Why flying makes you flatulent, how to reduce it – and whether just letting go is OK

If you find yourself feeling flatulent on a flight, don't hold it in. Photo / Getty Images

Eating unhealthy food before getting on an aeroplane is far from the only thing that will have you feeling flatulent during your flight. And in extreme cases, holding it in could lead to rises in blood pressure and heart rate, the South China Morning Post reports.

Flying can affect our bodies in different ways. Delays can cause stress; changes in air pressure wreak havoc with our ears while sucking moisture from our body and leaving the mouth desert dry; and the increased risk of blood clots forming in veins (deep-vein thrombosis) for some long-distance travellers has been widely discussed.

Less talked about, however, is an increase in flatulence and bloating.

So curious was Danish surgeon Jacob Rosenberg about in-flight flatulence that he and his University of Copenhagen colleagues wrote a paper on it for The New Zealand Medical Journal. Rosenberg says his "light bulb" moment was triggered by a plastic bottle.

"I watched a bottle shrink on a descent and it gave me the idea," says Rosenberg by email. "Several times while flying I noticed that my belly increased in size and sometimes with extensive air passage."

Rosenberg says the reason this happens is simple. "When cabin pressure decreases, the natural air inside the bowel will expand. And since there is only limited space in the large bowel, it is a natural consequence to fart."

The paper states that the average human produces between 0.7 litres and 1 litre (24 and 34 US fluid ounces) of intestinal gas a day, and passes gas about 10 times daily. It also states that studies have not proven that men produce more flatus than women or that younger people pass wind more than older people. Good to know flatulence does not discriminate.

Rosenberg's advice regarding in-flight flatulence is simple: "Let it go." And for good reason.

Rosenberg and his team says those who "hold back" could suffer pain, bloating, indigestion and heartburn. In more extreme cases, this could lead to rises in blood pressure and heart rate, which is dangerous for passengers with cardiovascular complications.

Fortunately, commercial aircraft already use charcoal filters in their ventilation systems, which effectively absorb a range of odours.

"We learned that from an airline mechanic at the Copenhagen airport, and it is true that they have these effective filters installed," Rosenberg says. "In the [paper] we also discuss briefly the possibility of making seats with charcoal filters woven into the fabric. This could be a very good solution. Another solution is to wear special underwear with charcoal filters."

Rosenberg said that since the paper was published in 2013, a Japanese company has started selling charcoal underwear. British firm Shreddies also makes flatulence-filtering garments, and says on its website that The American Journal of Gastroenterology found "activated carbon" underwear to be the most effective method of removing flatulence odours.

According to cabincrewprotection.org, an information-sharing platform for flight crew, people should avoid fried and fatty takeaways before flying. This means resisting the unhealthy food options available at many airports, Hong Kong International Airport included (think McDonald's, Burger King, Popeyes). Accompanying many fast food meals is another big preflight no-no: fizzy carbonated drinks.

But the website says fast food is not the only culprit. "Jet bloat", as it has been coined by flight crew, is also triggered by healthy foods such as onions, cauliflower, cabbage, beans and lentils, which cause bloating even when you're not at 35,000 feet.

So what is the best preflight meal? The website says to eat pineapple, as it contains an enzyme that eases belly issues, and swap booze and coffee for fennel tea, which is a digestive aid. And ditch the McDonald's Happy Meal for a green leafy salad.

Happy – and flatulence-free – flying.