Have We Got Smoothies All Wrong?

How a ‘Smoothies Are Toxic’ claim sent me down a rabbit hole

Recently, the YouTube algorithm decided I need rescuing from my breakfast.

It keeps serving me a very earnest 'doctor' warning that “smoothies might be the most toxic drink known to man,” or words to that effect.

Usually, I'm laid back enough to shrug off that kind of clickbait. After the fifth repeat, I caught myself yelling at the iPad.

Here’s why it got under my skin: I genuinely like smoothies - berries, milk, a spoon of Greek yoghurt, flaxseeds. Fruit, fibre, protein, omega-3s, polyphenols. That’s a lot of goodness for a 60-second blend.

Surely that’s healthy… right?

But here’s the nagging thought that wouldn’t go away: what if there’s a sliver of truth hiding in the hype?

So I’ve parked the outrage and donned the lab coat. This week I’m stress-testing smoothies - and fruit juice while I’m at it - to see whether they’re a shortcut to five-a-day or a cleverly blended sugar bomb.

If that YouTube doctor turns out to be right, I won’t be happy. But at least we’ll both know.

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What Fruit Brings to the Table

We’re advised to eat about two cups of fruit a day as part of our five a day of fruit and veg. In practice, most of us manage barely half of that, and about a third of what we do consume comes from fruit juice.

Fruit is one of our best sources of dietary fibre, so it’s no surprise that low fruit intake is part of the reason so few of us hit the target. Only around 5% of adults get the recommended 30g of fibre a day. The fact that you’ve signed up for One Health Tweak a Week suggests you take a better-than-average interest in your health, so I’m guessing you do better. If not, I’ll look away while you grab an apple.

Fibre isn’t just about keeping you regular. Low-fibre diets - like the one most of us are eating - are linked to weight gain, poor blood sugar control, inflammation, irritable bowel syndrome, and an unhealthy gut microbiome. They’re also associated with a higher risk of type 2 diabetes, heart disease, and bowel cancer.

Fruit brings more than just fibre. It’s also rich in polyphenols - natural compounds with antioxidant and anti-inflammatory properties that can help slow down some of the processes involved in ageing and chronic disease.

So yes, most of us would benefit from eating more fruit.

But does the form matter?

Can smoothies offer a simple, delicious shortcut to better health — or do they come with unintended consequences?

To answer that, let’s begin by comparing the two obvious alternatives: eating whole fruit versus drinking fruit juice.

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Why Juice Doesn’t Cut It

Let’s be clear from the outset: we’re not talking about Sunny D.

Those “juice drinks” may contain a splash of concentrate, but they’re mostly water, sugar, artificial sweeteners, colours, and gums. Nutritionally, they belong in the same category as Coke.

Here, we’re talking about 100% fruit juice - whether squeezed at home or poured from a carton.

You might expect that to count as a healthy choice. The UK’s NHS isn’t so sure. It caps juice at 150ml a day - about five fluid ounces - and counts it as no more than one of your five-a-day, regardless of how much you drink.

So what’s the issue?

It’s all about the sugar

The key distinction is between intrinsic sugars - those locked inside whole fruit and its fibre matrix - and free sugars, which are unbound and rapidly absorbed.

Juicing turns intrinsic sugars into free sugars. It ruptures plant cell walls, removes fibre, and concentrates the sugar load. The result is a fast-track to elevated blood glucose and insulin - and all the metabolic mischief that follows.

Compare that to eating an orange. The fibre slows digestion, buffers the sugar spike, and delivers nutrients more gradually. You absorb less sugar overall, and some of what remains even ends up nourishing your gut bacteria.

Juice, by contrast, is sugar in solution.

And it’s not just the sugar. You lose other benefits, too. One study comparing strawberry purée to frozen whole strawberries found a 77% drop in vitamin C and a 30–40% reduction in polyphenols after processing.

That’s the paradox: you can squeeze fruit and lose its goodness.

Juice doesn’t fill you up

There’s also a problem with how juice behaves once it’s in your body.

