Are bananas in your smoothies blocking key nutrients?
A 2023 study about bananas & berries put fear into smoothie lovers – suggesting that adding bananas (which are high in an enzyme called PPO) can slash the bioavailability of flavan-3-ols (a type of antioxidant linked to heart and gut health) by a whopping 84%!
Researchers at the University of California wanted to test whether certain fruits high in PPO (polyphenol oxidase) affect how well your body absorbs flavin-3-ols by testing three options in selected participants:
1. a mixed berry smoothie (low PPO)
2. a banana-based smoothie (high PPO)
3. flavan-3-ol supplements (control group)
The berry smoothie and supplements led to way better absorption of flavin-3-ols than the banana-based smoothie. Even when flavan-3-ols weren’t blended with banana before drinking, absorption was still lower—suggesting the enzyme keeps working in your stomach!
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Does this mean you should ditch your banana & berry smoothie? And what are the implications for fodmappers? Let’s dive into the science…
What are flavan-3-ols?
Flavan-3-ols are plant-based compounds found in foods like tea, cocoa, apples, pears, berries, peaches and grapes. A growing body of research supports the notion that eating more flavan-3-ols can boost heart health and brain function - so much so that the US Academy of Nutrition and Dietetics now recommend getting 400–600 mg per day of flavan-3-ols for better cardiometabolic health. While other health organisations have yet to recommend a specific daily flavan-3-ol intake, research indicates that increasing the uptake of flavan-3-ol rich foods may help improve blood pressure, cholesterol levels and blood sugar.
With only 4.2% of Aussies eating the daily recommendation of 2 fruit and 5 veg (ABS Dietary Behaviour, 2022), many have promoted smoothies as a convenient way of upping their intake. However, blending fruits and veggies into a smoothie can change their nutrient content - especially when it comes to flavan-3-ols and other antioxidants. This happens because of polyphenol oxidase (PPO), an enzyme that causes fruits to brown when cut or blended. The authors hypothesised that some high-PPO fruits (like bananas) may reduce the absorption of key antioxidants when blended.
What Happens to Flavan-3-ols After You Eat Them?
When you consume flavan-3-ols, your body absorbs them quickly and breaks them down into different forms. Scientists have found that after eating flavan-3-ols, more than 20 different metabolites (tiny molecules created as your body processes them) appear in the bloodstream almost immediately.
Some of these metabolites, like SREMs (structurally-related (-)-epicatechin metabolites), are linked to flavan-3-ols’ heart and brain health benefits. Others, like γ-VLMs (gut microbiota-derived metabolites), are created with the help of your gut bacteria.
Scientists know a lot about how flavan-3-ols are processed when eaten alone or in simple foods, but not much is known about what happens when they’re blended into a smoothie. And it’s this knowledge gap that is the authors were hoping to fill. This study explores whether certain fruits—especially those high in an enzyme called PPO (polyphenol oxidase) - affect how well your body absorbs flavan-3-ols.
How was the experiment conducted?
In this study, researchers wanted to see how different fruit smoothies affect the absorption of flavan-3-ols. Here's how they did it…
🔬 Who participated?
A group of volunteers drank different smoothies and a control drink on different days. The study included 8 healthy male adults aged 25-60. Exclusion criteria included high BMI, high blood pressure, peanut allergies, history of gastro disorders and surgery, those currently taking herbal/plant or botanical dietary supplements, and those following a vegetarian, vegan and/or weight loss diet. Participants completed health and lifestyle questionnaires and provided a blood sample for complete blood count, liver panel, lipid panel and metabolic panel assessments. To control for flavan-3-ols from the diet, participants were asked to follow a low flavan-3-ol diet on the day before and during the study days. They were then asked to fast for 12 hours before each study day.
🥤 What did they drink?
1. Banana Smoothie (High PPO) 🍌 – Made with bananas and almond milk.
2. Berry Smoothie (Low PPO) 🍓 – Made with a mix of strawberries, blueberries, blackberries, and raspberries, plus yogurt, almond milk, water and ice.
3. Control (Capsule) 💊 – Instead of a smoothie, participants took a flavan-3-ol capsule with cow’s milk.
📏 How was the study controlled?
Each smoothie was freshly made and consumed within 1 hour to keep conditions the same.
The study was not randomized in this phase, meaning everyone drank the same smoothies in a set order.
Other flavan-3-ol-containing foods were also tested to explore how different food types affect absorption.
🔬 Blood Samples & Testing
Volunteers gave a blood sample before drinking the smoothie or taking the capsule (this is called the “baseline” sample).
They then drank their smoothie or took the capsule within 5 minutes.
More blood samples were taken at different times—1, 2, 3, 4, 5, and 6 hours after consumption—to see how flavan-3-ols were absorbed.
