Many of you might be familiar with the word “bile.” It’s a term that’s been around for centuries.
Around 1,000 years ago, the humoral theory of medicine was born. It stated that to maintain good health, your four “humors” needed to be properly balanced.
Those four humors were phlegm, yellow bile, black bile, and blood. And the theory persisted for centuries.
People believed that if you had too much or too little of these compounds in your system, you'd likely have problems.
For instance, if you were seen as overly angry, people might attribute it to an excess of yellow bile. Still today, if someone says you’re “full of bile,” it means you’re full of anger.
It won’t surprise you to learn that doctors no longer follow these guidelines.
We now know that bile plays many vital roles, none of which have to do with rage. So, what is bile?
Bile is a yellow-green compound that your liver produces, and it does so constantly.
From there, bile is moved to your gallbladder — a hollow organ below your liver. Then, it’s concentrated or it travels directly to your gut to get to work.
Bile is mostly water, roughly 95%. The remaining 5% contains some of these chemicals and compounds:
bile salts, which are important for breaking down fats
bilirubin, which is part of broken-down old red blood cells
amino acids, which are the building blocks of protein
All vertebrates — animals with backbones — produce bile. This is a clue that it might be pretty important. So, what’s it up to?
What does bile do?
Like many compounds that your body produces, bile does a whole host of jobs — it’s a busy secretion. We’ll run through some of these jobs below.
Perhaps bile's most well-known function is helping to digest fats. So, let’s start with that.
Bile the fat-breaker
Bile is released into your intestines when you eat food containing fats. It emulsifies fats, meaning that it turns large fat droplets into smaller droplets called micelles.
And the way bile manages this feat is fascinating.
Bile salts are electrically charged. One end is hydrophilic, meaning that it’s attracted to water. The other end is hydrophobic, meaning that it's repelled by water.
The hydrophobic ends tend to face the fat, and the hydrophilic ends face outward, toward the more watery contents of your gut. This helps form neat, small globules of fat covered in bile salts.
And because the hydrophilic ends of the bile salts repel fat, the little fat droplets can’t join back together to form bigger droplets again.
If fat is in a large clump, it’s tricky for enzymes to dig in and break down the fat toward the center.
However, the micelles’ small size means more surface area is available for your enzymes to get to work. The enzymes slip through the gaps between the bile salts and break down the fat within.
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Micelles then move to the lining of your intestines. Once there, they break down, and the fat is absorbed into your blood so your body can use it.
Without bile, much of the fat you consume would exit your body in poop.
So, what else do bile and micelles do?
We can think of vitamins as falling into two groups: water-soluble and fat-soluble. As the names suggest, one type can dissolve in water and the other in fat.
Water-soluble vitamins are relatively easy for your body to absorb, but fat-soluble ones — like vitamins A, D, E, and K — are trickier.
But don't worry, bile and their micelles are here to save the day.
Fat-soluble vitamins, which don’t like mixing with water, end up in the hydrophobic center of micelles. There, they can make their way into your blood along with the broken-down fats.
Your stomach produces powerful acids. Luckily, it has defenses to make sure it doesn’t digest itself. Your intestines, however, lack these defenses.
So, as the contents of your stomach enter your intestines, the acid could damage your gut lining.
But don’t fret; bile is on hand. Because bile is alkaline, it helps neutralize the acidity and protects your gut.
Taking out some ... trash?
Bile's third important job is a little bit of housekeeping. Specifically, it helps your body get rid of bilirubin and cholesterol.
Bilirubin is produced when old or abnormal red blood cells are broken down. So, historically, scientists viewed it as a waste product.
High levels of bilirubin are associated with certain conditions, like liver disease. However, more recent research paints a more complex picture.
Either way, bile removes bilirubin from your system via poop, helping to make sure you have healthy levels.
Meanwhile, cholesterol is essential for every one of your cells to function. But elevated levels of “bad” cholesterol are linked to heart disease.
Bile helps remove cholesterol. You might remember that cholesterol is one of its components.
As you produce bile and release it into your gut, much of your cholesterol gets pooped out. This means that there’s less around to enter your blood.
Interestingly, your gut bacteria, which feed on bile acids, might also play a role in your blood cholesterol levels.
Although stomach acid is an excellent defense against food-borne bacteria, it’s not perfect, and some bacteria sneak through.
Bile acids can also activate receptors that “turn on” genes involved in fending off infections and protecting your gut lining.
Bile is one of your body’s unsung heroes. It carries out numerous tasks and asks for nothing in return.
It helps you digest fat and absorb some vitamins. At the same time, it lowers the acidity of your gut contents, removes some unwanted compounds, and helps protect against invading microbes.
So, the next time someone suggests you're “full of bile,” you might take it as a compliment.
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