If your morning begins with a colorful smoothie that feels like a dose of pure health, you may want to rethink what you put in the blender. A study from the University of California, Davis found that adding just one banana can significantly reduce the drink’s nutritional value.
The reason is surprising. Polyphenol oxidase, an enzyme found in high levels in bananas, breaks down natural compounds called flavanols. These compounds are linked to improved blood flow, better brain function and heart health. When a banana is blended with flavanol-rich fruits such as berries, grapes, apples or cacao, it can hinder the body’s ability to absorb those beneficial nutrients.
In simple terms, a single banana can cut the absorption of these health-supporting compounds by up to 84 percent. It does not mean bananas are “bad,” but it does change the overall effect of a smoothie when they are mixed with certain fruits.
Beyond the study, Harvard experts also emphasize the importance of flavanols in daily nutrition. Research shows these compounds, found in berries, grapes and cacao, help maintain healthy blood flow, support memory and lower the risk of heart disease. So when a flavanol-rich smoothie loses much of its potency because it is blended with a banana, the body misses out on nutrients that can directly support cognitive function and long-term heart health.
The study, published in the journal Food and Function of the Royal Society of Chemistry, began with a simple question: Do the combinations we make in a blender change what the body receives? Researchers tested two smoothies, one with a banana, which has high PPO activity, and one based on berries, which have low PPO activity. After participants drank the smoothies, researchers measured flavanol levels in their blood and urine. The results were clear. Those who drank the banana smoothie had 84 percent lower flavanol levels than the control group.
Dr. Javier Ottaviani, who led the study, said, “We were surprised by how much one banana reduced flavanol levels, both in the smoothie and in the body. It shows how important not only what we eat is, but how we prepare it.”
Flavanols are natural polyphenols found in berries, apples, grapes and cacao. They support blood vessel health, improve circulation, aid memory and reduce inflammation. Many people add berries or cocoa powder to smoothies thinking they are superfoods, but when blended with a banana, much of that benefit disappears.
The recipe for the perfect smoothie
Ottaviani recommends choosing fruits with low PPO activity, such as pineapple, oranges, mango or yogurt, when mixing them with flavanol-rich ingredients. This way you can enjoy both flavor and health benefits. For those who do not want to give up banana’s creamy texture, he suggests adding slices at the end, after the smoothie is already blended, rather than blending it together with the other ingredients.
He noted that bananas remain a highly nutritious food, rich in potassium, vitamin B6 and fiber. But their composition affects other nutrients when they are blended. “When we talk about healthy eating, it is not just what we eat, but how. Preparation changes everything.”
Researchers say the findings open the door to further studies on how food preparation affects nutrient absorption. They also plan to examine how brewing methods in tea, one of the main sources of flavanols, influence how much the body can absorb.
The study was conducted in collaboration with researchers from the University of Reading in England, King Saud University in Saudi Arabia and Mars Inc., known for research on how cocoa flavanols affect human health.