Surprising Insights: The Reason to Skip Bananas in Your Smoothies According to Latest Research

The Hidden Effect of Bananas

A 2023 study published in the Royal Society of Chemistry’s Food & Function journal examined how the enzyme polyphenol oxidase (PPO) affects nutrient absorption. PPO is the enzyme responsible for fruit browning — like when a banana or apple turns brown after cutting.

The UC Davis team wanted to know whether PPO could also interfere with the absorption of flavan-3-ols, compounds found in foods such as berries, cocoa, grapes, and tea. Their findings were eye-opening: when smoothies included fruits with high PPO activity, such as bananas, the enzyme broke down flavan-3-ols before the body could absorb them.

What the Study Did & Found

Researchers recruited 8 healthy men in a crossover trial. Each participant consumed:

• A banana-based smoothie (high PPO)

• A mixed-berry smoothie (low PPO)

• A flavanol capsule (control)

They then measured plasma flavanol metabolite levels (Cₘₐₓ). The results:

• The low-PPO berry smoothie produced similar flavanol absorption as the capsule.

• The banana smoothie yielded absorption that was 84% lower than the capsule.

• In a follow-up test where banana and flavanols were ingested separately (to prevent direct contact before ingestion), flavanol levels still dropped. This suggests PPO activity can degrade flavanols even inside the body (e.g. in the stomach).

Why This Happens: The Role of PPO & Flavanols

PPO is the enzyme that causes fruit browning when exposed to air, cut, or bruised. In the UC Davis study, banana had a very high PPO activity (≈ 3,258 KU/100 g), compared to much lower values in other fruits like apples or berries.

Flavan-3-ols (like epicatechin, catechin, and procyanidins) are plant compounds known to support cardiovascular function, cognitive health, blood pressure, cholesterol balance, and more. When PPO interacts with these compounds, it oxidizes them, causing their levels to plummet.

Because the reaction appears to persist during digestion, the negative effect on flavanol availability may not be avoidable simply by altering blending techniques.

What This Means for Your Smoothies

✅ Strategies to Maximize Flavanol Absorption

• Use low-PPO fruits like berries, grapes, pears, or apples in your blends.

• Combine flavanol-rich fruits with ingredients that have low PPO activity, such as pineapple, mango, oranges, or yogurt.

• Avoid blending bananas with berries, cocoa, or grapes in the same smoothie if your goal is to maximize flavanol benefits.

• If you love bananas, consume them separately (not in the same blend) so that PPO doesn’t interfere with other flavanol-rich ingredients.

⚠️ Caveats & Context

• The study had a small sample size (n = 8 men) and used added flavanols in the smoothies for standardization.

• All participants were male; effects in women are less clear.

• The negative impact is specific to flavan-3-ols and may not apply equally to all antioxidants or nutrients.

Final Takeaway

Blending bananas with flavanol-rich fruits may dramatically blunt the health benefits of your smoothie. The enzyme PPO in bananas appears to degrade flavan-3-ols before your body can use them. To get more of those heart- and brain-healthy compounds, choose low-PPO fruits and avoid mixing bananas with high-flavanol ingredients. Bananas still offer fiber, potassium, and sweetness — but for maximum flavanol absorption, let them fly solo. PRIME

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