Sources and Functions of Short-Chain Fatty Acids

When we talk about intestinal bacteria or dietary fiber, we often hear about "short-chain fatty acids". So what exactly are short-chain fatty acids? Based on the number of carbon atoms in the carbon chain, fatty acids with less than 6 carbon atoms are commonly referred to as short-chain fatty acids (SCFAs), those with 6 to 12 carbon atoms are called medium-chain fatty acids, and those with 12 or more carbon atoms are long-chain fatty acids. Long-chain and medium-chain fatty acids are usually derived from dietary triglycerides of some animal fats and vegetable oils, while SCFAs are the main metabolites produced by specific colonic anaerobic bacteria after fermentation of dietary fiber and resistant starch, including acetic acid, propionic acid, butyric acid, valeric acid and capric acid. Among them, acetic acid, propionic acid, butyric acid and lactic acid (isovaleric acid) are the most common SCFAs, which are also known as volatile fatty acids due to their small molecular weight, low boiling point and volatility at room temperature.

Sources of SCFAs

The main site of SCFAs production in humans is the colon, and the highest concentration is in the proximal colon. SCFAs mainly originate from the fermentation of fibers and indigestible sugars (indigestible polysaccharides and resistant starch) in the intestine by anaerobic bacteria in the colon. Isobutyric acid and isovaleric acid are also produced during the catabolism of the branched-chain amino acids valine, leucine and isoleucine. In addition, intermediate products of microbial fermentation such as lactic acid or ethanol can also be metabolized into SCFAs. in addition to intestinal fermentation, cellular metabolism, especially fatty acid oxidation, can also produce SCFAs. The total amount of acetic acid, propionic acid and butyric acid in the normal colon of the organism accounts for about 90%-95% of SCFAs, and the molar ratio of the three is 60:20:20. This ratio changes when the health status and nutritional level of the organism changes.

Both Bacteroidetes and Firmicutes, the dominant phylum of SCFAs-producing bacteria in the intestine, can produce butyric acid, accounting for about 20% and 60% of the total intestinal flora, respectively. In contrast, Proteobacteria and Actinobacteria produced relatively small amounts of SCFAs, 5% to 10% and 3%, respectively. Veillonellaceae can convert lactic acid to propionic acid, and sulfate-reducing bacteria can use lactic acid to produce acetic acid and hydrogen sulfide. The phylum Bacteroides can convert succinic acid to propionic acid, and its population density is proportional to the propionic acid concentration in the intestine.

Physiological functions of SCFAs

SCFA has a variety of important biological functions in living organisms:

1. Provide energy: SCFA can provide energy for colon cells, mucosal epithelial cells and muscles, etc. Among them, glucose produced by propionic acid in the process of gluconeogenesis can meet 30%-50% of the energy demand of animals, butyric acid can provide energy for the organism because it is converted into?-hydroxybutyric acid, and acetic acid, propionic acid and butyric acid can be used as important energy sources for intestinal mucosal epithelial cells after they are absorbed.
2. Maintain water-electrolyte balance
3. Improve intestinal blood circulation
4. Stimulate the secretion of gastrointestinal hormones (such as gastrin)
5. Regulation of gene expression

Creative Proteomics offers a one-stop service for the quantification of SCFAs, including SCFAs of C2-C12 carbon chain length in various biological samples (feces, serum, etc.). Our method is unique in its ultra-high sensitivity, allowing precise quantification of trace amounts of SCFAs in 0.1 g of feces and 50 µl of serum, eliminating contamination by exogenous SCFAs through rigorous experimental procedures, and allowing high-throughput analysis of valuable medical samples for medical research on the intestinal flora.

Creative Proteomics has gradually grown into an integrated service provider with targeted lipidomics and untargeted lipidomics analysis services for researchers in pharmaceutical, biotechnology, agriculture, and nutrition industries.