Diet & Nutrition – Fiber & Constipation


What is constipation?

Constipation is a condition of infrequent and/or hard dry bowel movements. It is normally related to the consistency of the faeces rather than the frequency of bowel movements. Constipation is a common occurrence in Western countries and its main cause is a lack of dietary fibre. The mildly laxative properties of wheat bran have been recognised since the time of Hippocrates (460-377 BC) whose writing suggest he was aware of its usefulness in the treatment of constipation.

What is fibre?

Fibre is a term used to refer to the parts of the diet that cannot be digested in the stomach or small intestine by endogenous enzymes. It is also known as ‘roughage’.

Dietary fibre can be divided into 2 groups:

Soluble Fibre:

This group includes gums, pectin’s, and some hemicelluloses, found in oats, legumes, barley, apples, citrus fruits and strawberries. This fibre forms a thick gelatinous sol when mixed with food in the digestive system and can be fermented in the colon by bacteria but it doesn’t contribute significantly to stool bulk. It does however help to lower cholesterol by absorbing bile (which contains cholesterol) and excreting it from the body. Less bile is then reabsorbed in the intestine and so more bile is made in the liver, which in turn requires cholesterol.

Insoluble Fibre:

This group contains cellulose and some hemicelluloses found in whole grain products, vegetables and bran. Compared to soluble fibre it is relatively resistant to bacterial fermentation.

How does fibre prevent constipation?

Fibre is necessary in the diet to promote peristalsis in the large intestine by providing bulk. As the fibre passes through the intestine it also absorbs large amounts of water, which results in softer, bulkier stools that are easier to pass. (In healthy western populations it has been shown that for every 1g of wheat bran consumed per day the output of stool is increased by between 3 and 5g). This in turn can lead to a decrease in the occurrence of or relief from haemorrhoids, by reducing the strain that constipation causes. More bulk in the colon means less pressure and this fact can be used in the treatment of irritable bowel syndrome and diverticulosis (pockets in the bowel which may become infected leading to diverticulitis or break open to form an abscess or lead to peritonitis).

How much fibre should I eat?

It is recommended that adults should consume 20-35g per day which will usually produce 1 to 2 soft and formed stools a day. It is important to remember that fluid intake should also be consciously increased (6-8 glasses per day) so that enough water can be absorbed to increase the bulk of the faeces and aid peristalsis.

How do I increase my fibre intake?

For breads and cereals use wholemeal grains (brown rice contains 2g fibre per cup) and high fibre cereals (weetabix 4g/serving, All bran 9.5g/serving etc…) The fibre is present in the outer layer of the grain and is removed in the manufacturing of white flours and pastas etc (white bread 0.5g/slice, wholemeal bread 2.5g/slice, white pasta 4g/serving, wholemeal pasta 9g/serving). In relation to fruit and vegetables, try to leave the skins on wherever possible, because just like cereals that’s where the fibre is contained. Try introducing dried, stewed, tinned or fresh fruit to breakfast cereals. A fibre increase should be done gradually to prevent bloating in the abdomen due to increased bacterial fermentation and production of associated gases (hydrogen, methane and carbon dioxide).


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