Why am I so bloated after flying?

Why does my weight fluctuate after a flight? Even my daughter says her stomach feels strange and bloated after flying.

-- Anonymous

This question led our team to a discussion about post-flight bloat and what causes it. Does air travel actually have an effect on our weight? Or is it just a bunch of hot air?

I felt bloated for hours after I got home from a Los Angeles to D.C. flight last week. Was it the cabin pressure? The salty in-flight snacks? The breakfast sandwich I slammed before I boarded?

According to the doctors I spoke to, it's all of the above. The airplane environment, your stress and activity level, as well as what you eat and drink throughout your trip, all affect your gut health.

Here's what you can blame on the plane. When the cabin experiences a change in atmospheric pressure, air cavities in our digestive system can expand, explains Ali A. Khan, a gastroenterologist with Gastro Health in Fairfax, Va. "That can cause some bloating sensation, some discomfort and even a delay in the digestive process as a whole," he says. "People on longer flights may experience more bloating, nausea or constipation."

After landing, Khan says your body gets back to normal by way of burping or "passing flatus" over time.

Adding to the mix, our sedentary behavior can contribute to belly woes. New Jersey-based dietitian and author Erin Palinski-Wade says sitting in a cramped seat for long periods can compress the abdomen and make it harder for gas to pass through the gastrointestinal tract. That's why "it's important to do everything you can to stay active when you're traveling," said Josh Forman, a gastroenterologist at the University of Maryland St. Joseph Medical Center. Moving around (when the seat belt sign is off, of course) will help with gut function. "Particularly if you're on a long flight, it's worth getting up and taking a stroll back to the back of the plane," he says.

While you're back there, ask for a cup of water. Because of low humidity air, airplane cabins are dehydrating for travelers, and dehydration is a one-way ticket to bloat town. Megan Lyons, a clinical nutritionist and owner of the Lyons' Share Wellness in Dallas, said our bodies respond to that super-dry environment by retaining more water, leading to swelling and bloat. You can combat the issue by drinking lots of water throughout your travel day, and limiting dehydrating beverages such as coffee and alcohol.

What you eat matters as much as what you drink. Every expert I spoke to advocated for eating food that's high in fiber and protein before or during a flight. But for many travelers, we end up "at the mercy of whatever restaurant is at the airport," Khan says.

"It's processed foods on top of processed foods on top of processed foods," says Janese Laster, a gastroenterologist and expert in nutrition and obesity medicine with Georgetown University Hospital. "No fiber, typically -- or not anywhere near as much you would be eating at home."

That one-two punch takes a toll on your gut microbiome, leading to -- you guessed it -- bloating and constipation.

Instead of fighting the uphill battle of finding gut-friendly foods at the airport, pack your meal or snack at home. Forman recommends snacks that are easy and simple to put together, like celery and carrots with a side of hummus, cashews, jerky or protein bars. Laster loves oatmeal with chia or hemp seeds, berries and Greek yogurt (don't forget it needs to be 3.4 ounces or less to pass through security). Khan tends to eat light on travel days, but brings along fruit or foods rich in whole grains and lean protein.

The culprit that surprised me the most was stress. "There's a thing called the gut-brain axis," Khan said. "The gut is heavily innervated and closely linked with the brain ... so if there's underlying anxiety, that can cause G.I. symptoms like bloating, constipation or diarrhea and just overall discomfort."

When you're stressed, your body releases cortisol, Laster said, and elevated cortisol affects digestion.

"Your body does not care if you are anxious about a flight or a tiger running after you, it's the same cortisol," she says.

Another tip on preventing bloat: "We want to make sure that the bowels are moving as much as we can -- in a healthy way," Khan says.

Whether you're out of sync thanks to a disruption in your circadian rhythm due to a wonky travel schedule or have anxiety using the restroom away from home, not going is going to mess with your G.I. system.

Laster said some of her patients take travel packets of Miralax, which is a powder you add to water to treat constipation. "That way you can keep yourself on track so you're not feeling bloated," she said.

Back to the original question: Are we heavier after flying? Given all of these factors -- the water retention, potential constipation, gas buildup -- "I would not be surprised if someone measured their weight before and after and found themselves to be maybe a little bit heavier after," Khan says.

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