Bananas could be ruining your smoothie’s health benefits

Their research, published in the Royal Society of Chemistry's journal Food and Function, examined how polyphenol oxidase (PPO) -- an enzyme found naturally in many fruits and vegetables -- affects the body's ability to take in flavanols. These bioactive compounds are linked to improved heart and brain health and are abundant in foods like apples, pears, blueberries, blackberries, grapes, and cocoa (all popular smoothie ingredients).

Lead author Javier Ottaviani, director of the Core Laboratory of Mars Edge, part of Mars, Inc., and adjunct researcher at UC Davis, explained: "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 flavanols to be absorbed after intake."

Anyone who has sliced an apple or peeled a banana has seen the fruit quickly turn brown. That browning occurs when PPO reacts with oxygen after the fruit is cut or bruised. The UC Davis team wanted to know if that same enzyme activity affects how much of these beneficial flavanols the body absorbs when fruits are blended together in smoothies.

Bananas vs. Berries: The Smoothie Showdown

To test this, participants consumed two different smoothies -- one made with banana, which has high PPO activity, and another made with mixed berries, which have low PPO activity. They also took a flavanol capsule for comparison. Afterward, researchers measured flavanol levels in blood and urine samples.

The results were striking. People who drank the banana smoothie had 84% lower flavanol levels compared to those who took the control capsule.

"We were really surprised to see how quickly adding a single banana decreased the level of flavanols in the smoothie and the levels of flavanol absorbed in the body," Ottaviani said. "This highlights how food preparation and combinations can affect the absorption of dietary compounds in foods."

What Are Flavanols?

Flavanols are natural compounds found in foods like cocoa, berries, apples, and grapes. They're part of a larger group of plant nutrients called polyphenols and are known for supporting heart and brain health. Research suggests that flavanols can help improve blood flow, support memory, and reduce inflammation when consumed regularly.

Choosing the Right Fruit Pairings

In 2022, the Academy of Nutrition and Dietetics recommended consuming 400 to 600 milligrams of flavanols each day for cardiometabolic health. Ottaviani noted that for people aiming to reach that target, it helps to pair flavanol-rich fruits such as berries with ingredients that have low PPO activity, like pineapple, oranges, mango, or yogurt.

Bananas are still a nutritious fruit, but Ottaviani advised that if you enjoy banana smoothies, it may be best not to mix them with flavanol-heavy foods like berries, grapes, or cocoa. The same principle applies to other foods with high PPO activity, including beet greens.

Ottaviani added that these findings could open the door to more studies on how food preparation affects nutrient absorption. For instance, tea is a major dietary source of flavanols, and the way it is brewed could alter how many of those compounds become available for the body to absorb.

"This is certainly an area that deserves more attention in the field of polyphenols and bioactive compounds in general," said Ottaviani.

Jodi Ensunsa, Reedmond Fong, Jennifer Kimball and Alan Crozier, all affiliated with the UC Davis Department of Nutrition and researchers affiliated with the UC Davis Department of Internal Medicine, University of Reading, King Saud University and Mars, Inc. contributed to the research.

The study was funded by a research grant from Mars, Inc., which collaborates with researchers to study potential benefits of cocoa flavanols for human health.