Are your smoothies actually healthy?

A study from the University of California, Davis, and the University of Reading has found that blending certain ingredients in smoothies can influence whether your body is getting a nutritional boost.

The researchers used smoothies to test how levels of polyphenol oxidase (PPO), an enzyme found in many fruits and vegetables and particularly high in bananas, can affect the levels of flavanols in food to be absorbed by the body. Flavanols are a group of bioactive compounds that are good for heart and cognitive health, naturally found in apples, pears, blueberries, blackberries, grapes and cocoa. According to a dietary recommendation from the Academy of Nutrition and Dietetics in the USA, we should all be consuming 400–600 mg of flavanols daily.

Participants in the study drank either a smoothie made with banana, which has naturally high PPO activity, or made with mixed berries, which have naturally low PPO activity. As a control, some participants also took a flavanol capsule. Blood and urine samples were analysed to measure the quantity of flavanols present in the body after ingesting the smoothie samples and capsule. Those who drank the banana smoothie were found to have 84% lower levels of flavanols in their body compared to the control.

People who are trying to consume flavanols should consider preparing smoothies by combining flavanol-rich fruits like berries with other ingredients that also have a low PPO activity, such as pineapples, organies, mango or yoghurt. Bananas remain a great fruit to be eaten. Anyone who wishes to consume smoothies with bananas or other high-PPO fruits and vegetables, such as beet greens, should consider not combining them with flavanol-rich fruits.

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.”

The findings of this study could spur future research into how other foods are prepared and the effects on flavanols. According to lead researcher Javier Ottaviani, 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,” Ottaviani said.

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