Staring down in the toilet bowl, Professor Tim Spector had momentarily forgotten he’d eaten a muffin filled with food colouring. Poking from the well of water was the contents of his bowel, in a shocking shade of electric blue. 

Spector, professor of genetic epidemiology at King’s College London and author of The Diet Myth, is calling for members of the public to follow suit and eat blue-coloured muffins to monitor their gut transit times. This is the time it takes for food to travel from your mouth to the other end.

The aim is to educate people about their biology, specifically their gut health, and to get people talking about the glamorous topic of poo.

Prof Spector was involved in a study, published in the medical journal Gut, which saw 863 healthy individuals eat food with blue dye to monitor gut transit times. It found longer gut transit times were generally linked with more undesirable bacteria, while shorter transit times indicated a healthier gut.

The gut microbiome is crucial for our health, says Prof Spector. Think of it a bit like a community of microbes made up of things like microorganisms, bacteria, viruses and fungi. “There are trillions of these guys and they are crucial for many bits of our body running well,” says Prof Spector. “This includes things like how well we digest food, how we deposit fat, our mental state, whether we’re hungry or full, and it’s really important for our immune system as well.”

He wants people to eat blue-coloured food – specifically two blue muffins – and then time how long it takes for them to have a blue-green poo. It’s one of the “easiest ways” to get an idea of what’s happening in your gut, he says, as you can monitor exactly how quickly your body processes it.

How to take part

1. Bake your own muffins (with food colouring) at home. Eat two for breakfast and start your timer.

2. Look out for blue-green poo when you go to the toilet. Jot down the time you spot it.

3. Get your results and discover your ‘poo personality’ on the Blue Poop Challenge website.

We know from Prof Spector’s research that shorter gut transit times of around 20 hours are indicative of a healthier and happier gut, while longer transit times (30+ hours) suggest a more unhealthy microbiome.

People who are constipated have a slow gut transit time. “They are generally more likely to have bad gut health and bad microbes,” Prof Spector says. “This study showed there was … a clear link between having a speedy transit time and having a healthy range of diverse microbes that are good for your health.”

His study suggests gut transit times are a more informative marker of your gut microbiome function than traditional measures used currently, such as the Bristol stool chart. (You might remember this from a trip to your GP. The poster shows you different poo types, from hard, rabbit-like rocks to runny sludge. Patients are asked to pick which one of these seven types they are.)

Ultimately, Prof Spector hopes the #BluePoopCampaign campaign will get people talking about their bowel movements a bit more – because we’re pretty crap at it compared to other countries. 

“We want to educate people so they start talking about gut health without embarrassment,” says Prof Spector, who admits he’s done this experiment himself a couple of times. “It’s always a shock because I forget until I look in the toilet,” he laughs. “It’s a shocking blue!” His gut transit time is around 18 hours, which is pretty healthy. 

What if my gut transit time is too slow?

It you take part and notice your transit time is on the slow side, there are four changes you can make to improve your gut microbiome (and speed things up).

1. Eat more diverse type of plants. Ideally you should be eating 30 plants a week, says Prof Spector, which includes fruit, veg, nuts, seeds and herbs. This helps improve the diversity of your gut microbiome while also giving you plenty of fibre to move things along. 

2. Pick brightly coloured plants to eat. Prof Spector notes foods with polyphenols in them are great. Think: brightly coloured berries, apples, nuts, green lettuce, apricots.

3. Eat more fermented foods like yoghurt as well as the four Ks: kefir, kombucha, kimchi and kraut (or sauerkraut).

4. Avoid ultra processed foods as these are bad for gut health. Ultra processed foods are not simply ‘modified foods’ – like frozen or tinned products – but foods that have undergone multiple processes which result “in little, if any, intact whole foods being present”. Examples include sweets, packaged snacks like biscuits and crisps, ready meals and soft drinks.