Why you shouldn't add a banana to your smoothies - study

Banana smoothie of organic bananas. There is a high glass filled with banana smoothie in the centre, and bananas and banana peels around the drink. With an environmentally friendly paper straw.
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When it comes to the humble smoothie, bananas are an essential ingredient for many of us. Its creamy texture lends itself perfectly to a thicker, smoother consistency, while its natural sweetness helps offset the tartness of other additions.

But according to new research, your favourite banana-berry concoction might not be as beneficial for your body as you might think.

Researchers at the University of California, Davis have found that the combination of ingredients in your morning smoothie can make or break its health benefits, meaning certain mixtures might not be the best if you're wanting that welcome boost of nutrients. 

The study, published last week in the Royal Society of Chemistry's journal Food and Function, used smoothies to test how various levels of polyphenol oxidase - an enzyme in many fruits and vegetables - can affect the body's absorption of heart-healthy flavanols. 

Flavanols, a group of bioactive compounds that are good for heart and cognitive health, are naturally found in apples, pears, blueberries, blackberries, grapes and cocoa - all of which are commonly used in smoothies.

Polyphenol oxidase, or PPO, is the enzyme responsible for the browning of your fruit. The browning occurs when the food containing that enzyme, like an apple or banana, is exposed to air, cut, or bruised.

The researchers wanted to determine whether consuming fresh smoothies made with different PPO-containing fruits impacted the amount of flavanols available to the body.

"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," said lead author Javier Ottaviani, director of the Core Laboratory of Mars Edge, as reported by SciTechDaily

The researchers had participants drink a smoothie made with banana, which contains high levels of PPO, and a smoothie made with mixed berries, which have low amounts of the enzyme. Participants also took a flavanol capsule as a control. 

Blood and urine samples were then analysed to measure how much of the flavanols were present in the body after ingesting the smoothies and capsule. The researchers found those who drank the banana smoothie had 84 percent lower levels of flavanols compared to those who had the mixed berry sample. 

"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, as per SciTechDaily.

"This highlights how food preparation and combinations can affect the absorption of dietary compounds in foods."

Ottaviani added that those who want to boost their intake should consider combining flavanol-rich fruits, like berries, with ingredients that contain low levels of PPO - think pineapple, oranges, mango, or yoghurt - to optimise their flavanol absorption.

Of course, if you enjoy bananas in your smoothies but want to reap the nutritional benefits, Ottaviani noted that your best bet is steering clear of other ingredients with high levels of flavanols to avoid compromising their availability.