Flatulence, or passing gas, is a normal daily phenomenon. Most individuals, yes, that includes you, will make anywhere from 500-1500 milliliters of gas and can pass gas ten to twenty times a day. But where does this bodily gas come from? A small proportion may come from ingesting air during sleep, or at other times, but the majority of gas is produced by bacteria in our intestines as they digest parts of food which we cannot. Our intestine is home to trillions of bacteria living in a symbiotic relationship with us.
We provide them with a safe place to stay and food to eat. In exchange, they help us extract energy from our food, make vitamins for us, like vitamin B and K, boost our immune system, and play an important role in gastrointestinal barrier function, motility and the development of various organ systems. Clearly, it’s in our best interest to keep these bacteria happy. Gut bacteria get their nutrition primarily from undigested food, such as carbohydrates and proteins, which come to the large intestine.
They ferment this undigested food to produce a wide range of compounds, such as short-chain fatty acids and, of course, gases. Hydrogen and carbon dioxide are the most common gaseous products of bacterial fermentation, and are odorless. Some people also produce methane due to specific microbes present in their gut. But methane is actually odorless, too. Well then, what stinks? The foul smell is usually due to volatile sulfur compounds, such as hydrogen sulfide and methanethiol, or methyl mercaptan.
These gases, however, constitute less than 1% of volume, and are often seen with ingestion of amino acids containing sulfur, which may explain the foul smell of gas from certain high protein diets. Increased passage of gas is commonly noticed after eating foods with high amounts of indigestible carbohydrates, like beans, lentils, dairy products, onions, garlic, leeks, radishes, potatoes, oats, wheat, cauliflower, broccoli, cabbage, and brussel sprouts. Humans lack the enzymes, so the bacteria able to ferment complex carbohydrates take over, and this naturally leads to more gas than usual.
But if you feel uncomfortable, bloated or visibly distended, this may indicate impaired movement of gas along the gastrointestinal track. It’s important not to just blame certain foods for gas and bloating and then avoid them. You don’t want to starve the bacteria that digest these complex carbohydrates, or they’ll have to start eating the sugars in the mucus lining of your intestines. Your personal gas will vary based on what you eat, and what bacteria are in your gut. For example, from the same starting sugar, the bacteria clostridium produces carbon dioxide, butyrate and hydrogen, while propionibacterium can produce carbon dioxide, propionate and acetate.
At the same time, methanogens can use hydrogen and carbon dioxide produced by other bacteria to generate methane, which can reduce the total volume of gas by using up hydrogen and carbon dioxide. So there’s a complex web among intestinal bacteria allowing them to flourish by either directly consuming undigested food, or using what other bacteria produce. This interaction largely determines the amount and type of gas produced, so gas production is a sign that your gut bacteria are at work.
But in some instances, people may develop abnormal increased flatulence. A common example is lactose intolerance. Most individuals have the enzyme for breaking down lactose, a sugar present in milk and milk-derived products. But some people either lack it entirely, or have a reduced amount, such as after a gastrointestinal infection, so they’re unable to digest lactose products and may experience cramping, along with increased flatulence due to bacterial fermentation.
But remember, most gas is produced as a natural result of bacterial fermentation in the intestine, and indicates healthy functioning of the gut. The amount and type can vary based on your diet and the bacteria in your intestine. Exercise social courtesy while passing gas, and do try to forgive your bacteria. They’re only trying to be helpful.