10 Smart Facts About Your Gut

Colorized scanning electron micrograph of E. coli, a common gut bacteria
Colorized scanning electron micrograph of E. coli, a common gut bacteria
National Institute of Allergy and Infectious Diseases, Flickr // CC BY 2.0

Gut feelings get all the press, but your gut may be more of a thinker than you know. Some scientists now consider it a second brain. While it won’t necessarily help you study for an exam or get a promotion, your gut can influence the chemistry of your mood, emotions, immune system, and long-term health. Research even suggests the gut can “learn” new tricks through conditioning. These powerful connections are part an emerging field of science called neurogastroenterology designed to study the gut-brain link. Here are 10 facts you may not know about your gut.

1. THE GUT DOESN'T NEED THE BRAIN'S INPUT. 

You might think of your gut as a rebel against authority. It doesn’t wait for your brain’s impulses to do the important work of digestion, because it doesn’t need to—it acts as its own “brain.” No other organ, not even the all-powerful heart, can pull that off.

2. THERE ARE MORE THAN 100 MILLION BRAIN CELLS IN YOUR GUT.

Your gut’s power to think for itself is no surprise; there are millions of neurons in its lengthy coils (9 meters of intestines, from esophagus to anus). That’s more neurons than are found in the spinal cord or peripheral nervous system.

3. YOUR GUT HAS ITS OWN NERVOUS SYSTEM.

The enteric nervous system—the controlling mechanism of digestion and elimination—is the overlord of your gut, and functions all on its own. Some scientists see it as part of the central nervous system, while others consider it its own entity. It likely evolved to give the gut the go-ahead when the “got to go” impulse strikes, without requiring the brain’s sign-off, particularly when you consider the helplessness of an infant with its brand-new brain.

4. THERE'S AN INFORMATION HIGHWAY FROM YOUR GUT TO YOUR BRAIN.

There’s one big visceral nerve embedded in your gut—the vagus nerve. Research has revealed that up to 90 percent of its fibers carry information from the gut to the brain, rather than the other way around. In other words, the brain interprets gut signals as emotions. So you really should trust your gut.

5. MOST OF YOUR SEROTONIN IS IN YOUR GUT.

Some 95 percent of your body’s serotonin, that marvelous mood molecule that antidepressant drugs like Prozac keep in your body, can be found in the gut. So, it’s no wonder that diet, medications, and antibiotics can wreak havoc on one’s mood.

6. A HEALTHY GUT MAY PROTECT YOUR BONES.

In a study of the serotonin-gut relationship, scientists discovered an unexpected link between the gut and the bones. Inhibiting the gut’s release of serotonin counteracted the bone-density reduction of osteoporosis in mice. This research is going into studies on new osteoporosis-fighting drugs.

7. RESEARCH SHOWS LINKS BETWEEN AUTISM AND HAVING FEWER STRAINS OF GUT BACTERIA. 

In as many as nine out of 10 cases, autistic people have common gut imbalances such as leaky gut syndrome, irritable bowel syndrome, and fewer strains of “good” bacteria. Research on mice is looking at possible treatments of some of the behavioral disorders of autism by balancing microbes in the guts, though many warn that such treatments can’t produce a “cure” for autism.

8. FOOD REALLY DOES AFFECT YOUR MOOD. 

Different foods, when introduced to the gut via feeding tubes, have been shown to change a person's moods without the person’s awareness of what they were "eating." Fat, for instance, increased feelings of happiness and pleasure (no surprise there) because appeared to trigger the release of dopamine—the brain’s natural opiate. Carbohydrate consumption stimulated the release of serotonin, the “feel good” neurotransmitter.

9. YOUR GUT IS YOUR BEST FRIEND IN COLD AND FLU SEASON.

Not only does your gut hold brain cells, it also houses the bulk of your immune cells—70 percent—in the form of gut associated lymphoid tissue, or GALT, which plays a huge part in killing and expelling pathogens. GALT and your gut microbiome—the trillions of bacteria that live, like an immense microbial universe, in your gut—work hard to help you get over what ails you. That’s all the more reason to be careful with the use of antibiotics, which wipe out the good bacteria along with the bad.

