05/30/2026
A banana cancels most of your berry smoothie's antioxidants.
Firstly, bananas are a good food. This is about an enzyme and what it does to a specific group of compounds.
Flavanols are antioxidants found in berries, cocoa, grapes, and apples that have been linked to heart and brain health. Bananas are high in polyphenol oxidase (PPO), the enzyme that turns a cut banana brown within minutes. PPO breaks flavanols down into forms the body absorbs poorly.
The study that measured this was careful about one thing worth understanding. Ottaviani et al. (2023) did not simply compare a berry smoothie to a banana smoothie and assume berries had more to begin with. They added the same standardized dose of cocoa flavanols to every drink, so the starting amount was identical. Then they gave healthy volunteers three things on separate days: that flavanol dose in a capsule, the same dose in a low-PPO berry smoothie, and the same dose in a high-PPO banana smoothie.
The capsule produced peak blood flavanols of about 680 nmol/L. The berry smoothie landed in the same range. The banana smoothie reached only about 96 nmol/L, roughly 84 percent lower than the capsule, from an identical starting dose. The only thing that changed was the enzyme it was blended with.
A second detail sharpens the mechanism. When the banana drink and the flavanols were swallowed together but not blended beforehand, levels still dropped. That points to PPO continuing to act after you swallow it, likely in the stomach, not only during blending.
Two honest limits. This was a small mechanistic study. The comparison behind the 84 percent figure was a crossover in eight healthy men, and it measured absorption, not a long-term health outcome. It was also funded by Mars, Inc., which has a commercial interest in cocoa flavanols. That does not change the underlying chemistry, which is well established, but it is worth knowing.
The practical takeaway is narrow and specific. This does not mean bananas reduce the nutritional value of your food, and it is not a reason to stop eating them. It means that if flavanol intake is something you care about, the fruit you blend with your flavanol source is worth considering. Berries and pineapple are low in PPO. If you want those compounds to reach your blood, keeping the banana out of that particular smoothie, or eating it on the side, is a reasonable choice.
Ottaviani et al., Food & Function, 2023 (DOI: 10.1039/d3fo01599h)
