A surprising study found that adding bananas to your smoothie reduces the absorption of anti-aging flavanols by a whopping 84%. That’s because bananas contain an enzyme called polyphenol oxidase, or PPO, that turns fruits brown and is particularly abundant in bananas. The enzyme blocks the absorption of flavanols, which are natural compounds found in fruits and vegetables known to support heart and brain health,

According to Food & Wine, flavanols help improve our overall well-being and can aid in aging gracefully. A 2025 study in the American Journal of Clinical Nutrition showed that individuals who consumed higher quantities of flavanols had a lower risk of frailty and a decreased risk of poor mental health as they age. The findings were more pronounced in women; however, men also experienced a net positive benefit.

According to Gunter Kuhnle, a professor of nutrition and food science at the University of Reading and co-investigator of the study, “If you don’t consume enough flavanols, it can negatively affect cardiovascular health. In older adults, a deficiency of flavanols is also linked to cognitive decline. So, it’s clear we need them, but the question is how best to get flavanols from the food and drinks we consume.”

The study authors recruited volunteers who drank smoothies that included high PPO bananas and others who consumed smoothies with low PPO fruits, such as berries. Participants also took flavanol supplements to act as a control. Blood tests conducted after participants drank the smoothies showed that bananas did more harm than good in smoothie mixes, reducing the absorption of flavanonols by a whopping 84%.

 “Smoothies are a popular way to pack fruit and vegetables into our morning routines. We know from previous studies that flavanols can be broken down by polyphenol oxidase. The extent of the effect from adding a single banana was still very surprising – it had enough polyphenol oxidase to destroy the vast majority of flavanols found in the berries,” says Kuhnle.

However, don’t throw away those bananas. “Bananas may be ruled out of the morning smoothie if you want to boost your flavanol intake, but on their own, they are still great fruits and can play an important role in many healthy diets.”

Kuhnle suggests blending flavanol-rich smoothies that contain berries with foods that have a low PPO activity such as mangoes, pineapple or yogurt.