10. YOUR GUT CAN BECOME ADDICTED TO OPIATES.

Inside your gut are opiate receptors, which are also found in the brain. The gut is just as susceptible to addiction as the brain and may contribute to the intense difficulty some addicts have trying to kick the habit.

What Causes Hiccups?

iStock/damircudic
iStock/damircudic

The cause of hiccups depends on whom you ask. The ancient Greek physician Galen thought hiccups were violent emotions erupting from the body, while others thought they were a sign of liver inflammation. Today, evidence points to spasms in the diaphragm, the large muscle between the chest and abdomen that aids airflow during breathing. This involuntary contraction can be brought on by a number of things that might irritate the nerves that control the movement of the muscle. A full stomach, heavy boozing, rapid shifts in temperature either inside or outside of the stomach, and certain emotions like shock or excitement are all common culprits.

No matter the cause, the result is the same: The diaphragm spasms and causes us to take a quick breath. The sudden rush of air causes the epiglottis (the flap that protects the space between the vocal cords) to shut and interrupt the breath, which makes the familiar "hic" sound.

WHAT CURES THEM?

The best cure for hiccups also depends on the person you ask. Almost all cures are based on one of two principles: One type works its magic by overwhelming the vagus nerve with another sensation. The vagus nerve is a cranial nerve that innervates the stomach and conveys sensory information about the body's organs to the brain. When distracted by overwhelming information of another sort, it basically tells the brain that something more important has come up and the hiccuping should probably be stopped (vagus nerve stimulation is also used to control seizures in epileptics and treat drug-resistant cases of clinical depression). The other method for curing hiccups is to interfere with the breathing, increasing the amount of carbon dioxide in the blood, and causing the body to focus on getting rid of the of the CO2 and not making hiccups.

Swallowing a spoonful of sugar is probably the most commonly prescribed hiccup cure and falls into the first category. A teaspoon of sugar is usually enough to stimulate the vagus nerve and make the body forget all about the hiccups. Even ardent supporters of the sugar cure disagree if the sugar should be taken dry or washed down with water, though.

If this home remedy doesn't work, and your hiccups are both severe and persistent, you may need to bring out the big guns. For chronic cases like this, doctors sometimes use a cocktail of Reglan (a gastrointestinal stimulant) and Thorazine (an anti-psychotic with sedative properties) to quiet things down. In some cases that resist these drugs, Kemstro, an anti-spasmodic, is also used. Other doctors have used vagus nerve stimulators implanted in the upper chest of patients. The pacemaker-like devices send rhythmic bursts of electricity through the vagus nerve to the brain to keep the hiccup cycle in check.

Many people prefer home remedies to battle their hiccups, which may include holding your breath, gargling ice water, or breathing into a paper bag. While the same people will swear by the treatment they've been using all these years, there's no firm scientific consensus that any of them actually work. But if it helps you, isn't that all that matters?

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

An earlier version of this article appeared in 2012.

12 Facts About Belly Buttons

iStock
iStock

Belly buttons are many things bundled up into one tiny knot: Collectors of lint. Harborers of bacteria. Objects of desire. Symbols of creation and birth. From the gross to the sexy to the spiritual, there’s a lot to unpack about the belly button’s place in history, culture, science, and religion. Let's get started.

1. THEY'RE REALLY JUST SCARS.

That little spot in the center of your belly marks the place where your umbilical cord once connected you to your mom’s placenta. When that cord is cut, a little, shriveled piece of it gets left behind. It eventually falls off—usually within the first week of a baby’s life—and what remains is a scar. Of course, “belly button” sounds a lot cuter than “belly scar.”

