Small intestinal bacterial overgrowth (SIBO) is a condition characterized by an excessive amount of bacteria in the small intestine. SIBO symptoms are often caused by the gas that is made when extra bacteria use up some types of carbohydrates (sugars and starches found in food that your body uses for energy) in your diet, such as certain types of fiber (a substance in food that helps you pass solid waste), starches and/or sugars. This overgrowth can lead to various gastrointestinal symptoms and discomfort. While antibiotics are the first-line treatment, dietary interventions, particularly the low-FODMAP diet, are often explored to manage symptoms and prevent recurrence. This article delves into the role of the FODMAP diet in SIBO management, its potential benefits, limitations, and how to implement it effectively.
Understanding SIBO
SIBO is a bacterial overgrowth in the small intestine. All of us have bacteria in our gut, but most of it is located in our large intestine. Small intestinal bacterial overgrowth (SIBO) happens when there’s a disruption to the normal amount of bacteria found in your small intestine. Risk factors for developing SIBO include taking proton pump inhibitors or opioids, gastric surgery, nerve damage to the small intestine, or a failure of the ileocecal valve.
Left untreated, SIBO can cause symptoms including pain, diarrhea, and malnutrition (due to the loss of the body’s main nutrients). In rare cases, a serious neurological condition called D-lactic acidosis can occur.
Common Symptoms of SIBO
There are many common symptoms of SIBO. SIBO can affect your stools, making them fatty or greasy, light, soft, and unusually foul-smelling. Some people with SIBO find that high fat foods can also make their symptoms worse.
What are FODMAPs?
FODMAP is an acronym for a certain class of carbohydrates, called fermentable short-chain carbohydrates, which are more difficult for people to digest. (The full acronym stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols.)
Read also: Weight Loss with Low-FODMAP
FODMAPs are:
- Fermentable: These are all foods that your gut bacteria feed on, converting them to gasses in a chemical process called fermentation.
- Oligosaccharides: These are soluble plant fibers known as prebiotics, which feed the beneficial bacteria in your gut. Oligosaccharides include onions, garlic, beans/lentils and many wheat products. Sensitivity to oligosaccharides may help explain some cases of non-celiac gluten sensitivity. Since gluten-free grains are lower in fermentable sugars than grains that have gluten, some people who think they are sensitive to gluten may actually be sensitive to the oligosaccharides residing in wheat products.
- Disaccharides: Lactose is the fermentable sugar in this group, the sugar in dairy and breast milk. Lactose intolerance is one of the most common food intolerances worldwide.
- Monosaccharides: Fructose, the sugar in fruit, is the fermentable sugar in this group. But only in certain quantities and proportions, so not all fruits are affected.
- Polyols: These are sugar alcohols, commonly used as artificial sweeteners. They are also found naturally in some fruits.
Why are FODMAPs difficult to digest?
FODMAPs are fermentable short-chain carbohydrates. Translated, that means two things: They are sugar molecules that are linked together in chains, and they are fermentable by the bacteria in your gut. Molecules in chains need to be broken down into single molecules to be absorbed through your small intestine. But FODMAPs can’t be broken down, so they can’t be absorbed there. Your small intestine draws in extra water to help move the FODMAPs through to your large intestine. There, the bacteria living in your colon have a field day fermenting them (eating them). This produces gasses and fatty acids as byproducts inside your gut.
Are FODMAPs bad for everyone?
Not at all. In fact, our digestive systems are designed to process some foods that we can’t fully digest ourselves - for example, dietary fiber, which has an important place in digestive health. And feeding the bacteria in our gut is part of our symbiotic arrangement with those bacteria. But some people with sensitive guts experience a level of indigestion from these foods that significantly impacts their quality of life. For these people, the byproducts of fermentation cause chronic symptoms of gas, bloating, abdominal pain and distension. The extra water drawn by the small intestine may cause diarrhea in excess, or constipation if there isn’t enough.
Who might benefit from a low-FODMAP diet plan?
The low-FODMAP diet is often prescribed for limited periods for people diagnosed with irritable bowel syndrome (IBS) and small intestinal bacterial overgrowth (SIBO). Studies show that a majority of people living with these conditions benefit from the diet. It can also be used as a short-term elimination diet for anyone who has digestive problems and wants to try and isolate the foods that are causing them. An elimination diet removes common problem foods and then adds them back in systematically to observe how your system reacts. The low-FODMAP diet is just one of many elimination diets that you can use to discover food sensitivities.
