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Unsurprisingly, those with faster gut transit times tended to have microbiomes dominated by faster-growing species that thrive on a high-carbohydrate, low-fat diet. Slower transit times, meanwhile, were sometimes dominated by species that thrive on protein.

Each of these extremes also had lower gut microbiome diversity than people with average gut transit times, suggesting that fast and slow movement creates environments where specialist species come out on top.

That would then create a feedback loop in which the dominant species in each environment releases metabolites that maintain the status quo.

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This may also help explain why the same gut health advice may not work for everyone. Two people can eat the exact same meal and get two very different results, depending on how fast their poop usually moves.

Transit times may even influence how your body responds to probiotics and certain supplements or medications that interact with the gut. This suggests that recognizing the individual gut rhythm of the patient could help tailor treatments and dietary advice that precisely matches their body.

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