Flavan-3-ols are plant compounds found in fruits and vegetables that have been associated with health benefits, but a new study reveals that the way these foods are prepared could significantly affect how much of these beneficial compounds the body actually absorbs. Researchers discovered that polyphenol oxidase, an enzyme present in many fruits, can dramatically reduce the bioavailability of flavan-3-ols when consumed in smoothies.
The research team conducted a controlled, single-blinded, crossover study with eight healthy male participants. Each person consumed three different preparations containing flavan-3-ols: a banana-based smoothie high in polyphenol oxidase activity, a mixed berry smoothie with low polyphenol oxidase activity, and flavan-3-ols delivered in capsule form as a control. The crossover design meant each participant tried all three preparations, which strengthens the findings by reducing individual variation.
The results showed substantial differences in absorption. When participants took the capsule, their peak plasma concentration of flavan-3-ol metabolites reached 680 nanomoles per liter. The low polyphenol oxidase berry smoothie produced similar levels, suggesting that the beneficial compounds were absorbed effectively. However, the high polyphenol oxidase banana smoothie resulted in peak concentrations of only 96 nanomoles per liter, representing an 84% reduction compared to the capsule. This finding indicates that the enzyme substantially interfered with the availability of these compounds.
To investigate whether the enzyme worked before or after consumption, researchers conducted a follow-up study with 11 participants. In this experiment, flavan-3-ols were consumed alongside a high polyphenol oxidase banana drink, but the two were kept separate until immediately before ingestion. Despite minimizing pre-consumption contact, plasma levels of flavan-3-ols remained reduced, suggesting that polyphenol oxidase continues to degrade these compounds even after they enter the stomach.
The research team also examined polyphenol oxidase activity across 18 different fruits, vegetables, and plant-based dietary products. They found considerable variation in enzyme activity levels, indicating that this effect would vary depending on specific food choices and combinations.
These findings have practical implications for dietary recommendations and food preparation. Smoothies are frequently promoted as an effective way to increase fruit and vegetable consumption, particularly for people who struggle to meet recommended intake levels. However, this research suggests that combining certain high polyphenol oxidase fruits with flavan-3-ol sources could substantially reduce the health benefits consumers expect to receive.
The study has limitations worth noting. The sample size was relatively small, with only eight participants in the primary experiment and 11 in the follow-up study. Additionally, the research focused exclusively on male participants, so whether these effects apply equally to women remains unclear. The study examined acute bioavailability rather than long-term health outcomes, so while absorption was clearly affected, the ultimate health impact requires further investigation.
The implications extend beyond home food preparation to industrial settings where smoothies and blended fruit products are manufactured. The research suggests that food producers and consumers alike should consider enzyme activity when combining ingredients, potentially choosing low polyphenol oxidase options or using preparation methods that minimize enzyme activity to maximize the nutritional benefits of flavan-3-ols and potentially other polyphenol compounds.