Small intestinal bacterial overgrowth (SIBO) is a functional digestive disorder increasingly recognized by medical associations like the American Gastroenterological Association. SIBO is characterized by an excessive amount of bacteria in the small intestine, leading to gastrointestinal symptoms. The incidence of SIBO is notable, with estimations suggesting that 14% to 40% of patients diagnosed with irritable bowel syndrome (IBS) also have SIBO. This overlap highlights the importance of accurate diagnosis to enable effective treatment plans. Nutrition and diet therapy play a pivotal role in SIBO management, not only in alleviating symptoms but also in preventing relapses.
Understanding SIBO and IMO
Gut dysbiosis refers to any proliferation or change in the composition of the microbiota. SIBO is a type of gut dysbiosis that has recently garnered public attention despite its longstanding presence in the medical digestive field. Advances in metagenomics have facilitated a better understanding of SIBO, emphasizing its role in the broader context of intestinal microbiology.
SIBO symptoms can overlap with other digestive disorders, primarily involving abdominal distension, diarrhea, constipation, flatulence, indigestion, belching, and changes in gastrointestinal transit. These symptoms are essentially due to the activity of gastrointestinal bacteria when they come into contact with fermentable carbohydrates in the diet. SIBO can also produce extraintestinal symptoms, including asthenia or headache, as well as cardiovascular, endocrine, neurological, nephrological, connective tissue, or dermatological complications. SIBO has been reported to be associated with an increase in lipopolysaccharides and inflammatory cytokines in the intestinal mucosa, which can cause intestinal hyperpermeability and contribute to chronic low-grade systemic inflammation.
Moreover, this excessive presence of bacteria in the small intestine can have additional negative consequences beyond the symptoms, such as malabsorption of certain nutrients like vitamin B12, steatorrhea, and deficiencies in fat-soluble vitamins. These issues stem from interactions between the bacteria and their metabolites with these nutrients and have the potential to damage the intestinal mucosa.
Another type of microbial overgrowth disorder involves the production of methane, where hydrogen is used as a substrate. In this case, the methanogens are archaea, not bacteria, and the overgrowth can occur in both the small and large intestines. Therefore, we refer to this condition as intestinal methanogen overgrowth (IMO), which is typically associated with constipation.
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Causes of Small Intestinal Bacterial Overgrowth
Various factors have been associated with the onset of SIBO and could explain the higher prevalence in patients with these characteristics. The intestine has mechanisms that, if functioning properly, prevent the excessive proliferation of bacteria in the small intestine. These mechanisms include gastric acid, bile, and pancreatic enzymes, which have bacteriostatic and bactericidal properties, as well as peristaltic movements that propel food and bacteria toward the end of the digestive tract and the ileocecal valve, which prevents bacteria from the colon from migrating back into the small intestine. However, if these mechanisms fail, the likelihood of developing SIBO increases.
First, it has been demonstrated that SIBO is more prevalent in women and elderly individuals. Additionally, its occurrence is common alongside other digestive disorders such as dyspepsia, intestinal motility dysfunction, and systemic sclerosis. Regarding other potential etiologies, SIBO has been associated with various conditions such as hypothyroidism, diabetes, pancreatitis, rosacea, Parkinson’s disease, and coronary heart disease, as well as with patients who have undergone abdominal surgeries.
The use of certain medications is also linked to the development of SIBO, including opioids, which reduce intestinal motility. Moreover, there is a significant correlation between the continuous use of proton pump inhibitors and the subsequent prevalence of SIBO in these patients; they inhibit gastric acid production, creating a less acidic environment in the stomach, which is thought to facilitate bacteria reaching the intestine more easily.
Diagnosis of Small Intestinal Bacterial Overgrowth
As mentioned above, the gold standard for diagnosing bacterial overgrowth is the duodenal aspirate with a threshold of 103 CFU/mL, above which the result is considered positive. However, this procedure is quite invasive for the patient, expensive, and carries the risk of sample contamination by the oral, gastric, and esophageal microbiota. Therefore, the breath test is currently the most commonly used technique.
