Flying frequently leads to the uncomfortable sensation of increased intestinal gas and bloating, a common experience for air travelers often called “aeroplane bloat” or “jet belly.” This phenomenon is directly related to the reduction in atmospheric pressure that occurs when an aircraft ascends to cruising altitude. The discomfort arises because the volume of gas already present within the body naturally expands as the external pressure drops.
The Physics of Altitude
The expansion of gas during ascent is governed by a fundamental principle of physics: the inverse relationship between the pressure and volume of a gas. Simply put, as the surrounding pressure decreases, the volume of a trapped gas must increase proportionally.
While commercial aircraft cabins are pressurized for safety, the pressure inside is still significantly lower than at sea level. Cabin air pressure is typically maintained to simulate an altitude of around 6,000 to 8,000 feet. This simulated altitude is sufficient to cause the gas within the body’s cavities to expand, which is the root cause of discomfort. The gas volume can increase by as much as 30% or more at a typical cruising altitude compared to ground level.
Physiological Impact and Symptoms
The most noticeable symptoms of gas expansion occur in the gastrointestinal tract, where gas is naturally present. As the aircraft gains altitude, the gas trapped in the digestive system expands, causing abdominal distension, commonly known as bloating. This expansion can lead to sensations of fullness, pressure, and sometimes intense abdominal pain.
The body attempts to relieve this internal pressure through the passage of gas, resulting in increased flatulence and belching. A high-fiber diet consumed before the flight can exacerbate these symptoms because the undigested food is fermented by gut bacteria, which produces additional gas (hydrogen, carbon dioxide, and methane).
Gas expansion is not limited to the digestive system; it also affects other air-filled body cavities, a phenomenon known as barotrauma. The ears and sinuses are particularly susceptible because they contain small, fixed volumes of air connected to the outside environment. The pressure difference between the expanding air inside the middle ear and the lower cabin pressure causes the eardrum to bulge, resulting in the familiar “popping” sensation or pressure pain. Similarly, air trapped in the sinus cavities can cause a painful “sinus squeeze.”
Preventing Discomfort
Mitigating the symptoms of gas expansion involves a combination of dietary adjustments and in-flight strategies. To reduce the amount of gas available for expansion, it is helpful to avoid carbonated beverages and gas-producing foods for at least 24 hours before flying. Common culprits include beans, broccoli, cauliflower, cabbage, and foods high in fermentable carbohydrates.
During the flight, staying hydrated with plain water is recommended, as dehydration can slow down digestion and worsen bloating. Standing up and walking around the cabin every hour or two helps stimulate the digestive system, which aids in the natural passage of gas. Over-the-counter aids can also provide relief; for example, simethicone works to break down gas bubbles in the gut, making them easier to pass.