Gas, GERD, and Bacteria


The human digestive tract is designed so that stomach acid and enzymes don't have to do all the work. In the small intestine, Lactobacillus acidophilus and other Lactobacillus bacteria thrive in an acidic environment. They like to feed on sugars that most humans can't digest very well, such as the lactose found in milk (not that you'll be getting a lot of that on a paleolithic diet). They colonize the lining of the small intestine so that disease-causing bacteria can't form a film that helps them cling to its surface, and they don't make gas. Some other species of “heterolactic” bacteria, unfortunately, can become established in the small intestine and do release gases including carbon dioxide, methane, and hydrogen.

Further downstream, in the colon, our bodies host trillions of bacteria of up to 500 different species. There are Lactobacillus bacteria in the colon, but there are also Bacterioides and Bifidobacteria in great abundance, as well as Acintoncyces, Clostridia, Corynebacteria, Enterobacter, Enterococci, E. coli, Fusobacteria, Klebsiella, Propionibacteria, and Proteus, and over 400 other species. Most of these bacteria break down the fibers and starches that our bodies can't break down with human digestive enzymes. By the time the remainders of the digestive process reach the colon, the leftover liquid is almost devoid of oxygen, so colon bacteria have to be able to survive by fermentation. The process of fermentation releases the gases we know as flatulence.

“Farting” isn't polite in company but it usually isn't painful. GERD, however, sometimes is a matter of flatulence working in reverse.

Flatulence in Reverse

Intestinal gas usually leaves the body by going down rather than by coming up. But for intestinal gas to build up pressures that start forcing stomach acid out of the stomach and into the throat, two things have to go wrong:

  • The first segment of the small intestine, the duodenum, is normally relatively acidic. This allows the acid- loving Lactobacillus bacteria (that don't produce gas) to thrive and keeps gas-producing bacteria at bay. When this part of the small intestine isn't acidic enough, gas-producing Bacteriodes, Clostridium, E. coli, Fusobacterium, Klebsiella, Peptostreptococcus, Proteus, Staphylococcus, Streptococcus, and Veillonella can begin to grow and produce gas.
  • Gas-producing bacteria feed on starches and poorly absorbed carbohydrates. When these bacteria accumulate in the small intestine, they can cause inflammation. The inflammation results in even poorer absorption of carbohydrates, leaving more to feed the bacteria, which in turn cause even more inflammation.

These bacteria can release enormous amounts of gas. The process of fermentation can transform just 10 grams (1/3 of an ounce) of carbohydrate into 4 liters (a gallon) of gas. The fermentation of 100 grams of carbohydrate (the equivalent of maybe six slices of bread) can release 10 gallons of gas. Is it any wonder that fermentation can cause heartburn and GERD?

But why should these “bad bacteria” multiply where they aren't supposed to be and cause stomach acid to churn upward into the throat? What causes excess alkalinity and how do excess starches get into the gut? The answer to these questions may make you mad.


About Andy Williams

Andy Williams has a Ph.D. in biology and a strong interest in health and nutrition. The Paleo Gut web site was created to explore the health benefits of the Paleo diet and see how it is changing lives. Also, get our free daily Paleo Gut newspaper delivered to your inbox. Please feel free to contact me and let me know about your Paleo experiences or favorite recipes.

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