The review, published in the journal Nutrition Reviews, found that the majority of studies “suggest that polyphenols may have greater bioavailability when they are ingested in combination with other polyphenols than when taken alone, such as in a supplement”.
However, taking other antioxidant micronutrients at the same time, such as vitamins C and E, may have the reverse effect, the researchers said.
The review concluded that more knowledge is needed so ingredients can be tailored to optimise nutrition and the bioavailability of polyphenols.
Bioavailability is the ability of an organism to use a compound in its intake for energy and metabolism.
Being available
Polyphenols constitute a diverse class of secondary plant compounds, or phytochemicals. High concentrations are found in the outer parts of fruits and vegetables, such as apple or potato peel, in leafy vegetables, cereals, cacao and coffee beans.
Polyphenols lay claim to antioxidant activity and have been associated with a reduction in the risk of cancer and cardiovascular disease, among other health benefits.
The review states: “While many epidemiological studies have associated the consumption of polyphenols within fruits and vegetables with a decreased risk of developing several chronic diseases, intervention studies (trials with supplements) have generally not confirmed these beneficial effects.
“The reasons for this discrepancy are not fully understood but include potential differences in dosing, interaction with the food matrix, and differences in polyphenol bioavailability.”
Factors impacting bioavailability
The review said that polyphenol bioavailability appears to depend on a variety of factors related to diet and the food matrix, such as the dose, smaller particle size and heating and the presence of lipids, as well as low levels of proteins and indigestible carbohydrates.
The simultaneous intake of antioxidant micronutrients such as vitamins C and E may, to some extent, reduce gastrointestinal degradation of polyphenols, while the presence of additional polyphenols may enhance polyphenol availability by influencing efflux transporters.
The review concluded that: “A largely neglected factor appears to be the potential effect of nutrients and non-nutrients on polyphenol biodistribution and excretion.
“Thus, in view of the potential relationship between polyphenols and the reduction of chronic diseases on one hand, and the risk of micronutrient deficiencies such as zinc and iron with elevated polyphenol intake on the other, as well as the plethora of dietary supplements on the market, more research in this domain is warranted.
“The combination of food science and technological knowledge to tailor these aspects and steer the bioavailability of polyphenols by optimally combining various ingredients is desired to guarantee optimal nutrition.”
Several polyphenols, including phenolic acids and flavonoids, reduce the absorption of some minerals and trace elements, including iron, zinc, copper and sodium, they wrote.
Source: Nutrition Reviews
Published online ahead of print, doi: 10.1111/nure.12114
“Dietary factors affecting polyphenol bioavailability”
Authors: T. Bohn