We all poop. But the shape, size, consistency, smell, frequency, and color of our poo varies widely from person to person. Well, not if a team of scientists gets their way. They want us to each have blue poo-at least for a little bit.

It's all part of the Blue Poop Challenge.

By eating food made with blue food coloring, which will turn what you poop out blue, nutrition research company ZOE wants you to track how long it takes for food to travel through your gut. Why? Because knowing your gut transit time (aka, how long it takes for you to eat something and poop it out) can reveal really interesting things about what's happening inside of you.

"Poop is like a message from your gut, and it has a lot to say," gut health nutritionist Amanda Sauceda, RDN, said in a video about the challenge.

How the Blue Poop Challenge works

First, you have to make blue muffins. ZOE includes a recipe on its site that lists all the ingredients you'll need, as well as step-by-step instructions. The company even offers some recommendations about the specific poo-changing royal blue food dye you should use: go with a gel or paste, not a water-based dye. If you don't feel like baking the muffins yourself, you can also buy a blue muffin straight from ZOE.

Once you have your blue muffins, it's time to eat. You're supposed to consume two for breakfast and record the time you ate them. Then, let nature do its thing. As you wait for your blue (or greenish-blue) bowel movement, you can eat whatever you want (no matter the color) for the rest of the day, Will Bulsiewicz, MD, explains in the ZOE video.

When you see blue poop show up in the toilet, make note of the time. Then, go to the ZOE website. You'll be instructed to plug in the time you ate the muffins as well as when you pooped blue. It will also ask you to put in some information about your height, weight, and general diet habits. Based on all that info, the site will give you what they've dubbed your "poop personality": not only your gut transit time, but also tips on what you're doing well and what you can work on when it comes to your gut health. It will also show you how your gut transit time compares to other people who've taken the challenge and give you a personalized gut health tip.

The science behind it

ZOE has already tracked the gut transit time of more than 1,000 people using this blue muffin experiment in a study, and the findings were published in the journal Gut in March 2021. Gut transit time lasted anywhere from less than 12 hours to several days, but the median time was 28.7 hours. Researchers compared these times to what microorganisms were in the poo, so they can better understand what was going on inside each person's gut microbiome.

Basically, your gut microbiome is where trillions of microorganisms, including bacteria and fungi, live; they help you break down your food and make nutrients to keep your system healthy. Knowing how well your gut microbiome is working is important in understanding your overall health. That's because your gut microbiome plays a role in supporting digestion and immunity, as well as other health factors, including your weight and levels of blood sugar and cholesterol.

In the study, the shorter gut transit times were generally associated with better health, less abdominal fat, healthier responses to food, and a healthier gut. (The connection between your gut and health is complex, though, and transit time is just one way this connection could be better understood.)

The researchers behind the study at ZOE are now inviting the general public to take part in the Blue Poop Challenge.

"The key to health and weight loss lies not in the latest fad diet or calories consumed, but in the microbes inside us," study author and ZOE co-founder Tim Spector said in a press release. "The Blue Poop Challenge is a simple way to find out what is going on in your gut. All you need are a couple of blue muffins and a spirit of curiosity to take that first step."

But as the folks behind the Blue Poop Challenge point out, the information you get can't diagnose, prevent, or treat any condition. So if you do have any concerns about your poop or digestive system, it's best to check in with your doctor.