The blue poop challenge, developed by a group of researchers at ZOE, can give a person important information about their gut health.

Healthcare science company ZOE worked with Dr. Sarah Berry, the head of nutrition sciences at King’s College London, to publish their research in the scientific journal Gut.

The study built on previous research, which found strong links between the foods people eat, their health, and their gut microbes. It looked at the transit time between eating two blue muffins and passing them as stool. The results gave insight into gut microbiome function and its relation to other health factors.

To take part in the blue poop challenge, people simply need to eat two muffins dyed blue for breakfast and track their stools for changes. Then, they can record their results on the ZOE website to receive personalized insights about their gut microbiome.

Read more to learn how the blue poop challenge works, why people are doing it, how to make the muffins, and what the results say about gut health.

A rack of blue muffins.Share on Pinterest
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To take part in the blue poop challenge, a person needs to:

  • eat two blue muffins for breakfast and note the date and time
  • eat as they typically would for the rest of the day
  • look at their poop after going to the bathroom to keep an eye out for green-blue shades, noting the date and time they see it
  • visit the ZOE website and click on “get results”
  • enter the gut transit time and answer a few questions about height, weight, and nutrition habits
  • receive personalized insights about their gut microbiome

Although tracking a person’s own stool may seem strange, it can give them valuable insights into their gut health.

In its study, ZOE tracked the gut transit time of 863 people who ate the blue muffins. They found that the time between eating and passing the muffins averaged 28.7 hours, but it ranged from just 12 hours to several days. The researchers were then able to compare each person’s gut transit time with the microorganisms in their poop.

Trillions of microorganisms, including fungi and bacteria, live inside the gut microbiome. They help break down food and produce nutrients necessary for proper bodily function.

A person’s overall health is closely linked to their gut microbiome. It plays a vital role in supporting the immune system, the digestive system, blood sugar, cholesterol, and weight.

Since the study drew connections between gut transit times and gut microbiome, the research can give people insights into what their microbiome may be like. This could improve their understanding of their digestive health and overall well-being.

In their published study, the researchers found that shorter gut transit times were associated with better overall health, a healthier gut, healthier responses to food, and less abdominal fat.

Taking part in the blue poop challenge could help a person understand whether they are likely to be negatively affected by these factors and be better prepared to address them.

However, it does not provide any definitive information about a person’s individual microbiome. So while it can provide interesting insights for curious people, it is not a diagnostic tool.

A person can modify the recipe to their liking. The most important thing is to use the correct amount of royal blue food dye.


This recipe makes 12 muffins.

  • 1 3/4 cups (245 grams) plain, all-purpose flour
  • 1 tbsp. (15 g) baking powder:
  • 1 cup (200 g) granulated sugar
  • 1/2 cup (100 g) vegetable oil
  • 1 cup (230 g) water
  • 1 tsp. vanilla extract
  • 1 tsp. (6 g) royal blue food dye


To make the muffins, a person should:

  • preheat the oven to 325°F (170°C)
  • combine flour, baking powder, and sugar in a large bowl
  • in a separate bowl, combine sunflower oil, water, and vanilla extract
  • form a well in the center of the flour mixture and pour in wet ingredients
  • add the blue food dye to the mixture
  • mix with a whisk until the wet and dry ingredients are well combined and the blue dye is evenly distributed
  • pour equal amounts of batter into each muffin case
  • bake for 24–26 minutes, or until a skewer inserted into the center of a muffin comes out clean
  • set aside to cool for 20–30 minutes

ZOE recommends the following food dyes:

Available in the United States:

  • AmeriColor Soft Gel Paste
  • Ann Clark Royal Blue Food Coloring Gel
  • Wilton Royal Blue Icing Color
  • Sugarflair Royal Blue Food Dye

Available in the United Kingdom:

  • Ann Clark Royal Blue Food Coloring Gel
  • Wilton Royal Blue Icing Color
  • Sugarflair Royal Blue Food Dye
  • PME Ocean Blue Food Dye

Find a gluten-free recipe here and a vegan option here.

Each time a person passes stool, they pass billions of gut microorganisms. What a person eats significantly affects these microorganisms, and this influences a person’s overall health.

An unhealthy balance of good and bad gut microbes can contribute to various health issues, and is associated with obesity, high cholesterol, liver disease, diabetes, high blood pressure, inflammatory bowel disease, and other issues.

Measuring gut transit time with the blue-dyed muffins could help a person understand their gut function. However, the challenge really only provides a small piece of the puzzle to a person’s overall health.

In line with the published study, a shorter gut transit time — which is the time between eating the muffins and seeing blue poop — could indicate better gut health. Longer transit time could indicate an unhealthy balance of gut bacteria, which may indicate that changes in diet and lifestyle may be beneficial to a person’s gut health.

Crowdsourced science is beneficial in many ways, and the blue poop challenge can help both researchers and the individuals who try it.

Mutually beneficial

The blue poop challenge, for example, is beneficial to the researchers, as it gives them large-scale data. It also benefits the participants, as they each receive specific health insights.


Researching in this way allows scientists to gather and analyze data on a much larger scale than they may be able to achieve without crowdsourcing. This means they can perform research faster and at a lower cost.


Various scientific disciplines could benefit from crowdsourcing, especially those that may otherwise have difficulty getting participants or funding.


By involving the public, researchers can take into account the perspectives of individuals and communities. Society can also better understand the scientific findings, which can strengthen trust in the scientific community and foster an interest in science.

The blue poop challenge involves a person eating two blue-dyed muffins and noting how long it takes for them to pass a blue stool. Based on research conducted by healthcare science company ZOE and researchers at King’s College London, the results give individuals insights into their gut health.

Researchers have found that faster transit times are associated with better gut health.