Fibre is like the middle child of macronutrients. Protein gets all the glory while carbohydrates and fats get the flak. But fibre just gets ignored until something goes wrong. And yet, talk to gut experts and they’ll tell you it’s the quiet achiever, responsible for setting off a huge number of key biochemical chain reactions essential to long-term health – and regularity, of course.

We already know that adequate fibre intake promotes digestive health, aids in weight management, lowers the risk of heart disease and helps regulate blood sugar levels. Now, a new study has found that a daily fibre supplement could improve brain function for over-60s. The research, from King’s College London, was published in the journal Nature Communications and found that giving people a cheap daily supplement of prebiotics – plant fibres that can help healthy bacteria grow in your gut – for 12 weeks helped them perform better in cognitive tests.

But with the average Brit getting about 18g of fibre a day, just over half the national dietary recommendation of 30g, it’s time for fibre to come out of the shadows and on to our plates.

Why fibre is the unsung hero in our diet

“Everyone’s obsessed with protein but deficiency is virtually unheard of in Britain,” says Dr Federica Amati, the head nutritionist at the Zoe app and a research associate at the School of Public Health, Imperial College London. “As many as nine in 10 people aren’t getting enough fibre, though,” she says. And we’re suffering the consequences. About 16 in 100 of us have symptoms of constipation and among over-60s, that figure rises to 33 (see below). Plus, at any given time, about 5 per cent of us have chronic diarrhoea – ironically, often for the same reason. “While a large proportion of people are living with constipation daily, another large group have regular diarrhoea and don’t realise this is often caused by a low-fibre diet that’s high in meat and ultra-processed foods,” Dr Amati says.

The long-term effects could be even more wide-reaching. A large-scale meta-analysis published in The Lancet in 2019 analysed 185 observational studies and found a 15-30 per cent reduction in all-cause and cardiovascular-related mortality in those who ate 25-29g of fibre each day compared with those who had less. They also had 16-24 per cent lower chances of developing coronary heart disease, stroke, type 2 diabetes and colorectal cancer. Not surprisingly, a higher-fibre diet is also related to a lower risk of irritable bowel syndrome (IBS).

What is fibre?

At its simplest, fibre is the indigestible component of plant foods. It comes in various forms, each of which plays its part in supporting health. There’s soluble fibre, found in oats, legumes and fruits, which dissolves with water to form a gel-like substance that helps regulate blood sugar levels and lower cholesterol. Insoluble fibre, on the other hand, is found in vegetables, nuts, seeds, whole grains – and All-Bran – and adds bulk to stools and helps prevent constipation (among many other things – see below). Then there’s resistant starch, which resists digestion in the small intestine and is found in bananas, beans and cooled starchy foods such as potatoes, and plays a key role in a healthy gut.

They’re all essential – and linked – so nutritional experts insist it’s superfluous to emphasise the different categories. “Speaking about soluble and insoluble fibre is unhelpful because in nature, most foods contain a bit of both, which is why we try to get people to eat a mix of different fibrous foods,” says Dr Amati. “But when you take fibre supplements, these will usually contain isolated soluble fibre, which is helpful if you have constipation or diarrhoea as well as for regulating the bowel.”

How can you tell if you have had enough fibre?

First, are you regular? “The primary way of knowing if you’re getting enough fibre is having a bowel movement once or twice a day, and that your poo is coming out comfortably and quickly with no straining,” says Dr Amati. In fact, findings from Zoe’s Big Poo Review undertaken in July last year found that Brits poo an average of 1.6 times a day, and that women spend about 3.53 minutes on the loo while men spend an average of 5.26 minutes. Reading on the loo is off, then.

Second, what’s your poo like? They should break off easily, be more like a long, smooth sausage instead of pellets, well formed and “not smushy”, advises Dr Amati. “Unless you have irritable bowel syndrome, you shouldn’t be feeling bloated if you’re getting enough fibre.” The third clue comes from your overall well-being. Your gut plays such a big role in your mental health and immunity, so that things such as low mood or a tendency to catch any bug going could also be subtle signs that your gut health could do with some help.

Why is it so important for health?

Unlike with protein, fats and carbs, our bodies lack the enzyme to break down fibrous foods, Dr Amati explains. “High-fibre meals are bulky and usually low-energy, which means it takes a lot longer for your stomach to empty. So if you have fibrous wholemeal bread with an egg and avocado, it will take longer to digest and absorb and help to keep your blood sugar stable more than if you removed the bread. That also promotes fullness.”

