This month, The New Scientist reported that when it comes to trumping, macho, muscle building protein generates the most noxious smell.
Farts, as journalist Alice Klein explains, are mostly composed of odourless gases. These include oxygen and nitrogen from swallowed air, and hydrogen, methane and carbon dioxide, generated when bacteria in the large intestine ferment the carbohydrates we eat. The distinctive rotten-egg whiff is caused by traces of hydrogen sulphide, which gut bacteria produce from protein. Hydrogen sulphide is toxic. In addition to causing red-face moments, this gas can trigger colitis and increase the risk of bowel cancer.
Chu Yao and her colleagues from Monash University in Melbourne, Australia, have recently reported how different foods influenced the amount of hydrogen sulphide emitted by samples of faeces from seven healthy people. They found that mixing faeces with cysteine – a major sulphur-containing amino acid found in meat, eggs, dairy and other types of protein – increased hydrogen sulphide emissions seven-fold. “This explains why bodybuilders who consume lots of protein powder are known to have smelly farts,” says Yao.
There is competition between the bacteria which produce methane and those that produce hydrogen sulphide. Hydrogen sulphide production declined substantially when the team mixed the faeces with four complex carbohydrates, that are not fully digested in the small intestine and are fermented by bacteria in the colon to release hydrogen and methane. Resistant starch, which is found in potatoes, bananas, legumes and cereals, and fructans, which are found in wheat, artichokes and asparagus – both reduced hydrogen sulphide production by about 75 per cent. These foods are broken down in preferences to protein. Psyllium, ispaghula husk and sterculia gum, all components of soluble fibre, are only slowly broken down and fermented; they soak up water and swell in the colon , adding bulk to the faeces aiding their evacuation. They also reduce hydrogen sulphide, but only by 25 per cent. Yao now plans to test their findings with a clinical trial of a low protein, high fibre diet.
The team’s findings overturn conventional wisdom that people with stinky gas should eat less fibre. Contrary to current advice, they indicate that avoiding fibre will reduce the volume of gas expelled, it will increase emission of hydrogen sulphide. For many people, it is not so much the act of farting that worried people, it is the smell, she says. It is possible that many people are scared to treat their constipation with fibre because they might do a ‘bad fart’. They could of course try taking the antispasmodic Colpermin, which releases peppermint oil in the colon and is said to disguise the rotten egg smell of farts with a sweet aroma of peppermint.