Bananas can destroy the health benefits of your juice

Their research published in Royal Society of Chemistry magazine Food and functionResearchers studied how polyphenol oxidase (PPO) — an enzyme naturally found in many fruits and vegetables — affects the body’s ability to take up 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 juice ingredients).

“We sought to understand, on a very practical level, how a common food and food preparation such as banana-based juice might affect the availability of flavanols that can be absorbed after ingestion,” explained lead author Javier Ottaviani, director of the Mars Edge Core Laboratory, part of Mars, and a research associate at UC Davis.

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

Banana vs. Berries: The Juice Showdown

To test this, participants consumed two different smoothies – one made from banana, which has high PPO activity, and the other made from mixed berries, which has low PPO activity. They also took a flavanol capsule for comparison. Next, the researchers measured flavanol levels in blood and urine samples.

The results were amazing. People who drank banana juice had 84% lower levels of flavanols than those who took the control capsule.

“We were really surprised at how quickly adding one banana reduced the level of flavanols in the juice and the levels of flavanols absorbed by the body,” Ottaviani said. “This highlights how food preparation and formulations affect the absorption of nutritional compounds in foods.”

What are flavanols?

Flavanols are natural compounds found in foods such as cocoa, berries, apples and grapes. They are part of a larger group of phytonutrients called polyphenols and are known to support heart and brain health. Research suggests that flavanols can help improve blood flow, support memory, and reduce inflammation when taken regularly.

Choose the right fruit pairings

In 2022, the Academy of Nutrition and Dietetics recommends consuming 400 to 600 milligrams of flavanols daily for heart and metabolic health. For people aiming to reach this goal, it helps to pair flavanol-rich fruits like berries with ingredients with low PPO activity, like pineapple, orange, mango or yogurt, Ottaviani noted.

Bananas are still a nutritious fruit, but Ottaviani advises that if you enjoy banana smoothies, it may be best not to mix them with flavanol-rich 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 further studies on how food preparation affects nutrient absorption. For example, tea is a major food source of flavanols, and the way it is brewed can change how many of these compounds become available for the body to absorb.

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

Judy Inconsa, Redmond 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, the University of Reading, King Saud University, and Mars, contributed to the research.

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