We’ve all experienced it: after a particular meal, the bloating, pressure and eventually, the release of gas. Call it gas, flatus, flatulence, farts—or petard, as Shakespeare famously punned—it can be embarrassing, noisy and sometimes smelly.
But what causes it? Until recently, scientists assumed that the odor emanated from undigested amino acids that made their way down the colon. But more recent studies showed that these amino acids don’t become gaseous at physiological temperatures, and are in volumes too small to make for scatological snickering. More recently, the culprit has been found to be the same chemical that makes rotten eggs or seaweed smell; sulfur.
Most intestinal gas is non-offensive; it’s a product of digestion and consists of oxygen, nitrogen, carbon dioxide, hydrogen and methane—the same stuff of air. But the stinky vapors are made by bacteria in our large intestines; these bacteria rely on sulphur to support their own metabolism. The sulfur itself is either in the gut lining, or in our food. And since our internal bacterial populations—the microbiome—is more genetically diverse than we are, and that can make for more diversity in the composition of intestinal gas.
But hey, at least it’s all normal.
Suarez, F., Springfield, J., & Levitt, M. (1998). Identification of gases responsible for the odour of human flatus and evaluation of a device purported to reduce this odour Gut, 43 (1), 100-104 DOI:10.1136/gut.43.1.100
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