Fermentation in the Human Colon
Posted February 1, 1998
What happens when you eat foods that contain carbohydrates or fatty acids that are not absorbed into your body in the small intestine? If these carbohydrates or fatty
acids pass into the colon, bacteria found in the colon can ferment these molecules and produce gases. Does a diet high in indigestible carbohydrates and fatty acids affect the digestive
system?
At the Nutrition Research Laboratory in Nantes, France, three groups of healthy volunteers were tested to see how their digestive systems responded to various carbohydrates
and fatty acids. One group of volunteers was fed the sugar lactulose, a sugar that humans cannot digest, but that colonic bacteria are able to ferment. A second group was given infusions
of lactose directly into their colons. Lactose-fermenting bacteria are commonly found in the human colon. A third group of healthy volunteers had short-chain fatty acids infused directly
into their colons. Short-chain fatty acids can also be fermented by colonic bacteria. Then scientists measured the stomach pressure of each volunteer. Stomach pressure is a measure of
gastric muscle tone. In the lactulose experiment, researchers also monitored hydrogen gas levels of expired air as a measure of anaerobic fermentation.
To those volunteers given lactulose, there was a significant decrease in gastric muscle tone. This decrease in tone was rapidly followed by an increase in hydrogen
gas concentration. The volunteers given lactose directly into their colons also experienced a decrease in gastric tone. The volunteers who received the short-chain fatty acids had the
largest decrease in gastric tone.
The researchers drew the conclusion that colonic fermentation of carbohydrates can inhibit gastric tone and that short-chain fatty acids arriving in the colon may
greatly decrease the movement of materials through the digestive tract.
References
Cherbut, Christine, Alain Ropert, Claude Roze, Alain Le Quellec, Jens Juul Holst, Ziaomei Fu-Cheng, Stanislas Bruley Des Varannes, and Jean Paul Galmiche. "Colonic
Fermentation and Proximal Gastric Tone in Humans." Gastroenterology, 1996, Vol. 111, No. 2, p. 289.
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