A recent review, led by Dr Nuria Salazar from the Institute of Dairy Products of Asturias (Spain), belonging to the Spanish National Research Council, summarizes the up-to-date scientific evidence regarding the role of short-chain fatty acids (SCFAs) in host health and the impact of diet on their production.
SCFAs are the end products of fermentation of non-digestible carbohydrates (CHO) and proteins in the large intestine by the anaerobic intestinal microbiota. Acetate, propionate and butyrate represent 90-95% of the SCFAs present in the colon, whereas branched-chain SCFAs produced from dietary protein that is unabsorbed in the small intestine only represent 5% of total SCFAs production. Lactate is also produced by some members of the microbiota and is recycled into different SCFAs in order to avoid metabolic acidosis in the host.
SCFAs are produced by colonic microbiota through several metabolic pathways. Acetate is the most abundant one in the colon. It is noticeable that low levels of butyrate- and propionate-producing bacteria have been linked to inflammatory disorders, such as ulcerative colitis and asthma.
There is a high inter-individual gut microbiota variation, even among healthy individuals, both in organismal composition and in metabolic function. Diet impacts the gut microbiota composition and activity and, as a result, SCFA production may be affected. For instance, it has been found that high dietary fibre intake from fruit, vegetables, and legumes is linked to a rise in health-promoting SCFAs. Indeed, SCFA levels may be considered as a biomarker of a healthy status. Both epidemiological and intervention studies carried out with different populations have shown that dietary components have an impact on microbial composition and can modulate the synthesis of SCFAs. The profile of SCFAs synthesized and their presence in faecal content may one day help us to distinguish populations with diseases such as obesity and irritable bowel syndrome. Knowing the SCFA profile in a person might shed light on how bacteria contribute to gut microbiota dysbiosis, which perhaps could be modulated by appropriate probiotics.
SCFAs have several effects on human health. They play an important role in the maintenance of the gut barrier function by reducing luminal pH and inhibiting some pathogenic microorganisms. Besides this, during intestinal absorption, SCFAs (mainly butyrate) are used as a source of energy by colonocytes and bacterial communities. SCFAs have also been reported to protect against the development of colorectal cancer and to control intestinal inflammation. Butyrate and propionate serve a number of epigenetic functions such as balancing histone acetylation and deacetylation activity, which can explain in part their biological effects. In addition, a new field of research shows that SCFAs may have a critical role in appetite regulation and energy homeostasis.
In conclusion, although it can be hypothesized that high levels of SCFAs are beneficial for host health, their role in the interplay between diet, gut, microbiota, and host energy metabolism is likely more complex. Further studies are needed in order to elucidate the role of SCFAs in mammalian energy metabolism and develop personalized strategies to mitigate disease risk through modulating SCFA production.
Ríos-Covián D, Ruas-Madiedo P, Margolles A, Gueimonde M, de los Reyes-Gavilán CG, Salazar N. Intestinal short-chain fatty acids and their link with diet and human health. Front Microbiol. 2016. doi:10.3389/fmicb.2016.00185.
De Filippis F, Pellegrini N, Vannini L, et al. High-level adherence to a Mediterranean diet beneficially impacts the gut microbiota and associated metabolome. Gut. 2015. doi:10.1136/gutjnl-2015-309957.