The issue isn't sugar or calories. It's an enzyme.

What the researchers looked at

The study was published in the Royal Society of Chemistry's journal Food and Function, and focused on flavanols - plant compounds linked to heart and brain health.

Flavanols are commonly found in cocoa, apples, grapes, berries, and other smoothie staples. Researchers wanted to see whether mixing fruits with different enzyme levels would change how much of those flavanols end up being absorbed.

Polyphenol oxidase, or PPO, became the central point of the study. It's the same enzyme that causes browning when fruit is cut or bruised. Bananas carry high levels of it. Berries have far less.

Adding a banana to smoothies reduces flavanol absorption

Participants in the study consumed two smoothie versions. One with banana, the other made with mixed berries. They also took a flavanol capsule for comparison. The result? Blood and urine readings showed a sharp difference.

The banana-based smoothie brought down flavanol absorption by about 84% compared to the control capsule. Lead author Javier Ottaviani said the finding surprised the team. He added that even a single banana shifted the flavanol levels measurable in the body.

Why flavanols matter?

Flavanols fall under the broader polyphenol group. Regular intake is associated with better blood flow, reduced inflammation, and potential cognitive benefits. Flavan-3-ols and Cardiometabolic Health: First Ever Dietary Bioactive Guideline, a 2022 study by the Academy of Nutrition and Dietetics, suggested a daily intake of 400-600 milligrams for cardiometabolic health.

What to pair and what to avoid in smoothies

The study notes that high-flavanol fruits, such as berries, apples, or grapes, may retain more of their benefits when blended with low-PPO ingredients like pineapple, oranges, mango, or yogurt. Bananas remain nutritious but may be better used alone or with ingredients that don't rely on flavanol retention. Other high-PPO foods, including beet greens, may have similar effects.

The findings open the door to further work on how food prep affects nutrient absorption. Researchers pointed towards tea, another major flavanol source, as an area where brewing methods could influence availability.