May 18, 2024

TikTok loves a banana smoothie. In a few minutes of scrolling you can see smoothie recipes, banana-freezing tips (peel it first!), and video after video of people with visible abs loading bananas and other fruits into a blender in their kitchen. But wait! There’s a new genre of smoothie content, now warning us to never put bananas in our smoothies, lest they destroy the nutritional value.

Let’s debunk that smoothie advice you heard on TikTok

Wait, since when do bananas ruin smoothies? Since August, apparently. A study published in the journal Food & Function found that bananas can reduce the bioavailability of flavon-3-ols in smoothies.

The study is real, and several of the TikToks about it have described the study more or less accurately. Where they go wrong is concluding that we shouldn’t put bananas in our smoothies. That’s not what the scientists concluded, and there’s no need to give up your bananas.

The press release announcing the study probably started this mess (it calls adding a banana to your smoothie a “mistake”) but it also mentions that the lead author of the study, Javier Ottaviani, “said bananas remain a great fruit to be eaten or consumed in smoothies.” So clearly the banana warnings are overblown.

What the study actually found

The study wasn’t about the nutritional value of bananas or smoothies in general. It was looking at a particular question of biochemistry: Does an enzyme in bananas react with one particular type of antioxidant found in cocoa extract?

Antioxidants are a broad class of chemicals. Vitamin C is an antioxidant, but so are lycopene and resveratrol (compounds famously found in tomatoes and grapes) and so are anthocyanins, the red and blue pigments found in berries. The antioxidant studied here is not any of the above, but a different one found in tea and cocoa. It’s called (-)-epicatechin, and it’s part of the antioxidant family called flavon-3-ols.

In the study, eight healthy men recruited from around the UC Davis campus were given each of the following, on different days:

  • A smoothie made with bananas, almond milk, and an epicatechin-containing cocoa extract.

  • A smoothie made with the same cocoa extract plus strawberries, blueberries, blackberries, raspberries, almond milk, water, crushed ice, and yogurt (presumably the yogurt and ice were required for texture).

  • A glass of milk and a capsule containing the cocoa extract.

Bananas contain an enzyme called polyphenol oxidase (PPO), and the scientists wanted to find out if the PPO in a banana could affect the levels of (-)-epicatechin, one of those flavon-3-ols, in food such as smoothies.

Somewhat surprisingly, it did! Our bodies convert epicatechins into other chemicals in the same family, and the researchers took blood samples from the volunteers to look for these chemicals after each of the experiments. After drinking the berry smoothie or taking the capsule with milk, blood levels of these chemicals were elevated. But after drinking the banana smoothie, they weren’t.

This strongly suggests that the PPO in the banana had destroyed a lot of the epicatechins present in the cocoa extract. Further experiments described in same paper suggest that this chemical activity happens when the ingredients are sitting together in the smoothie glass, and it likely also happens in our stomachs.

More importantly, what the study did not find

The study did not test a berry smoothie with an added banana. None of the smoothies combined berries and bananas.

The study did not test levels of antioxidants or other nutrients from berries. They were looking specifically at what happened to the antioxidants provided in the cocoa extract.

The study also did not look at other aspects of nutrition besides this very specific chemical reaction (PPO from bananas plus (-)-epicatechins from cocoa extract).

Therefore, we cannot conclude that the banana in a mixed fruit smoothie “destroys” or “ruins” the nutrients or even the antioxidants from the berries.

Why you can’t really “destroy” nutrition, anyway

If an enzyme in bananas can reduce the bioavailability of a certain family of antioxidants…what does that matter? Were you drinking smoothies for the express purpose of increasing your intake of flavon-3-ols? More likely you were trying to get some fruit in your diet and/or have a nice breakfast or drink because you were hungry.

Regardless of their PPO activity, bananas also provide fiber, which is good for you, and carbs, which are a macronutrient our bodies can use in many ways. A medium banana contains 20% of our vitamin B6 needs for the day, 17% of our vitamin C, and 8% of our magnesium.

The recent study did not take any of that away from you. You still get all of the benefits above, no matter what’s happening to the flavon-3-ols in your smoothie.

If you’re really worried about your flavon-3-ols, there’s a better solution than giving up bananas

OK, but what if you really were looking forward to getting lots of good antioxidants in that fruit smoothie? After all, flavon-3-ols like (-)-epicatechin are so good for us that the Academy of Nutrition and Dietetics (AND) issued a guideline for them, even though flavon-3-ols are a non-essential nutrient. The guideline tells us that there are heath benefits to be gained by consuming at least 400 milligrams of flavon-3-ols per day.

If you want to get more flavon-3-ols, the best thing you can do is drink some tea. You can hit that 400-milligram recommendation with just 10 ounces of green tea (two small cups), or 12 ounces of black tea. There are flavon-3-ols in berries, but in lesser amounts; it would take 6 cups of blackberries or 40 cups of blueberries to provide the same amount as those two cups of green tea.

By the way, the same AND paper that recommended 400 milligrams of flavon-3-ols says it’s best not to get this nutrient from supplements. That’s because the most common supplements to provide it are green tea extracts, and green tea extracts can cause stomach upset and even be toxic to your liver in large amounts.


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