The Low-FODMAP Diet for SIBO: A Detailed Overview
One popular plan to manage SIBO symptoms is called the low-FODMAP diet. On this diet, patients eat less of certain carbohydrates that are likely to make more gas in the intestines or worsen diarrhea. Ideally, a strict low-FODMAP diet should only be followed for as long as you need to follow it to manage your symptoms.
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Because many people with IBS also have SIBO, a low-FODMAP diet is sometimes suggested for people with SIBO.
How the Low-FODMAP Diet Works
The low-FODMAP diet temporarily restricts these carbohydrates in order to relieve uncomfortable symptoms and give your digestive system a rest. Removing irritants gives your gut lining a chance to repair itself and can help restore a healthy balance of gut flora. If your symptoms improve, you can use the low-FODMAP diet to figure out which foods to limit in the future.
The diet has three phases: an elimination phase, a reintroduction phase and a maintenance phase that’s customized to you. During the elimination phase, you'll avoid all of the high-FODMAP foods - a list of specific fruits, vegetables, dairy products and grains. At first glance, the elimination phase of the diet may seem very limited. But there’s still a good list of foods in each category that you can eat. It takes some mental discipline to follow, but you won’t go hungry on the diet. After two to four weeks, you’ll begin the reintroduction phase, in which you systematically add foods back in. The third phase keeps what works for you and leaves out what doesn’t.
Foods to Limit on a Low-FODMAP Diet
According to the American College of Gastroenterology, most diets proposed for SIBO reduce your intake of foods that are fermented by gut bacteria. These may include:
- High fiber foods
- Sugar alcohols, a type of low calorie sweeteners
- Sucralose, a zero calorie artificial sweetener
- Inulin and other prebiotics
The main categories of FODMAPs include:
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- Fructose, simple sugars commonly found in fruits and some vegetables, honey, and agave nectar
- Lactose, a sugar molecule in dairy products
- Fructans, a sugar compound found in gluten products, fruits, some vegetables, and prebiotics
- Galactans, a compound found in some legumes
- Polyols, sugar alcohols often used as low-calorie sweeteners
Foods that contain higher amounts of FODMAPs include:
- High-fructose corn syrup
- Agave nectar
- Honey
- Soda and soft drinks
- Garlic
- Onions
- Asparagus
- Butternut squash
- Cauliflower
- Artichokes
- Beans
- Apples
- Dried fruits
- Sausage
- Flavored yogurt
- Ice cream
- Sweetened cereals
- Barley
- Rye
- Grains
- Peas
- Mannitol
- Sorbitol
Everyone reacts to these foods differently. Even if some FODMAPs cause symptoms for you, other FODMAP-containing foods may not.
Acceptable Foods on a Low-FODMAP Diet
If you’re avoiding FODMAPs during your elimination diet, the list of foods you should avoid can be restrictive. But there are still a number of foods you can enjoy while on this temporary diet. Some foods contain low amounts of FODMAPs in small servings but may be limited because larger servings would increase the FODMAPs. Some of the acceptable foods for a low-FODMAP diet include:
- Meat
- Fish
- Eggs
- Crackers, gluten-free
- Oatmeal
- Unsweetened cereal (made from low FODMAP grains)
- Spaghetti squash and summer squashes
- Broccoli (heads only, less than 3/4 cup)
- Leafy greens
- Carrots
- Rice or gluten-free noodles
- Olives
- Peanuts
- Potatoes
- Pumpkin
- Quinoa
- Seeds
- Some fruits (blueberries, grapes, oranges, and strawberries)
Reintroducing FODMAPs
During the reintroduction stage, foods with higher FODMAP contents are reintroduced into the diet systematically by adding one new food every 1-2 days. It is important to keep a food log during this stage to record any symptoms that may occur after reintroducing a food. If a reintroduced food doesn’t cause any GI symptoms, it can be added back into the diet. If symptoms do occur with a reintroduced food, it must be eliminated again. Any eliminated foods can be reintroduced again at a later time. If GI symptoms do occur with a reintroduced food, it is best to wait until symptoms are gone before reintroducing another high FODMAP food.
Customization
Making changes to what you eat to improve SIBO symptoms takes collaboration between you and your healthcare team. One of the more intimidating aspects of dealing with SIBO is the thought that some foods will always be on the no-go list. But food plans to manage SIBO aren’t black-and-white - and what you eat and what you need to limit or avoid can be personalized for you.
After treatment, if you’re feeling better, you can start to reincorporate the FODMAP foods into your diet. They’re often better tolerated. That being said, you may find certain foods will always trigger your symptoms. Those are the ones you may need to continue to avoid or reduce how much of the specific foods you eat.
