A recent study from the University of California, Davis, has uncovered a surprising nutritional twist: adding bananas to your “healthy” smoothie could drastically reduce its benefits. Researchers found that the popular fruit contains an enzyme that interferes with the body’s ability to absorb flavanols, powerful compounds known to support heart and brain health.

The culprit is an enzyme called polyphenol oxidase (PPO)—the same one that causes bananas and apples to turn brown after being peeled. According to the findings, this enzyme reacts with flavanols and weakens their biological activity, reducing their absorption by as much as 84% in participants who drank banana smoothies compared to others.

Flavanols, found abundantly in apples, berries, cocoa, and grapes, play a vital role in improving blood flow, memory, and overall cardiovascular health. However, when combined with bananas, their effectiveness drops dramatically, making the smoothie far less beneficial than expected.

Published in Food & Function, the research noted that even a single banana was enough to significantly reduce flavanol levels in the bloodstream. The team emphasized that while bananas remain a nutritious fruit, they should be avoided in flavanol-rich smoothies to preserve their health-promoting effects.

Experts recommend a daily intake of 400–600 mg of flavanols for optimal heart and circulatory health. The researchers concluded that understanding how different foods interact can help people build smarter, more effective diets—because sometimes, even a small ingredient can change everything.

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