top of page

Fibre: Conventional Wisdom is Wrong!


This post shows how everything you thought you knew to be true and good about fibre is wrong. It is a story of mistaken science, flawed assumptions, ignorance of evidence and the fibre-industrial complex gone mad.

The Classic Fibre Narrative: where it all went wrong.

There are two types of dietary fibre: Soluble and Insoluble.

One acts as the accelerator (insoluble) and the other acts as a break (soluble) to the speed of digestion. Used in conjunction with each other, the theory goes, they keep an expedient rhythm to digestion, which minimises your intestines exposure to carcinogens and tumour promoting substances.

So, how do we know that? What are the roots of this wisdom?

The Fibre Myth

Denis Burkitt, a one-eyed Irish surgeon, and physician became known as the ‘fibre man’ after spending time in Africa, where he observed Africans, who ate a lot of vegetables and produced stools that were far easier to pass and more frequent than those passed by Westerners. He also observed the rate of Western diseases to be lower. Denis came to the belief that the reason Westerners had issues with their digestion and prevalence of certain western diseases was due to a deficiency in fibre.

“Western diets are so low on bulk and so dense in calories, that our intestines just don’t pass enough volume to remain healthy.”

The medical community at large bought into his fibre belief and began to think that the addition of dietary fibre could be used to combat a variety of diseases. Very little hypothesis testing was done and with a strong gust of wind from cereal and fibre manufacturers, the fibre myth caught the wind, set sail, and has become the guiding star ever since.

What does the evidence say?

Fibre might just be another case where conventional wisdom is wrong. Many studies are being published showing that consuming dietary fibre does not lower your chances of certain diseases, as purported to do, and in some cases, fibre may exacerbate certain conditions, like IBS (Irritable Bowel Syndrome).

Colon Cancer

One of the big claims often made for the inclusion of dietary fibre is that it reduces the risk of, and is protective against, the development of colon cancer. However, evidence and data for this claim are inconclusive.

Here is a study that is substantive in its aim was to evaluate the association between dietary fibre intake and risk of colorectal cancer. The study is a pooled analysis of 13 prospective cohort studies, which included over 725,000 men and women, who were followed up for 6 to 20 years across the studies. The study found that dietary fibre was not associated with a reduced risk of colorectal cancer.

Here is another study that conducted a systematic review and meta-analysis of randomised or quasi-randomised controlled trials, which assessed the effect of dietary fibre on incidence and recurrence of benign polyps in the colon, as well as incidences of colon cancer. The study concluded, over the period assessed there is no evidence to suggest that increasing dietary fibre will reduce polyps.

Type 2 Diabetes

The Type 2 diabetes advice has become synonymous with the healthy wholegrain high fibre movement. The classic low-GI food argument goes something like this:

Low-GI foods keep you fuller for longer; they help lower insulin spikes, thus, you maintain stable blood sugar levels, and that way you won’t have an energy crash and then need to start the snacking for energy roller coaster all over again. More stable blood sugar levels reduce your risk of Type 2 diabetes.

That is the only benefit; plus, there are other, more effective ways to control blood glucose levels than through the consumption of fibre. Other lifestyle-related changes, like exercise, or low carb ketogenic diets may be more effective. Especially so, if you factor in the connection between high carbohydrate diets increasing the incidence of Type 2 diabetes, then the benefits of fibre for diabetes are a stretch.

Heart Disease

Following the conventional advice purported by the diet heart-hypothesis (as discussed here) it was thought fibre could be used to bind to fat during digestion, and this would help would lower assimilated levels of fat and thus help reduce cholesterol levels. However, as found in this study, the addition of fibre to meals had no effect on lowering cholesterol.

This study argues, that even those studies that do show a reduction in the incidence of heart disease with the consumption of wholegrain high fibre cereals, should be interpreted with caution; because the studies were short term, of poor quality and most were funded by companies with commercial interests in wholegrain high fibre cereals.

The evidence is not currently there to be able to say with any significance that dietary fibre has a positive effect in reducing incidences of heart disease and any claim for it should be taken likely.

IBS & Constipation

One of the first recommendations given when suffering from constipation, whether it be from your grandmother, mother, or doctor, is to increase your fibre intake or take a fibre supplement. The logic goes a lack of dietary fibre contributes to slower digestive transit time, the extra time allows for greater water absorption to take place. This leads to smaller, harder stools to form, which compact in the intestines and cause constipation.

Thus, the consumption of fibre helps lower bowel pressure and loosen hardened stools. However, in this randomised, placebo-controlled trial, the study concluded that dietary fibre supplements do nothing more than relieve constipation and support...

