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Poop is no laughing matter. The scientists and doctors who study feces have found that it's the by-product of a diverse community of bacteria in your gut that impacts your health in all sorts of ways. Paying closer attention to your stool can tell you about the condition of these vital bacteria — and your overall health.
With that in mind, I spoke to Robynne Chutkan, a gastroenterologist at Georgetown Hospital and the author of Gutbliss and The Microbiome Solution: a pair of books about the gastrointestinal tract, the microbes that live in it, and the stool that comes out of it.
Lactobacillus johnsonii, a beneficial species of gut bacteria. (Kathryn Cross, IFR)
It's tempting to think of feces as simply the used-up remains of the food you ate — the stuff that makes it through after digestion.
In reality, this stuff is present, but 50 to 80 percent of your poop (excluding water) is actually bacteria that had been living in your intestines and was then ejected as food passed through. Many of the bacteria in poop are still alive, but some are dead — carcasses of species that bloomed as they fed on the indigestible plant matter you consumed, then died shortly afterward.
But it's not all bacteria. Your poop also includes some of this indigestible plant matter — like the cellulose in vegetables — with the exact proportions dependent on your diet. Your poop also contains small amounts of your own tissue: intestinal lining cells that were sloughed off during digestion. And, of course, there's water.
Your feces' color is the result of a chemical called stercobilin. That chemical ends up in your poop in two ways: it is a by-product of the hemoglobin in broken-down red blood cells, and it also comes from bile, the fluid secreted into your intestines to help digest fat.
Chutkan says that in a person with an optimally-functioning digestive system, "the ideal stool is a deep chocolatey color — like melted chocolate.”
Without stercobilin present, poop would be a pale grey or whitish color. We know this because people who have liver disease or clogged bile ducts (causing little or no bile to get to their intestines) have light-colored feces, a condition known as acholic stool.
Other colors of poop can be a sign of other conditions. Yellow stool can be the result of a parasitic infection, or pancreatic cancer. Black or dark red poop can be an indication of bleeding in the upper GI tract — or of eating beets. Green feces can also be the sign of an infection. If your poop is blue, it's probably just because of blue food coloring.
Because of anatomical differences, men and women's GI tracts work a little differently. These differences are so significant, in fact, that Chutkan says she could perform a colonoscopy and correctly guess the patient's sex without knowing it beforehand.
For starters, women have wider pelvises than men, as well as extra internal organs (such as the uterus and ovaries) in the region. As a result, their colons hang a bit lower than men's, and are a bit longer: on average, by ten centimeters. Finally, men have more rigid abdominal walls that help push food through the GI tract more effectively.
All this, Chutkan says, "makes the passage of stool much more challenging for women." Food takes longer to transit through most women, she says, making them more prone to bloating. Men, on the other hand, are generally much more regular.
Although Chutkan cautions that there's no single "ideal poop," she notes that there are some characteristics that are a sign of a healthy digestive system and microbiome.
There are some doctors that say pooping three times a week is sufficient, but Chutkan says that you should probably make a bowel movement every day — assuming you're eating food every day. (In some cases, irregularity can actually be caused by extreme stress, as hormones like adrenaline and cortisol can slow down the digestive process.)
Under ideal conditions, she says, "it should be very easy to pass — almost effortless." And it should take the form of a continuous log or two, with a diameter similar to that of a circle you can make with your index finger and thumb.
Finally, poop should sink, not float. Floating stool is usually a sign of poor nutrient absorption or excessive gas.
Of course, poops come in all shapes and sizes — as shown in the Bristol stool scale, created by the University of Bristol's Ken Heaton, at right — but Chutkan says the ideal poop is a three or four on the scale.
If your poop isn't a perfect, easy, continuous log, it's not necessarily a sign that you're sick. But it may be a sign that you're not eating enough fibre, or that your gut microbiome isn't in great shape.
The key to good poops, Chutkan says, is straightforward: "What really makes a good stool is large amounts of the indigestible plant matter that feed gut bacteria." This plant fibre — mostly cellulose — also directly adds bulk to poop, so a plant-heavy diet is critical for nice, solid bowel movements.
But having a diverse and healthy community of gut bacteria is also essential — and for many people, overuse of antibiotics is a problem. Research has shown that a single course of ciprofloxacin, for instance, can disrupt a third of the microbe species naturally present in our gut, and other work has suggested that in some people, the microbiome might never really recover. Over-the-counter probiotic products, meanwhile, usually just have a single species of bacteria, and can't replace the diversity of microbes that have been lost.
Killing your gut bacteria can lead to many problems, in some cases giving harmful bacteria, like C. difficile, more space to proliferate. But it can also lead to overly soft, unpleasant poops. For these reasons, Chutkan recommends thinking carefully before asking for (or accepting) a case of antibiotics, and making sure that the infection you're seeking to treat really needs it.
The explanation for the widely-observed corn-kernel-in-poop phenomenon is pretty simple: the outside of a kernel of corn is made of cellulose, that indigestible plant fibre. We can digest the inside of the kernel, but the hull makes it through us unscathed.
This is also true for lots of other parts of plants — like, for example, kale stems — but corn's bright yellow color stands out, making it easy to spot.
There's a benefit to this phenomenon. If you're interested in tracking how long it takes food to transit through your body — whether to gauge the health of your digestive system, or just to satisfy your curiosity — you can use corn kernels as a tracker.
It might not be a huge surprise, because different diets lead to different types of poop. But Chutkan says that the feces of most people in the developing world are noticeably different from those of people eating a Western diet, mostly because the latter contains so much less fibre.
A very fibre-heavy diet — the type eaten by many people in developing countries, and by some vegetarians in the US — leads to much denser and bulkier poops. "They're bigger movements that come out more easily," she says. "And there's very little need to wipe — it's a much cleaner evacuation.”
Western-style stools, by contrast, are much softer, and the colon has to push harder to get them out.
The first few bowel movements of a newborn infant are called meconium — and if you've never seen it before, it's pretty bizarre.
It's the result of nutrients consumed by the infant inside the womb, and it's a dark green, tar-like substance. It looks so different from normal poop because of the sorts of things the baby was consuming in the uterus: amniotic fluid, blood and skin cells, and mucus.
Strangely, meconium is also usually odorless. The baby's poop will not stay that way.
It might seem crazy, but research increasingly tells us that the most effective way to treat C. diff — the harmful bacteria that can proliferate in your intestines if beneficial bacteria are wiped out — is by taking a healthy person's poop and putting it in your own GI tract. The formal name for this is a fecal transplant.
That doesn't mean you should try it at home. But controlled studies have found that fecal transplants have success rates around 90 percent, higher than any antibiotic. This makes sense: a C. diff infection is often caused by an antibiotic indiscriminately killing beneficial bacteria in someone's intestines, so re-colonizing them with healthy bacteria is a means of crowding the C. diff out.
This is becoming an increasingly mainstream procedure, and researchers are currently working on alternate means of fecal transplant deliveries, like frozen poop or pills that can be taken orally.