Dietary Fibre
Lifestyle Preventative Health and Medications > Dietary Fibre
What is dietary fibre?
Dietary fibre is commonly found in plants. Fibre is not broken down by the digestive tract and it passes through undigested. The main sources of dietary fibre are fruits, vegetables, legumes, whole grains, nuts and seeds. Dietary fibre is an important component of a healthy, well-balanced diet.
What is the daily dietary requirement for fibre?
The daily recommended dietary intake (RDI) for fibre is 25g/day for women and 30g/day for men.
What are the different types of dietary fibre and where can I find them?
Dietary fibre can be classified as soluble and insoluble fibre, which can be fermentable or non-fermentable.
- Soluble fibre is soluble in water; therefore, it forms a gel which moves through the stomach and small intestine, slowing digestion. Examples include beta-glucan from oats, barley and rye; pectin from fruits (e.g. apple, berries), vegetables, and legumes (e.g. beans and lentils); inulin/oligofructose from vegetables such as onion, chicory root and legumes; and guar gum from seeds and seaweed.
- Insoluble fibre acts like a sponge which absorbs water in the stomach, increasing bulk of stool and intestinal transit time. Sources of insoluble fibre include wholemeal bread, brown rice, nuts, and vegetables such as cauliflower, carrots, potatoes (with skin) and beans.
- Fermentable fibre is readily fermented by the bacteria living in our colon. This produces acids that create a favourable environment for the growth of health-promoting bacteria (i.e. bifidobacteria, lactobacilli). It is mainly found in yam, onion, oats, garlic, unripened banana, leek, asparagus, wheat, chicory root, and Jerusalem artichoke.
- Non-fermentable fibres are resistant to bacterial fermentation in the colon and work by adding bulk to stool. Examples include cereal fibre (e.g. wheat bran), whole grains (e.g. brown rice), fruits’ skin, celery, nuts and seeds.
Why is it important to have adequate dietary fibre in the diet?
Research has proven the many health benefits of dietary fibre.
- Maintains a healthy body weight
Foods high in dietary fibre induces early satiety (the sense of fullness after a meal) and delays gastric emptying (transit of food through the intestines), helping one to feel fuller for a longer period of time. Thus, a diet rich in dietary fibre aids weight management and prevents obesity. - Improves blood sugar control in Diabetes Mellitus
As soluble dietary fibre slows down the absorption of food in our body, it also reduces the rate at which sugar from carbohydrate-containing foods is released into the blood, preventing sudden spikes in blood sugar levels after a meal. - Lowers blood cholesterol
Bile acids are synthesized in the liver and are responsible for the digestion of lipids and fat-soluble vitamins. Soluble dietary fibre binds to and removes bile acids from your body, which reduces re-circulating amounts of bile acids. The liver then uses more cholesterol to produce more bile acids. This lowers the amount of cholesterol in the body available to make low-density lipoprotein (LDL) cholesterol. As LDL cholesterol, also termed ‘bad’ cholesterol, increases the risk of blood vessel blockage, its reduction results in a significantly lower risk for cardiovascular diseases and stroke. - Maintains bowel health
Insoluble dietary fibre adds bulk to stool, hastening its passage through the intestines, promoting regular bowel movement and reduces the risk of constipation. There is also evidence to suggest that dietary fibre from fruits, vegetables and whole grains may offer protection against diverticular disease and colorectal cancer.
Is a high fibre diet for everyone? Are there certain medical conditions in which a high fibre diet should be avoided?
The general healthy population should aim to meet the daily RDI for fibre to reap its health benefits. However, there are certain patient populations who will require a low fibre or low residue diet.
A low residue diet is often prescribed a day before bowel preparation protocols such as colonoscopies, colonography or gynaecological surgery. The intent is to cleanse and empty the colon of its contents to improve visibility and the handling of the colon during endoscopy or surgery.
In patients with gastric intestinal diseases such as Crohn’s disease, ulcerative colitis, diverticulitis, pre/post abdominal surgery and gastrointestinal inflammatory disorders, a low fibre diet may help to reduce discomfort from symptoms by minimizing the frequency and volume of stools. When symptoms are resolved, patients may gradually increase fibre intake to meet the RDI
Lastly, a low fibre diet may also be beneficial in individuals with conditions an increased risk of bowel obstruction, by decreasing the risk of intestinal blockage by reducing faecal bulk. Consult a dietitian to determine if you require a low fibre diet as it may be restrictive.
Is there a difference between a low fibre diet and a low residue diet?
A low fibre diet is defined as 10-15g of fibre a day. There is currently no clear definition of a low residue diet as it is impossible to estimate the amount of residue (i.e. indigestible material) derived from digestion, but it should not exceed 10g of fibre a day.
How will I know if a packaged product that I buy contains fibre?
To determine if a food product contains fibre, look at its Nutrition Information Panel. If a product contains fibre, there will be a figure listed under “Dietary fibre” or “Fibre”, occasionally found under “Carbohydrates”.
For fibre supplements, keywords to look out for in the ingredients list on the food label are wheat bran, cellulose, lignin, wheat dextrin, inulin, guar gum, acacia gum, beta-glucan, psyllium, or pectin.