Flavanols are a group of bioactive compounds that are good for your heart and cognitive health and are naturally found in apples, pears, blueberries, blackberries, grapes and cocoa — common smoothie ingredients.
In a study, published in the journal Food and Function, scientists used smoothies to test how polyphenol oxidase — an enzyme found in many fruits and vegetables that is responsible for the browning when these are cut or bruised — affects the absorption of flavanols by the human body.
This enzyme is found in particularly high levels in bananas.
The team led by University of California, Davis, in collaboration with the University of Reading, found that adding banana to a berry smoothie reduces the flavanols taken in by the consumer by 84 per cent, compared to the control group, who took a flavanol capsule.
Flavanols are bioactive compounds that have been proven to support good heart and cognitive health. We should all be consuming 400-600 milligrams of flavanols, daily, according to a dietary recommendation from the Academy of Nutrition and Dietetics in the US.
“If you don’t consume enough flavanols, it can negatively affect cardiovascular health. In older adults, a deficiency of flavanols is also linked to cognitive decline,” said Gunter Kuhnle, Professor of Nutrition and Food Science at the University of Reading.
“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 yoghurt,” Kuhnle said.
While bananas in the smoothie can cut down flavanol intake, Kuhnle said, “on their own, they are still great fruits and can play an important role in many healthy diets”.
The team explained that bananas contain polyphenol oxidase, or PPO, which makes it turn brown when left in the open without the peel.
The browning occurs when the food containing that enzyme is exposed to air.
“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,” said lead author Javier Ottaviani, adjunct researcher with the UC Davis Department of Nutrition.
“This highlights how food preparation and combinations can affect the absorption of dietary compounds in foods.”
The findings of this study could spur future research into how other foods are prepared and the effects on flavanols, for example, Ottaviani said tea is a major dietary source of flavanols and depending on how it is prepared, a different amount of flavanols would be available for absorption.
“This is certainly an area that deserves more attention in the field of polyphenols and bioactive compounds in general,” said Ottaviani.
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