Study Reveals Low-Carb Diets Outperform Medication in Easing IBS Symptoms

A recent study has found that diet—specifically a low-carb diet—could be more effective for relieving symptoms of irritable bowel syndrome (IBS) than medication.

The study, conducted by Swedish researchers and published in The Lancet Gastroenterology and Hepatology in April, compared the effects of a low-FODMAP diet, low-carb diet, and traditional medical treatments for IBS.

According to study author and dietitian Sanna Nybacka, PhD, a postdoctoral researcher at the Chalmers University of Technology in Gothenburg, Sweden, previous studies have not quantified the differences between these approaches. “This is the first study that has tested the efficacy of medical treatment (according to clinical routine) compared to dietary treatment,” she told Health.

The inclusion of a low-carb diet was a particularly new element in the research since the current treatment of IBS often focuses on medications or a low-FODMAP diet. “This was also the first study to test the efficacy of a diet low in total carbohydrates, and the results were surprisingly good,” Nybacka said.

Considering that about 10–15% of American adults live with IBS, these findings could have implications for a large swath of the population. Here’s what to know about what this research might mean for you if you have IBS.

To conduct their study, Nybacka and her colleagues gathered 294 Swedish adults with IBS of any type with moderate-to-severe symptom severity. About one-third were assigned to follow a low-FODMAP diet, one-third to a low-carb diet, and one-third to receive medical treatment.

A low-FODMAP diet was defined as containing approximately 3.4 grams per day of fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. These types of carbohydrates (found in foods like dairy products, certain fruits and vegetables, lentils, and some grains) are known for increasing the amount of fluid in the bowels, creating gas, and changing the speed of digestion.

For this reason, a low-FODMAP diet is often used as a first line of defense for people with IBS whose symptoms are related to food, William Chey, MD, a professor of gastroenterology at the University of Michigan Medical School, told Health.

The low-FODMAP diet in the study was also optimized to contain approximately 30 grams of fiber per day, and included recommendations to limit intake of coffee, alcohol, and carbonated drinks.

The low-carb diet, on the other hand, was defined as a maximum of 50 grams of carbohydrates per day. “To be able to maintain weight stability on this kind of restrictive diet, participants were given more protein and fat,” Nybacka noted. “We also optimized the fiber intake in this diet to provide approximately 25 grams of dietary fibers per day.”

Medications used in the third group of subjects included three for constipation (sterculia, macrogol, and linaclotide) and three for diarrhea (loperamide, cholestyramine, and ondansetron).

After 4 weeks, the majority of participants in each group reported improvements in their symptoms, but those in the low-FODMAP and low-carb groups reported the most benefit. Seventy-six percent of those on a low-FODMAP diet and 71% of those on a low-carb diet experienced a drop of at least 50 points on the IBS-SSS, a test that scores IBS symptom severity.

“Overall, between the two diets, we found very similar improvements; both diets managed well in reducing symptom severity of IBS, and the two diets did particularly well in reducing abdominal pain and bloating,” Nybacka said. “Both diets also improved quality of life in a similar way.” By contrast, just 58% of those receiving medication experienced the same degree of improvement in IBS-SSS scores.

It’s worth noting that the study did have a few limitations. Besides being conducted solely on Swedish adults, it only lasted four weeks, which Nybacka said may not be long enough to draw firm conclusions about dietary versus medical treatments for IBS. It’s possible that future research will extend this comparison to test this study’s findings in the longer term.

The low-FODMAP diet has been well established in medical literature as a strategy for improving IBS symptoms—so the new study’s discoveries aren’t all that surprising on that account.

The more pressing questions: Why might a low-carb diet have similar results to a low-FODMAP diet—and why might both be superior to medication?

“It’s possible that [a low-carb diet] worked well for people because it restricted other carbs that people with IBS may have issues with breaking down,” Amanda Sauceda, MS, RDN, gut health dietitian and lecturer at California State University, Long Beach, told Health. (A low-FODMAP diet is, after all, technically a carb-restricted diet.) “It could also work well because it changed how quickly food moves through the gut, improving harder stool.”

Sauceda suggested that including plenty of fiber in the low-carb diet probably also helped people’s symptoms improve.

“When you optimize your fiber within a certain amount of carbs, you have to be very selective (in a good way) with your food,” she said. “You have to focus on eating carb foods that are higher in fiber, and those tend to be less processed and more nutrient dense.”

As for why a low-carb diet could outperform meds for people with IBS, Chey said current medical treatment of this condition is sometimes spotty, since it’s difficult to match medications to the underlying causes of different people’s symptoms.

“That’s why, in almost every study on medication for IBS, only about 50% of subjects improve,” he said. Until biomarker-based medications are created for targeted IBS treatment, “we have no way to identify which of the medical options we have is the right medication for an individual patient,” he said. Therefore, diet could be a more effective approach.

Chey noted that not everyone with IBS will benefit from a dietary intervention. For some, stress relief, talk therapy, or other interventions may be more successful. Still, for many people, dietary changes are an important part of symptom management.

“Diet is a big factor for IBS because food can trigger digestive symptoms, which can really cut into someone’s quality of life,” says Sauceda. Plus, since IBS has no cure—and medications are sometimes ineffective or have side effects—changing your diet is a relatively low-risk proposition.

Of course, this study’s findings don’t mean a low-carb diet is a silver bullet for people with IBS. “There is no one standard approach to managing IBS with diet,” Sauceda points out.

But if you’d like to implement a low-carb or low-FODMAP diet to manage IBS symptoms, a registered dietitian can help guide you. Both Chey and Sauceda also encouraged logging your food intake, stressors, and symptoms to get a sense of your own triggers.

“Keeping a food journal where you track what you’re eating, how you’re feeling, and your stress levels can be very helpful for info to start figuring out the food piece,” Sauceda said. “This info can also be very helpful when you work with your dietitian.”