What your GI transit time says about your gut health

GI transit time is how long food stays in your gut. It starts when food enters your mouth and ends when it becomes cannon fodder to your morning coffee.

A recent paper found that GI transit time tells us a lot about our gut and metabolic health. But the most interesting thing about the study isn’t so much what they found as how they found it. To measure GI transit time, they turned people’s poop blue.

Participants in the study ate blue muffins and timed how long it took to get the blue out by looking at the color of their poo. Consequently, the time from eating the blue muffins to having blue poo tells them their GI transit time.

In the study, they found that transit time correlated to variations in the microbiome and postprandial lipid and glucose responses to meals. For instance, people with faster transit time had lower microbial diversity but lower visceral fat and lower postprandial meal responses.

Fortunately, they made the muffin recipe available and even created a program to enter your data. Just head on over to https://joinzoe.com/bluepoop and you can get some info on what your transit time says about you. Simply:

  • Bake and eat your muffins
  • See how long they take to come out
  • Answer some questions about your diet

They’ll even generate a little report and even tell you about some likely members of your microbiome.

My GI transit time

Of course, I was game for doing this. Therefore, I baked my muffins and ate them last Wednesday morning at 10:30am.

I suspected that they’d be out the next day, and I was right. From start to finish, it took a total of 21 hours from eating my muffins to finding the blue(actually green for me) at 7:30am the next day. This made me Sir Poops A Lot:

My GI transit time

This wasn’t all that surprising to me, though it’s a bit of a misnomer. I only poop once a day, but it’s always a full elimination between 7:30am-8am every day.

Overall, my GI transit time is about 7 hours faster than average.

What’s interesting to me is that many of their predictions based on faster transit time seem to hold true for me:

  • Low visceral fat
  • Low microbiome diversity
  • Lower postprandial glucose response(I crush an OGTT and have an A1c of 4.8%)
  • The microbes they predict I should have all pop up on my older Ubiome reports

They also discuss how each of the beneficial microbes I have play a role in my better metabolic response to meals. Much of this is based on their data from the PREDICT trials.

Furthermore, the microbes that correlate with longer GI times, Akkermansia muciniphila and Methanobrevibacter species, never showed up on any report. Thought, I’m not sure Ubiome ever measured the latter.

I have no idea what my postprandial triglyceride response is, but my fasting triglycerides are normally in the lower 40s mg/dL.

What does it all mean?

This project is part of a collaboration between King’s College & ZOE to help bring personalized nutrition to the masses. The goal is to use data from the microbiome, postprandial meal responses, and other information to develop optimal diets for the individual.

It also gives us some insight on the way things may drive these changes. For instance, slower transit time gives bacteria more time to act on the food we eat.

Therefore, longer transit times may promote greater diversity by giving slower growing species time to grow. This seems to be the case with Methanobrevibacter species, which are important for removing excess hydrogen and other end-products generated by other bacteria.

They also discuss how longer transit times may cause an increase in protein fermentation in the gut. Protein fermentation causes an increase in the production of branch-chain fatty acids at the expense of short-chain fatty acids.

We covered the metabolic flexibility of the microbiome and how it shifts in a blog you can check out here. Interestingly, a new paper found that treating people with epilepsy with a ketogenic diet led to decreases in both BCFAs and SCFAs.

Of particular note is that the protein intake of the keto diet was quite low. Therapeutic ketogenic diets are generally lower in protein. As we covered in another blog you can read here, certain foods/amino acids promote the production of butyrate.


A personalized approach to diet is likely the best one. Over the course of the last 15 years, I’ve worked rather diligently to find out what works best for me. This included forays in to Keto, Paleo, gluten-free, and dairy-free diets.

The #bluepoopchallenge is pretty interesting. Researchers found that GI transit time is more predictive of gut health and the microbiome than stool frequency or consistency. It wouldn’t surprise me if we each have our personal transit time range that make some diets more appropriate than others.

Give the blue poop challenge a go and see where your GI transit falls.

3 thoughts on “What your GI transit time says about your gut health

    • cincodm says:

      It depends, you have to determine the cause. That could be any number of reasons: Poor metabolic health, dysbiosis, postinfectious pathology, etc.

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