The importance of flavanols

Flavanols are naturally occurring plant compounds linked to a range of health benefits, but most people don't realize how easily those benefits can be altered by what else is on their plate.

"Flavanol is a type of flavonoid, a class of natural compounds found in fruits, vegetables, tea, and cocoa," said Scott Keatley, co-owner of Keatley Medical Nutrition Therapy.

Flavanols have strong antioxidant properties, which help protect the body from free radicals that can damage cells and increase the risk of chronic diseases. They're most abundant in foods like berries, apples, grapes, and cocoa — all common smoothie ingredients. Research has tied flavanol consumption to better heart and brain health, improved blood flow, and reduced inflammation.

According to lead study author Javier Ottaviani, director of the Food & Nutrition Core Laboratory at Mars Edge and adjunct researcher at UC Davis, "[r]esearch over the past 20 years has shown flavanols can help to maintain health as we age." He pointed to a clinical trial showing that a daily intake of 500 mg of flavanols "reduced cardiovascular deaths, including heart attacks and stroke, by 27%."

The Academy of Nutrition and Dietetics recommends consuming 400 to 600 milligrams daily to support heart and metabolic health, which can help lower risk factors like obesity, hypertension, and diabetes.

Flavanol absorption

For the study, researchers from UC Davis and the University of Reading set out to understand how different smoothie ingredients interact in the body — and whether common combinations affect flavanol absorption.

The team focused on polyphenol oxidase (PPO), an enzyme that causes many fruits and vegetables to turn brown when cut or bruised. Bananas are especially high in PPO, leading scientists to wonder whether that same enzyme could also interfere with nutrient uptake.

In the small trial, eight healthy men between ages 25 and 60 were given three treatments: a banana-almond milk smoothie (high PPO activity), a mixed-berry smoothie (low PPO activity), and a flavanol capsule as a control. The day before, participants followed a low-flavanol diet to control for outside variables.

When researchers measured the flavanol levels in their blood and urine, the results were striking: consuming the banana-based smoothie led to 84% lower flavanol absorption compared to the capsule or the berry smoothie.

Commentary

While the 84% figure has generated buzz, experts caution that the real-world implications are more nuanced.  

"While flavan-3-ols are beneficial, they're just one piece of the puzzle when it comes to fruit smoothies," said Lauren Manaker, a registered dietitian nutritionist. She noted that "most people don't eat enough fruits and vegetables to meet the recommended intake of flavan-3-ols to begin with, so the real-world impact of this interaction may be limited."

According to Keri Gans, a dietitian and host of The Keri Report podcast, bananas remain highly nutritious despite their PPO content. "While bananas may reduce the absorption of flavanols due to their polyphenol oxidase content, they still offer valuable nutrients like vitamin C, a powerful antioxidant, plus potassium to help regulate blood pressure and fiber to support digestive health," she said.

Still, Ottaviani advised people aiming to maximize flavanol intake avoid mixing bananas with flavanol-rich ingredients like berries, grapes, or cocoa. "Bananas remain a great fruit and a great option for smoothie preparation, but not if you're aiming at maintaining the flavanols in your smoothie," he said.

Kuhnle suggested opting for low-PPO fruits instead. "If you want to boost your flavanol intake with a smoothie, you should combine flavanol-rich fruits like berries with foods that have a low polyphenol oxidase activity like pineapple, oranges, mango, or yogurt," he said.

For those who love bananas for sweetness or texture, Carolyn Williams, a professor of culinary arts and nutrition at Shelton State Community College, offered simple swaps. "If the banana is adding sweetness and/or creaminess, you may want to replace it with ingredients that add those same qualities," she said. "For instance… a little honey for sweetness, and for texture, you can add some mango and Greek yogurt, which has a higher protein content compared to regular yogurt."

And for those unwilling to give up the classic blend, Gans says not to overthink it. "If you enjoy a banana, still include a banana," she said. Manaker agreed. "Enjoying a smoothie packed with fruits you love and nutrients your body needs is better than skipping it altogether," she said.