In this article I aim to provide a general overview of fibre, its benefits and the best sources to include in your diet.
What is Fibre?
We’ve all heard of fibre and most of us know that it’s good for us. But what actually is it?
Dietary fibre is comprised of a wide variety of compounds and complex carbohydrates that cannot be digested in the small intestine by human enzymes so they end up intact in the large intestine.
Simply put: fibre is the part of certain carbohydrates (typically fruit, vegetables, legumes & whole grains) that cannot be broken down by digestive enzymes and therefore moves through a majority of the digestive tract unchanged.
There are many different types of fibres including lignins, cellulose, pectins, inulins, gums and resistant starches – to name just a few.
How is Fibre Classified?
Fibre is classified in a few different ways, according to different properties. These include:
Dietary Fibre: Fibre that is found naturally in foods.
Functional Fibre: Fibre that has been isolated & extracted from whole foods and shown to have beneficial physiological effects in humans. It is either added to processed foods or used as individual supplements.
Soluble Fibre: Fibre that forms a gel-like substance by mixing well with water in the digestive tract.
Insoluble Fibre: Fibre that acts like a ‘bulking agent’ and does not mix well with water in the digestive tract.
Fermentable Fibre: Fibre that can be readily digested (fermented) and used as fuel by the naturally-occurring bacteria in our large intestine.
Non-fermentable Fibre: Fibres that are resistant to bacterial fermentation, such as cellulose & wheat bran.
Viscous Fibre: Fibres that are similar to soluble fibre in that they form a thick gel thereby delaying the emptying of the stomach & prolonging the feeling of fullness.
Non-Viscous Fibre: Fibres that cannot form a gel-like substance in water.
What are the Benefits of Fibre?
Some of the benefits of fibre include:
As previously indicated, certain fibres can be fermented into short chain fatty acids such as butyrate, propionate & acetate. These provide beneficial bacteria in the digestive tract with the necessary fuel for functioning. Although an animal study, it has also been shown that bacteria that don’t receive enough fibre feed off the gut lining thereby ultimately compromising the integrity of the gut.
Following on from the above, fibre helps to soften the stool as well as add bulk to it. This then helps to alleviate constipation by shortening the time taken to move through the large intestine whilst also increasing the mass of the stool. Sufficient fluid is also a key ingredient in preventing & treating constipation.
Blood Sugar Control & Insulin Management
When added to a meal that contains carbohydrates, fibre, particularly viscous fibre, creates a lower and more sustained rise in blood sugar levels thereby significantly lowering the need for insulin.
And then, from a Disease Prevention perspective:
The European Prospective Investigation Into Cancer & Nutrition (the EPIC project), the largest prospective study on diet & cancer (with 52 000 male & female participants at time of reporting the findings), established a protective effect of dietary fibre and protection against colon cancer development. It’s important to note that there is plenty of discrepancy in the literature regarding the protective effect of fibre and colon cancer. Reasons for this include inadequate quantities of fibre used in research, timing of intervention, other ‘confounding’ factors and different methods of assessment in different studies.
When it comes to breast cancer, a recent systematic review established that the inclusion of dietary fibre “is significantly associated with a reduced risk of breast cancer.”
Numerous studies have consistently established that there is an association between a high fibre intake and a reduced risk of heart disease.
Type 2 Diabetes
The risk for developing type 2 diabetes is multifactorial and includes aspects such as obesity, low physical activity, genetics and a high-refined carbohydrate diet that’s low in fibre. It’s clear that low fibre is not the only cause for concern when it comes to an increased risk in developing type 2 diabetes. However, observational studies and intervention trials indicate that diets high in fibre are associated with significant reductions in the development of type 2 diabetes, especially in these high-risk individuals.
Digestive fibre is thought to have a beneficial effect on weight by resulting in a reduction in energy intake through increasing satiety and therefore decreasing subjective appetite – with certain types of fibre potentially having greater benefit than others. Even though research remains somewhat unclear as to whether this comes down to the fibre alone, common sense and anecdotal experience indicates that replacing a processed, fibre-free meal with a nutrient-dense, high-fibre meal does often assist in weight loss.
Are there any adverse effects of Fibre?
Some people do experience digestive issues such as bloating, gas & abdominal cramping or pain with the introduction of fibre. This is however often linked to a too rapid increase in fibre or as a result of an already compromised digestive tract. It is always advisable to increase fibre intake gradually and to do this concurrently with an increase in fluid intake such as water.
Where do we find Fibre?
The best sources of fibre include legumes (such as beans, split peas, lentils & chickpeas) vegetables (such as avocado, artichokes & spinach), fruit (such as berries, apples & pears) whole grains (such as quinoa, rice, & amaranth) and nuts & seeds (such as chia seeds, almonds & cashews). As we’ve already highlighted, these different foods contain different fibres so by including a wide variety of these types of food will assist in getting in a wide variety of different types of fibres.
How much Fibre do we need?
UK Government Guidelines revised in 2015 recommend an intake of 30g of fibre/day, however higher levels are more likely to be optimal.
- Fibre is the part of certain carbohydrates (typically fruit, vegetables & whole grains) that cannot be broken down and therefore moves through a majority of the digestive tract unchanged.
- Fibre is classified many different ways.
- Fibre has many beneficial outcomes for health.
- The minimum amount of fibre to be consumed/day is 30g according to government guidelines.
- If fibre intake is low, then it needs to be increased gradually otherwise a too rapid increase may result in unpleasant digestive symptoms.
- Individuals with an already compromised digestive tract may find that fibre exacerbates symptoms – in these instances, one-to-one support is recommended.
This article was written by my colleague, Lara Rickard, who is a Registered Dietitian specialising in female hormone health.
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