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The Right Chemistry: The many uses of butyric acid

Versatile chemical can be wielded as a stink bomb and might be helpful against irritable bowel syndrome.

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To put it mildly, butyric acid has a most unpleasant smell. Less mildly, it stinks! That’s why Sea Shepherd, a marine conservation society, used the foul-smelling liquid in its confrontations with Japanese vessels engaged in illegal whaling. For five years, from 2005 to 2010, butyric acid stink bombs were hurled from Sea Shepherd ships onto the deck of whaling ships to interfere with the crews’ activities. The practice stopped after accounts in the Japanese media claimed that some sailors were burned by the acid, which is actually not likely, because butyric acid is actually a weak acid. It may be a weak acid, but it sure has a strong smell! And if you have ever smelled, umm … vomit, you have encountered butyric acid.

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Fibre, the parts of plants or seeds that we cannot digest, is a tasty treat for the bacteria that inhabit our gut. When these microbes dine on some types of fibre they release butyric acid as a waste product. The acid announces its presence emphatically in the aroma of vomit. It also happens to be the aroma of rancid butter.

Milk contains a variety of fats: “triglycerides,” in chemical terms. These are molecules consisting of a backbone of glycerol to which fatty acids, butyric acid being one, are attached. Milk also contains lipoprotein lipase, an enzyme that can detach the fatty acids from glycerol. Agitation, such as the churning of butter, can bring the lipase into contact with the milk fat, resulting in the release of fatty acids. Rancidity is the result of the buildup of these fatty acids, with butyric acid making a major contribution to the unpleasant fragrance of butter that has gone “off.” Interestingly, it doesn’t seem to bother lovers of Parmesan cheese, where it is also present.

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Butyric acid does no favours for the nose, but in the gastrointestinal tract, it is a different story. Here, it seems to prevent the irregular multiplication of cells and also has anti-inflammatory activity. Furthermore, there is accumulating evidence that it may be useful in the treatment of irritable bowel syndrome, a condition that affects roughly 10-15 per cent of the adult population. It is characterized by abdominal pain or discomfort that occurs in conjunction with altered bowel habits.

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Pure butyric acid is not suitable for treatment because of its smell, and in any case, if it is orally administered it is absorbed in the upper part of the gastrointestinal tract and doesn’t make it to the colon. However, if the butyric acid is microencapsulated, it can be administered orally. In one study, 66 adults with irritable bowel syndrome were randomized in a double-blind, placebo-controlled study to receive either 300 mg per day of microencapsulated butyric acid or placebo. After four weeks of treatment, there was a significant decrease in gastrointestinal problems in the group that received the butyric acid. A second trial showed similar results with microencapsulated sodium butyrate. No significant side effects were noted in either trial.

Butyrate concentration in the colon can also be increased with a diet rich in “prebiotics,” indigestible food components that bacteria in the gut can use to produce butyric acid. Resistant starch, found in whole grains and seeds, as well as in green bananas, is particularly efficient in producing butyrates. The increased intake of highly processed grains in the western diet, and the resulting decrease in short-chain fatty acids in the colon may be a reason for an increased incidence of irritable bowel disease. Another reason to eat those fibre-filled whole grains and veggies.

joe.schwarcz@mcgill.ca

Joe Schwarcz is director of McGill University’s Office for Science & Society (mcgill.ca/oss). He hosts The Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3 to 4 p.m.

Note: This column has been updated to remove erroneous information about U.S.-made Hershey’s chocolate.

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