💧 Other Rules
Volunteers could drink water after 2 hours.
After 4–5 hours, they had a meal without flavan-3-ols (so it wouldn’t affect results).
Each test day was at least 6 days apart, so the effects of one smoothie didn’t carry over to the next.
📊 Study Design & Participants
The study aimed to detect a 25% difference in flavan-3-ol levels between smoothies and the capsule.
The study took place from in 2016-17 (but not published until 2023 – thanks COVID!)
What did the researchers find?
Flavan-3-ol Absorption & Banana’s Effect:
Flavan-3-ol levels in the blood significantly increased after consuming all test drinks, except when the flavan-3-ol source was mixed into a banana smoothie.
Compared to flavan-3-ol capsules, the banana smoothie resulted in flavan-3-ol levels that were 81–84% lower.
Banana’s Polyphenol Oxidase (PPO) Activity:
The enzyme PPO, naturally present in bananas, rapidly broke down flavan-3-ols in the smoothie before it was even consumed.
Within an hour of making the smoothie, (−)-epicatechin, a key flavan-3-ol, had mostly degraded.
Adding inhibitors to block PPO prevented this breakdown, confirming that PPO was responsible.
Impact of PPO After Consumption:
Even when flavan-3-ols and banana were consumed separately but simultaneously, flavan-3-ol absorption was still reduced (by about 37–41%).
This suggests that PPO may continue breaking down flavan-3-ols in the stomach.
Lab tests mimicking stomach digestion confirmed that banana PPO remained active and continued to degrade flavan-3-ols.
Wider Implications:
Other high-PPO foods, such as beetroot leaves and certain fruits, may also reduce flavan-3-ol bioavailability when blended into smoothies.
This suggests that consuming polyphenol-rich foods with high-PPO ingredients (like bananas) may limit their potential health benefits.
What does this mean for fodmappers and our favourite smoothies?
While intriguing, this research study should come with a warning label – especially for those with irritable bowel syndrome. The low fodmap diet is restrictive – the last thing we need is MORE do’s and don’t’s. While high PPO fruits can reduce the absorption of flavan-3-ols and other polyphenols when blended or pureed, they still offer valuable nutrients like fibre and potassium.
Limitations & Considerations:
⚠️ Small Sample Size: With only eight male participants, the findings cannot be generalised to broader populations, including women or individuals with different metabolic profiles and those with gastrointestinal issues like IBS.
⚠️ Short-Term Study: The study measured acute absorption, but it’s unclear if long-term dietary patterns would alter the effect.
⚠️ Single Food Pairing: The focus was on bananas, but other high-PPO foods (e.g., apples, pears, eggplants) weren’t tested. It’s uncertain whether similar effects occur with different flavanol-rich foods and different PPO-containing foods.
⚠️ Dietary Relevance: While the study shows a reduction in flavan-3-ol absorption, it does not determine whether this impacts health outcomes or offsets other benefits of consuming bananas and flavanol-rich foods together.
So instead of ditching bananas from our smoothies, here’s some other options:
🥤Focus on berry smoothies, including blueberries, strawberries and raspberries which are rich in flavonoids and have a lower impact on the absorption of polyphenols. Berries all have low fodmap serving sizes that can be tolerated by most people with IBS. If you’re looking for a low fodmap option, try this age-defying smoothie recipe 👉🏽
🥤If your goal is to enjoy the gut health benefits and taste of bananas without compromising antioxidant intake, try mixing up your smoothie rotation – bananas one day, berries the next. Want a low fodmap option, try this bananarama smoothie recipe 👉🏽
🥤You could also mix bananas with other nutrient-dense, polyphenol-rich ingredients like dark leafy greens (spinach, kale) or nuts (walnuts, almonds) to help boost the antioxidant profile of the smoothie. Want a recipe, try this pecan pie smoothie recipe 👉🏽
Final Verdict
This study makes for alarming headlines on social media but before you go ditching bananas from your smoothies, further research with larger, more diverse populations, longer-term studies, and varied food combinations is needed before making broad dietary recommendations. For now, those aiming to maximise flavanol absorption might consider separating high-PPO fruits from flavanol-rich foods—but this shouldn’t discourage overall fruit consumption, given their numerous health benefits.
Fodmappers – don’t overthink this! You’ve got enough to worry about, rather than what happens when you blend bananas & berries in your smoothie!
Share our blog with smoothie lover who loves science! 🥤👇
Blog written by: Noisy Guts CEO Josephine Muir, PhD. Prior to co-founding Noisy Guts with Dr Mary Webberley, Josephine was the Associate Director of the Marshall Centre for Infectious Diseases at The University of Western Australia.