If fruit smoothies are a regular part of your diet, you might be interested in study findings published in 2023. According to scientists from the University of California, Davis, certain fruit combinations may not be as nutritious as you think.
The researchers discovered that the types of fruits blended together can change how much nutrition your body actually absorbs.
Their study examined how polyphenol oxidase (PPO) -- an enzyme found naturally in many fruits and vegetables -- affects the body's ability to absorb flavanols. These phytochemicals are linked to improved heart and brain health and are abundant in foods like apples, pears, blueberries, blackberries, grapes, and cocoa (all popular smoothie ingredients).
Anyone who has sliced an apple or peeled a banana has seen the fruit quickly turn brown. That browning occurs when PPO reacts with oxygen after the fruit is cut or bruised. The UC Davis team wanted to know if that same enzyme activity affects how much beneficial flavanols the body absorbs when fruits are blended together in smoothies.
Bananas vs. berries
To test this, participants consumed two different smoothies -- one made with banana, which has high PPO activity, and another made with mixed berries, which have low PPO activity. They also took a flavanol capsule for comparison.
Afterward, researchers measured flavanol levels in blood and urine samples.
People who drank the banana smoothie had 84 per cent lower flavanol levels compared to those who took the control capsule.
The researchers were 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.
This finding highlights how food preparation and combinations can affect the absorption of dietary compounds in foods.
What are flavanols?
Flavanols are phytochemicals found in foods such as cocoa, berries, apple and grapes. They're part of a larger group of plant compounds called polyphenols and are they’re known for supporting heart and brain health.
Research suggests that flavanols can help improve blood flow, support memory and reduce inflammation when consumed regularly.
Choosing the right fruit pairings
In 2022, the Academy of Nutrition and Dietetics recommended consuming 400 to 600 milligrams of flavanols each day for cardiometabolic health. For people aiming to reach that target, it helps to pair flavanol-rich fruits such as berries with ingredients that have low PPO activity, like pineapple, oranges, mango or yogurt.
Bananas are still a nutritious fruit, but the researchers advised that if you enjoy banana smoothies, it may be best not to mix them with flavanol-rich foods like berries, grapes or cocoa.
The same principle applies to other foods with high PPO activity, including beet greens.
These findings could open the door to more studies on how food preparation affects nutrient absorption. For instance, tea is a major dietary source of flavanols, and the way it is brewed could alter how many of those compounds become available for the body to absorb.
Source: Food and Function, August 24, 2023.
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