Dr Rhonda Patrick, a biomedical scientist, stated on the Mel Robbins Podcast that adding banana to a blueberry smoothie could reduce the berries' nutritional benefits. The claim, which quickly spread, centers on an enzyme called polyphenol oxidase found in bananas that may break down polyphenols—antioxidant compounds abundant in blueberries. However, experts suggest that while the interaction exists, its real-world impact is minimal.
The Science Behind the Claim
Patrick's assertion is based on a 2023 study examining how polyphenol oxidase affects the absorption of flavanols, a type of polyphenol. The study found that participants who consumed banana smoothies with added flavanols had lower blood levels of these antioxidants compared to those who drank mixed-berry smoothies with the same additive. Patrick explained, "Polyphenol oxidase, it's essentially an enzyme that's breaking down the polyphenols. And there have now been studies … showing if you add bananas to blueberries, you're not getting as many polyphenols. In fact, it's quite a bit lower. So the banana is killing the benefit."
Limitations of the Study
Dr Joe Schwarcz, a science communicator and director of McGill University's office for science and society, points out several caveats. The researchers "never, ever made a smoothie with bananas and blueberries together," and the study "only had eight subjects … not a big enough number to have significant conclusions." However, he acknowledges that "there is a statistical difference in the amount of polyphenols that may be present in your smoothie as the result of the banana." When contacted, a spokesperson for FoundMyFitness, Patrick's company, stated, "The fact that this enzyme breaks down some polyphenols is essentially beyond reproach and not dependent on any one study she cites."
Context: Blueberries' Key Compounds
Blueberries contain various polyphenols, but anthocyanins—the pigments giving them their color—are more significant and abundant than flavanols, says Schwarcz. Anthocyanins are linked to reduced risks of cardiovascular disease, type 2 diabetes, and overall mortality. Thus, the study measured "not even the important compounds of blueberries," he notes. Additionally, the research was funded by Mars, and the flavanols used were derived from cocoa, a product Mars sells supplements and chocolate containing.
Nutrient Interactions Are Common
Nutrient interactions in food are common, says Alyssa Northrop, a registered dietitian in Minneapolis. "Some nutrients enhance the absorption of other nutrients, like vitamin C and iron. Others can reduce absorption, such as the oxalates in spinach, which bind to calcium and reduce its bioavailability." But she advises against micromanaging food combos: "Rather than trying to micromanage every food combination, I encourage people to focus on the bigger picture: eat a varied diet with plenty of fruits, vegetables, whole grains, nuts, seeds and other nutrient-dense foods to meet your body's needs."
Practical Advice for Smoothie Lovers
Northrop emphasizes that eating too few fruits and vegetables is a greater concern than optimizing polyphenol absorption. "Most of us aren't consuming the recommended five servings of fruits and vegetables daily. If adding a banana makes a berry smoothie more delicious and encourages someone to eat more fruit, I see that as a win," she says. Sheri Gaw, a registered dietitian nutritionist in the San Francisco Bay Area, adds that bananas offer potassium, vitamin B6, vitamin C, manganese, magnesium, and about 3 grams of fiber per medium fruit, making them a healthy, affordable addition.
If you're still concerned about flavanol levels, consider swapping banana for mango or pineapple, which are lower in polyphenol oxidase. Or try other creamy add-ins like oats, yogurt, silken tofu, kefir, avocado, or frozen cauliflower, suggests Gaw.
The Bottom Line
Schwarcz concludes that in the context of an overall diet, the interplay is "insignificant." He says, "Your health is a very complex business of nutrition, of genetics, of your activity levels. And to try to make a big deal out of whether you put a banana in your smoothie or not – it's just scientific nonsense. It makes no practical difference in your life."
