Bananas could be cancelling out some of your smoothie’s benefits

Bananas may be sabotaging your smoothie’s superpowers by destroying key heart-healthy compounds. Fortunately, there is a solution: you can still enjoy a banana smoothie by adjusting the combination.

Smoothies are a quick and delicious way to load up on fruits and vegetables, but some ingredient combinations may not be as healthy as they seem. Researchers at University of California-Davis have discovered that adding a banana to your smoothie may drastically reduce the absorption of flavanols — powerful compounds linked to heart and brain health. The culprit is polyphenol oxidase (PPO), an enzyme abundant in bananas and many other fruits and vegetables. In experiments, banana-based smoothies cut flavanol absorption dramatically compared to berry-based ones.

The research, published in the Royal Society of Chemistry’s journal Food and Function, examined how PPO 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 such as apples, pears, blueberries, blackberries, grapes, and cacao — 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, explains: “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’s sliced an apple or peeled a banana has seen the fruit browns quickly. 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 in smoothies.

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, flavanol levels in blood and urine samples were measured.

The results were striking. People who had 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 says. “This highlights how food preparation and combinations can affect the absorption of dietary compounds in foods."

So what are the best combos?

In 2022, the Academy of Nutrition and Dietetics recommended consuming 400-600mg of flavanols daily for cardiometabolic health. Ottaviani notes that to reach that target, it helps to pair flavanol-rich fruits such as berries with low PPO activity foods, such as pineapple, oranges, mango, or yogurt.

If you enjoy banana smoothies, it’s best not to pair them with flavanol-heavy foods such as berries, grapes, kiwi fruit, pomegranates or cacao. Keep them simple: bananas on their own is best, with your favourite milk and yogurt and any powders such as a protein powder — but not cacao — is probably enough. You could add a Medjool date, or a soaked dried fig or two for extra sweetness.

What are flavanols? 

Flavanols are naturally-occurring compounds found in foods such as cacao, 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 flavanols can help improve blood flow, support memory, and reduce inflammation when consumed regularly.

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