Fibre and the Microbiome

Dr Charles Akle

How does fibre fit into my microbiome “farming” diet?

Fibre is the cellulosic component of many food ingredients and as we cannot digest cellulose it passes through into the large bowel. There it acts as a food for the resident bacteria which are able to digest it. So, animals that live on grass and other cellulosic material can only digest it and benefit provided they let it ferment in special stomachs containing the bacteria that can break it up.

Humans are omnivorous but a lot of the vegetable matter we eat that is fibre will pass through and in theory only feed the gut bacteria. In fact, this is beneficial in so many ways to us and the bacteria.

Fibre acts as roughage and helps to bulk our faeces and make it easier to keep the system moving and prevent constipation and high pressure in the bowel. A good comfortable bowel action is such a great comfort for one’s day!

The condition known as diverticular disease is almost certainly a result of chronic high pressure which causes the wall to bulge out at weak points and produce lots of little sacs where material can stagnate and cause infection. This can be very serious and life threatening and is very much a disease of Western Society as those places with a natural high fibre diet are rarely affected.

Did you Know! The Latin word ”diverticulum” means a bordello or house of ill repute! These little side rooms were sited along the main shopping mall, the “forum”, and were entered through an archway or “fornix”, hence the term to “fornicate”. You can’t say we don’t improve your classical education on this site!


There is undoubtedly an association also with the incidence of cancer of the colon and those whose fibre intake is low and fat intake is high. 

There is also a strong relationship between a high fibre diet and avoiding one of the commonest causes of abdominal pain, so-called irritable bowel syndrome (IBS – not to be confused with Inflammatory Bowel Disease). It is amazing how much benefit you can derive by simply paying attention to your fibre intake and microbiome at the same time as keeping stress levels under control, or at least coping with stress responses.

By ensuring that we have enough fibre in our diet, we ensure that our resident bacteria in the microbiome are well fed and “farmed” and so maximise the commensal effect (mutual benefit) that we want and is so essential to our immunological wellbeing.

I tried fibre and I developed a lot of colicky pain in my abdomen. Why?

I treated patients with Irritable bowel for nearly forty years and soon learnt to ensure that added fibre was introduced gradually. At one time, the easiest source of fibre was bran but this often caused colic as it was too rough! You have to think of a workman’s hands – when you first start working they are soft and sensitive and can blister easily. (My surgeon’s hands are like a baby’s – more than five minutes gardening is impossible without wearing gloves!). After some weeks however, the skin gets really tough and copes and you can manage without gloves.

The same applies to the gut. Start with small amounts and preferably soluble fibre which is far gentler, before adding more insoluble types. I used to “prescribe” psyllium husk (also known as ispaghula) to be taken as two dessert spoonfuls in a tub of yoghurt or in orange juice at least twice a day. After six weeks you could then be more adventurous and should be able to tolerate the hard stuff! Make sure you take lots of water with the diet as the material swells and absorbs water which makes it soft and jelly like.

For those who want to pay, you can use supplements sold as Metamucil which come in sachets and are easy to use. You can discuss with your pharmacist but, frankly, good old psyllium husk in yoghurt is so easy why pay more?

Can you give me some examples of soluble and insoluble fibre?

Soluble fibre is contained in psyllium but also oats (great as they are also gluten free), barley, carrots and similar root vegetables, citrus fruits and apples. Pease are also good though other legumes such as beans have more insoluble material.

Insoluble fibre is in many beans, wheat (watch out for gluten sensitivity), brassicas (cauliflower, broccoli and cabbage), potatoes (keep the skin!), and many nuts. 

Prunes and dried fruit have been known for many years as an aid to help constipation and the best agent to get your bowels working is prune juice! So good that I always used it on my patients after major surgery to get the bowels working, rather than chemical laxatives or harsher natural ones based on cascara etc.

What matters is that you “farm” your microbiome by giving it food which you cannot digest but which actually helps you indirectly by improving gut action but especially by maintaining a great immune system. The extra effects on blood sugar and diabetes, lowering cholesterol, and keeping weight down are surely well known to you and add up to helping you lead a healthier and longer life!