Researchers Found a Genetic Pattern Behind a Very Personal Daily Routine

A massive genetic study has uncovered a connection few people would expect: how frequently you go to the bathroom may be tied to how your body processes vitamin B1.

After analyzing genetic and health data from more than 268,000 people, researchers found that variations in how the body handles thiamine, better known as vitamin B1, are linked to bowel movement frequency.

The findings, published in Gut, suggest that something as ordinary as digestion may be quietly shaped by both diet and genetics.

What Your Bathroom Habits Reveal About Your Gut

Bowel movement frequency is more than a daily routine. It is one of the clearest indicators of gut motility, the speed at which food moves through the digestive tract.

When that system runs too slowly or too quickly, it can contribute to constipation, diarrhea, or conditions such as irritable bowel syndrome.

Despite how common these issues are, the biological mechanisms that control gut motility are still not fully understood.

To explore them, an international research team led by Mauro D’Amato examined genome-wide data from 268,606 participants of European and East Asian ancestry.

The researchers, based at LUM University and CIC bioGUNE, searched for DNA variations associated with how often people passed stool.

Twenty-One Genetic Signals, and an Unexpected Nutrient

Their analysis identified 21 regions of the human genome linked to bowel movement frequency, including 10 that had never been reported before.

Many of these regions aligned with well-known gut-control systems, such as bile acid metabolism and acetylcholine-based nerve signaling, both of which help regulate intestinal muscle contractions.

But two genes stood out.

The genes SLC35F3 and XPR1 are directly involved in how vitamin B1 is transported and activated in the body. Their presence in the genetic signals surprised researchers and shifted the focus of the study toward nutrition-related pathways in gut function.

In short, vitamin B1 suddenly became a central piece of the puzzle.

Not Everyone Responds to Vitamin B1 the Same Way

To test whether thiamine intake actually affects bowel habits, the team turned to dietary records from 98,449 participants in the UK Biobank. The results showed a clear trend: people who consumed more vitamin B1 tended to have more frequent bowel movements.

However, the effect was not uniform.

Individuals carrying specific variants of SLC35F3 and XPR1 were far more sensitive to thiamine intake than others. For them, increases in vitamin B1 consumption were more strongly associated with changes in stool frequency.

Researchers described this interaction as a combined genetic score, emphasizing that diet alone does not explain gut behavior; genes matter too.

Why This Could Matter for IBS Treatment

The implications extend beyond everyday digestion. The researchers found evidence of a shared biological basis between bowel movement frequency and conditions such as irritable bowel syndrome.

Since altered gut motility lies at the core of IBS, mapping the genetic pathways that influence intestinal movement could help guide future therapies. Rather than treating symptoms alone, clinicians may eventually tailor treatments based on how a patient’s body processes nutrients like vitamin B1.

As the study’s first author, Dr. Cristian Diaz-Muñoz, explained, genetics offered a new way to see the digestive system as a whole.

“We used genetics to build a roadmap of biological pathways that set the gut’s pace. What stood out was how strongly the data pointed to vitamin B1 metabolism, alongside established mechanisms like bile acids and nerve signaling.”

A Reminder That Digestion Is Deeply Personal

The study does not suggest that vitamin B1 supplements are a cure-all for digestive issues. Instead, it highlights something more nuanced: the same nutrient can have very different effects depending on a person’s genetic makeup.