Dr. David Borenstein on Why 1 in 7 People Have IBS, and Why Elimination Diets Alone Rarely Fix It
Dr. David Borenstein says an IBS diagnosis should start the workup, not end it, and explains why more patients are trying a less strict low-fermentation diet
Irritable bowel syndrome affects roughly one in seven people worldwide, according to a meta-analysis of 96 studies from 2006 to 2024 across 52 countries that put global prevalence at 14.1% under combined Rome III and Rome IV diagnostic criteria. That makes IBS one of the most common conditions in gastroenterology. It's also one of the hardest to pin down, since there is no blood test, biopsy, or imaging study that confirms it. Diagnosis still rests almost entirely on a symptom checklist.
That gap between how common IBS is and how little objective testing exists for it is exactly what frustrates Dr. David Borenstein, owner of Manhattan Integrative Medicine, an integrative and functional medicine practice with offices in Boca Raton, Fla., and New York. "Patients come in having already been told they have IBS, and that's often where the workup stopped," Borenstein said. "A symptom pattern tells you what's happening. It doesn't tell you why."
The diagnostic criteria themselves have moved considerably in recent years, which complicates the picture further. The Rome Foundation's own global epidemiology study found IBS prevalence of 10.1% in its internet survey using the older Rome III criteria, compared with just 4.1% under the tighter Rome IV standard, largely because Rome IV requires abdominal pain at least one day a week on average rather than the three days a month Rome III allowed. That's a big enough swing to change how common the condition looks in national health statistics depending on which definition a given study uses.
Borenstein, who is board certified in physical medicine and rehabilitation and whose practice lists board certifications from the American College for Advancement in Medicine and the American Academy of Anti-Aging Medicine, argues that whichever criteria a patient technically meets, the label is a starting point rather than an endpoint. "Two patients can both qualify for an IBS diagnosis and have almost nothing in common underneath it," he said. "One might have an altered gut microbiome, with lower microbial diversity and shifts in key bacterial populations. Another might have an undiagnosed food sensitivity, or a nervous system stuck in a stress response that's driving the gut symptoms. Treating all of them the same way is why so many people feel like they've tried everything and nothing works."
Diet is usually the first intervention offered, and the evidence for one piece of it is real. A systematic review that pooled six controlled trials found that patients following a low-FODMAP diet reported higher quality-of-life scores than those on control diets, though the researchers themselves noted it's unclear whether the improvement was large enough to be clinically meaningful. Borenstein cautions that a low-FODMAP plan was designed as a diagnostic and short-term therapeutic tool, not a permanent way of eating. "I see patients who've been avoiding entire food groups for years because nobody ever walked them back through reintroduction," he said. "That's not treatment, that's just restriction, and it comes with its own costs, nutritionally and socially."
Borenstein says more practitioners are now having their patients follow a low-fermentation diet instead, because it is less strict than low-FODMAP and easier for patients to tolerate. The approach is associated with Dr. Mark Pimentel, a Cedars-Sinai gastroenterologist whose research links many IBS cases to bacterial overgrowth in the small intestine. As Cedars-Sinai describes it, the diet restricts foods that are harder to digest, such as fiber and non-digestible sweeteners like stevia and sucralose. Pimentel has said it won't cure IBS on its own, but that once the bacteria are treated, diet can help prevent a recurrence.
His practice layers additional tools around dietary work rather than treating diet as the whole plan. That includes addressing the gut-brain axis through stress-reduction techniques and, in appropriate cases, medical acupuncture, in which he is separately certified. It also includes screening for small intestinal bacterial overgrowth and other overlooked contributors, and sequencing food reintroduction methodically instead of leaving patients on an indefinite restriction. "The gut and the nervous system are in constant communication," Borenstein said. "If you only ever address one side of that conversation, you get partial results at best."
Borenstein's broader clinical background spans more than gut health. He has been published in the European Journal of Ultrasound and served as chief investigator on a spinal cord injury research project, and he says the same principle that shaped that research applies to IBS care, looking for the mechanism before settling on a label. "The greatest feeling of accomplishment comes from helping make real changes in people's lives, especially after they've been through a difficult time," he said. "For a lot of IBS patients, that difficult time is years of being told their labs are normal while they still don't feel right."
His advice to patients living with chronic gut symptoms is simple. An IBS diagnosis should prompt more questions, not fewer. "If a diet alone hasn't fixed it after a real trial, that's information, it's telling you the cause lives somewhere else," he said. "Chronic symptoms deserve a root-cause workup, not just a label and a pamphlet."
