FOOD & FIBRE

By: 

ION Archives

Issue: 
Spring
Year of publication: 
2000

There’s more to fibre than simply maintaining bowel function. It also plays a role in the prevention and treatment of numerous ailments and enhances healthy gut flora. Paula Bartimeus DHD investigates

When British surgeon, Dr Denis Burkitt (co-author with Dr Hugh Trowell of When British surgeon, Dr Denis Burkitt (co-author with Dr Hugh Trowell of Western Diseases: Their Emergence and Prevention, 1981) studied rural East African villagers (in the late 1960s), he found that the ravages of Western disease were rare among these people. Ailments such as heart disease, high blood pressure, varicose veins, gallstones, diabetes and cancer were virtually unheard of, as were weight problems. He associated these findings with their diet which was rich in fruit, vegetables and coarse cereal grains - and concluded that dietary fibre was indeed a great disease preventer.

Burkitt’s hypothesis, which was largely based on the concept of faecal bulk and “transit time” (the length of time it takes for food to pass through the alimentary tract) has since been supported by many epidemiological and case control studies. Three decades later, much more is now known about the role of dietary fibre and its benefits.

 

DIETARY FIBRE

Basically, dietary fibre, formerly referred to as “roughage” is a collection of food substances (non-starch polysaccharides) that cannot be digested by the enzyme secretions of the human digestive tract. Consequently it enters the large intestine unchanged. Although fibre does not supply the body with nutrients as such, it is still a vital component in the daily diet. Fibre can be divided into two categories - soluble and insoluble. Most plant foods contain a combination of both, the percentage of each varying from species to species.

INSOLUBLE FIBRE

Types of insoluble fibre include cellulose, some hemicelluloses and lignin, found in considerable amounts in whole grains and the skins of fruit and vegetables. This form of fibre doesn’t dis-solve in water but has the ability to bind with it, increasing the bulk of faecal matter, thus promoting regular bowel movements. Insoluble fibre helps decrease transit time through the gastro-intestinal tract, preventing the accumulation of waste materials and reducing the risk of bowel conditions such as constipation, diverticulitis and haemorrhoids. The removal of toxins from the bowel is also encouraged.

This reduction in transit time is thought to explain why fibre is associated with protection from colon and other gastro-intestinal cancers. However, the true relationship between fibre and colon cancer risk appears more complicated than first believed. For example, wheat bran (high in insoluble fibre) has been reported in animal research to be significantly more protective than diets not containing wheat bran, but equally high in insoluble fibres.

Besides helping to stabilise blood glucose, soluble fibre has a remarkable effect on lowering elevated cholesterolFibre may have other anti-cancer effects unrelated to transit time or even the gastro-intestinal tract. (2) Some researchers believe that changes in bile acid metabolism in the gastro-intestinal tract may partially explain the link between wheat bran and the prevention of colon cancer; (3) a protective link sometimes not found when scientists study total fibre or even total grain fibre intake and colon cancer incidence.

SOLUBLE FIBRE

Soluble fibre was initially considered to be insignificant and although positive reports on pectin, guar, legume fibre and oat bran appeared in the 1960s, it wasn’t until the mid 1970s that it began to receive attention.

Soluble fibre compounds, which include some hemicelluloses, mucilages, gums and pectin are associated with slowing stomach emptying time, probably due to their gelling properties when mixed with water. Soluble fibres are characteristically sticky and mesh with water to form gels. This mechanism causes food to be absorbed into the blood stream at a much slower rate, preventing sudden surges in blood sugar. Soluble fibres can also lower blood sugar levels in people with diabetes, and some researchers have found that increasing dietary fibre decreases the body’s need for insulin.

Besides helping to stabilise blood glucose, soluble fibre has a remarkable stabilise blood effect on lowering elevated cholesterol.

Types of insoluble fibre

CELLULOSE

Cellulose is the main fibrous component of plants and is responsible for providing rigidity of cell walls. Rich food sources of cellulose include whole grains (the outer layer), vegetables and fruit.

 

HEMICELLULOSE

Hemicellulose, present in whole grains, fruit, vegetables, nuts, seeds and legumes, forms the matrix of the plant cell wall in which cellulose fibres are enmeshed. Besides helping to increase faecal weight and size, because it contains both insoluble and soluble properties, hemicellulose aids the reduction of cholesterol levels and binds bile acids.

LIGNIN

Lignin is related to cellulose and forms the woody cell walls of plants. It is present in fruit, vegetables and whole grains.

Investigations have shown that they are useful in the dietary management of diabetes and cholesterol. They may also be beneficial in reducing appetite, by promoting a feeling of fullness, thereby influencing satiety and weight control.

