Everything You Should Know About Fibre

But what really is fibre?  

Basically, fibre consists of the indigestible portions of plants, and it includes multiple categories – gums, waxes, pectins, mucilage, cellulose, hemi-cellulose, lignins, and oligosaccharides. Because fibre is not digestible, it is also not absorbed. As fibre passes through the digestive tract, it reaches the large intestine where it undergoes fermentation, which is what allows it to provide all sorts of beneficial byproducts – referred to these days as postbiotics. 

There are two main types of fibre – soluble and insoluble fibre.

Insoluble fibre includes cellulose, hemi-cellulose, and lignins – they don’t dissolve in water. Examples of soluble fibre include gums, pectins, and mucilage, which combine with water and become gummy.¹ Because soluble fibres are more fermentable, they can provide more beneficial byproducts, while insoluble fibres are great bulking agents that improve the mechanics of elimination and help prevent constipation. 

Health benefits of fibre include: 

• Increased fecal bulk 
• Decreased transit time 

• Support for healthy blood sugar by slowing its absorption into the bloodstream 
• Decreased cholesterol by decreasing its absorption and enhancing its elimination 
• Trapping toxic substances and eliminating them from the body 
• What is emerging to be one of its most important functions – dietary fibre interacts positively with the gut flora 

Fibre as a prebiotic 

The interaction between dietary fibre and the intestinal microbiota (bugs in the gut) significantly impacts many metabolic processes of the body. And this is something my mother didn’t know about fibre – scientists didn’t even know this in the 60s – which really places my mom ahead of her time. When discussing fibre in this context it is often referred to as a prebiotic – the food that feeds the good bugs or supports the probiotic. 

But how does all this work?  

We know some of the answers, while other answers are still being discovered. The bacteria in the large intestine ferments the fibre, resulting in the formation of health-promoting substances like short-chain fatty acids (SCFAs) – the most well-known one being butyric acid (or butyrate). 

SCFAs protect the mucus membranes in the GI tract, while prolonged lack of fibre damages these protective mucus membranes. Butyrate provides the main energy source for the cells of the large intestine, helping keep them healthy. 

SCFAs also enter the circulation where they act as signaling molecules that benefit immunity and metabolism. In the case of a low-fibre diet, metabolism does not favor production of beneficial SCFAs, but instead results in less favorable metabolites that can be pro-inflammatory and carcinogenic. 

Diets high in fibre (or what is sometimes referred to as microbiota-accessible carbohydrates or MACs) contribute to more microbial diversity in the gut – more different types of bugs – which is a good thing. 

On the flipside, diets high in sugar and fat and low in fibre result in less microbial diversity, which in turn is associated with inflammation and chronic conditions such as inflammatory bowel disease, autoimmune diseases, colorectal cancer, allergies, and obesity.²  Regarding obesity, several human studies point to low-fibre intake resulting in low microbial diversity, which  in turn contributes to increased risk for weight gain. 

How diverse is your microbiota?  

Microbiome Testing can give you insights into this, email techsupport@fxmed.co.nz to find out which test is the best option for your goals. 

Low-fibre diets have long-term effects 

In a mouse study, the effect of a long-term, low-MAC diet led to significant decreases in microbial diversity over three generations that could not be reversed by adding MACs.³ It appears that eliminating fibre for short periods has no long-term effects on the microbiome. On the other hand, long-term elimination, which occurs with chronic consumption of a Western diet high in fat and sugar and low in fibre, can literally cause extinction of some beneficial bacterial strains. 

What are the best dietary sources of fibre? 

Vegetables, fruits, legumes, whole grains, nuts, and seeds are good fibre sources. Whole grains, vegetables, and some fruits are good sources of insoluble fibre, while soluble fibre is found in beans, peas, lentils, apples, and oats. Fibre doesn’t have to be harsh on a sensitive gut. For example, one avocado has 9g of fibre. Here are some fibre amounts in other common foods:⁴ 

• 1 cup cooked black beans – 17g 

• 1 cup cooked lentils – 16g 
• 1 cup cooked garbanzo or pinto beans – 11g 
• 2 tablespoons chia seeds – 10g 
• 1 cup guava – 9g
• 1 cup collard greens – 8g 

• 1 cup raspberries – 8g 
• 1 cup butternut squash – 7g 
• 1 cup blackberries – 7g 
• ¼ cup almonds – 7g 
• 1 medium-sized pear – 6g 

• 1 cup oatmeal – 5g
• 1 cup barley – 5g

How much fibre is enough? 

The jury is still out on this one. Current recommendations from the NZ Nutrition Foundation are 25-30g daily – many New Zealanders are not adequately meeting these requirements. Even amounts of 30g daily might not be enough to significantly impact biomarkers associated with disease risk. Some studies indicate that 50g or more daily might be necessary to make a significant health difference.² 

This amount might not be easily achieved with diet alone, suggesting additional supplemental fibre might be indicated or a protein-multivitamin-metabolic formula with 10g of fibre per serving. If you have not been eating a lot of fibre but wish to increase your intake, then it’s recommended that you do so gradually, particularly if you have a GI condition such as IBS. 

The takeaway 

To ensure you’re getting the fibre you need to support your gut health, supplementation may be helpful. If you’re interested in learning more about fibre containing products, login to the Practitioner Hub to view available datasheets.