What does foul-smelling flatulence indicate?

There’s a few topics that people like to avoid discussing around the dinner table - passing wind is most likely one of them.

Gas, flatulence, or slightly less polite but perhaps most common - farting - is what we’re talking about. These words are used to describe the expulsion of air from the digestive tract. This process happens more frequently than you might be aware. 

Intestinal gas is perfectly normal and will likely go completely unnoticed until it passes out of your mouth as a burp or through the rectum as flatulence. 

On average, a human adult produces between half a litre and two litres of gas each day. It is expelled in the form of burping or flatulence about 14 times a day, according to the National Institute of Digestive Health and Diabetes in the United States.

The majority of the gas we pass each day does not smell bad, but why is there some gas that smells especially foul? 

What does bad-smelling gas reveal about what’s going on inside your body?

The digestive tract produces gas by breaking down undigested foods (especially carbohydrates) in the large intestine, also known as the colon. This process creates gases such as hydrogen, carbon dioxide and methane. Many common and healthy foods produce gas. These include beans, milk and dairy products, cabbage, bran and pasta.

The type of gas the body expels can give you a lot of information about how your body is processing nutrients, explains Dr, Tormo Carnicé, a physician who specialises in digestive system diseases. 

"When ingested proteins are partially catalysed (the process by which the speed of a chemical reaction is increased) and in that process hydrogen sulphide is formed, which is eliminated from the body by burping. Hydrogen sulphide has a smell similar to rotten eggs," Dr Carnicé explains.

When carbohydrates reach the colon undigested, excess hydrogen or methane, among other gases, may be produced, which can once again produce a bad smelling gas. If there are high levels of methane or hydrogen in a person’s flatulence, this means that the individual has ingested too much fibre, or has difficulty absorbing sugars. If it’s a case of too much fibre - the simple solution is to slightly reduce the amount of fibre rich foods consumed per meal. Occasionally, some abdominal discomfort or pain may reveal other dietary issues. This is sometimes referred to as irritable bowel syndrome (IBS). If someone presents discomfort of this type, Dr. Carnicé recommends going to the doctor to discuss their diet to ascertain whether an intolerance to either lactose, sucrose, starch, fructose, sorbitol, stachyose, raffinose or cellulose may be present.

Take a look at your poo…

You don’t necessarily need to go to the doctors to evaluate the levels of hydrogen or methane that is expelled by the body. Sometimes it is enough to take a look at your poo to detect changes in the body. Dr Carnicé clarifies: "We now know that excess methane causes faeces to weigh less, meaning they float." This discovery is relatively new, as it was previously thought that fat was responsible for stool buoyancy. 

What foods cause excessive gas?

Gas is a normal result of digestion and completely unavoidable. Some foods do cause the body to produce more gas than others. "The most common products that produce gas are those that contain stachyose and raffinose, which are found inside legumes. Cellulose, hemicellulose, pectins and lignins, which are found in the walls of vegetables also produce high levels of gas," says Dr. Carnicé.

Putrescine, cadaverine, indole and skatole, which are present in both vegetables and legumes, usually cause the smelliest gases. Bad odor does not necessarily indicate poor health or poor digestion, but merely a sign of an excess of these foods in the diet. On the other hand, "hydrogen and methane, which are eliminated primarily by the anus, are not foul smelling," reminds the doctor.

What kind of gas should be a cause for concern? 

Generally speaking gases should not be a cause for concern says Carnicé. The only gas that should be investigated further is hydrogen sulphide, with its characteristic smell of rotten eggs. Hydrogen sulphide highlights the presence of gastritis and delayed gastric emptying. The other gases such as hydrogen, methane and CO2 do not have a bad smell and are not cause for concern”, concludes Dr Carnicé.

This article has been written with the support of Dr. Tormo Carnicé, a specialist in Digestive Diseases in Barcelona and a member of Top Doctors.

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