2. DOCTORS CAN’T CHOOSE A BABY'S BELLY BUTTON SHAPE …

Whether your belly button caves in or sticks out has nothing to do with how your doctor cut or clamped your umbilical cord. It all comes down to the amount of space between the skin and the abdominal wall, which determines how much skin—and scar tissue—is left behind. "You can't do anything to make sure babies have an innie or outie," Dr. Dan Polk, a neonatologist at Children's Memorial Hospital in Chicago, told the Chicago Tribune. "It has to do with how much baby skin leads onto the umbilical cord from the baby's body. Less skin makes an innie; more skin makes an outie." About 90 percent of people have innies, and the rest are outies. In some cases, an outie orientation is the result of an umbilical hernia, which occurs when part of the intestine pokes through the umbilical opening in the abdominal wall. It usually seals up naturally by the time a child reaches the age of 2, but more persistent cases may require surgery.

3. … BUT A COSMETIC SURGEON CAN TURN AN OUTIE INTO AN INNIE.

For those who don't like their outie, cosmetic surgery is an option—albeit a drastic one. Umbilicoplasty is a surgery that alters the size or shape of the belly button, often by removing excess skin or tightening abdominal skin. A 1971 article in the Honolulu Star-Bulletin called belly button beautification the “newest gimmick in the cosmetic surgery game.” The article cited a Japanese physician who had performed more than 3000 navel operations in the ‘60s and early ‘70s for about $80 to $150 a pop. (Now, the surgery costs about $2000 in the U.S.)

An article in The Ottawa Citizen suggested that the surgical technique dates back to the early 1900s, when it was usually done as a corrective measure in conjunction with tummy tuck surgeries, which often displace the belly button. Even if there’s no medical need, a patient can now opt for umbilicoplasty to get the “ideal” shape. “What was favored through the Greek, Roman, and Western civilization to our time is an oval belly button that is more or less vertically oriented,” New York City cosmetic surgeon Bruce Nadler told the paper in 2002, when these surgeries were starting to become more popular. By contrast, Nadler said, horizontal belly buttons are considered more desirable in Asian cultures because they’re associated with good fortune.

4. MOST MAMMALS HAVE ONE.

Dogs, chimpanzees, lions, and armadillos have one, but their navels aren’t always easy to spot. For one, most mammalian mothers chew off the umbilical cord attached to their newborns, leaving a flat scar that’s harder to detect than a human belly button. Gorillas and chimpanzees are an interesting case for navel-gazers because they have what some scientists call an “in-betweeny”—a navel that looks like a human’s but is neither an innie nor an outie.

However, there are a few notable exceptions to the mammal belly button rule. Platypuses, which lay eggs, have no umbilical cord and therefore no belly button. As for marsupials like kangaroos and koalas, their umbilical cords generally fall off while they’re still inside mom's pouch, so a scar never forms.

5. THE FEAR OF BELLY BUTTONS IS CALLED OMPHALOPHOBIA.

Some people feel anxious, afraid, or disgusted when their belly button is touched or when someone else's bare midriff is on display. This is called omphalophobia, which stems from the Greek word omphalo for navel. This fear is believed to be linked to the navel's association with umbilical cords and wombs, or perhaps the irrational childhood fear that a belly button will come undone, letting one’s guts spill out. The phobia has gained more national exposure ever since TV personality Khloé Kardashian admitted she has a fear of belly buttons.

6. IF YOU POKE IT, YOU MIGHT SUDDENLY GET THE URGE TO PEE.

Speaking of touching your belly button (and all the grossness that comes with it), you may feel a tingly sensation when you stick your finger in it. That’s because you're stimulating fibers lining the inside of your abdomen, which then send a message to your spinal cord. As Dr. Christopher Hollingsworth of NYC Surgical Associates explained to BuzzFeed, “Because your spinal cord at that level is also relaying signals from your bladder and urethra, it feels almost the same. You interpret this as discomfort in your bladder."

7. THEY CAN LEAK URINE.

In a similar vein, a rare abnormality can cause urine to leak out of the belly button. In the early stages of pregnancy, a tube called the urachus connects a fetus’s bladder and belly button and allows urine to drain. It usually atrophies and turns into a scar on the bladder at birth or soon after, but not always. Some people may never know they still have all or part of their urachus attached because it only becomes a problem if the tube doesn’t close up. In those cases, urine can travel up through the urachus and leak out of the umbilicus (navel). Surgery is generally needed to fix this issue.

