Long-term microbiome and clinical effects of a microbiome-guided personalized diet versus low-FODMAP diet in irritable bowel syndrome: A 12-month follow-up randomized controlled trial.

The short version

This 12-month follow-up study revisited 121 adults with irritable bowel syndrome (IBS, a common gut condition causing pain, bloating, and altered bowel habits) who had completed a 6-week randomized trial comparing two dietary approaches: a standard low-FODMAP diet (LFD, which restricts fermentable carbs known to trigger IBS symptoms) and a microbiome-guided personalized diet (PD, built from each person's own gut-bacteria profile using a machine-learning algorithm). The goal was to see whether the benefits people got in the first 6 weeks actually lasted a full year, and whether either diet changed the gut microbiome (the community of bacteria living in the digestive tract) over that time. Participants, recruited at four Turkish gastroenterology clinics, were followed with symptom, quality-of-life, and mood questionnaires plus stool samples for gut-bacteria testing at 6 and 12 months after their original 6-week diet ended (nobody's diet plan was updated again after the start). Seventy people who got the personalized diet and 51 who got the low-FODMAP diet were included at the start of follow-up, though many dropped out over the year, leaving 40 and 29, respectively, providing data at 12 months. Both diets worked well at first, cutting symptom-severity scores by roughly 100 points within 6 weeks. But by 12 months the picture diverged: people on the personalized diet kept most of that improvement (still about 78 points better than baseline), while people on the low-FODMAP diet had drifted back close to where they started. About 63% of the personalized-diet group still counted as meaningful responders at 12 months, compared with about 35% of the low-FODMAP group. The personalized-diet group also showed steadier gains in quality of life and in anxiety and depression scores. On the microbiome side, gut-bacteria diversity rose more and stayed higher in the personalized-diet group throughout the year, though the two groups' overall bacterial makeup looked similar by 12 months, and no single type of bacteria reliably separated the two diets. The takeaway is that tailoring a diet to someone's own gut bacteria may help IBS relief last longer than a standard restrictive diet, which seemed to lose its effect without further guidance. That said, the researchers are careful to call these findings hypothesis-generating rather than proven: many participants dropped out, everyone knew which diet they were on, and the gut-bacteria testing used here cannot show which bacterial genes or byproducts, if any, actually drove the improvement. Larger, purpose-built trials are needed before personalized, microbiome-guided diets become a routine part of IBS care.

Key findings

• In a 12-month follow-up of 121 adults with irritable bowel syndrome (IBS), a diet personalized to each person's own gut bacteria (using a machine-learning analysis of a stool sample) kept most of its symptom-relief benefit a year later, while a standard low-FODMAP diet (which restricts fermentable carbohydrates) lost much of its early benefit over the same period.
• At 12 months, about 63% of people on the personalized diet still counted as meaningful responders (at least a 50-point drop in symptom severity), compared with about 35% on the low-FODMAP diet.
• The personalized-diet group showed steadier gut-bacteria diversity (a measure of how many different types of bacteria are present) over the year, though the two diets' overall bacterial makeup looked similar by 12 months and no single bacterial species reliably told the groups apart.
• Both diets improved symptoms, quality of life, and anxiety/depression scores within the first 6 weeks; the personalized diet's advantage only became clear over the following months.
• The researchers call these findings hypothesis-generating, not proof: many participants dropped out over the year, nobody was blinded to which diet they were following, and the gut-bacteria testing used cannot show which bacterial genes or products actually drove the improvement. Larger, purpose-built trials are needed.

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