherries, broccoli and tea. In some cases, a small serving of these foods contains more quercetin than several apples combined.
The problem is that, in the human body, quercetin is poorly absorbed and has little effect on its own. This is when a factor that classical nutrition ignored for decades comes into play: the intestinal microbiome. A new study, published in Cell Metabolism, shows that quercetin only unleashes part of its potential when certain intestinal bacteria chemically transform it. It is not the original molecule that matters, but what our microbes do with it.