“...western civilization’s obsession with the need for frequent defecation”.

The same prescription is often given to IBS sufferers, even though it often leads to worsening of symptoms. This is because excess fibre leads to more bacterial fermentation, giving off more gas, leading to greater aggravation of the gut wall - think SIBO and FODMAP as examples. The studies looking into fibre as a way of reducing IBS symptoms conclude:

“Any effectiveness of fibre in the long-term management of IBS remains questionable. Clinically, bran is no better than a placebo in the relief of the overall symptoms of IBS, and is possibly worse than a normal diet for some symptoms.”

Overall, from the studies that exist on fibre, conventional wisdom does not hold, as the addition of dietary fibre does not lead to the benefits often purported in the media.

So are there any benefits to fibre?

Fibre can act like activated charcoal during digestion. Activated charcoal came to notoriety in 1831 when Professor Touery ingested 15 grams of the deadly poison strychnine, in front of these colleagues, and lived to tell the tale. He lived because he mixed the strychnine with activated charcoal, which acts as a binder - it latches onto the poison and stops it from being absorbed by the body. Fibre can have the same effect. Fibre can bind onto many damaging plant compounds, such as anti-nutrients, and stop them from wreaking havoc on your digestive system.

As mentioned earlier, fibre has been shown to slow the digestion of carbohydrates and thus allow for better blood sugar regulation and can also relieve symptoms of constipation in some individuals.

The Fibre-Industrial-Complex

Ever since Dennis Burkitt came out with his fibre hypothesis, companies that produce and manufacture dietary fibre-based products – think grain farmers, breakfast cereal, and biscuit brands – have supported Burkitt’s fibre hypothesis. It’s no surprise why, given the fiduciary responsibility of the shareholders to maximise profits, it makes financial sense to push the fibre hypothesis as these companies stand to make a lot of money from dietary fibre products.

When an industry gets behind an idea, especially one that is based on dubious science, it sets off a series of perverse incentives, that compound over time to creates an industry with a large concentration of wealth and many invested interests, that become blind and hostile to opposing voices*.

On top of that, dietary fibre-based products are fantastic products for large consumer goods corporations. Cereal bars, for example, can become extremely profitable; they are perfect for vertical and horizontal economies of scale.

Agri-business is an expert in its ability to produce consistent large yields of cereals. These cereals due to their durability and flexibility can be transformed with the help of food science into a plethora of different shapes and sizes to make a variety of products that have long stable shelf lives. These can then be stored and transported all over the world to supermarkets, corner shops, coffee shops, and vending machines.

The corporate machine is almost unstoppable once it gets going, as it is constantly being streamlined and refined for organisational efficiency throughout the supply chain. It is not just within the organisation where the economising stops – it pays to influence external actors

When a brand is globally worth hundreds of millions, spending just a few million on lobbying a government for preferential legislation, such as farm subsidies can cut the cost of production substantially, thus spending a couple million can yield a phenomenal return on investment. Similar savvy collusions can be seen when corporations back government health policies. This becomes a win-win situation for the government and corporations. The government receives extra funding and it makes their policy look successful – good for votes. In return, the corporation gains preferential legislative treatment, it can now influence research and benefits from positive PR.

Now compound this with the branding and marketing experts that the corporations hire to promote and advertise their products, which they do very effectively. The effectiveness can be seen when you look at the cereal bar shelf at a supermarket. Despite the many different brands, at their core, the products are 80% similar. Look at blind tastings between branded vs value branded goods. Capitalising on the psychology of marketing and influence, over time repeated statements become ‘fact’ – heart healthy high fibre cereal.


This story of fibre, like many other stories in nutrition, is sadly just another myth; fibre has over time, based on dubious scientific claims and perverse incentives, come to be regarded as truth in nutrition – as shown above this truth just ain’t so. So if you are looking to start eating a Carnivore diet, or maybe just want to cut down on carbs and vegetables, but are afraid the lack of fibre may be a cause for concern – fear not – we don’t need as much fibre as conventional wisdom dictates.

*I am not arguing that these actors are evil in any way, on the contrary, most are very good-hearted people. I have personally worked very closely with brand executives of these corporations. It is just a natural outcome of people doing their job to the best of their ability but where systemically there are incentives that lead to the promotion of ideas and products that are not nutritionally optimal. The way to combat these perverse incentives is not to attack and vilify the corporations, but instead to educate and empower the consumer – because these corporations react and adapt with vigour when their brand’s market share decreases.

bottom of page