Fibre also aids the removal of excess waste products from the body as these are put back into the gut for release after the body has used what it needs. “If you have plenty of fibre in your colon, it will take with it as it passes, substances that could build up and be harmful like cholesterol, unused oestrogen and other hormones as well as toxins like those from the breakdown of alcohol.”

But how can something that does most of its work in the large intestine have benefits as far-reaching as the brain, as occurred in the King’s College research? It’s because fibre’s third and most crucial function is as a prebiotic; this is the non-digestible type of fibre found in certain foods – all plants contain them but some are especially high, such as Jerusalem artichokes, chicory, garlic, onions, apples, flaxseeds, leeks, asparagus and wheat bran. Prebiotics feed the beneficial bacteria (probiotics) in our guts through a fermentation process. “By-products of that fermentation process are what we call postbiotics, which are healthy compounds like short-chain fatty acids that produce enzymes, hormones and neurotransmitters that benefit many different functions in your body including immunity, weight, mood and brain health,” says Dr Amati.

There may be other things at work too, says Claire Steves, a professor of ageing and health at King’s College London, who led the research (above). Participants were given a powdered supplement to put over their breakfast cereals each day. It contained inulin and FOS (fructooligosaccharides), which are types of prebiotic fibres. After 12 weeks, their performance on cognition tests improved.

More research is needed on how this happened, but it could be the potential reduction of inflammation in the body impacting brain function, Professor Steves points out. “There may be direct communication from the gut microbiome to the brain through what we call the gut-brain axis, which is believed to happen through the vagus nerve,” she says. “The vagus nerve is a long nerve found in the neck that travels through the chest and abdomen connecting the brain to major organs such as the large intestine, heart and lungs.”

Would a bowl of All-Bran help brain health?

In a word, no. “All-Bran doesn’t contain much inulin or FOS, which is the supplement we used in the trial, so we can’t use it to replicate what we’ve done,” Professor Steves says. “But I’m a fan of bran for older people because it increases gut motility and helps alleviate constipation. This is really important for the over-60s as they tend to be much more constipated.” Do keep in mind, though, that All-Bran is 8 per cent sugar and a high sugar diet can feed harmful bacteria in the gut. “We know that reducing the amount of refined sugar we eat is important for our gut and overall health,” says Professor Steves.

Should you take a fibre supplement?

“A lot of people aren’t getting enough fibre and it takes time to get used to eating more,” says Dr Amati. “I recommend taking a fibre supplement alongside dietary changes if people need to substantially increase their fibre intake.” Inulin and FOS used in the King’s brain research has a lot of other research and benefits, she says. “But avoid it if you have IBS as it could make it worse.” You can ask for supplements of inulin and FOS from your local health food store.

How about old-fashioned – and dirt-cheap – psyllium husks, made from the Plantago ovata plant that absorbs water and swells in the digestive tract? Too harsh for daily use, says Dr Amati, as they could clog up your bowels and make your symptoms worse if overused. Psyllium is helpful for occasional times when you need them. “If you have a period where your bowel is quite irregular, for example post-antibiotics, taking psyllium husks until things level out again can help.” They’re available from pharmacies and health stores and you mix them with a large glass of water.

How to get more fibre in your diet

There are simple shortcuts, says Robert Hobson, a registered nutritionist and the author of Unprocess Your Life: Break Free from Ultra-Processed Foods for Good. “Add a serving of beans into your diet every day – this equates to a third of your intake. You can add them easily into salad, soups, stews and other one-pot dishes,” he advises. Try adding a cup of lentils to your bolognese or curry sauces and reducing the amount of meat or chicken you use. “Keep nuts and seeds to hand as they make good fibre boosters that can be sprinkled over any dish, and switch to whole over more refined grains. This may be oats for breakfast, wholemeal bread with lunch or brown rice or pasta for dinner.”

Try not to get too fixated on getting 30g of fibre, though, says Dr Amati, and just focus on eating more plant foods – vegetables, fruits, whole grains, nuts and seeds – as this will dramatically increase your intake of all types of fibre. “Make plant-based, minimally processed foods about three-quarters of your plate at each meal and that will easily take care of your fibre needs.”

The Telegraph, London