Bile

Ancient Greeks believed your temperament literally flowed from your bile—yellow bile made you choleric and angry, while black bile caused melancholy and depression. This wasn't just poetic metaphor; physicians actually examined patients' bile to diagnose mental states and prescribed treatments to "balance the humors." We still use "bilious" to describe someone irritable or bad-tempered, carrying forward a 2,000-year-old medical theory in everyday language.

Your bile acids complete an extraordinary 12-round-trip journey each day between your liver and intestines, being reabsorbed and reused with 95% efficiency. This enterohepatic circulation is so effective that you only need to manufacture about 5% new bile acids daily to replace what's lost. It's one of the most efficient recycling systems in nature, more effective than any human-designed process.

That yellow-green color of bile comes from bilirubin, the beautiful byproduct of your body breaking down 200 billion red blood cells every single day. As bilirubin travels through your digestive system, it transforms like a natural dye—creating the brown color of feces and, when filtered by kidneys, the yellow of urine. When this process goes awry, the same pigment paints your skin and eyes the telltale yellow of jaundice.

Gallstones form when bile becomes oversaturated, like rock candy crystallizing in sugar water—except these "crystals" can grow as large as golf balls. Most are made of cholesterol that precipitates out when bile composition shifts, though some form from bilirubin pigments, creating striking black stones. Napoleon likely suffered from gallstones, which some historians argue affected his decision-making during crucial battles.

Bile acts as your body's biological detergent, using the same chemical principle as dish soap to break down fats. Its bile salts have both water-loving and fat-loving ends that surround grease droplets and make them dissolve in water—emulsification in action. Without this internal "soap," you couldn't absorb vitamins A, D, E, and K, making bile essential for nutrition beyond just fat digestion.

The phrase "don't get your bile up" connects directly to the ancient belief that anger literally heated and agitated bile within the body. Medieval physicians thought sudden rage could cause bile to "boil over," leading to the expression "blood boiling" and linking bile permanently to intense emotion in language. Even today, we call someone "jaundiced" when they have a bitter, prejudiced view—as if excess bile has colored their entire worldview yellow.