The morning smoothie habit that's quietly backfiring
Here's a setup you've probably seen: blueberries, raspberries, a splash of almond milk, and a banana for creaminess. It looks healthy. It tastes good. The problem is that the banana is working against you.
A controlled study from UC Davis, published in late May 2026, found that adding a banana to a berry smoothie reduces flavanol absorption by 84%. Not a small dip — nearly everything that makes berry smoothies worth drinking.
Flavanols — also called flavan-3-ols — are the bioactive compounds in berries, dark chocolate, grapes, and green tea that research links to heart health, better insulin sensitivity, and reduced oxidative stress. If you're blending blueberries for the health benefits, a banana in the same blender is wiping out most of them.
Meet PPO: the enzyme no one talks about
The culprit is an enzyme called polyphenol oxidase, or PPO. Bananas are loaded with it — it's the same enzyme that turns a cut banana brown within minutes.
When you blend a banana with berries, PPO gets released into the mix and immediately starts oxidizing the flavanols in the fruit. The process degrades these compounds and makes them largely unabsorbable by the time you drink the smoothie.
But here's the part that surprised even the researchers: when participants consumed berries and banana separately — not blended together, just at the same time — the effect was still there. PPO stays enzymatically active in the stomach and continues breaking down flavanols after ingestion, not just during blending.
The study was a controlled crossover trial. Eight healthy men each consumed three preparations: a banana-almond milk smoothie, a mixed-berry smoothie, and a flavanol capsule as a control. Blood and urine samples were analyzed for flavanol metabolites after each.
The banana smoothie produced 84% lower flavanol levels compared to the berry-only smoothie.
Which fruits work instead
The fix is simpler than it sounds. Banana isn't the only way to get a creamy texture. Mango, pineapple, and citrus fruits have very low PPO levels and don't meaningfully interfere with flavanol absorption. Kiwi is another solid option.
Apples and pears, on the other hand, have high PPO content — avoid those too if flavanol preservation is the goal.
For creaminess without PPO, a spoonful of almond butter, half an avocado, or plain Greek yogurt all work well in a berry smoothie base.
The practical takeaway
If you're adding berries to a smoothie for cardiovascular support or recovery benefits, a banana in the same blend is canceling out most of that effect.
This doesn't mean bananas are bad. They're a great source of potassium, carbohydrates, and fiber. The issue is the specific interaction with high-flavanol fruits in a blended format.
The call is simple: keep bananas in your smoothies if you enjoy them — just don't count on the blueberries to do their job when a banana's in there. If flavanols are the point, swap in mango or pineapple for creaminess and leave the banana for another time.
Sources: ScienceDaily, May 2026; UC Davis Health