To assess microbial overgrowth, these tests use two possible substrates: glucose or lactulose. These substrates are fermented by the enteric microflora, producing gases that can subsequently be measured: methane and/or hydrogen. There is no clear consensus as to which substrate is preferable. Glucose is a monosaccharide that is absorbed in the proximal intestine, whereas lactulose is a non-absorbable disaccharide that reaches the colon. Consequently, the use of glucose might increase the risk of false negatives since it could be absorbed in the small intestine before reaching the more distal segments where the bacteria could reside. In contrast, the use of lactulose could result in another gas peak upon reaching the colon due to fermentation by the colonic microbiota.
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Regarding diagnostic criteria, it has been determined that an increase of ≥20 ppm of hydrogen from baseline level within the first 90 min is considered positive for hydrogen SIBO. Additionally, a methane level of ≥10 ppm at any point during the test is indicative of IMO, as these patients tend to have elevated methane levels from the beginning of the test.
The Elemental Diet: A Dietary Intervention for SIBO
An elemental diet is a restrictive, liquid-only diet that provides the body with essential nutrients in a “predigested” form. It is a special low-fat liquid formulation that is designed to be easily digested and contains all the essential nutrients necessary for a healthy diet. Healthcare professionals often prescribe an elemental diet for people with certain gastrointestinal conditions as the nutrients are more easily digestible. Doctors may recommend it for people with small intestinal bacterial overgrowth (SIBO).
The diet is "elemental" as it provides proteins, fats, and carbohydrates already broken down into their basic building block forms: amino acids, fatty acids, and sugars. Elemental diets also provide vitamins and minerals. These predigested nutrients do not cause additional stress on the digestive tract before the body absorbs them. Healthcare professionals, such as gastroenterologists and registered dietitians, prescribe them to people with compromised digestive systems, such as those with SIBO.
The goal of the elemental diet is to provide a person with all the necessary nutrients in an easily digestible form while reducing the amount of food in the small intestine. The elemental diet starves the bacteria, reducing the number of bacteria in the small intestine and improving symptoms.
Mechanisms of Action
Elemental diets have been employed for the management of various diseases for over 50 years, with several mechanisms mediating their beneficial effects. EDs are devoid of allergens and can be largely absorbed without active digestion, allowing for rapid absorption and high nutritional efficacy. As such, EDs have favorable characteristics to be effective for several gastrointestinal (GI) and systemic diseases, particularly those driven by atopy, indigestion, and malabsorption. They further possess anti-inflammatory and mucosal healing properties that contribute to their utility in inflammatory conditions. Given their high absorbability index, EDs generate little fecal bulk, which provides additional benefit in severe diarrhea, high output ostomies, and gastrointestinal fistulae.
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Several mechanistic pathways were identified to mediate the effects of elemental diets, including food additive and allergen-free content, high passive absorption rate, and anti-inflammatory properties.
Research on Elemental Diets for SIBO/IMO
A new study from Cedars-Sinai examined whether a specialized diet could improve symptoms of gastrointestinal disorders linked to an imbalance in gut microbiota. Researchers tested the elemental diet’s effectiveness and explored whether improving its unappealing taste-a major barrier-could help patients adhere to the diet’s stringent protocol.
In this study, 30 adults ages 18 to 85 diagnosed with SIBO or IMO strictly adhered to only a more palatable version of the elemental diet for two weeks. This was followed by two weeks during which study participants resumed their normal diet. The researchers analyzed changes in the gut microbiome, how well the diet was tolerated, symptom relief and breath test results, along with tracking any side effects.
The results were encouraging. Most participants reported tolerating the diet well, with no serious side effects. A key finding was a reduction in unfavorable microbes linked to gut issues. Methane levels also dropped significantly, with many returning to normal. In addition, 83% of participants reported feeling better, with significant relief from common symptoms like bloating and discomfort. These findings suggested that a tastier version of the elemental diet helped restore balance in the gut and eased symptoms of SIBO and IMO.
Elemental Diet vs. Antibiotics
While antibiotics are the mainstay of treatment for small intestinal bacterial overgrowth (SIBO) and intestinal methanogen overgrowth (IMO), their overall efficacy is limited at 50% or less. Elemental diet provides an alternative option to treat patients who are refractory, cannot tolerate antibiotics, or prefer a non-antibiotic treatment approach.
