Study Shows You Should Skip Bananas in Smoothies

Research helps maximize the health benefits of fruit smoothies.

If you’re blending a smoothie to boost your health with flavanol-rich berries, you may want to leave out the banana. New research suggests that adding banana could significantly reduce the health benefits you’re hoping to gain.

In a study published in Food and Function, scientists tested how a naturally occurring enzyme, polyphenol oxidase, affects the body’s ability to absorb flavanols. This enzyme, responsible for the browning that occurs when fruits are cut or bruised, is found in many fruits and vegetables but is especially abundant in bananas.

Bananas Slash Flavanol Uptake by 84%

The study, led by researchers at the University of California, Davis in partnership with the University of Reading, found that adding a banana to a berry smoothie reduced the absorption of flavanols by a striking 84%. For comparison, participants who took a flavanol capsule absorbed significantly more of these beneficial compounds.

Flavanols are natural compounds known to support heart and brain health. The Academy of Nutrition and Dietetics recommends a daily intake of 400–600 milligrams. A lack of flavanols, especially in older adults, has been linked to cognitive decline and poor cardiovascular function.

Gunter Kuhnle, Professor of Nutrition and Food Science at the University of Reading and co-investigator of the study said: “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. So, it’s clear we need them, but the question is how best to get flavanols from the food and drinks we consume.”

How Smoothie Ingredients Alter Nutrient Absorption

Lead scientist Javier Ottaviani, director of the Core Laboratory of Mars Edge, which is part of Mars, Inc., and an adjunct researcher with the Department of Nutrition at the University of California, Davis said: “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.”

Professor Kuhnle said: “Smoothies are a popular way to pack fruit and vegetables into our morning routines. We know from previous studies that flavanols can be broken down by polyphenol oxidase. The extent of the effect from adding a single banana was still very surprising – it had enough polyphenol oxidase to destroy the vast majority of flavanols found in the berries.

“Bananas may be ruled out of the morning smoothie if you want to boost your flavanol intake, but on their own, they are still great fruits an can play an important role in many healthy diets.”

Which Fruits Are Best for Flavanols?

Flavanols are found in apples, pears, blueberries, blackberries, grapes, and cocoa, which are all common smoothie ingredients. But is blitzing them up in a smoothie an effective way to get what you need?

Participants were given a smoothie with banana and berries, one with just mixed berries, or a flavanol capsule. The researchers then took blood and urine samples to measure the flavanols that actually made it through and into the participants’ body.

The researchers found that both the flavanol levels in the smoothie, and the levels absorbed by the body, were reduced when banana was included.

Professor Kuhnle said: “We still know very little about food-food and food-nutrient interactions, even though they can have a huge impact on the uptake of nutrients and bioactives like flavanols.

“Here, we could show that the uptake of flavanols can vary by more than fivefold depending on the combination of foods.

“Bananas are a great ingredient in smoothies to provide a nicer texture, but they can affect flavanol uptake.

Tips for Maximizing Flavanol Intake in Smoothies

“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.”

Reference: “Impact of polyphenol oxidase on the bioavailability of flavan-3-ols in fruit smoothies: a controlled, single blinded, cross-over study” by Javier I. Ottaviani, Jodi L. Ensunsa, Reedmond Y. Fong, Jennifer Kimball, Valentina Medici, Gunter G. C. Kuhnle, Alan Crozier, Hagen Schroetera and Catherine Kwik-Uribe, 24 August 2023, Food & Function.