We might often judge health by external appearances, but a better indicator is what lies within.

Fibre is important. A diet with plenty of fibre is essential for healthy bowel movements (generally once a day is good).

Plus, it’s associated with a lower risk of heart disease, stroke, type 2 diabetes and bowel cancer.

In 2015, UK government guidelines stated that adults should be eating about 30g of fibre each day, but that most of us were barely making 18g.

What is fibre?

All dietary fibre, soluble and insoluble, whether as part of our diet or taken in supplement form, comes from plant sources including wholegrains, vegetables, fruits, legumes, nuts and seeds – even our morning coffee.

When we eat, food is digested in the small intestine.

But because we don’t possess the enzymes capable of breaking down fibre, it passes further along the gut to the large intestine, where it provides food for our gut bacteria.

By breaking down insoluble fibre, our gut bacteria produce short-chain fatty acids that nourish the gut lining and play a role in protecting gut health.

One of these fatty acids, called propionate, has been found to protect the body against harmful consequences of high blood pressure, and also to protect the heart.

A shortage of short-chain fatty acids has been associated with a range of diseases including type 2 diabetes.

Fibre and the gut

Fibre is also essential for supporting the gut’s defence mechanism.

One 2017 study found that when mice were put on a low fibre diet, problems occurred in their colons after just three to four days.

Not only did large amounts of beneficial gut bacteria die off, resulting in imbalance (dysbiosis), but the mucus layer that protects the colon became penetrable, enabling harmful bacteria to reach the cells lining the colon.

The animals’ colons were also found to have shrunk in thickness.

Fibre and blood sugar

Research also shows that fibre can help to stabilise blood sugars — but the less processed, the better.

In a recent randomised crossover trial, for two weeks, 31 adults with type 2 diabetes ate minimally processed wholegrain foods such as intact oats, brown rice, and wholegrain bread made with coarsely ground flour and kibbled wheat kernels.

Afterwards, for another two weeks, they ate more processed wholegrain foods such as instant oats, brown rice pasta, and wholegrain bread made with finely milled flour.

Glucose monitors recorded their blood sugar levels, night and day, for the duration of the study.

Eating minimally processed wholegrains was found to not only stabilise blood sugars after meals — particularly breakfast — but also throughout the day.

What the authors did not anticipate, however, was that the volunteers’ weight would be affected.

Although participants were asked not to lose weight by eating less during the trial, results showed their average weight increased slightly after two weeks of eating processed wholegrains and decreased slightly after eating minimally processed wholegrains.

Speaking to Optimum Nutrition, corresponding author Dr Andrew Reynolds said: “I think we can extend the message to say that when we process foods we are degrading the fibres [that are] present.”

Other shorter studies, he added, had already shown this in foods such as vegetable and fruit smoothies.

“Mechanical processes like milling and blending are cleaving and rupturing the fibres in the food — so they don’t function like they could,” he said.

“You could say the same about chewing, which is valid, except we don’t chew to the same extent that products are milled or blended.”

Emphasising the word “one” he said: “This might also be one reason why we don’t always see the benefits when fibres are isolated and put in capsules or consumed as a supplement — they’ve been broken down during processing.”

Fibre to feel full

Minimally processed fibre slows the breakdown of the carbohydrates they accompany and the release of their sugars.

So, although a vegetable mash might make a comforting addition to any winter meal, there may be more benefit to keeping our veggies al dente.

After all, it is much easier to eat a large portion of mash than a large portion of raw or minimally cooked veg.

This may also be why foods with fibre help to fill us up — by the time we have chewed and swallowed it, our brain is starting to get the message that we have eaten.

Also by slowing down the release of sugars, fibre helps to protect the liver from becoming overwhelmed, helping to protect it from non-alcoholic fatty liver disease.

Adding in fibre

If your diet is low in natural fibre, adding it in may initially cause gas and bloating, so it may be prudent to increase your intake gradually.

If you suffer with IBS or IBD, some forms of fibre can also cause gut irritation.

If concerned, speak to your GP, or a registered nutritional therapist who can advise on a dietary approach.

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