Satiety - the sense of fullness that helps regulate appetite - depends partly on chewing, partly on stomach stretch, and partly on how quickly food moves through the gut. Juice scores poorly on all counts.

In a beautifully designed study, researchers gave people one of four pre-meal snacks:

• Whole apple

• Applesauce

• Apple juice with fibre

• Apple juice without fibre

Then they measured how much they ate at the next meal.

As this apple example shows, consuming whole fruit before a meal reduces the appetite more and thus calories consumed at the next meal more than a liquified version or juice | Data: Flood-Obbagy & Rolls 2008 | Image: Author + Adobe stock

In short: the more processed the apple, the less it helped suppress appetite, and so the more people ate at the next meal.

Applesauce, which is arguably closer to a smoothie, sat somewhere in the middle between whole fruit and juice.

Juice and overconsumption

That same lack of satiety makes juice easy to overconsume. You wouldn’t eat four oranges in one sitting, but it takes barely a minute to drink their juice, and your body won’t even register it as food.

In small amounts, juice isn’t harmful. That’s why the NHS sets a sensible cap at 150ml. But once you go beyond that, the health effects start to turn.

Studies show that moderate juice intake is neutral for weight. But drink more than 200ml a day and the risk of weight gain, high blood pressure, and type 2 diabetes starts to rise.

Whole fruit, by contrast, protects against all three - and more.

The case for whole fruit keeps getting stronger

• Whole fruit is linked to a reduced risk of type 2 diabetes.

• Fruit juice shows either no benefit or a 7% increase in risk. For sugar-sweetened juice, the risk is even higher.

When it comes to cardiovascular health:

• Eating 300g of fruit per day is linked to a 16% lower risk of coronary heart disease.

• A meta-analysis showed an 18% lower risk of stroke in high fruit consumers.

• Fruit juice was associated with a reduced stroke risk, but no protection for heart disease.

And when researchers looked at all-cause mortality, the differences were even starker:

Whole fruit: 13–27% lower risk of early death for those eating the most.

Fruit juice: Neutral up to ~150ml/day, but each extra 350ml (~12 oz) was linked to a 24% increase in mortality.

That 'healthy' bottle of juice you pick up with your lunchtime sandwiches everyday may not be doing you any favours.

Why the difference?

It’s not just about sugar content - whole fruits offer a radically different experience to fruit juice, and the health impacts reflect that.

Chewing and the volume of whole fruit contribute to satiety, helping you feel full and naturally limit intake. Juice, on the other hand, is easy to chug in large quantities, often delivering a hefty calorie hit before you realise it.

Then there's fibre - abundant in whole fruit and essential for gut health and feeding a healthy microbiome, but largely stripped out in juice.

And crucially, many of the beneficial polyphenols in fruit are bound to the skin and fibre - again, often lost in the juicing process. So it’s no surprise that the health effects of eating fruit and drinking juice diverge so sharply.

Juice isn’t poison. But it’s not health food either.

If you’re choosing between juice and a can of 7Up, of course the juice wins. But let’s not confuse “better than a fizzy drink” with good for you.

Takeaway

• Fruit juice is no substitute for whole fruit.

• It contains some vitamin C, potassium, and polyphenols, but lacks fibre and doesn't curb appetites.

• Moderate consumption (100–200ml/day) is likely neutral.

• Beyond that, juice starts to behave more like sugar-sweetened beverages.

• Compared to fizzy drinks? Better.

• Compared to whole fruit? Not even close.

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What about smoothies?

Smoothies have become wildly popular, but the science hasn’t quite caught up. We don’t have the same depth of data as we do for whole fruit or fruit juice.

Part of the challenge is that smoothies aren’t a single thing, they’re a mixed bag. A smoothie might be based on fruit juice or milk (dairy or plant-based), bulked out with seeds, oats, nut butters, avocado, or yoghurt. It could be high in protein and fibre, or just a sugar-laden blitz.

These differences matter. More fruit juice? Expect a sharper blood sugar spike. More fat, fibre, or protein? That’ll help slow absorption and blunt the metabolic impact.

