Next time you're making yourself a berry smoothie, you might want to hold off on the banana.Sure, it's full of potassium and makes a drink deliciously thick and creamy, but it could actually be impacting the nutritional benefit of your fruity drink.According to research from the University of California, Davis (UCD), there's something in bananas that might overpower the antioxidants in berries.The antioxidants in this case are called flavonols. They are found in plant-based foods like berries, tea, cocoa, apples, pears, and peaches, and many of us do not get enough of them in our diet.When a person eats food rich in flavonols, the compounds are rapidly absorbed into the bloodstream, where they are processed.The resulting metabolites have been associated with benefits like improved cardiovascular health and cognitive function.But experiments suggest that when just a single banana is added to a berry mix, these metabolites are not nearly as abundant.In a controlled, blinded study published in the journal Food and Function in 2023, researchers at UCD gave a small group of eight participants either a flavonol-rich berry smoothie or a simple flavonol capsule.Tests later showed an increase in levels of the flavonol metabolites in their blood.(Anjana Sharma/500px/Getty Images)When volunteers consumed a banana-berry smoothie, however, the metabolites in their blood were 84 percent lower than after a pure dose of flavonol."We were really surprised to see how quickly adding a single banana decreased the level of flavonols in the smoothie and the levels of flavanol absorbed in the body," said nutritionist Javier Ottaviani from UCD at the time."This highlights how food preparation and combinations can affect the absorption of dietary compounds in foods."The reason why bananas have this effect on flavonols probably has to do with an enzyme called polyphenol oxidase (PPO), which is involved in the oxidation process that turns bananas brown when they're peeled.