What Is Poop?

Poop is a key biomarker of human health—a window into our inner world that can tell us a great deal about what’s happening inside our gastrointestinal tract. But, in our rush to get rid of this data dump, we don’t pay attention to the insights it could offer. Simple markers like Bristol stool type and regularity, if tracked, could inform our choices and help us better understand how they, in turn, impact our poop.

In order to decode what our poop is telling us, we need to understand the poop basics: how it’s made, what it really is, and what characteristics to pay attention to.

Poop is one of the end results of the digestive process. After you eat, food makes its way through your digestive system, and is broken down into accessible nutrients your body can absorb along the way. By the time food makes its way through your stomach and small intestine, the bulk of nutrients have been absorbed and any leftover material is shipped to the large intestine (or colon), where trillions of bacteria continue the process of breaking down what your body couldn’t.

Any additional nutrients, including water, are absorbed in the large intestine, and anything that’s left exits your body as waste. There are many key stakeholders involved in coordinating a bowel movement, including muscles, nerves, and signaling molecules like neurotransmitters. Resident gut microbes also play a role in regulating intestinal motility and stimulating muscle contractions for evacuations. 🤓

Now, let’s break poop down by zooming in (6,000x).

The composition of human feces is roughly 75% water and 25% solid waste, including: cellular lining, plant fibers, fats, proteins, mucus, bile, and a collection of other substances your body couldn’t digest.¹ This 25% also contains an invisible galaxy of microbes—bacteria, viruses, archaea—both living and dead. In fact, it’s estimated that within each gram of stool there are nearly 100 billion bacteria.² (To put that into perspective, the Milky Way galaxy has an estimated 100–400 billion stars within.)

You can’t see these microbes with the naked eye, of course, but you definitely can see one of their byproducts…

Ever wonder why your poop is brown? The answer is mostly bile (and bacteria). Your liver secretes something called bilirubin (found in bile), which makes its way to the large intestine. Certain bacteria work to change this bilirubin to urobilinogen, which is then converted by other bacteria into something called stercobilin. This stercobilin is ultimately excreted through your #2, and gives it its characteristic brown hue.⁠

What should you look out for when you take a #2? Here are a few characteristics of poop that can provide clues about your overall gut health:

• Shape and texture: Get acquainted with the Bristol Stool Chart. Developed by Dr. Stephen Lewis and Dr. Ken Heaton at the University of Bristol in 1997, it’s a universal classification tool for human feces. You can think of it as a decoder for your toilet bowl—and for your digestive health. A few days of “abnormal” stool are no big deal. Your poop’s shape and texture naturally shift depending on factors like your diet, alcohol consumption, and stress levels. If irregular stool becomes a pattern for you, however, you’ll want to flag it to a doctor.
• Frequency: Pooping anywhere from three times per day to three times per week can be considered healthy.³ Temporary changes in frequency are also normal and can be a result of diet, physical activity, and stress. If you’re not pooping as much as usual, it could be because you’re dehydrated or lacking fiber in your diet. 
• Color: Yes, it’s usually brown, but color variations (green, clay-colored, yellow, black, and red) are possible. Variations in color can be a result of dietary inputs (food dyes, certain supplements or medications, vegetables with deep colors) or a variety of medical issues (hemorrhoids, for example). If your stool color is out of the ordinary and you’re experiencing other digestive symptoms, reach out to a doctor just to be safe. 
• Smell: As your resident bacteria help break down your food, they release byproducts like indole that give your poop its signature smell. Poop odors can also vary when you eat certain foods (like cheese, meat, and wine).

EXPLORE FURTHER: How to “Read” Your Poop

Your poop provides a window into your gut microbiome—so it’s worth taking a peek at its color, shape, and texture before you flush it down the toilet. If stool grosses you out, resist the conditioning, strip away the stigma, and recognize poop for what it is—water, undigested food, bacteria, and one of the most visible biomarkers of your gastrointestinal and overall health.

Still have some burning queries about your bowels? We answered the top five poop questions here.

1. Stephen, A. M., & Cummings, J. H. (1980). The microbial contribution to human faecal mass. Journal of medical microbiology, 13(1), 45–56. https://doi.org/10.1099/00222615-13-1-45
2. Sender, R., Fuchs, S., & Milo, R. (2016). Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLoS biology, 14(8), e1002533. https://doi.org/10.1371/journal.pbio.1002533
3. Mitsuhashi, S., Ballou, S., Jiang, Z. G., Hirsch, W., Nee, J., Iturrino, J., Cheng, V., & Lembo, A. (2018). Characterizing Normal Bowel Frequency and Consistency in a Representative Sample of Adults in the United States (NHANES). The American journal of gastroenterology, 113(1), 115–123. https://doi.org/10.1038/ajg.2017.213