Many people start their mornings with a smoothie because it seems like one of the healthiest breakfast choices available.
A blender full of bananas, blueberries, strawberries, yogurt, and other fruits looks packed with vitamins and antioxidants. But researchers from the University of California, Davis say one common smoothie ingredient may reduce some of the very nutrients people hope to gain from these drinks.
The researchers found that bananas can dramatically reduce the body’s ability to absorb flavanols, natural compounds linked to heart and brain health. Their findings were published in the Royal Society of Chemistry journal Food & Function.
Flavanols are a type of plant compound found in foods such as berries, grapes, apples, cocoa, tea, and pears.
Over the last several years, flavanols have become an important topic in nutrition research because studies suggest they may support blood circulation, help regulate blood pressure, improve blood vessel function, and possibly benefit cognitive health.
As a result, many people now try to eat more flavanol-rich foods, especially berries and cocoa products. Smoothies are often viewed as an easy way to consume these ingredients daily.
However, scientists wanted to investigate whether some smoothie ingredients might interfere with flavanol absorption.
The key to the study was an enzyme called polyphenol oxidase, or PPO. This enzyme naturally exists in many fruits and vegetables and plays a major role in the browning process people see after fruit is cut or bruised.
For example, apples and bananas quickly turn brown after being sliced because PPO reacts with oxygen in the air. Bananas are known to have especially high PPO activity.
The research team wondered whether this same enzyme could also break down flavanols inside smoothies before the body had a chance to absorb them.
To test the theory, scientists created different freshly prepared smoothies. Some smoothies contained bananas, while others used mixed berries with lower PPO activity.
Study participants drank the smoothies and also took a flavanol capsule used as a comparison control. Researchers then measured flavanol levels in blood and urine samples after consumption.
The difference between the smoothies was dramatic. Participants who drank the banana smoothie had flavanol levels that were 84% lower than those seen with the control capsule. Meanwhile, people who drank the berry smoothie without bananas maintained flavanol levels similar to the control group.
The findings surprised even the researchers themselves. Lead author Javier Ottaviani explained that the team did not expect a single banana to reduce flavanol levels so strongly.
The study also suggested that the PPO enzyme may continue affecting flavanols even after a smoothie is swallowed. In one experiment, researchers kept banana ingredients and flavanols separated before participants consumed them together. Even then, flavanol levels still fell significantly.
This suggests the enzyme may remain active inside the digestive system, continuing to break down flavanols after consumption.
Importantly, researchers emphasized that bananas are not unhealthy foods. Bananas remain rich in potassium, fiber, vitamins, and carbohydrates. They can still be part of a healthy diet and may offer many benefits.
The findings are more about food combinations than individual foods. Scientists say bananas may simply not pair well with flavanol-rich ingredients such as berries, grapes, cocoa, or apples if the goal is maximizing flavanol absorption.
The research highlights a growing area of nutrition science showing that food interactions can strongly affect nutrient absorption. The body does not simply absorb every nutrient exactly as it appears on a nutrition label. Different ingredients may either improve or reduce how nutrients are processed.
For people who want to preserve flavanol levels in smoothies, the researchers suggest pairing berries with ingredients lower in PPO activity. Better smoothie combinations may include berries with oranges, mangoes, pineapples, or yogurt.
Bananas can still be enjoyed separately or used in smoothies when flavanol intake is not the main concern.
The study also fits into broader research involving flavanols and health. Scientists continue studying whether flavanols may reduce the risk of cardiovascular disease and improve blood vessel health.
Some studies involving cocoa flavanols have shown possible benefits for memory and cognition in older adults, although evidence remains mixed.
The researchers caution that the smoothie study was relatively small and should not be considered the final answer for all diets or populations. More studies involving larger groups of people are still needed.
Experts also point out that overall eating patterns matter far more than a single smoothie ingredient. A smoothie with bananas and berries can still be nutritious compared with many processed breakfast foods.
Still, the findings offer an important reminder that healthy eating is often more complicated than simply adding together nutritious ingredients. Sometimes the way foods interact can change what the body actually receives.
The study may even influence future nutrition advice and smoothie recipes as scientists continue learning more about how foods work together inside the body.
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The study was published in Food & Function.
Source: University of California, Davis.
