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Increasing fibre: why and how

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VOL: 97, ISSUE: 16, PAGE NO: 54

Diane Palmer, RN, BSc, PGCE, is lecturer in nursing, University of Hull

Pamela Barker, RN, is nutrition nurse specialist, Scarborough Hospital

The secret of a good diet is balance, and this should be stressed in all discussions and advice sheets. It is important to recognise and incorporate foods high in fibre into the diet, but this should not be at the expense of all other foods. A daily diet of beans and baked potato may incorporate the necessary fibre into the diet, but it is boring and does not necessarily supply all essential nutrients.

The secret of a good diet is balance, and this should be stressed in all discussions and advice sheets. It is important to recognise and incorporate foods high in fibre into the diet, but this should not be at the expense of all other foods. A daily diet of beans and baked potato may incorporate the necessary fibre into the diet, but it is boring and does not necessarily supply all essential nutrients.

Non-absorbable substances in the form of fibre are metabolised by colonic bacteria. The result is flatus, and an excess may result in cramping abdominal pain.

Dietary fibre is a complex mix of plant materials resistant to breakdown by the digestive system. It promotes elimination by providing bulk for stool formation, thereby assisting the passage of stool through the colon. In the UK the average daily intake of fibre is 12-13g (Cummings, 1994).

Fibre is found in foods derived from plants and is divided into two types - soluble and insoluble. It is not broken down by the digestive enzymes but is utilised by colonic bacteria. Soluble fibre dissolves in the fluid of the intestine to form a viscous gel which slows down the absorption of nutrients. It is fermented by the bacteria of the colon to short-chain fatty acids, CO2, hydrogen and methane. These are absorbed to provide energy. As fibre is food for the colonic bacteria their numbers are increased with a diet high in fibre. This increases the bulk of residues in the colon and defaecation is promoted.

It is suggested that 20-35g a day of dietary fibre should be the aim when a high intake is required. From a general healthy eating perspective an intake of 18g a day is sufficient (Department of Health, 1991).

Foods high in soluble fibre lead to an increase in the volume of flatus. Insoluble fibre does not have the same fermentation effect but acts like a sponge increasing in size. Sudden increases of dietary fibre will produce uncomfortable effects of bloating and excessive flatus. Therefore the advice should be that a balanced gradual increase of soluble and insoluble fibre is required. People are unlikely to comply with dietary advice that produces pain and discomfort. Excessive intake of fibre may result in diarrhoea and should not be recommended.

Functions of the colon include propulsion of faecal matter and absorption of fluids. People with slow bowel motility are more likely to be constipated owing to reabsorption of water from stored waste matter. Therefore the importance of fluids should not be underestimated.

Stools high in fibre are soft, bulky and easier to pass. Changes in the diet will eventually result in less pain or discomfort on elimination. However, this effect will not be immediate. The patient should be reassured that changing to a high-fibre diet is not an instant remedy. Colon cancer, constipation and diverticular disease in particular are all linked to inadequate dietary fibre.

Constipation
Constipation can be described as straining during defecation, the passage of hard stools, a sensation of incomplete evacuation or increased frequency of bowel habit (Sandler and Drossman, 1987). Stools may be passed only once or twice a week and in extreme circumstances defaecation may only occur once a month.

The causes of constipation are multifactorial, and this can make assessment and finding the cause difficult. From the patient's perspective constipation is not strictly limited to the frequency of bowel movements. Their concerns often include abdominal fullness, discomfort and difficult evacuation. Not only does constipation cause severe discomfort, it often leads to painful and bleeding haemorrhoids.

Illnesses such as Parkinson's disease, depression, hypothyroidism and hypercalcaemia may also cause constipation. Pregnancy, travel or a change in diet may also aggravate it. Presenting symptoms may include abdominal discomfort and/or distension, loss of appetite, nausea, vomiting, halitosis, malaise and depression, urinary retention, overflow of stools and, in severe cases, obstruction.