Homemade smoothies usually start with whole fresh or frozen fruit. In contrast, store-bought versions are often blends of juice and purée, sometimes with added yoghurt or vitamin fortification. They may be lower in fibre and polyphenols, and higher in sugar - even if the label says “all natural.”

And because they’re quick to make and even quicker to drink, smoothies can be a stealthy source of calories. A banana, a cup of berries, orange juice, and yoghurt might seem harmless, but you’re looking at around 350 kcal and 48g (12 teaspoons) of sugar. That’s 40% more sugar than a can of cola, and 60% over the recommended daily limit for free sugars.

As shown in the earlier graph, smoothies are more filling than juice, but less so than whole fruit. If you’re watching your weight, that’s worth bearing in mind.

Apart from the potential for being a sugar bomb, what else do we know about smoothies?

Fibre

On the plus side, smoothies retain all the fibre of the whole fruit. But because it’s blitzed into tiny pieces, it’s far easier to digest. That means less fibre may reach the lower bowel - where it plays a key role in keeping us regular, protecting against bowel cancer, and supporting a healthy microbiome.

Vitamins and minerals

Like juice, smoothies typically contain all the vitamins and minerals of the whole fruit. But vitamin levels can degrade with time, so a smoothie made fresh is better than one that’s been sitting in the fridge for a day or two.

Polyphenols

As we’ve seen, polyphenols - natural plant compounds with antioxidant and anti-inflammatory properties - may be one of the main drivers behind the health benefits of fruit, right alongside fibre.

Because smoothies often include the skin and seeds of fruit, they tend to retain these valuable compounds. And in some cases, there’s evidence that polyphenols are more readily absorbed from a smoothie than from whole fruit.

But, and it’s a big but, if you, like me, enjoy throwing a banana into your smoothie to make it thick and sweet, you might be undoing a lot of that good.

Thanks to the excellent

Mick Skolnick, MD

for bringing this to my attention: bananas contain an enzyme called polyphenol oxidase, which rapidly breaks down polyphenols. (If you don't already follow Mick, go check out his writing).

Adding banana to a smoothie rapidly destroys polyphenols in the glass and in the body | Data: Ottaviani et al. 2023 | Image: Author + Adobe stock

As the graph shows, this enzyme gets to work fast. Just 10 minutes after blending, you’ve already lost half your polyphenols. After 30 minutes, you’re down to about 10% of what you started with. So don’t hang around - drink your smoothie straight away. No saving half for later. Drink first. Wash the blender later!

Even more surprising, the effect isn’t limited to blending. The right-hand graph shows that just eating a banana at the same time as a polyphenol-rich smoothie reduces how much of those compounds get into your bloodstream.

Takeaway? Keep bananas at a distance - time-wise - from your berries, grapes, cherries or citrus. Beet greens, apples and pears have a similar effect, though it’s much milder.

And if you’re already a smoothie drinker, here’s something encouraging: one small study found that regular smoothie drinkers - those enjoying at least one a week over two months - tended to have healthier habits overall. They were more active, ate more fruit and veg, less meat and processed food, and were more likely to have lost weight than gained it.

So, if you’re reading this and thinking carefully about what goes into your blender, you’re probably already ahead of the curve.

So, fellow smoothie lovers, where does this leave us?

We don’t yet have long-term studies on smoothie intake like we do for juice and whole fruit, which makes definitive health claims harder.

But we can say this much with confidence: drinking smoothies won’t deliver the full benefits of eating whole fruit. If your goal is health and longevity, whole fruit still wins, hands down.

That said, smoothies aren’t health villains. They're just not a free pass either. They’re nutrient-dense, tasty, and incredibly convenient - but they come with baggage, especially in the form of sugar.

If you enjoy smoothies, the key is to be strategic. With a few smart choices, you can shift the balance away from sugar bombs and closer to a genuinely nourishing option.

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HEALTH TWEAK OF THE WEEK - 🥤 Smoothie Smarts

Smoothies can be part of a healthy diet -but only if you’re mindful of what’s in the blender.

