Smoothies are a quick way to add fruit to your day. Many people blend a banana with berries and think the drink is super healthy. New research from the University of California, Davis says the mix may not work as well as we thought.
The problem is not that bananas are bad. It is about an enzyme called polyphenol oxidase (PPO). When PPO meets oxygen, it turns fruit brown and can also lower the amount of flavanols that your body can use.
Flavanols are natural plant chemicals that support heart health and brain function. They are found in apples, pears, blueberries, blackberries, grapes, cocoa, and other common smoothie items.
The Enzyme That Browns Fruit
Anyone who has sliced an apple or peeled a banana has seen PPO in action. The researchers wanted to know if the same reaction happens inside a blended drink and reduces the good nutrients.
Banana vs. Berry Smoothies
In the study, volunteers drank three drinks: a banana‑based smoothie, a mixed‑berry smoothie, and a flavanol capsule (used as a control). Blood and urine tests showed how much flavanol reached the body.
The results were clear. The banana smoothie lowered flavanol levels by about 84% compared with the control. The berry smoothie kept flavanol levels almost the same as the capsule.
Even when the banana drink was kept separate from flavanols until the moment of drinking, flavanol absorption still dropped, suggesting PPO may keep working in the stomach.
What This Means for Your Drink
Bananas are still nutritious—they give fiber, potassium, and other vitamins. The finding only says that bananas might not be the best choice if you want to maximize flavanols from berries, grapes, or cocoa.
Health groups recommend getting 400‑600 mg of flavanols each day for heart and metabolic health. Good sources include tea, apples, berries, grapes, and cocoa.
To keep flavanol levels high, pair berries with low‑PPO foods such as pineapple, orange, mango, or yogurt. You can still enjoy bananas on their own or in smoothies where flavanols are not the main goal.
Small Study, Big Idea
The research involved only a few participants (eight men in the first test and eleven people in the second). The data are interesting but not definitive for everyone.
Experts say not to panic. A banana‑filled smoothie can still be part of a balanced diet. Overall eating patterns and digestion matter more than a single ingredient.
Practical Smoothie Tips
If you aim for a flavanol‑rich drink, blend berries with low‑PPO ingredients like mango, pineapple, orange, or plain yogurt. This keeps the drink sweet and creamy without the flavanol‑blocking effect of bananas.
Banana lovers can still use them for creaminess, potassium, and natural sweetness—just separate them from flavanol‑focused recipes.
Beyond Smoothies
The same principle may apply to other flavanol sources, such as tea, where preparation methods could affect nutrient absorption.
More research is needed, but the key message is simple: the way ingredients interact can change what your body actually gets from food.