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Small intestinal bacterial overgrowth (SIBO) is a condition in which excess bacteria inhabit the small intestine and cause intestinal symptoms.
This overgrowth of bacteria can also cause fat malabsorption and vitamin deficiencies.
Although antibiotics are usually the first line of treatment for SIBO, diet may also play a role in managing SIBO.
This article explains what to eat and avoid with SIBO and provides a sample SIBO diet menu.
What is SIBO?
SIBO is a condition that occurs when excess bacteria grow in the small intestine and cause digestive symptoms.
SIBO is thought to develop when bacteria pass from the large intestine into the small intestine, which normally contains few bacteria (1).
Other potential causes of SIBO include low levels of stomach acid, an unusually slow passage of digested food through the small intestine, and a weakened immune system.
Risk factors for SIBO include (2):
- chronic opiate use
- chronic antacid use
- Crohn’s disease
- ulcerative colitis
- irritable bowel syndrome
- nonalcoholic fatty liver disease (NAFLD)
- leaky gut
Female gender and older age are also risk factors for SIBO.
Symptoms and treatment
The symptoms of SIBO are nonspecific and generally include (1):
- abdominal pain
- excessive gas
- brain fog
These symptoms vary in frequency, duration, and severity.
SIBO can also cause fat malabsorption, leading to fatty stools, unintentional weight loss, and deficiencies in fat-soluble vitamins, A, D, and E (3).
Levels of vitamin K, another fat-soluble vitamin, and folate are usually increased since bacteria produce them (3).
Intestinal inflammation and increased bacterial usage of nutrients can also cause deficiencies in certain B vitamins, especially B12.
Currently, there is no validated gold standard diagnostic test for SIBO, but small bowel aspiration and culture is regarded as the most accurate method (3).
This method involves taking a sample of fluid from the small intestine and sending it to the lab to create a culture.
A hydrogen breath test can also be used and tends to be more preferred since it’s inexpensive, noninvasive, and relatively simple to administer.
Antibiotics are commonly prescribed for SIBO, but antibiotic therapy isn’t always effective and can lead to the development of antibiotic-resistant organisms and infections, like Clostridium difficile colitis (2).
When possible, treatment also focuses on treating the conditions associated with SIBO development, such as gastroparesis and diabetes.
Types of diets for SIBO
Although the research remains limited, two diets have been shown to be beneficial for SIBO — an elemental diet and a low-FODMAP diet.
An elemental diet consists of nutritionally complete formulas that contain pre-digested nutrients.
These formulas contain nutrients that are absorbed within the first few feet of the small intestine, limiting the availability of nutrients for the bacteria located towards the end of the small intestine.
The diet may also support bowel health and directly reduce or eliminate bacteria within the small intestine (4).
In a small study, 85% of patients who followed an elemental diet for 21 days experienced decreased bacteria in the small intestine which translated to improvements in bowel regularity and other digestive symptoms (4).
However, the elemental diet can be difficult to follow, the formulas tend to have an unpleasant taste, and it’s unknown whether SIBO will return after resuming a normal diet.
Research suggests that nearly 40% of people but up to 84% with irritable bowel syndrome (IBS) have SIBO (5).
IBS is a disorder that causes recurrent episodes of abdominal pain and uncomfortable digestive symptoms, which may be worsened by SIBO.
A low-FODMAP diet has been traditionally recommended to manage IBS symptoms and remains the most evidence-based diet for IBS (6).
Studies suggest that the low-FODMAP diet can relieve symptoms in 50–80% of people with IBS (7).
It’s believed that a low-FODMAP diet is in part effective for relieving IBS symptoms because it improves SIBO.
With IBS, gut bacteria ferment certain carbohydrates, such as fructose, lactose, oligosaccharides, disaccharides, and monosaccharides, resulting in symptoms.
A low-FODMAP diet limits these carbs, depriving the bacteria that feed on them of the nutrition they need to grow and multiple, helping to improve SIBO.
FODMAP stands for fermentable oligo, di, and monosaccharides and polyols.
The primary sources of FODMAPs include (8):
- Oligosaccharides: artichoke, asparagus, beetroot, beans, broccoli, brussels sprouts, cabbage, fennel, garlic, leek, okra, onion, peas, and shallot
- Disaccharides: lactose-containing foods, including milk, yogurt, and soft and fresh cheeses.
