What Is the Best Diet for IBS? Long Island Dietitian Tips
What Is IBS?
Until recently, Irritable Bowel Syndrome (IBS) was considered a diagnosis of exclusion. It is now understood to be a functional disorder involving the gut-brain axis.
The condition is characterized by a combination of symptoms, including abdominal pain, bloating, distention, flatulence, and altered bowel habits—constipation (IBS-C), diarrhea (IBS-D), or a combination of both (IBS-mixed)—as defined by the Rome IV Diagnostic Criteria.
Understanding the Root Causes of Irritable Bowel Syndrome
The science has progressed significantly over the last several years. Although IBS is not fully understood, it is evident that it involves dysfunction in the gut microbiota. Two primary and often overlapping issues are:
- SIBO (small intestinal bacterial overgrowth), contributing to approximately 65% of those diagnosed with IBS
- Dysbiosis, an imbalance in the gut microbiome
Microbial richness—reflected in bacterial diversity—is generally considered an indicator of good health. In contrast, reduced diversity and imbalance of the gut microbiota (dysbiosis) have been associated with impaired metabolism and a wide range of diseases.
Recommendations to Manage and Resolve Irritable Bowel Syndrome
There are two interdependent issues:
Dysbiosis:
An imbalance in the microbial communities (bacteria, fungi, viruses) living in or on the body, particularly in the gut, where harmful microorganisms outweigh beneficial ones.
Small Intestinal Bacterial Overgrowth (SIBO):
The presence of excessive bacteria in the small intestine.
SIBO is a significant underlying cause of symptoms in a large portion—estimated at 60–70%—of patients with IBS. While IBS is a functional disorder defined by symptoms, SIBO involves a measurable excess of bacteria. Both conditions share symptoms such as bloating, abdominal pain, diarrhea, and constipation.
The Goal of Medical Nutrition Therapy for IBS
The goal is to restore balance in the gut microbiota:
- From dysbiosis: an imbalance in gut bacteria, with higher levels of harmful microbes and lower levels of beneficial microbes, along with reduced microbial diversity
- To eubiosis: a balanced microbiome in which beneficial microbes outnumber harmful ones
If SIBO is present, a targeted approach may include specific antibiotics based on gas type (hydrogen, methane, or hydrogen sulfide) to eliminate excess bacteria.
What Is the Best Diet to Resolve the Underlying Causes of IBS?
Dysbiosis:
A diversified, balanced eating pattern—such as a whole-food, plant-based, flexitarian approach
SIBO:
A low-fermentation diet, which restricts foods that are more difficult to digest, such as certain fibers and non-digestible sugars (e.g., stevia and sucralose)
This diet alone will not cure IBS. Antibiotic treatment may be required, but following dietary strategies for several months can help reduce recurrence.
Why Many Dietary Recommendations for IBS Are Unsuccessful
Dietary recommendations for IBS often fail because it is not a one-size-fits-all condition. IBS is highly individualized, with symptoms arising from different underlying causes—such as SIBO, food intolerances, or motility issues—rather than a single factor. What works for one person may worsen symptoms for another.
Many approaches are too generalized. Success requires a personalized strategy that considers:
- Individual triggers
- Misunderstood root causes
- The gut-brain axis
- Lifestyle factors
- Non-dietary influences
- Misconceptions and misapplication of the low-FODMAP diet
Is a Low-FODMAP Diet an Effective Treatment for IBS?
While widely used, up to 50% of patients do not respond to a low-FODMAP diet. It is intended as a temporary elimination strategy followed by reintroduction, yet many people follow it long-term without dietitian guidance. This can lead to nutritional deficiencies and limited improvement.
More specifically, the low-FODMAP diet is a highly restrictive, short-term protocol—not a lifelong plan. When all phases are not followed correctly, dysbiosis may persist.
There are three required phases:
- Elimination phase: 4–6 weeks on a structured elimination diet
- Reintroduction phase: 6–8 weeks to systematically identify food sensitivities
- Personalization phase: expanding the diet by reintroducing tolerated foods to support long-term symptom management
Is There a Best Diet to Only Relieve Symptoms?
Effective symptom management often involves identifying foods and factors that worsen or improve symptoms. Examples may include:
- A higher-fiber diet for constipation
- A lower-fiber diet for diarrhea
- A gluten-free diet
- A dairy-free diet
- A balanced, healthful diet
- Lifestyle changes
- Nutritional health supplements
- Herbal remedies
Many patients I see with IBS feel they have “tried everything.” Successful medical nutrition therapy must be individualized and tailored to each person. As a Registered Dietitian Nutritionist, I work with you to manage symptoms while also identifying and addressing the underlying causes.
Further Reading
