Scientists Discover Unexpected Reason Bananas May Not Belong in Smoothies

Your morning smoothie may not be as healthy as you think - especially if you're blending bananas with berries. New research from the University of California, Davis suggests that one of the world's most popular smoothie ingredients could dramatically reduce your body's ability to absorb beneficial plant compounds called flavanols.

Flavanols are natural compounds linked to heart and brain health. They are abundant in foods such as blueberries, blackberries, apples, grapes, cocoa, and tea. But according to a study published in Food & Function, combining these foods with bananas may sharply cut how much of those compounds your body actually absorbs.

The reason comes down to an enzyme called polyphenol oxidase, or PPO. This is the same enzyme responsible for the browning seen when bananas or apples are sliced and exposed to air. Bananas contain especially high PPO activity, while berries contain relatively low levels.

Researchers tested how different smoothies affected flavanol absorption in healthy volunteers. Participants consumed a banana smoothie, a mixed berry smoothie, and a flavanol capsule used as a control. Blood and urine tests later revealed a striking result: people who drank the banana smoothie had 84% lower flavanol levels compared with the control group. Meanwhile, the berry smoothie preserved flavanol absorption almost as effectively as the capsule.

Scientists say the enzyme appears to break down flavanols before the body can absorb them. Even when flavanols and banana were consumed separately but at the same time, absorption still dropped significantly.

The findings do not mean bananas are unhealthy. Bananas remain rich in potassium, fiber, and important nutrients. The study simply suggests that if your goal is to maximize flavanol intake from berries, grapes, apples, or cocoa, bananas may not be the best smoothie partner.

Instead, researchers recommend combining flavanol-rich fruits with low-PPO ingredients such as mango, pineapple, oranges, or yogurt.

REFERENCE: Javier I. Ottaviani, Jodi L. Ensunsa, Reedmond Y. Fong, Jennifer Kimball, Valentina Medici, Gunter G. C. Kuhnle, Alan Crozier, Hagen Schroeter, Catherine Kwik-Uribe. Impact of polyphenol oxidase on the bioavailability of flavan-3-ols in fruit smoothies: a controlled, single blinded, cross-over study. Food, 2023; 14 (18): 8217 DOI: 10.1039/D3FO01599H