 

Types of soluble fibre

MUCILAGES

Mucilages are generally found within the inner layer (endosperm) of grains, legumes, nuts and seeds. Examples of mucilaginous fibre supplements include
glucamannan and psyllium seed husk.

Hemicellulose, present in whole grains, fruit, vegetables, nuts, seeds and legumes, forms the matrix of the plant cell wall in which cellulose fibres are enmeshed. Besides helping to increase faecal weight and size, because it contains both insoluble and soluble properties, hemicellulose aids the reduction of cholesterol levels and binds bile acids.

GUMS

Gums are extracted from plants and trees and used commercially as emulsifiers, thickeners and stabilisers by the food industry. Examples of plant gums are gum arabic, guar gum, and locust bean gum.

PECTIN

Pectin, a soluble fibre present in the pulp of apples and the rind and skin of citrus fruit and vegetables, has a marked effect on lowering cholesterol in the blood. It has also been found to protect the body against heavy metals such as lead and cadmium, by chelating these anti-nutrients and removing them from the alimentary tract.

Table 1 - Non-starch polysaccharide (NSP) content of some common foods

FOODSTUFF
NSP (g/100g) SOLUBLE INSOLUBLE TOTAL
WHOLEMEAL BREAD
WHITE BREAD
SPAGHETTI(wholewheat)
SPAGHETTI
BROWN RICE
WHITE RICE
KIDNEY BEANS
BAKED BEANS
CABBAGE
CARROTS
RUNNER BEANS
POTATOES
PEANUTS
HAZELNUTS
APPLES
RAISINS
BANANAS 1.66
1.16
2.18
1.67
0.12
0.11
2.80
1.70
0.94
0.92
0.59
0.54
0.90
0.45
0.72
0.70
0.51
4.55
0.44
6.78
1.05
1.62
0.39
3.30
1.50
1.00
1.02
3.15
0.5
5.1
2.87
1.21
1.00
0.5 6.21
1.60
8.96
2.72
1.74
0.50
6.10
3.20
1.94
1.94
3.74
1.04
6.00
4.32
1.93
1.70
1.11

Source: Food Science, Nutrition & Health (sixth edition), Brian A Fox & Allan G Cameron, Edward Arnold, 1995.

 

Benefits of Fibre

TRANSIT TIME

The length of time it takes for food to travel through the system is greatly reduced in those eating a high fibre diet. The transit time for a person eating a typical British diet may average at 50-60 hours as compared to those eating a fibre-rich diet, whose passage of food through the alimentary tract may be as little as 12-18 hours. A prolonged transit time has shown to give rise to putrefaction which can result in the production of carcinogens. Colon cancer may have its origins in these toxins, which can also be absorbed into the bloodstream, potentially affecting overall health.

In most cases dietary fibre has a normalising effect on bowel emptying. It not only prevents symptoms such as constipation, but may counteract abnormally rapid transit times associated with loose, watery or unformed stools.

How long is your transit time?
To measure your transit time swallow 5-10 charcoal tablets, immediately following a bowel movement. Record the day and time of the tablet ingestion and continue to eat your normal diet. When the black, charcoal-looking material is eliminated, note down the number of hours that have elapsed. This will give you an accurate figure of how long food takes to pass through your alimentary canal. As an option to charcoal tablets you can use a few kernels of raw corn (swallowed whole) or cooked beetroot.

BLOOD SUGAR BALANCE

Although insoluble fibre aids the passage of food through the intestines, as mentioned previously, soluble fibre has a slowing action on gastric emptying. This results in food being released slowly into the blood stream, preventing blood sugar imbalances.

 

FAT METABOLISM

Soluble fibre, particularly mucilages and pectin, is capable of lowering cholesterol and triglyceride levels. It achieves this by binding with bile acids that emulsify fats in the gut, promoting their excretion. It also helps to inhibit the manufacture of fats in the liver.

WEIGHT CONTROL

In relation to weight control, fibre fills the stomach, reducing appetite. In addition, because fibre has a stabilising effect on blood sugar, this may prevent food cravings, especially for sugar and stimulants.

 

SHORT CHAIN FATTY ACID (SCFA) PRODUCTION

Although fibre cannot be broken down by digestive enzymes, it is partially degraded by the microflora in the gut. This natural fermentation process results in the manufacture of short-chain fatty acids – acetic, proprionic and butyric acids – which have many positive functions. Acetic and proprionic acids are transported to the liver where they are utilised for energy production. Butyric acid is required as a primary source of energy for rapidly growing intestinal cells. It also aids the adherence of “friendly” bacteria to gut epithelial cells. This discourages the proliferation of toxin producing bacteria and yeast. Butyrate is also likely to be a contributing factor to the anti-cancer activity of dietary fibre.

