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Adding bananas, particularly frozen ones, to a smoothie is one of the best ways to make it taste more like a milkshake. They’re sweet and have a creamy texture. Best of all, they’re full of potassium and fiber! But what else should you put in that smoothie? If you said berries for the antioxidants, you might want to think twice.

Researchers from the University of California Davis (UCD) suggest that bananas could neutralize the antioxidants you’re looking for in berries.

The antioxidants in question are called flavonols, which are present in plant-based foods like berries, tea, cocoa, apples, pears, and peaches. Unfortunately, many of us don’t consume enough of these antioxidants in our daily diet.

When consuming food rich in flavonols, these compounds are quickly absorbed into the bloodstream and processed. These metabolites are associated with several benefits, such as improved cognitive function and cardiovascular health. 

However, recent experiments reveal that adding a single banana to a mix of berries reduces the abundance of these metabolites. In a controlled and blinded study conducted by researchers at UCD, eight participants were given a flavonol-rich berry smoothie or a simple flavonol capsule. Subsequent tests showed increased levels of flavonol metabolites in their blood.

After consuming a banana-berry smoothie, the metabolites in the volunteers’ blood were 84% lower compared to a pure dose of flavonol.

“We were really surprised to see how quickly adding a single banana decreased the level of flavonols in the smoothie and the levels of flavanol absorbed in the body,” says nutritionist Javier Ottaviani from UCD.

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

When we consume bananas, our body’s antioxidants may not fully utilize the flavonols in them. This is because of an enzyme called polyphenol oxidase (PPO) that causes bananas to turn brown when peeled. The antioxidants in our body react with PPO instead of performing their beneficial functions. Essentially, when exposed to the banana, the antioxidants ‘mop up’ PPO, preventing them from doing all that good work inside our bodies.

In experiments, a banana-berry smoothie with high levels of PPO was found to have fewer flavonols than a pure berry smoothie after an hour of being left at room temperature. However, when the PPO in the bananas was inhibited, the flavonols remained unchanged. This suggests that PPO can restrict the availability of flavonols before humans consume them.

The researchers also conducted a study investigating whether bananas can affect the absorption of antioxidants in the stomach. They asked 11 participants to drink a banana smoothie and a berry smoothie at the same time. This was done to prevent the interaction of the flavonols with PPO before ingestion. Despite this, the researchers found that the flavonol metabolites were present in lesser amounts in the participants’ bloodstreams after consuming the smoothies separately compared to when they drank only the berry smoothie.

The study was published in Food and Function and was conducted with a limited number of male participants. However, the researchers at UCD believe that their initial findings warrant further scientific attention.