Dietary Fibre Q & A
Fibre, in a nutshell (pardon the pun), is generally any plant material that the body cannot digest and use. Although our gastrointestinal secretions and enzymes cannot break down the fibre, given the right colonic microflora (bacteria, yeasts), our body can still derive some nutritive benefit from it. For example, some bacteria are able to break down soluble fibres to produce short chain fatty acids, which the colonocytes (cells lining the large colon) are able to use. Vitamin K is another by-product of colonic bacteria activity.
How much fibre do I need in my diet?
Fibre requirements vary according to age and gender. Women who are pregnant or lactating generally require more fibre in their diet. Here are the recommended daily adult Adequate Intake (AI) quantities (grams of fibre/day), according to Health Canada’s Dietary Reference Intakes1.
| Age |
19-50 |
>50 |
| Women |
25g | 21g |
| Men | 38g | 30g |
Am I getting enough fibre in my diet?
There are a number of ways to see how much fibre is in your current diet. You could keep a detailed food diary for about a week, and then look up fibre values of the common foods you consume to see if you are on target. If you eat foods that are not easy to analyze, then contact a registered dietitian who can help you out. You can find fibre values online at the Canadian Nutrient File, or in a more easily searched format, at the USDA Nutrient Data Laboratory. Product labels are a great information source.
What are the different types of fibre?
Fibre, the structural material of plants, is made mostly of non-starch polysaccharides, which our small intestines cannot digest, and some non-polysaccharides, which are non-starches, non-sugars, and non-carbohydrates such as lignins, cutins, and tannins. Now, we divide all these fibres into soluble and insoluble fibres. Soluble means that the fibre can dissolve in water and form a gel. There are three sub-divisions of soluble fibres: gums, mucilages, and pectins. Some hemicelluloses fall within this category as well. Insoluble fibres include cellulose, most hemicelluloses, and lignins. Most plants contain a mix of the two fibre types, although some have higher concentrations of one or the other.
How do I increase the amount of fibre in my diet?
You should not rush incorporating fibre into your diet because you need to give your system time to adjust. Look at fibre as giving your digestive system a workout. As with lifting weights, you should start slowly and with a small amount. Increase fibre amounts in your diet slowly, by making one change at a time. For example, switch to whole grain bread and then after 1 to 2 weeks of gastrointestinal tolerance, increase fruit intake, or choose another strategy to boost fibre intake gradually, such as switching to brown rice.
To optimize the gut-modulating properties of fibre, adequate fluid intake is very important. Imagine having a very high fibre intake and no water to help move it along – the good intentioned fibre will turn to a substance akin to cement. (Well, not really, but it might feel like that going through!) Make sure, if you drink coffee, alcohol, or both, that you increase fluid intake further to counteract the diuretic (water losing) effects of caffeine and alcohol. It may even take as much as a few months to get to the fibre intake quantity that is right for you.
Try these dietary changes:
- Eat at least 5 servings of whole fruits and vegetables per day
- Try a high fibre cereal for breakfast
- Buy high fibre breads, brown rice, and whole wheat pasta
- Incorporate more lentils and beans into diet
- Choose higher fibre foods for meals and snacks
- Add dried fruits, nuts, and seeds to your diet2
Which is better, fibre from foods or fibre supplements?
Can you skip all this diet revamping and go straight to a commercial fibre product? Maybe, but that could take a little work too. Commercial fibre products are expensive and there is insufficient research confirming their specific effectiveness. If your current diet is low in fibre, say only 5 grams/day, and you are a 45 year-old male, then you would need an additional 33 grams of fibre according to Health Canada’s Dietary Reference Intakes (the ultimate authority on recommending nutrient intakes). Since the amount of fibre derived from most commercial fibre products is moderate, even at maximum dosages, obtaining fibre from food sources might be easier.
What about high-fibre cereals and bars?
