The Truth About Fibre and Constipation

  • 31 Mar 2019
  • Reading time 4 mins
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Popular advice for constipation is to eat more fibre rich foods such as wholegrains. These are more fad than fact since there is no consistent evidence that fibre works. In fact, in some studies having more fibre makes matters worse, not better.

For example, in a study of 63 adults who suffered from chronic constipation and were on a high fibre diet and/or were taking fibre supplements. Of these, 41 were put on a no-fibre diet, 16 on a reduced fibre diet and 4 remained on their high fibre diet.[1]

Of those put on the no-fibre diet frequency went from once every 3.75 days to once a day. Those on the reduced fibre diet went from once every 4.19 days to very 1.9 days while there was no change in those who stayed on their high-fibre diet.

This study is one of quite a few which show no benefit, or worsening on a high fibre diet. A review on studies treating IBS sufferers with high fibre diets shows much the same thing, with an increase in regular ‘insoluble’ fibres found in wholegrain wheat, probably making matters worse not better. Linseed or flax seeds also contains insoluble lignins. Evidence of their benefit in studies of people with IBS is rather thin.[2]

Before you throw the baby out with the bathwater most studies do, however, show a benefit for ‘soluble’ fibres[2] which is what you find in oats and chia seeds. People given soluble fibres in studies were almost twice as likely to report benefit, with increased frequency and ease, than those on placebo.

What you want are fibres that absorb the most water, thus bulking up and lightening the contents in the colon. I put fibres to the test in my short film ‘ the truth about fibre’ [link]

One way to increase your intake of soluble fibres is to have a tablespoon of chia seeds a day, which is what I do. Another is to eat whole oat products. You can further up your soluble fibre intake by adding a teaspoon of oat bran to cereal. Soluble fibres are also in vegetables, although somewhat destroyed by heat and hence prolonged coking. They behave quite differently to, for example, wheat fibre.
Natural foods stay soft in the digestive tract because they contain fibres which absorb water and expand inside the digestive tract. Fruits and vegetables naturally contain a lot of water in themselves. Provided they are prepared properly, whole grains, such as oats and rice, absorb water and provide watery bulk for the digestive tract. Given that we are literally 65 per cent water, it makes sense to eat foods with a high water content. Meats, cheese, eggs, refined grains and wheat (because of its gluten content) can all be constipating. While it should not be necessary to add fibre to a good diet, oat fibre has particular benefits. This is naturally present in oats which are best soaked and eaten cold.

The most super-soluble fibre of all is glucomannan fibre, derived from the konjac plant. This is what I use in my Carboslow product. Glucomannan has been shown to be helpful in a study in China with adults prone to constipation, both increasing frequency and ease by 30% in a week. It has the added advantage of helping to promote weight loss, as shown by numerous studies, the most recent of which reported almost 2.5kg weight loss over 60 days compared to placebo, in volunteers taking 3 grams 9a teaspoon or 3 1g capsules) a day.[3]
It is one of the very few natural supplements that has an allowed weight loss claim in the EU, as part of a controlled, ideally low GL, diet and also helps to normalise cholesterol, according to a recent review in the American Journal of Clinical Nutrition[3]. You want to take in 3 grams a day, which means 3 capsules taken twice a day, or a teaspoon of powder, both always taken with a large glass of water.


1 Heizer WD, et al., ‘The role of diet in symptoms of irritable bowel syndrome in adults: a narrative review’, J Am Diet Assoc. 2009;109(7):1204-14. []

2 Chen, H.L. et al., ‘Supplementation of konjac glucmannan into a low-fiber Chinese diet promoted bowel movement and improved colonic ecology in constipated adults: a placebo-controlled, diet-controlled trial’, J Am Coll Nutr. 2008 Feb;27(1):102-8. []