What Causes HAFE and How to Prevent Gas When Flying

Airplane travel can definitely make you feel lethargic and dehydrated, but have you ever noticed that it makes you gassy, too? It's not in your head — flying leads to farting for a lot of people, and there's a good reason for it.

Basically, extreme changes in pressure and altitude directly affect your digestive system.

"As air pressure decreases, the gas [in your gut] expands, and the air needs to be released," New York City-based internist and gastroenterologist Niket Sonpal, MD, tells LIVESTRONG.com. Hence, the need to pass gas more often than usual.

What's more, all of that gas in your bowels adds pressure to the intestine walls, which can lead to GI discomfort and bloating. And unfortunately, people assigned female at birth are more likely to experience gassiness when flying. "Because of women's incredibly intertwined intestines, they tend to experience more intense pain and discomfort on planes compared to men," Dr. Sonpal says.

Plus, the way in which you're seated on an airplane doesn't do the body any favors. You're cramped, so gas gets more easily trapped in the bowels and can contribute to excess flatulence throughout the flight. It's worse at a specific point mid-air, though, and it's due to a phenomenon known as high-altitude flatus expulsion (HAFE).

The idea of HAFE came about from a study published in the ‌Western Journal of Medicine‌ back in 1981, which described hikers who experienced increased gas (and flatulence) as they reached higher altitudes when hiking up the San Juan Mountains of southwestern Colorado.

According to this study, HAFE can affect anyone exposed to such rapid altitude changes, hikers and airplane passengers alike.

"Since both high-altitude hikers and passengers on a plane reach very high altitudes, the colonic gas expands as the air pressure decreases, where they may experience discomfort and gassiness during their ascent and after the descent," Dr. Sonpal says.

HAFE is a result of low air pressure as you're in the air, where gas within the intestines starts to expand until it can't any further. "Because of this, the gas must escape," Dr. Sonpal says.

Extreme gassiness can be really uncomfortable, especially if you're not able to stretch your legs and relax to let it pass. Airplane seats are tiny, and you're likely cramped, in a position that's not ideal for getting that gas out in order to find some relief.

According to Dr. Sonpal, you may feel gassy even after landing and deplaning. "HAFE reaches its peak flatulence around 11 hours after a rapid ascent," he explains.

So, don't be surprised if you remain gassy once you're on the ground.

While increased gas may be inevitable, you can certainly reduce symptoms of HAFE by eating and avoiding specific foods both before and during your flight, and by staying active to promote greater blood flow and circulation as well as relief from gas and bloating.

Dr. Sonpal recommends avoiding high-FODMAP foods starting the day before your flight. FODMAPs are a type of short-chain carbs that can cause GI distress.

Dr. Sonpal lists the following high-FODMAP foods as the biggest offenders:

• Legumes and beans, including chickpeas
• Cruciferous vegetables, such as Brussels sprouts, broccoli and cauliflower
• Cashews
• Onions and garlic
• High-fiber snacks like protein bars, packaged desserts and other processed foods made with inulin (a kind of fiber)

You also want to avoid sugar and artificial sweeteners, Dr. Sonpal says, especially foods with high-fructose corn syrup or a large amount of fructose in general. Examples include:

• Certain dairy products, like flavored yogurt and kefir
• Many packaged snack foods, juices and condiments

"High-FODMAP foods produce more gas naturally, so if you limit intake the day before a flight there will simply be less gas available and present for expansion," Dr. Sonpal explains.

Limiting carbonated beverages like seltzer, soda and booze can help too. "Don't drink carbonated beverages while in the air, as the carbon dioxide in carbonated drinks can contribute to the buildup of gas, which is likely to expand in your bowels," Dr. Sonpal says.

You should definitely get up and stretch your legs a few times, especially during long flights. Set a reminder if you're worried about remembering to take those breaks.

"Sitting in a cramped position for an extended period of time can interrupt the flow of gas in your bowels, which can result in discomfort, pain and bloating," Dr. Sonpal says.

Stand up and walk around for a few minutes at a time and routinely when mid-air to eliminate gas and prevent buildup.

You can also take over-the-counter medications, like simethicone (Gas-X or Phazyme) before boarding and during longer flights, as it'll help break up larger gas bubbles so you have an easier time passing gas when in the air. As bigger bubbles get smaller, you won't feel the intensity of gas pressure as much in your gut, Dr. Sonpal says.

Keeping anxiety low in general when on a plane may also help reduce HAFE symptoms, because many people experience GI discomfort when worrying or stressed. Anything that puts your mind at ease will in turn benefit your gut.

Stretching in your seat could help, or you could try deep breathing exercises or following along with a meditation app.

OK, so these won't reduce gas or bloating, but they might make it less embarrassing.

You can wear reusable charcoal-lined underwear or opt for disposable charcoal liners, both of which can help reduce bad odors. If you often have super stinky farts, the charcoal might be especially helpful for you, so you won't feel as anxious about passing gas in public.

Check out Shreddies for flatulence-masking undies and Flat-D for charcoal liners.