- Monosaccharides: foods high in fructose, including peaches, mangoes, watermelon, honey, fruit juice, regular soda, and concentrated sweets
- Polyols: apples, apricots, avocado, cherries, pears, cauliflower, mushrooms, and sweeteners ending in “-ol” like sorbitol and xylitol
Each person reacts differently to FODMAPs, depending on the type and amount consumed, so an elimination diet strategy is best to identify which foods trigger or worsen symptoms.
Which is the best SIBO diet?
There currently isn’t any research directly comparing the effectiveness of the elemental diet with a low-FODMAP diet for managing SIBO.
However, of the two, there is more and stronger evidence to support the low-FODMAP diet.
- Elimination: This phase involves eliminating the primary sources of FODMAPs from your diet until your symptoms become minimal or non-existent, which usually takes 4–6 weeks.
- Reintroduction: This phase involves reintroducing the primary sources of FODPAPs you eliminated, one by one, slowly over several days while you look for symptoms. This phase can take 6–10 weeks.
- Personalization: This phase continues long-term in which you continue to restrict the foods that you identified as triggers for your symptoms but incorporate those that did not induce symptoms during reintroduction.
Low-FODMAP foods to eat during the elimination phase include:
- Fruits: bananas, berries, grapes, honeydew melon, kiwi, oranges, and tomatoes
- Vegetables: bok choy, carrots, celery, eggplant, green beans, lettuce, pumpkin, green onion
- Grains and starches: gluten-free and spelt bread and cereal products
- Dairy: lactose-free milk and yogurt and hard cheeses
- Proteins: beef, chicken, eggs, pork, seafood
- Olive oil
- Beverages: water, tea, coffee
- Condiments: maple syrup, soy sauce, mustard, spices without onion or garlic, salt, pepper, mayonnaise, and sweeteners, except sugar alcohols
Avoid foods that tend to promote inflammation and may worsen SIBO, like processed meat, fried foods, and high sugar foods.
Although the evidence is stronger for the low-FODMAP diet for managing SIBO, incorporating elemental formulas in your diet can be useful if you struggle to consume enough calories to maintain your weight or experience fat malabsorption.
Here’s a one-day sample SIBO diet menu low in FODMAPs:
- Breakfast: scrambled eggs with gluten-free toast with margarine
- Snack: elemental formula drink blended with frozen berries
- Lunch: tomato soup and a gluten-free baguette
- Snack: string cheese sticks and grapes
- Dinner: baked salmon, white rice, and sauteed green beans
Probiotic supplements for SIBO
Probiotic supplements contain beneficial bacteria that help with food digestion, inflammation, and immunity.
It may seem counterintuitive to increase the bacteria in your gut with SIBO by taking a probiotic supplement, but doing so may help alleviate symptoms by positively altering the composition of the gut microbiota and decreasing intestinal inflammation.
A review of 18 studies found that those with SIBO who supplemented with probiotics experienced decreased bacterial overgrowth and abdominal pain compared with those who didn’t take probiotics (10).
In another study, patients with IBS and SIBO who received a probiotic supplement containing four bacterial strains twice daily for 30 days experienced improvements in bowel regularity and reductions in abdominal pain and bloating (11).
Probiotics may also enhance the effectiveness of antibiotics.
One study showed that patients who were treated with rifaximin — a commonly prescribed antibiotic for SIBO — followed by a probiotic supplement experienced greater improvements in their symptoms compared with the antibiotic alone (12).
However, not all probiotic supplements are created the same, and some have been suggested to worsen symptoms in people with SIBO (13).
Some of the more commonly studied probiotic strains for alleviating symptoms include Lactobacillus acidophilus, Bifidobacterium lactis, Bacillus coagulans, Lactiplantibacillus plantarum, Saccharomyces boulardii, and Saccharomyces cerevisiae.
The bottom line
SIBO is a condition where excess bacteria grow in the small intestine and cause digestive symptoms.
Both an elemental and low-FODMAP diet have been suggested to improve SIBO, but of the two, there is more evidence to support the low-FODMAP diet.
In addition to diet, supplementing with specific probiotic strains has also been shown to alleviate SIBO symptoms.