BOWEL FLORA

The manufacture of short chain fatty acids helps maintain a slightly acid pH level in the colon, which promotes the growth of acid-loving “friendly” bacteria such as lactobacillus. This discourages the production of toxin-producing bacteria and yeast such as Candida albicans.

FIBRE FACTS

The 1991 COMA report Dietary Reference Values for Food, Energy and Nutrients in the UK, recommends that the average intake of fibre should be 18g a day in adults, with an expected range of individual intakes from 12-24g depending on body size. However, the current British diet averages 11-13g of dietary fibre a day, whereas intakes of 25-40g are linked to a reduced risk of developing heart disease, diabetes, high blood pressure, colon cancer and other intestinal disorders. It should be noted that “primitive” societies consume approximately 40-60g (some cultures eat up to 150g) a day.

Fibre is best obtained by eating a varied whole food diet rich in both soluble and insoluble fibres including whole grains, cereals, fruit, vegetables, legumes, seeds and nuts. Adequate fluid intake (approximately two litres a day) is vital for fibre to effectively perform its tasks and should be drunk throughout the day, ideally in between meals. In those who normally consume a refined food diet, fibre intake should be increased gradually over a period of several months, to allow the digestive tract to adapt. Introducing large amounts of fibre too quickly can result in bloating, gas and abdominal cramps. The regular intake of processed fibre, such as wheat bran, is not advised due to the presence of phytic acid, which may interfere with the absorption of minerals such as calcium, iron and zinc. This type of fibre is best consumed in its unprocessed state e.g. wholemeal bread, however other types of supplementary fibre sources can be beneficial. For information on fibre supplements and their functions, see table 2 below.

 

FIBRE SUPPLEMENTS

Table 2 - Properties & Functions

Psyllium Husk
Stimulates the implantation and growth of gut microflora and has a greater bulking activity of all researched fibres. Aids cholesterol reduction and delays the absorption of simple carbohydrates, thereby curbing insulin release.

Oatbran
Contains beta-glucans which interferes with the absorption and production of cholesterol.

Rice Bran
Contains gamma-oryzanol which is present in the oil of the bran. This substance is an antioxidant and has been isolated for use in the treatment of menopause, elevated cholesterol and various gastro-intestinal complaints.

Apple Pectin
Slows gastric-emptying time, improves glucose tolerance, lowers plasma cholesterol levels and acts as a heavy metal chelator.

Linseed Fibre
Contains lignans which are degraded by gut flora into enterolactone and enterodiol, compounds which have been found to be protective against cancer, especially of the breast.

Beet Fibre
Besides decreasing total cholesterol and improving glucose tolerance, beet fibre has been found to enhance the absorption of iron and zinc.

Note: Some advanced intestinal conditions such as Crohn’s disease may be aggravated by high fibre diets. In these instances, a nutritional therapist or other health professional should be consulted.

 

REFERENCES

Müller-Lissner SA. Effect of wheat bran on weight of stool and gastro-intestinal transit time: a meta analysis. Br Med J 1988;296:615–17.
Jacobs DR Jr , Marquart L, Slavin J, Kushi LH. Whole grain intake and cancer: an expanded review and meta­analysis. Nutr Cancer 1998;30:85–96.
Earnest DL, Einspahr JG, Alberts DS. Protective role of wheat bran fibre: data from marker trials. Am J Med 1999;106(1A):32S–7S.
Fuchs CS, Giovannucci EL, Colditz GA, et al. Dietary fibre and the risk of colorectal cancer and adenoma in women. N Engl J Med 1999; 340:169–76.
Anderson JW; Ward K. High­carbohydrate, high fibre diets for insulin-treated men with diabetes mellitus. American Journal of Clinical Nutrition, 1979, 32:2312-21.

BIBLIOGRAPHY

Michael T Murray. Encyclopedia of Nutritional Supplements. Prima Health, 1996.

Betty Kamen. New Facts About Fibre. Nutrition Encounter, Inc, 1991.

Brian A Fox & Allan G Cameron, Edward Arnold. Food Science, Nutrition & Health (sixth edition), 1995.

Dr Earl Mindell. What You Should Know About Fiber and Digestion. Keats, 1997.

Shirley S. Lorenzani. Dietary Fiber. Keats, 1988.

www.healthnotes.com/Demos/ qr/Supp/Fiber-F.htm

 

 

 

 

 

 

 

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