Whole fruit brings a powerful package of benefits - fibre, polyphenols, slow-release energy, and it helps you feel full for longer. Juice, by contrast, strips out the fibre and much of the polyphenol punch, leaving mostly sugar and vitamins. Smoothies fall somewhere in between.

They’re not the nutritional slam dunk wellness influencers claim, but nor are they junk food in disguise. The key is balance. Smoothies are quick, tasty, and often nutrient-rich - but they also deliver a stealthy load of sugar, and they likely don’t match the long-term health benefits of whole fruit.

Smoothies can be a sugar bomb with limited benefits, or a smart, targeted way to support your health goals. The difference comes down to what you put in the blender. Think like a formulator, not just a fruit fan. Here’s how to build a better smoothie:

• Add protein. A scoop of protein powder or a few spoonfuls of Greek yoghurt can help slow down sugar absorption, keep you feeling full for longer, and support muscle health, especially important as we age.

• Boost fibre and omega-3s. Flax, chia, or hemp seeds all add gut-friendly fibre and plant-based omega-3 fats, both of which are often lacking in typical diets.

• Include healthy fats. Nut butters, avocado, or even a splash of extra virgin olive oil add richness and help with absorption of fat-soluble vitamins. They also help smooth out blood sugar spikes and make your smoothie more satisfying.

• Top up polyphenols. A spoonful of cocoa powder, matcha, cinnamon, or turmeric can dial up antioxidant activity and add interesting depth of flavour, not just sweetness. Leave out the banana, or you’ll have no polyphenols left.

• Support your microbiome. Try adding kefir for probiotics or prebiotic-rich cooked and cooled oats. Your friendly gut bacteria will thank you.

• Sneak in micronutrients. Leafy greens like spinach or kale add iron, magnesium, and folate, and you’ll barely taste them. Feeling brave? A pinch of spirulina or chlorella brings an extra nutritional kick - just be mindful of colour combinations unless you enjoy sipping something that looks like swamp juice.

And finally, be sure to protect your teeth. Smoothies often contain a mix of natural sugars and fruit acids - great for flavour, not so great for enamel. Sipping slowly over an hour might seem virtuous, but it means your teeth are being bathed in sugar and acid the whole time. Better to drink it within 10–15 minutes, then rinse your mouth with water or brush your teeth afterwards (ideally after waiting about 30 minutes to let enamel re-harden).

So… how do I feel about those YouTube adverts now?

They still wind me up far more than they should. They're slick, shouty, clickbait nonsense. But credit where it’s due, they did send me down a rabbit hole. And what I found is that smoothies aren’t the guilt-free wellness elixirs they’re often made out to be.

Yes, they can be nutrient-rich, convenient, and genuinely tasty. But they also carry a quiet cargo of sugar and don’t deliver the same long-term benefits as just eating the fruit whole. So enjoy them - mindfully, strategically, and maybe without the banana.

Whole fruit still wins. Every time.

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🎧 Prefer to listen?

🎙️ This week’s episode of One Health Tweak a Week blends up the truth about smoothies:

• Why smoothies aren’t a shortcut to health (and when they can be helpful)

• The sneaky science of sugar and satiety

• What bananas are secretly doing to your antioxidants

Plus: simple smoothie upgrades that actually deliver.

👉 Tune in now - it’s free!

(Psst: these episodes are free for now - but won’t be forever. If you’ve been finding value here, consider upgrading to stay in the loop and ahead of the curve.)

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👉 What’s next?

💬 Got a favourite smoothie tweak or blender combo that changed your breakfast game? Hit reply. I’d love to hear what’s working in your kitchen.

📢 Got a friend who treats their blender like a shrine to wellness? Forward this on. Even good fruit can go rogue with the wrong combo.

❓ Have a label, myth or nutrition trend you want decoded? Send it over. It might feature in an upcoming issue.

🔒 Want to help keep this newsletter going strong? Upgrade to a paid subscription for bonus content, Q&As, community chats, and that quiet satisfaction of supporting clear, evidence-based health writing.

Until next Saturday - stay curious, stay well, and stay kind to your future self.

– Ben