Why a banana may sabotage the antioxidants in your smoothie

Bananas are one of the most common smoothie ingredients, which makes this finding worth knowing. In a controlled crossover study in Food & Function, researchers had people drink a banana-based smoothie or a mixed-berry smoothie, each containing the same dose of flavan-3-ols, the beneficial flavanols found in cocoa, berries, tea, and apples.

After the banana smoothie, blood levels of those flavanol compounds were about 84 percent lower than after the low-PPO berry smoothie or a capsule. The culprit is polyphenol oxidase (PPO), an enzyme abundant in bananas that oxidizes flavanols within minutes of blending, the same reaction that turns a cut banana brown.

The enzyme stayed active even under simulated stomach conditions, so the loss was not prevented by keeping the ingredients separate until drinking. This is a fascinating and practical finding, given how many people build smoothies around bananas. It is a reminder that plant foods sometimes contain compounds that block the absorption of nutrients, much like the oxalates in spinach that bind calcium.

If you want the flavanol benefits of cocoa, berries, or green tea in a smoothie, pair them with low-PPO fruits like the mixed berries used here, and save the banana for another time.

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Why a banana may sabotage the antioxidants in your smoothie