The Fuzzy Science of Fruit Mix-Ups

The latest controversy to hit the wellness world involves a seemingly innocuous combination: blueberries and bananas in a smoothie. A biomedical scientist, Dr. Rhonda Patrick, made waves on the Mel Robbins Podcast by claiming that adding banana to a blueberry smoothie can “kill” the nutritional benefits of the berries. But is this claim backed up by science?

To understand what’s going on here, it’s essential to examine the enzyme polyphenol oxidase (PPO), which Dr. Patrick says breaks down polyphenols in bananas and reduces their nutritional value. PPO is an enzyme found in fruit and vegetables that can degrade certain compounds, including polyphenols. However, research has shown that its effects are more nuanced than Dr. Patrick’s claim suggests.

A 2023 study explored the impact of PPO on flavanols, a type of polyphenol found in cocoa and other foods. The researchers found that participants who consumed banana smoothies with added flavanol had lower blood levels of these antioxidants compared to those who drank mixed-berry smoothies with the same additive. However, this study was small (only eight subjects), and its findings have been misinterpreted by some as a blanket statement about bananas ruining blueberry smoothies.

Science communicator Dr. Joe Schwarcz notes that we shouldn’t rely too heavily on this study for specific conclusions. He points out that the researchers never tested the effects of banana-blueberry combinations directly, and that the results may be more relevant to flavanol absorption than overall polyphenol levels in blueberries.

Registered dietitian Alyssa Northrop advises against micromanaging every food combination. “Rather than trying to optimize every food pairing,” she says, “focus on eating a varied diet with plenty of fruits, vegetables, whole grains, nuts, seeds, and other nutrient-dense foods.” In fact, Northrop argues that we should be more concerned about not getting enough fruits and veggies overall – most of us aren’t consuming the recommended five servings daily.

If adding bananas makes a berry smoothie more delicious and encourages someone to eat more fruit, that’s a win in Northrop’s book. Registered dietitian Sheri Gaw agrees: “Bananas are an excellent addition to smoothies due to their natural sweetness and unique texture.” They’re also packed with potassium, vitamin B6, vitamin C, manganese, magnesium, and about 3 grams of fiber per medium fruit.

Our bodies are incredibly resilient, and minor fluctuations in polyphenol levels aren’t likely to cause any harm. As Northrop notes, “we don’t know the physiological effects of polyphenol insufficiency on health” – and until we do, it’s time to stop sweating the small stuff. So go ahead, add those bananas to your blueberry smoothie. Just remember to balance things out with a variety of other fruits and veggies, and don’t be too hard on yourself if you can’t get every combination just right.