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What is gut transit time? And what's it got to do with blue poop?

Blue poop

Understanding whether our gut is healthy or not can seem a bit ethereal, it certainly does to me. Our gut is a highly complicated and efficient tube which runs from our mouth to our anus and is around 9m long - so how do we know if it's working as it should? There are a few ways we can try to check in with our gut health - do we have alright energy levels? Do we have pain or bloating in our belly area? What do our poops look like and how regular are we?

But have you ever heard of transit time? This is beginning to be understood to be a pretty good indicator of our gut health. It's kind of related to how often we poop, but basically means how long it takes for food to make it all the way from our mouth to out the other end. It's thought to be a better indicator of gut health and the health of our gut microbiome than the more traditional indicator of poop frequency, texture and colour, although this is also important information too. The more we can know about the inner workings of our body the more empowered we can be to help support our own health.

How long food hangs out in your gut is important for a few reasons. The thinking is that you don't want it either too fast, which might mean you're not extracting the maximum amount of nutrients from your food and there could also be effects on the diversity of our gut microbes as they don't have enough time to digest the fibre in our food. Too slow though and our health can be impacted in a few ways resulting in:

  • Greater extraction of water from poop so they're harder and more difficult to pass

  • Greater digestion of proteins by our gut microbes, with the production of undesirable, potentially harmful metabolites. This can increase the risk of diseases such as colorectal cancer

  • There have been studies which have also linked a longer transit time with greater abundance of potentially harmful gut microbes, however this research is in its infancy and so we need more evidence before the full picture is clear.

Either way it seems clear that there's a happy middle ground with gut transit time which suggests that our gut is functioning as it should, not too fast and not too slow. So how can we get an idea of what our gut transit time is?

How to measure transit time

There are a couple of easy ways to get an idea of your transit time. One of them you may have done by accident before, if you're partial to some corn on the cob... Oftentimes we don't chew corn particularly well and so it arrives in our poop pretty much intact as our body has a tough time digesting it fully. However, I wouldn't necessarily recommend swallowing whole pieces of corn so you can get a nice yellow-studded poop. Another way is using beetroot, as it tends to turn our poop a charming red-purple colour, however this can be easy to miss if you're not paying close attention. A potentially better, and maybe even enjoyable way to measure gut transit time is via the blue poop challenge, or essentially eating a couple of bright blue cupcakes and waiting until you get a bright, unusual poop the other end.

I've recently done this myself and so will share how I got on. Basically all you need to do is bake some bright blue cupcakes and eat enough of them for breakfast to ensure you'll see an effect on your poop. Once you've eaten them you can measure how long it takes to get a blue poop either by setting a timer or just making a note of the time you ate them and working out how many hours it's been. I used the Zoe blue poop challenge cupcake recipe, which I've modified below as I found it too sweet, too blue and a little stodgy. You can also add in extra ingredients to mix things up which I'd highly recommend as I found them a bit tough to get down.

Madi with blue cupcakes on plate

Recipe (makes 12 for 6 servings i.e. 2 cupcakes per challenge)

Plain flour x 250g

Baking powder x 1 tbsp

Granulated sugar x 150g

Vegetable oil x 110g

Water x 230g

Vanilla extract x 1 tsp

Blue food colouring* x 1/2 tsp (specific types)

Optional extras: chopped nuts, chocolate chips, cinnamon and raisin

* There are specific types of blue food colouring to use so that your poop will be dyed blue - PME Ocean Blue Food Dye, Sugarflair Royal Blue Food Dye, Ann Clark Royal Blue Food Colouring Gel, Wilton Royal Blue Icing Colour


1. Preheat oven to 180°C (170°C fan oven) and line a muffin tray with 12 small muffin cases.

2. Mix flour, baking powder and sugar in a large bowl.

3. In a jug combine water, vanilla extract and oil.

4. Make a well in the centre of the dry mix and slowly pour in the wet ingredients while mixing gently.

5. When well combined add in the blue food colouring and mix until evenly distributed.

6. Divide the mix evenly between the muffin cases and bake for 20-25 minutes until risen and an inserted skewer comes out clean.

7. Cool and then eat for breakfast with nothing else.

A 'normal' or healthy gut transit time is thought to range anywhere from 14 to 58 hours and anywhere within this range would be considered a healthy transit time. The self-reported results collected by Zoe indicate that the median transit time is 28.7 hours. My personal transit time was slightly longer than this at 31.5 hours, however I found that after eating the blue cupcakes I was about 8 hours slower to go than usual (I'm usually a very regular person), so I'm not sure if eating the cupcakes themselves slowed my transit time down. Who knows, but either way this transit time would be considered healthy. I also noticed that my poop wasn't actually blue it was in fact a shade of sea-green which surprised me somewhat!

If you input your results in the Zoe website and fill out some further info (including BMI and your dietary habits - I won't go into it here but just so you know BMI is a terrible marker of health) they give you a bunch of sort-of pointless but fun information about your result. I was given the title of 'party pooper' for my result (for some reason) and was assigned a 'gut twin'; someone who takes part in the Zoe study with similar characteristics to me. They then shared which 'good' gut microbes my twinny has which although sure is neat really tells me nothing about me, as a totally separate individual. Zoe are also all about personalised nutrition - an approach to nutrition based on individual requirements and responses and which is against blanket health recommendations - so give you a 'personalised' recommendation to improve health. Mine was to eat more whole foods and less processed foods, which doesn't sound particularly special to me as this is a recommendation given to absolutely everyone and relies more on common sense than any nutrition-tech insight.

But if you find yourself on the slower side of things when it comes to gut transit time, what are some ways to speed things up?

How to speed up transit time

There are lots of lifestyle changes you can make if your transit time is a little slower than what's considered 'normal':

  • Increase intake of different fibres by adding a variety of different plant foods to your diet. Some plant foods contain a natural source of polyols which can have a laxative - stone fruits, kiwi, apples, pears, avocados and mushrooms are all good sources of polyols.

  • Eating regular meals throughout the day can stimulate the gut to get going

  • Making sure you're drinking enough water is also so important to help food move along your gut, particularly when you're adding more fibre to your diet

  • Gentle and regular exercise can also stimulate your gut to move things along, so taking a walk after meals can really help.

  • Making toilet time a relaxing and unrushed experience as well as not ignoring the 'call to stool' is crucial - listen to your body!

These tips will all improve gut heath in general so can be applied to anyone, however if you're struggling then supplements can also help. Psyllium husk has some of the best evidence to support its use but partially hydrolysed guar gum (PHGG), a water-soluble fibre with prebiotic activity, also has some of the best research supporting its use to increase gut motility.

Finally, if you have any concerns about your gut health especially if you have unintentional weight loss, blood in your poop, severe pain or have been struggling with a condition for a while then please contact your GP for further investigation. It's always worth getting a professional to support you with your gut health.


Asnicar et al. (2021). Blue poo: impact of gut transit time on the gut microbiome using a novel marker. Gut. 70(9):1665-1674. doi: 10.1136/gutjnl-2020-323877.

Müller et al. (2018). Gastrointestinal Transit Time, Glucose Homeostasis and Metabolic Health: Modulation by Dietary Fibers. Nutrients. 10(3):275. doi: 10.3390/nu10030275.

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