What Is Fart: The Science Behind Flatulence

Fart, medically known as flatus, is the gas expelled from the digestive system through the rectum. It’s a natural byproduct of digestion and reflects your gut’s complex microbial activity. But what exactly is in a fart, and why do we produce it?

The Composition of Fart Gas

Farts are primarily a mixture of several gases: nitrogen, oxygen, hydrogen, carbon dioxide, and methane. Tiny amounts of sulfur-containing compounds—like hydrogen sulfide—contribute to the unpleasant odor. The exact blend depends on diet, gut bacteria, and digestive efficiency. According to recent gastroenterology research (2024), the average person passes gas 12–25 times daily, with each fart containing about 0.1 to 1 liter of gas (NIH, 2024).

How Gut Bacteria Create Flatulence

The main source of intestinal gas is fermentation in the colon. When undigested carbohydrates—especially from beans, lentils, cruciferous vegetables, and some dairy—reach the large intestine, they become food for trillions of bacteria. These microbes break down complex fibers into short-chain fatty acids and gases. This process, called microbial fermentation, is essential for nutrient absorption but also produces gas as a side effect.

Studies show that dietary choices heavily influence gas production. Foods rich in resistant starch and oligosaccharides increase fermentation and thus flatulence volume. However, this process is a sign of a healthy, active microbiome—one that thrives on fiber diversity and supports digestive wellness (Mayo Clinic, 2024).

What Is Fart Really Made Of? Breaking Down the Gases

• Nitrogen (N₂): Comes from swallowed air and protein metabolism. It’s odorless but vital for gas volume.
• Oxygen (O₂): Present in small amounts when air enters the gut during eating or swallowing.
• Hydrogen (H₂) & Methane (CH₄): Produced by anaerobic bacteria during fermentation. Methane-producing archaea are common in about 30% of the population (Gut Microbiome Project, 2024).
• Carbon Dioxide (CO₂): A byproduct of bacterial metabolism, often expelled with other gases.
• Sulfur Compounds (e.g., hydrogen sulfide): Responsible for the typical