Practical Considerations for Implementing an Elemental Diet
Before starting an elemental diet for SIBO, a person should meet with a healthcare professional to ask questions and clarify the process. People may wish to discuss the following topics:
- Diagnosis: It is important to have an accurate diagnosis and understand the goals of an elemental diet.
- Medications: A specialist may recommend adjusting or temporarily stopping certain medications and supplements for the duration of the diet.
- Readiness: An elemental diet can be both mentally and emotionally challenging. A person’s doctor can help prepare for those challenges and create a plan for dealing with them.
Following an elemental diet is fairly uncomplicated. A specialist will recommend either a prescription or nonprescription formula and explain how to implement the diet properly. Preparation depends on the specific formula. Some elemental diets come premixed in a ready-to-drink liquid, while others come as a powder to mix with water or another approved liquid. Someone beginning an elemental diet may consider drinking each serving of the formula slowly until they become familiar with the taste, texture, and how they feel after drinking it.
An elemental diet typically lasts 14-21 days. However, the duration may vary depending on factors such as symptom severity and coexisting conditions. Once a person completes an elemental diet, their doctor will advise them to reintroduce solid food gradually. This slow and controlled process allows the body to readjust to solid foods.
Tips for Surviving the Elemental Diet
This diet is very restrictive, and it can be challenging. To stick to the diet successfully, healthcare providers recommend that you:
- Keep it cold: Blending the formula with ice, smoothie-style, makes it more palatable.
- Sip it slowly: Prevent nausea and drink plenty of water between “meals."
- Make it portable: Have a temperature-controlled thermos to keep your formula in so you don’t get hungry when you’re out and about.
- Stay busy: Distract yourself with fun, non-food-related activities and good company.
Potential Side Effects
During the diet, you may experience symptoms that make you wonder if it’s actually helping your condition or making it worse. Medical guidance can help you sort through this. Symptoms may include:
- Abdominal cramping
- Detox symptoms
- Bacteria die-off symptoms
- Reduced motility
Reintroducing Foods After the Elemental Diet
It’s important to reintroduce foods gradually as your digestive system is ramping back up again. Healthcare providers typically recommend following a half-elemental diet or a low-FODMAP diet during the transition. They may also recommend probiotics to re-populate your gut with beneficial flora, and prokinetic agents to stimulate your bowels to begin moving more regularly again. As you return to your more regular diet, pay attention to the way different foods affect your digestive system.
Elemental Diets in Other Gastrointestinal Conditions
While the primary focus here is on SIBO, elemental diets have shown promise in managing other GI conditions:
- Eosinophilic Esophagitis (EoE): Exclusive elemental diets appear to be highly effective in induction of remission in EOE; however, a strategy needs to be adopted for maintenance of remission following completion of the diet.
- Eosinophilic Gastritis and Gastroenteritis (EGID): Similar to EOE, EGID appears to be highly responsive to exclusive ED.
- Inflammatory Bowel Disease (IBD): Exclusive enteral nutrition (EEN) with intake of liquid elemental, semi-elemental, or polymeric formulas for 6-8 weeks has been shown to be effective in Crohn’s disease (CD). In children and adolescents, EEN is recommended as first-line therapy for induction of remission.
Limitations and Future Directions
While large prospective trials are lacking, elemental diets appear to exhibit objective and subjective clinical benefit in several diseases, including eosinophilic esophagitis, eosinophilic gastroenteritis, inflammatory bowel diseases, small intestinal bacterial overgrowth, intestinal methanogen overgrowth, chemoradiotherapy-associated mucositis, and celiac disease. Although some data support the long-term use of elemental diets as an add-on supplement for chronic pancreatitis and Crohn’s disease, most of the literature on exclusive elemental diets focuses on inducing remission. Therefore, subsequent treatment strategies for maintaining remission need to be adopted in chronic/relapsing diseases.
High rates of intolerance up to 40% are seen in the trials where exclusive elemental diets were administered orally due to poor organoleptic acceptability; however, when tolerated, adverse events were rare. Other limitations of elemental diets are cost, access, and lifestyle/social restrictions. Moreover, judicious use is advised in presence of a concomitant restrictive food intake disorders.