Michael Greger on Flavonoids

Michael Greger posted a YouTube video titled Cancer, Interrupted: Garlic & Flavonoids in which he offers a dubious summary of a paper from 2012 on the protective effect of the flavonoids.

This paper studied two phytochemicals, quercetin and rutin, at doses from 100μM. Greger presents the results as if they're relevant for humans eating diets rich in these chemicals. While the study is interesting, it's preliminary and the dosages studied are not in the least environmentally relevant.

We can use the molar mass of the two flavonoids studied to understand this dose in parts per million:

(302.236 g/mol) * (100μM) = 30 ppm quercetin
(610.520 g/mol) * (100μM) = 61 ppm rutin

Notice these concentrations are similar to the doses found in the foods high in these phytonutrients.
Red onions contain 32 ppm quercetin and buckwheat contains 100 ppm rutin.

How much of each food would a 70kg human need to consume to match the doses in this study?

(70 kg) * (30 ppm) / (32 ppm) = 144 pounds of red onions
(70 kg) * (61 ppm) / (100 ppm) = 94 pounds buckwheat

That's a lot of red onions and buckwheat! It's clear that these doses aren't achievable through diet.

The lesson here is not to mistake food for medicine. Eating a varied diet containing lots of fruits and vegetables is a good idea for many reasons. The effects of high doses of phytochemicals are not among those reasons.