One of the ways in which gut bacteria can influence health is through the metabolites they produce. For instance, gut bacteria ferment insoluble fibre, complex structures the human body is unable to digest, such as FOS or inulin. During the breakdown process, short-chain fatty acids (SCFAs) are released.
The types of SCFA that predominate are acetate, propionate and butyrate. SCFAs contribute to a healthy colon and are important enablers of the proper functioning of the immune system and the intestinal barrier. Butyrate, in particular, has been frequently associated with gut health and related conditions such as ulcerative colitis. Butyrate is the main energy source for colonocytes (epithelial cells in the colonic mucosa) and is therefore associated with the preservation of the intestinal epithelium.
SCFAs play key role in preventing chronic inflammatory bowel disease
Differences in the composition of the microbiota between healthy and unhealthy individuals indicate SCFAs may have an important role in maintaining gut health. In people with chronic inflammatory bowel disease (Crohn’s disease or ulcerative colitis), for instance, the microbiota is known to contain lower numbers of Faecalibacterium prausnitzii. This bacterium is known for its butyrate-synthesizing capacity and anti-inflammatory properties. Although not all of the mechanisms have been fully explained, there is an increasing amount of evidence from medical studies about the specific role of SCFAs in preventing and treating disease (AAD, IBD, IBS and certain types of cancer).
Health effects of SCFAs:
- SCFAs cover between 10 and 15 percent of daily caloric requirement.
- Both propionate and butyrate possess anti-inflammatory properties, which is important in conditions such as allergies.
- Butyrate affects satiety.
- SCFAs strengthen the intestinal barrier function.
- SCFAs protect against (mucosal) oxidative stress.
- There is a strong link between butyrate and obesity-associated metabolic disease, possibly due to its involvement in lipid and glucose metabolism.
- There is a correlation between faecal SFCA concentration and IBD.
One of the ways to promote SCFA synthesis is to use prebiotics, which can boost the numbers of butyrate-synthesizing bacteria. Prebiotics are indigestible dietary fibres that boost the growth and activity of specific bacteria, thereby promoting health. In addition, the use of probiotic bacteria can induce an increase in butyrate synthesis. All SCFAs possess their own physiological health effect based on different mechanisms. See the bullet list on the left for a number of examples.
The importance of dietary fibre in allergies
De Filippo et al (2010) compared the faecal microbiota of European children with those of a cohort of African children living in rural areas. Significant differences in the composition of gut microbiota were seen. The SCFAs in stool samples were also different. African children had significantly more SCFAs than European children. That means they not only have different gut bacteria but that the activity of these bacteria is different as well. The higher level of SCFA synthesis is probably due to the fibre-rich diet African children eat. It has even been suggested that this difference in fibre intake may be a key contributor to the virtual non-existence of allergies and asthma in certain rural African communities (Maslowski & Mackay, 2011).