Maestri-Banks (1996) suggested that the assessment of constipation should take into account size, consistency, and ease of passage of the stool. Nurses can play a large part in the assessment of patients' bowel function and in health education about treatment and prevention. Many patients have their bowel function assessed on admission to hospital. This frequently consists of asking: 'How often do you have your bowels open?' and is not sufficiently explored further. Patients will often feel embarrassed or be unaware that constipation may be treated if the cause is explored. Many people live with constipation for years without investigation.

The causes of constipation are commonly a poor diet, lack of mobility, irritable bowel syndrome, effects of drugs (particularly opiates) and inadequate fluid intake. People who lead a sedentary lifestyle are more prone to constipation owing to reduced colonic motor activity. Their mobility may be restricted due to illness - for example, following orthopaedic surgery or a cerebral vascular accident. Some medications are particularly known to effect gut motility - for example, opiates, mebeverine, peppermint oil, sucralfate, iron and antacids containing aluminium (Hawkey, 1998).

Many people now are dependent on laxatives, either having failed in an effort to increase dietary fibre or preferring to use the pharmaceutical option, often seen as an easier remedy. It is, of course, possible to consider the use of laxatives in addition to fibre, but wholemeal bread, fruit and vegetables are better cures for constipation than laxatives. However, during the dietary transition period occasional use of medication may be required.

Inadequate fluid intake will have an impact on stool consistency, and a home diary should help to clarify if extra fluid is required. As fibre is known to draw water into the colon it is advisable to ensure that a good fluid intake of at least eight glasses of water a day be taken. Elderly people in particular may be reluctant to increase their fluid intake, especially if mobility is restricted and they anticipate extra visits to the toilet. However, low fluid intake may result in hard stools, and the combination of raw bran with a low fluid intake can lead to obstruction, due to swelling of the substance when in contact with intestinal fluids.

A jug of water can be measured out at the beginning of each day, kept in the fridge and consumed at intervals. This will be an indicator of outstanding fluid requirements. Fruit juices are a good source of fluids and a fibre provider. However, many are high in sugar, so they should be taken in moderation.

Foods high in fibre
The use of more peas, beans and lentils in the diet is highly recommended, and they are cheap, nutritious and readily available. Wholemeal bread and flour are also good sources of fibre. If wholemeal flour is found to be too heavy for baking a half wholemeal, half standard mix can be used. Potatoes in their skins and brown rice are tasty and high in fibre.

Breakfast cereals are good fibre sources, although the sugar-coated varieties are best avoided. The fibre content is often indicated on the package label.

Whole grains, nuts and seeds should also be regularly included in the diet. There is no fibre in meat, fish, poultry or dairy products, but they can be incorporated into healthy, tasty meals alongside high-fibre foods.

Gradually increasing dietary fibre may cause a few initial minor problems, such as increased flatus and abdominal bloating, but this will subside. If the diet is altered too rapidly diarrhoea may result, and in extreme cases nutrient absorption may be impaired. Therefore a gradual increase will be better tolerated.

Patients should aim for a good mix of soluble and insoluble dietary fibres. Soluble fibres dissolve in water and have been effective in reducing the risk of cardiovascular disease and diabetes by reducing blood cholesterol and regulating blood sugar levels. Good sources are oats, barley, legumes, as well as some fruit and vegetables. Insoluble fibres do not dissolve in water and are effective in reducing the risk of colon cancer, preventing diverticular disease and treating constipation. Good sources are wholegrain products, nuts, seeds and some vegetables.

The overall message has to be balance, moderation, and fresh is best. It is important to consider the way a person or family takes their meals. It may be that cooking from scratch is too daunting for many. There is evidence that families on a low income will be reluctant to purchase fresh vegetables and fruit if the family will not eat them.

Sometimes patients may need help with ideas on how their diet can be improved without too much effort. Lentils, peas and dried beans can be added to soups or casseroles, or dried fruit to desserts and cereals. It is possible to reduce fibre during preparation. Therefore, whenever possible, fruit and vegetables with edible skins and seeds should be used in cooking.

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