There are foods advertised as being high in fibre. For example, Kellogg’s All-Bran Guardian® is a new cereal that has 6 grams/cup total fibre, more than half of which is psyllium fibre. Another product is ReBar Seeds’n Greens® energy bar in a plum-pomegranate flavour. This bar boasts 10 grams of fibre per 50 gram bar. The popular All-Bran® cereal has 12 grams of fibre per ½ cup! Sprinkling a good amount of All-Bran®, or Bran-Buds® on your regular cold or hot cereal can really boost your daily fibre intake. Reading labels is the key. I am constantly surprised at the amount of fibre in some products, and the lack thereof in others.
What are some high and low fibre foods? How can I tell the difference?
Health Canada considers a food product to be a ‘high source of fibre’ if it contains 4-6 grams of fibre per serving, and a ‘very high source of fibre’ if it contains more than 6 grams of fibre per serving. The best way to tell is by reading the labels on those products that contain them, because you can’t always judge fibre content from looking at a food. A good example of this is celery, an apparently fibrous food, which only contains 1.5 grams of fibre per one medium stalk serving. For a definitive reference, consult a fibre value chart.
It is a good idea to choose higher fibre foods over lower fibre foods, even if the difference does not seem to be that great. Changing from white rice (0.4 grams of fibre/125 mg serving) to brown rice (1.5 grams of fibre/125 mg serving) might not seem like a big increase, but making a number of higher fibre choices, such as this one, throughout the day does pay off.
Can fibre help my digestive disorder?
Because the effects of the types of fibre used in controlled experiments may differ from the effects that the same fibre has in its natural state (for example in a whole food), the study of dietary fibre can be problematic. Foods may often contain more than one type of fibre and different proportions of each. To complicate matters even further, many foods high in dietary fibre may also contain other nutrients. For example, a high fibre diet may also be high in vitamin A and carbohydrates. It might be difficult to separate the effects of these nutrients on your digestive condition from the effect of the dietary fibre or a combination of the two. Another challenge in the study of dietary fibre is that the method in which the food is prepared may alter the effects of the fibre. For these reasons, published studies often show inconclusive or contradictory results.
We do know that fibre is part of a healthy diet, and there is evidence that changes in the amount and type of dietary fibre may have a beneficial effect for some bowel disorders (constipation, hemorrhoids, diverticular disease, and irritable bowel syndrome). If you suffer from a digestive disease, consult your health professional for specific advice regarding fibre.3
Are there any side effects or adverse reactions to consuming more fibre?
Increasing your fibre intake – either using dietary modifiers or fibre supplements – can sometimes result in unwanted digestive effects. Bloating, cramping, and increased intestinal gas are the most common side effects, mostly due to the methane, carbon dioxide, and hydrogen gases produced as by-products when bacteria in the colon metabolize the undigested fibre. These effects may lessen over time, and commercial products such as Beano® may help patients deal with gas symptoms. If adequate fluid intake does not accompany a high fibre diet, constipation may occur. Again, remember to add fibre gradually, introducing one change at a time and drinking plenty of water along the way.
Sources of Fibre and their Effects on your Body4
Soluble Fibres
|
Major Food Sources
|
Actions In The Body
|
| Gums (gum Arabic) Mucilages (guar, carrageenan) Pectins (veggies, fruits)Some Hemicelluloses |
Fruits (especially apples and citrus types), oats, barley, legumes, and psyllium |
delay GI transit; good for diarrhea delay glucose absorptionlower blood cholesteroldecrease serum total cholesterol |
Insoluble Fibres
|
Major Food Sources
|
Actions In The Body
|
| Cellulose (primary material of plant cell walls)
Many Hemicelluloses (cereal fibres) |
In woody parts of vegetables, small seeds (strawberries), wheat bran, corn bran, whole grain breads and cereals, vegetables (cabbage, carrots, Brussels sprouts), and legumes |
accelerate GI transit; good for constipation increase fecal weight; good for bowel movementsslow starch hydrolysis and delay glucose absorption |