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Volatile fatty acids (VFA) are substances typically formed in the intestines when food is digested. Usually made up of a chain of carbon molecules, they can form as a result of oxidation and are sometimes found in landfills and groundwater. The molecular chains are also called short chain fatty acids. Common varieties include acetic acid as well as proprionate and butyrate. These compounds are typically absorbed by the inner lining of the intestine and pass into the blood stream before passing through the liver.
Often produced in a process of extracting energy, called fermentation, in the intestine, volatile fatty acids typically provide much of an organism’s strength. They can be passed through the lining, or epithelium, of the intestine, where structures called papillae normally absorb nutrients such as electrolytes and lactic acid. The fatty acids can then pass into a network of blood vessels before entering the portal vein which leads to the liver. Typically removed from the intestinal tract on a continual basis, volatile fatty acids must be regulated so fluids do not become too acidic.
Acetic acid is one type of VFA that the body often uses for building energy as well as creating lipids. It is not used much by the liver, but proprionic acid is generally removed from the blood by the organ. The body normally uses this substance to make glucose, which is a sugar needed for energy and various biological processes. Another one of the volatile fatty acids is butyric acid, which is metabolized in the intestinal lining into beta-hydroxybutyric acid. Many tissues in the body often use this acid to produce energy.
While butyric acid is chemically changed as it is absorbed, acetate and proprionate can pass into the blood as they are, so the metabolic processes can vary depending on the substance. Bacteria often produce volatile fatty acids in the intestines, but they can also do so outside the body and even when they digest cellulose. This process usually occurs in animals that eat plants and the VFAs can usually be found in the milk produced as well. Volatile organic acids often form in nature through oxidation and are typically found in low concentrations.
Detection of most VFAs at the low levels seen in the environment is usually difficult with scientific instruments. They can build up in landfills. Even in water under the ground, metabolism can occur with lactic acid, for example, as it is converted into pyruvic acid which often turns into an acetic compound.