Definition and Metabolic Fate
Short-chain fatty acids have an aliphatic tail in which there are fewer than six carbon atoms; they are also called SCFA, an acronym for Short Chain Fatty Acids.
Fatty acids, fundamental components of lipids, are molecules made up of a chain of carbon atoms, called aliphatic chain, with a single carboxylic group (-COOH) at one end. The aliphatic chain that constitutes them tends to be linear and only in rare cases occurs in a branched or cyclic form. The length of this chain is extremely important, as it influences the physico-chemical characteristics of the fatty acid: as it elongates, the solubility in water decreases and consequently the melting point increases.
Short-chain fatty acids, as well as MCTs, are absorbed as such in the intestine and conveyed directly to the liver via the portal vein (they are in fact soluble in water); those with a long chain, on the other hand, are incorporated in lipoprotein particles in the form of triglycerides, together with fat-soluble vitamins and cholesterol; these particles, called chylomicrons, do not enter the bloodstream directly but are absorbed by the lymphatic capillaries and only later reach the saguinous circle at the level of the subclavian veins.
Short-chain fatty acids: acetic acid, propionic acid, isobutyric acid, butyric acid, isovaleric acid, valeric acid, caproic acid, lactic acid and succinic acid.
Food Sources and Benefits for the Body and the Intestine
Dietary sources of short-chain fatty acids are quite limited; they are mainly produced during the fermentation of fibers (carbohydrates not digested in the small intestine, in particular of resistant starch and pectin), operated by the bacteria that inhabit the colon. This fermentation leads to the synthesis of acetate, butyrate, propionate, hydrogen and anhydride carbon dioxide; other SCFAs are produced in lower quantities. Butyrate, in particular, represents - together with glutamine - the major energy source for colonocytes (colon cells), so much so that its deficiency causes mucosal atrophy. , could have positive effects in the prevention of colon cancer (in vitro, it has shown the ability to inhibit the proliferation of cancer cells but also to stimulate their differentiation). What is certain is that a diet rich in fiber has proved particularly useful to prevent various types of cancer, particularly of the colon and breast. This is at least in part due to the fact that - r representing the substrate for the synthesis of short-chain fatty acids - the fiber stimulates the proliferation of symbiont bacterial flora to the detriment of pathogenic bacteria and their toxic metabolites (acidifies the intestinal environment by inhibiting, among other things, also bacterial species such as putrefactive proteolytic action); Furthermore, the anti-inflammatory role of short-chain fatty acids should not be underestimated.
Propionate and acetate are easily absorbed by the colonic mucosa and enter the bloodstream where they are captured by the liver (propionate) and used as an auxiliary energy source by the muscles (acetate). It is estimated that the caloric contribution of these fatty acids to cover the needs energy is approximately 10%; this extremely variable share depends above all on the composition of the diet and the enteric microbial flora, as well as on the intestinal transit times.
For what has been said so far, short-chain fatty acids enjoy interesting therapeutic perspectives in the treatment of various chronic diseases of the intestine, such as diarrhea, ulcerative colitis and Crohn's disease.
