Can blue poo reveal how smart you are?
BBCWhat can our digestion tell us about how our brains work?
Experts at the University of Southampton say we still don't understand enough about this important connection.
A research team is asking thousands of people to take what's called the Blue Poo Test.
It involves tracking the speed muffins baked with edible food colouring are digested and then taking part in online brain games.
This science project aims to better understand the link between our gut and our brains.
Jonathan Swan is a Professor of biomolecular medicine at the University of Southampton.
"Everyone's gut works at a different speed – it's an indicator of gut function and tells us something about our gut health – but we still don't really know what that means for our brains.
"This is where our blue-poo toilet test comes in. By measuring how quickly the muffins pass through you, we can determine if a faster gut transit means a sharper mind or if slower digestion changes how you think."
The Southampton scientists want data from thousands of participants in the UK.
The muffins have been handed out in Southampton city centre but can also be baked at home using a vegan-friendly recipe with edible blue food dye purchased online.
The research teams says the blue poo test is open to children from as young as five all the way up to adults nearing 100 years old.
It takes 24 to 72 hours on average for food to travel through and leave the body.
Having eaten a muffin, once a participant's poo turns blue, they are asked to play online games to measure their problem solving skills and decision making under pressure.
After people complete these five-minute brain games, they get a summary of their results pitting their cognitive performance against others across the country.
Swann says 'We want to map out how gut-digestion times shift across age groups, sexes and regions, and how that correlates with brain performance.
"While faster digestion may sound better for health, there is likely to be a sweet spot. Food shouldn't take days to move through the body, but equally faster digestion caused by an illness is not the goal.
"Very slow gut transit can mean food takes days to move through our body but very quick transit can reduce the time available for water and nutrients to be absorbed."
The blue poo test is led by the Gut Immune Brain Axis Network+ which is funded by the Biotechnology and Biological Sciences Research Council (UK Research and Innovation).
Swann says: "Everyone wants to sharpen up how they think and so if we can understand how the gut can have that effect on the brain we can look at ways to fine tune the gut and it's processes to achieve that."
The Southampton scientists hope to publish their results next year.