What Blue Poop Can Tell You About Your Gut Health

Two blue muffins for breakfast can help reveal a lot about your gut microbiome.

We all poop. The shape, size, consistency, smell, frequency, and color of our poop varies widely from person to person. But these are not the only qualities that can reveal information about your health. A team of scientists—part of a nutrition research company called ZOE—are using blue poop to study another way to measure gut health.

Anyone can participate in ZOE's Blue Poop Challenge: By eating muffins baked with royal blue food dye, which turns your poop blue, you can track how long it takes food to travel through your gut.

So what? Well, here's what you should know about the Blue Poop Challenge—like how it tracks your gut transit time and can reveal some interesting secrets about your digestive system.

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What Is the Blue Poop Challenge?

In a study published in 2021 in the journal Gut, a group of researchers concluded that gut transit time—or how long it takes food to travel through your gut—may provide even more information about how your gut functions than what you can tell from stool consistency and frequency.

"Poop is like a message from your gut, and it has a lot to say," gut health nutritionist Amanda Sauceda, RDN, said in a ZOE video about the challenge. "The color, the consistency, how often you're pooping, how long it takes food to move through your gut reveals a lot about what is happening inside of you."

The researchers found that blue poop is a good marker of gut transit time, allowing us to reliably measure how quickly it takes us to digest and excrete blue food. And that's how the Blue Poop Challenge works.

To participate in the challenge, first, you need to bake some blue muffins. Follow the recipe, per ZOE, which lists all of the ingredients you need and step-by-step instructions. The most important ingredient is royal blue food dye. But if you are not a skilled baker, you can purchase a blue muffin directly from ZOE.

Once you have your blue muffins, it's time to eat. Enjoy two blue muffins for breakfast, being sure to make a note of the time. Then, let nature take its course. As you wait to have a particularly colorful bowel movement, you can eat whatever you want—no matter the color—for the rest of the day, Will Bulsiewicz, MD, gastroenterologist and author of The Fiber Fueled Cookbook, explained in the video.

When you finally see blue poop show up in the toilet, make another note of the time. Then, visit ZOE, where you can plug in the times you ate the muffins and when you noticed blue poop. The website also asks for information about your height, weight, and general diet habits.

Based on all of those data, ZOE populates what it refers to as your "poop personality," which includes your gut transit time, as well as what you can work on to improve your gut health. It will compare your gut transit time to others who took the challenge and give you personalized gut health tips.

What Gut Transit Time Says About Your Gut Health

In the 2021 study, the researchers recruited 1,000 people to test the Blue Poop Challenge. They found that gut transit time lasted anywhere from less than 12 hours to several days, but the median time was approximately 28.7 hours. The researchers compared those times to microorganisms found in stool samples to understand each person's gut microbiome.

According to a study published in 2015 in the journal Current Opinion in Gastroenterology, your gut microbiome is where trillions of microorganisms—including bacteria and fungi—live and help your digestive system break down food. Basically, it helps absorb nutrients that maintain your gut health.

Knowing how well your gut microbiome works is important to understanding your gut health. That's because your gut microbiome plays a role in supporting your digestive and immune systems, as well as other health factors—including your weight, blood sugar levels, and cholesterol.

In the 2021 study, shorter gut transit times generally corresponded to better gut health, less abdominal fat, and healthier responses to food than longer gut transit times. However, the connection between your gut transit time and gut health is complex. The Blue Poop Challenge is only one way to understand that connection.

A Quick Review

Like the participants in the 2021 study, you can also participate in the Blue Poop Challenge to measure your gut travel time and learn about your gut health.

"The key to health and weight loss lies not in the latest fad diet or calories consumed, but in the microbes inside us," Tim Spector, MD, professor of genetic epidemiology at King's College London in England, said in a press release from Cision PR Newswire. "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 scientists behind the Blue Poop Challenge point out, that information cannot diagnose, prevent, or treat any health condition. So, if you do have any concerns about your poop or digestive system, you should consult a healthcare provider.

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