Polyphenols

"Polyphenols" is an umbrella word for several classes of compounds, and foods differ in which classes they contain and how much. A 2004 review of polyphenol food sources set out the contents of the various polyphenols in foods and how agricultural practices and industrial processes change them [1].

The body handles polyphenols extensively. The gut and liver attach chemical groups to them (methylation, glucuronidation and sulfation) before they circulate and are eliminated in bile and urine, and gut microbes break some down into active metabolites [1]. For one class, the flavan-3-ols, a systematic review of 49 human studies counted up to 180 metabolites in blood and urine after intake [3].

A total polyphenol figure lumps together compounds that behave very differently in the body. Bioavailability appears to differ greatly between polyphenols, and the most abundant polyphenols in the diet are not necessarily those with the best bioavailability profile [1]. A study that reports only "total polyphenols" therefore tells you less than one that names the class and the main compounds.

Regulators sometimes set conditions in polyphenol terms. The UK Food Standards Agency authorization for an extract of defatted cocoa powder requires that consumers be instructed not to consume more than 600 mg polyphenols, corresponding to 1.1 g of the extract, per day [4]. That is a labeling condition for one authorized ingredient, not a finding about effects.

When a paper says "polyphenol-rich", look for the food or extract, the class measured and the method used to measure it.

• Flavonoids
• Flavanols
• Bioavailability