You likely throw this in the blender without a second thought, but it could be canceling out other beneficial produce, nutrition experts say.
For those of us to prefer to blend one up at home (or pick one up from a local cafe or juice bar), smoothies can provide a concentrated source of vitamins, minerals, antioxidants, and fiber—nutrients that support heart health, digestion, cognitive health, and overall wellness. They’re also an easy way to add more fruits and vegetables to your diet, especially when you’re short on time.
However, a 2023 study by a group of nutrition researchers at the University of California, Davis, suggests that including one popular ingredient could be sabotaging your smoothie’s benefits. That paper—along with insights from its lead authors that were more recently released in October 2025—reveals that including bananas could significantly limit your body’s ability to absorb key health-promoting nutrients.
Published in the journal Food and Function, the study examined how an enzyme called polyphenol oxidase affects the absorption of flavonols—plant-based compounds known for their antioxidant and anti-inflammatory benefits. Flavonols, found in natural foods like berries, apples, grapes, and cocoa, support heart and brain health by improving blood flow and reducing inflammation.
The team, led by nutrition scientist Javier Ottaviani, PhD, tested how fruit combinations influence flavonol absorption. Participants consumed two different smoothies: one containing banana, which has high polyphenol oxidase activity, and another made with mixed berries, which are low in polyphenol oxidase. They also took a flavinol capsule as a control.
“We sought to understand, on a very practical level, how a common food and food preparation like a banana-based smoothie could affect the availability of flavonols to be absorbed after intake,” Dr. Ottaviani said in an October 2025 news release.
When the researchers measured the flavonol levels in participants’ blood and urine, they found that the banana smoothie reduced flavonol absorption by an astonishing 84% compared to the capsule.
Polyphenol oxidase is the same enzyme that causes fruit like apples or bananas to brown after being cut, and bananas are known to have an especially high level of polyphenol oxidase activity. Though bananas are nutritious—rich in potassium, fiber, and vitamins—they may cancel out some of the heart and brain benefits of the other fruits blended alongside them.
“We were really surprised to see how quickly adding a single banana decreased the level of flavonols in the smoothie and the levels of flavonol absorbed in the body,” Dr. Ottaviani said. “This highlights how food preparation and combinations can affect the absorption of dietary compounds in foods.”
This could be especially harmful to the cardiovascular and cognitive health of older adults, said Gunter Kuhnle, professor of nutrition and food science at the University of Reading and co-investigator of the study, in a separate news release when the study was initially published.
For those aiming to boost their intake of flavonols, experts recommend combining flavonol-rich fruits such as berries, apples, or grapes with ingredients that have low polyphenol oxidase levels, such as pineapple, orange, mango, or yogurt.
And skipping bananas in your morning smoothie doesn’t mean giving them up entirely—just save them as a standalone snack, or pair them with foods that don’t rely on flavonols for their health benefits.
For daily wellness updates, subscribe to The Healthy by Reader’s Digest newsletter and follow The Healthy on Facebook and Instagram. Keep reading:
