Fibremaxxing is the new thing in nutrition. Online health influencers are adding chia seeds, beans, oats and berries to their aesthetically pleasing meals, aiming to eat as much fibre as possible – in many cases, the entire recommended daily amount in a single meal.
In short, fibre is fast becoming nutrient royalty. It’s not quite reached protein’s level of hype – which Dr Emily Leeming, dietitian and nutrition scientist at King’s College London, says is currently treated as the “prom king of nutrients.”
But Leeming thinks of fibre as the quirky wallflower in a 90s makeover movie. “They were always great, but we never fully recognised them for it.” Now, fibre is ready to be a princess.
But although all eyes are on fibre right now, most of us still don’t realise its full potential. Everyone knows it’s great for the gut – but fibre can also do wonders for your cholesterol levels.
Heart of the matter
Much in the field of nutrition is disputed, but the idea that fibre is good for the heart is backed by robust, well-established science.
“We have big, population-based studies with very consistent evidence to show that having a higher fibre intake is protective for heart health,” says Leeming.
For instance, a large observational study in 2012 found that, among more than 300,000 European men and women, those who ate more fibre were less likely to die from a heart attack after approximately 11 years.
Specifically, every 10g of fibre that a participant ate per day on average was associated with a 15 per cent lower risk of dying from a heart attack – and it didn’t seem to matter whether that fibre came from wholegrains, vegetables or fruit.
This was just based on observational data, so we can’t be sure about whether fibre caused that difference in risk – but the study’s findings have been backed up again and again.
For example, a 2019 review of a variety of studies – including randomised controlled trials (the scientific gold standard for nutrition research) – found similar results.
According to the results of 58 trials, people who ate more fibre improved their blood pressure and cholesterol levels, which are key risk factors for heart disease.
Fibre optics
So, it’s clear that there’s a link between fibre and heart health. But to understand why fibre has this effect, it’s useful to know what the nutrient actually is.
Dr Federica Amati, a medical scientist and health nutritionist currently working with wellness company ZOE, says: “Fibre is a type of carbohydrate formed of long strings of sugar molecules. But unlike other carbs, your body can’t break it down.”
Instead of being digested, fibre passes all the way through your gut to your large intestine (otherwise known as your colon), where your gut microbes start to break it down.
In the gut, fibre feeds beneficial microbes, encourages those microbes to produce helpful compounds, and bulks up digested food so we do healthy and regular poops.
But Amati explains that there are several types of fibre, each of which acts differently inside us. There’s insoluble fibre, which stays solid as it passes through, and soluble fibre, which dissolves in liquid.
A specific kind of soluble fibre, called viscous fibre, forms a gel-like substance when it dissolves in the gut.
Oats are a good source of viscous fibre. Leave them in water or milk, and they’ll turn slimy and gooey over time – exactly what they’ll do in your belly.
It’s this viscous fibre that seems to have particular heart health benefits.
“When it comes to fibre and heart health, we’re really talking about the ones that have viscous characteristics,” says Leeming. “This gel formation traps bile acids in the gut.”
Bile acids are substances that the body releases into the gut to help digest fat. And – here’s the important bit – bile acids are made from cholesterol.
Once bile acids have done their job, the body reabsorbs them in the small intestine, to be recycled – unless the acids encounter viscous fibre.
“What this viscous fibre does is trap the bile acids and then takes them out of the system so they can’t be reabsorbed,” explains Leeming. “Then your body has to make new bile acids out of the cholesterol that’s in your blood.”
In other words, viscous fibre catches bile acids and makes them leave the body via poop. In turn, our body must make more – and it does this by pulling LDL (low-density lipoprotein), known as ‘bad’ cholesterol, from our blood.
So, by capturing these bile acids, fibre is great at bringing down your cholesterol levels.
Having too much LDL cholesterol in the bloodstream is a key risk factor for heart disease, because it increases the likelihood that cholesterol will crash into the lining of blood vessels, leading to plaque build-up in our arteries.
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Cholesterol busters in your gut
That’s not the only reason that eating fibre is such a great way to protect your heart. Our gut microbes, which are boosted by fibre, may play a role too.
According to a recent study from Harvard University, in the US, some microbes may feed directly on cholesterol from the food we eat, preventing it from being absorbed into the body.
Specifically, scientists found that having more Oscillobacter bacteria in the gut was linked with lower levels of cholesterol in poop and blood plasma, suggesting they might be breaking dietary cholesterol down in the gut.
Leeming says the study is interesting as part of an emerging area of research. But it’s important to note that the vast majority – 80 per cent – of the cholesterol in our blood is made by the liver, not absorbed directly from food.
So, even if further research confirms the cholesterol-munching properties of these bacteria, they would still have a limited effect.
Pump up the fibre
For both your gut and your heart, fibre-rich foods are crucial for staying healthy. But does that mean we should cram way more of it into our meals? For most of us, the answer is probably ‘yes’.
“I think we all need to eat more fibre,” says Leeming. “It’s one of the best things that we can be doing for overall well-being.”
She explains that, in the UK, 93 per cent of us aren’t eating enough fibre. On average, we’re eating 20g rather than the recommended 30g per day – and across the pond, the average US adult is eating even less than this, at only 16g per day.
In Leeming’s words, this “huge fibre deficit” means that adding more fibre to our plates is likely to improve our health in a big way.
That doesn’t mean we should all bellyflop into the fibremaxxing deep end. Eating very large quantities of fibre – especially suddenly, when your body isn’t used to it – can lead to a range of gut issues, including bloating, diarrhoea, abdominal pains, and even trouble absorbing nutrients. So, it may be better to add fibrous foods gradually, to give your body a chance to adjust.
If you’re concerned about your heart health, it might make sense to prioritise sources of viscous fibre in your diet.
Oats are the classic example, but plenty of other foods contain viscous fibre, including barley, psyllium husk (a common fibre supplement) and beans.
Call it fibremaxxing, call it porridge for breakfast – either way, your cholesterol levels will thank you.
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