These days when you talk about fibre, most people think of high-speed fibre-optic broadband. Your sidewalks have most probably been dug up recently with the roll out of underground channels through which fibre-optic cables are passed.

The promise of faster connectivity, and reduction in broadband costs is attractive. But today we are going to continue the discussion of another kind of fibre – dietary fibre.

And this kind of fibre also has important mechanisms for sending information.

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A fibre-rich meal binds some ingested nutrients long enough that they reach the end of the small intestine – called the ileum.

When this part of the intestine senses those undigested kilojoules, it sends a message back to the brain to say the body has received sufficient food and turns the appetite off – a process called the “ileal brake”.

Without fibre, those kilojoules would have long since been absorbed higher up in the small intestine leading to excessive energy intake.

Another way in which dietary fibre communicates with the rest of the body is through short-chain fatty acids (SCFA) – like butyrate, acetate (vinegar) and propionate.

Healthy bacteria digest fibre and produce these SCFA which have multiple effects on the rest of the body.

For instance, a single high fibre meal can improve lung function in a chronic asthmatic in just a few hours by suppressing inflammation.

SCFA also stimulate fat cells to produce leptin – a hormone that tells your appetite centre to calm down, resulting in less craving for fatty foods, in the long term. But a more rapid effect by SCFA is the stimulation of L cells in the lining of the colon to release short-term appetite suppressing signals, called PYY and GLP-1 chemicals, which suppress the appetite centre in the brain very quickly.

So, fibre can work through a number of mechanisms to reduce our intake of excess energy and maintain a healthy weight.

Does this work in practice? Countries where large parts of the population still eat traditional high fibre diets, have far less obesity. As the diets change to more refined foods, so too does the obesity rate go up.

In fact some studies have shown that just increasing your diet by 2gm of fibre per day, can over two years result in around 500gm reduction in weight.

You may think that is not much, but when you consider that for most people over that time period, the weight typically rises by about 1kg per year.

Finally, increasing the production of SCFAs through a high fibre diet has been proven to increase your metabolic rate, burning fat by more than 25%.

That sounds like the type of “fibre” with which you would want to contract for a better life.
Dr David Glass

MBChB, FCOG(SA), DipIBLM
PS: References for the above insights can be found in Dr Michael Greger’s book “How not to diet”.

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