- Tension: The smoothie habit millions reach for as a nutritional shortcut may be quietly neutralizing the very benefit it’s built around.
- Noise: Wellness culture celebrates ingredient quantity and convenience, rarely asking whether common combinations actually deliver what we assume.
- Direct Message: Eating well isn’t just about what you add — it’s about whether what you add can actually reach you.
To learn more about our editorial approach, explore The Direct Message methodology.
Most mornings I make a smoothie for my family. Frozen mixed berries, a banana for creaminess, some oat milk, and if I’m feeling organized, a spoonful of peanut butter. It takes three minutes and I feel genuinely good about it. It’s one of those habits that seems like a pure win, nutritious, quick, no real thought required.
Pregnancy has made me more conscious of what I eat, and lately I’ve been paying closer attention to whether the things I reach for actually do what I think they do. That’s what led me to a 2023 study suggesting that the banana in my morning smoothie might be canceling out the majority of the antioxidant benefit from the berries. I had to sit with that for a moment.
I’m not a nutritionist, and I want to be clear about that upfront. What I do is read research with genuine curiosity and try to translate it into something useful for everyday decisions. This particular finding is worth understanding.
What the study found
Researchers at the University of California Davis, in collaboration with the University of Reading, ran a controlled crossover study published in the journal Food & Function. Participants consumed one of three things on different occasions: a banana and berry smoothie, a mixed berry smoothie without banana, or a flavanol capsule as a standardized control. Blood and urine samples were taken afterward to measure how much of the flavanols each person actually absorbed.
The berry-only smoothie produced absorption levels similar to the capsule, meaning the berries were delivering roughly what they were supposed to. The banana-berry smoothie produced flavanol levels 84% lower. One banana. That single addition reduced what made it into the bloodstream by the vast majority.
As Javier Ottaviani, director of the Core Laboratory at Mars Edge and adjunct researcher at UC Davis who led the study, described the goal: “We sought to understand, on a very practical level, how a common food and food preparation like a banana-based smoothie could affect the availability of flavanols to be absorbed after intake.”
That framing is worth holding onto. This wasn’t a laboratory technicality. It was an attempt to understand what happens in a real morning kitchen, with real ingredients, in a way that affects what actually ends up in your body.
The enzyme responsible
Bananas are high in an enzyme called polyphenol oxidase, or PPO. It’s the same enzyme that turns a sliced banana brown within minutes of being exposed to air, the same process you see when you cut an apple and leave it on the counter. In the context of a smoothie, PPO rapidly breaks down the flavanols from the berries before your body has a chance to absorb them.
The research team tested 18 different fruits, vegetables, and plant-derived products and found substantial variation in PPO activity across all of them. Bananas ranked among the highest. As noted by Professor Gunter Kuhnle, Professor of Nutrition and Food Science at the University of Reading and co-investigator of the study: “The extent of the effect from adding a single banana was still very surprising – it had enough polyphenol oxidase to destroy the vast majority of flavanols found in the berries.”
The team also ran a second experiment where the banana drink and the flavanol source were consumed at the same time but without prior mixing, so there was no pre-blending contact. Absorption was still reduced, by around 37 to 41%. This suggests the enzyme doesn’t just act in the blender. It may continue breaking down flavanols inside the stomach. That detail matters, because it means even eating a banana alongside a berry-based drink or snack could have a similar effect.
Why flavanols matter in the first place
Flavanols are bioactive compounds found in many foods most people already consider healthy: blueberries, blackberries, strawberries, apples, pears, grapes, green tea, and cocoa. They’ve been studied for their links to cardiovascular health and, in older adults, cognitive function. The Academy of Nutrition and Dietetics recommends a daily intake of 400 to 600 milligrams. Most people fall well short of that.
Smoothies, in theory, are one of the more practical ways to close that gap, especially for someone with a full schedule who can’t always sit down to a carefully composed breakfast. That’s part of why this finding stings a little. The smoothie habit that’s supposed to help you cover nutritional ground may be quietly undercutting itself, depending on what you’re putting in it.
That said, this is one study conducted in a small group of healthy men, and nutritional research is rarely this simple in real life. If flavanols are something you actively care about, speaking with a registered dietitian is worth more than any single article. What the research does give you is a reason to reconsider a specific ingredient combination that’s very common and very well-intentioned.
The habit that was working against itself
The smoothie wasn’t failing because of what was missing. It was failing because of what was there — and what those ingredients were doing to each other before the first sip.
What to blend instead
The practical fix is easy. Professor Kuhnle’s recommendation from the study: “If you want to boost your flavanol intake with a smoothie, you should combine flavanol-rich fruits like berries with foods that have a low polyphenol oxidase activity like pineapple, oranges, mango or yoghurt.”
Mango and pineapple both give you a creamy, naturally sweet base. Greek yogurt adds protein and thickness. Orange juice as the liquid brings brightness without the PPO issue and pairs well with mixed berries. None of these are dramatic departures in terms of taste. The texture difference compared to a banana base is small once everything is blended. You’re not sacrificing much.
Banana isn’t going anywhere from my kitchen. It’s great on its own, sliced onto porridge in the morning, eaten before a workout, or mashed into baked oats on a weekend. It’s nutritious in plenty of other contexts and doesn’t need defending on those fronts.
What’s changing is how I think about its role in a berry smoothie specifically. If the point of adding berries is the flavanols, and the banana is blocking most of them from being absorbed, the smoothie isn’t quite doing what I thought it was. A small, easy swap, and one I wouldn’t have known to make before reading this research.
