Bananas May Reduce the Benefits of Smoothies

Research suggests that adding bananas or other specific fruits to smoothies may significantly lower flavanol levels and influence how much the body can absorb.

Smoothies are nutrition-packed drinks made by puréeing fruits, berries, vegetables, and other ingredients, such as yogurt, in a blender. They can be a convenient way to increase the intake of flavanols — bioactive compounds that benefit overall health and wellbeing.

While the benefits of smoothies are widely known, scientists from the University of California, Davis, and Mars Edge, part of Mars, Inc., wanted to determine whether different smoothie ingredients could impact the absorption of flavanols.

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Their research, published on August 24 in Food & Function, found that adding certain fruits to a smoothie reduced the amount of flavanols in the drink. The scientists say these findings are important for those who hope to increase their consumption of this bioactive compound.

To investigate the impact of smoothie ingredients on flavanol levels, the researchers focused on fruits with a high level of polyphenol oxidase (PPO) — an enzyme present in specific fruits that causes them to turn brown when cut or bruised. Specifically, they wanted to know if adding PPO-containing fruit to a smoothie could change the availability of flavanols.

The scientists had the study participants drink a smoothie made with bananas and almond milk or a mixed berry smoothie made with strawberries, blueberries, blackberries, raspberries, almond milk, water, crushed ice, and yogurt.

The team used bananas because they have high PPO activity and mixed berries since they have a low amount of the enzyme.

For a control, the scientists gave another group of participants a flavanol capsule containing standardized cocoa extract. This extract was also included in the smoothies to ensure they had similar flavanol levels.

After consuming the smoothies or the capsule, the team tested the participants' blood and urine to determine the amount of flavanols they absorbed.

Their analysis found that participants who drank the banana smoothie had 84% lower flavanol levels than the control group.

The researchers say these findings suggest that combining high-PPO foods like apples, bananas, and avocados with high-flavanol foods such as cocoa, tea, and berries may destroy flavanols and reduce absorption in the body.

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"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," says lead author Javier Ottaviani, director of the Core Laboratory of Mars Edge, and an adjunct researcher with the UC Davis Department of Nutrition. "This highlights how food preparation and combinations can affect the absorption of dietary compounds in foods."

Still, the research only included a small number of male participants. In addition, the study's funding came from a Mars Inc. research grant. The company also provided the standardized cocoa extract used as a flavanol source in the research.

While the benefits of smoothies are still high, some may reconsider mixing bananas into their blender.

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