8. THEY GROW SPECIAL FLUFF-CATCHING HAIRS.

Have you ever wondered why bits of lint keep collecting in your belly button, despite your best efforts to keep clean? Blame it on a special type of hair that grows in navels. These hairs have tiny barbs that protrude and rub against your clothing, causing small fibers to scrape off. The hairs are arranged in concentric circles, which act as a funnel and suck fluff into your navel. Those who shave their stomachs or don't grow a lot of body hair to begin with likely don't have many problems with lint.

9. THEY CONTAIN THOUSANDS OF KINDS OF BACTERIA.

Beyond lint, a lot of dead skin, discarded fat molecules, and thousands of bacteria also live in your navel. One 2012 study led by the aptly named Belly Button Biodiversity project documented 2368 types of bacteria in the navels of 66 study participants. Fret not, though: They help to protect you against harmful pathogens. “We know that without these microbes our immune systems won’t function properly,” the head of the project, Dr. Rob Dunn, said in a statement. “In fact, this collection of microbes must have a certain composition—must form a certain microbial ecosystem—in order for our immune system to function properly."

10. THEY USED TO BE BANNED ON TV.

In Western culture, belly buttons have been regarded as "a feminine sexual center since ancient times," according to the Online Etymology Dictionary. As such, they were deemed too lewd to show on television, according to the Code of Practices for Television Broadcasters, established by the National Association of Broadcasters in 1951. Barbara Eden, who played the titular role in I Dream of Jeannie, said network executives at NBC held meetings over whether to let her flash her navel during the show’s run in the ‘60s. Her producer, George Schlatter, “said he had never seen so many suits sitting around a table in his life discussing someone's anatomy,” Eden told the TODAY show. Although Eden’s genie get-up never ended up revealing her belly button, other shows started to push the envelope around the same time. The belly-button ban technically remained in effect until 1983, but it wasn’t exactly enforced. Yvette Mimieux of Dr. Kildare became the first actress to bare her navel on television in 1964, and others followed suit soon after.

11. THEY ARE THE SOURCE OF A LONGSTANDING THEOLOGICAL DEBATE.

Among Christians, the debate over whether Adam and Eve had belly buttons is a little like the age-old “chicken or egg” question. One popular argument holds that Adam and Eve weren’t born naturally from a mother, and thus they wouldn’t have had umbilical cords or belly buttons. Others disagree for various reasons and insist that navels have been around since the dawn of time. Both Raphael and Michelangelo depicted Adam and Eve with navels in their artwork (including the Sistine Chapel's ceiling painting), leading one 17th-century doctor and philosopher to decry these “vulgar errors,” according to the book Umbilicus and Umbilical Cord by Mohamed Fahmy. Other artists tried to avoid the issue altogether by concealing the couple’s abdomens with foliage, forearms, or long hair.

A few centuries later, a U.S. House of Representatives subcommittee refused to distribute a booklet called Races of Man to World War II soldiers because it contained pictures of Adam and Eve with navels. Members of the committee ruled that this image “would be misleading to gullible American soldiers.”

12. THEY ARE CELEBRATED IN SOME CULTURES.

Think of Middle Eastern belly dancing and midriff-baring Indian attire. In some places around the world, the navel holds cultural and even spiritual significance. Some Hindus believe that a lotus emerged from the god Vishnu’s navel, and at the center of the flower was Brahma—the creator of the universe. Likewise, in Japan, the belly button may represent the point where life begins. In the Middle Jōmon period (2500-1500 BCE), Japanese artists emphasized the appearance of navels on their human-like figurines. Today, a belly button festival is held annually in the town of Shibukawa in central Japan. “The belly button is traditionally believed to be located in the middle of the body and the most important part,” festival organizer Kazuo Yamada told Reuters. “Our town, Shibukawa, is also called the belly button of Japan, and that is how this festival began.”

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