Limitations and Considerations
Although the low-FODMAP approach is popular, there is little evidence to show that a low-FODMAP diet can help with SIBO. Plus, restricting FODMAPs has been linked to potentially harmful changes in the types of bacteria growing in the gut. This effect was seen in people with IBS who followed a low-FODMAP diet for a prolonged period of time.
People with SIBO already have an overabundance of unhealthy gut bacteria, so some researchers caution that a low-FODMAP diet may not always be beneficial.
A low FODMAP diet should be done under the supervision of a registered dietitian or gastrointestinal specialist, since it is an extremely restrictive diet and persons following it need to make sure they are still eating adequately.
Potential Negative Shift in Gut Microbiota
Recent studies indicate that dietary manipulation may have a role in alleviating SIBO gastrointestinal symptoms. A low FODMAP diet proposed for IBS may promote a negative shift in the gut microbiota and deepen the existing state of dysbiosis in SIBO patients.
Individualized Approach
A low-FODMAP diet is only one example of an elimination diet for SIBO. Remember, it’s best to take an individualized approach when planning a SIBO elimination diet.
Additional Dietary and Lifestyle Considerations
Changing your diet can help reduce symptoms of SIBO, but diet alone is not able to cure SIBO.
Meal Spacing
Meal spacing helps your body’s natural cleansing waves in the gut. These waves help to keep bacteria levels lower in the small intestine.
Addressing Nutrient Deficiencies
Having SIBO for a long time can block how your body absorbs nutrients. This can lead to weight loss and deficiencies in vitamin B12 and vitamins A, D and E.
The Elemental Diet
When antibiotics alone do not help, the elemental diet is the only diet proven to treat SIBO. It is a predigested liquid diet prescribed by a doctor.
With the elemental diet, the dietary building blocks and nutrients are more easily digestible and absorbed sooner in the digestive tract, so it’s much less likely to make it to the bacterial source in your small intestine.
Research shows the elemental diet works. But it only works if you stay with it. That can be a challenge for reasons ranging from the way the formula tastes to being hungry, bored or frustrated because you can’t participate in family or social events that center around food.
Working with a Healthcare Professional
Now it is time to meet with a GI-expert dietitian.
If you decide to try an elimination diet for SIBO, it’s important to plan it out with the help of a registered dietitian. They can help you build a list of foods to eliminate temporarily, and a plan for gradual reintroduction of foods.
Prior to incorporating any dietary changes to your treatment plan, discuss your options with your doctor. To benefit from an elimination diet, it’s important to work with a registered dietitian with training in SIBO conditions.
To help you plan meals and make the right food choices, your dietitian may recommend using a FODMAP app like the one created by Monash University or Fast FODMAP.
Working with a registered dietitian or health coach while following the elemental diet can be helpful.
Treatment and Management of SIBO
Antibiotics are the first line of treatment for SIBO. In some cases, your doctor may also prescribe a liquid diet called an elemental diet. An elemental diet temporarily replaces all foods and beverages with a nutrient drink that’s easy for your body to absorb. This diet must be carried out with a doctor’s supervision. No other diet is proven to treat SIBO. However, some people claim that limiting certain types of foods or changing your eating pattern can stop SIBO from coming back after treatment.
Your doctor or a registered dietitian may suggest trying an elimination diet to find out if particular foods are contributing to your digestive symptoms.
To look for links between foods and SIBO symptoms, some people follow a short term elimination diet followed by careful gradual reintroduction of eliminated foods. The reintroduction of foods to the diet should be carefully guided by a registered dietitian who understands SIBO conditions. An elimination diet is a tool that can help you learn if certain foods are associated with your SIBO symptoms. However, it cannot replace other treatments prescribed to you to manage SIBO or other associated conditions.
Antibiotics
Antibiotics are the primary treatment for SIBO. These medications get rid of the bacteria that’s overgrowing in the small intestine.
Addressing Underlying Conditions
For some people, successfully treating the bacterial overgrowth does not eliminate digestive symptoms. If your symptoms continue after treating SIBO, you may have another digestive condition that requires treatment or management. For example, lactose intolerance can cause symptoms similar to SIBO, such as bloating, gas, and diarrhea. If a food intolerance is causing digestive symptoms, you may need to make changes to your diet. These changes should be guided by your doctor or a registered dietitian.
Preventing Recurrence
In other cases, treating SIBO provides temporary relief, but not a long-term solution. In about 44% of cases, SIBO symptoms come back within 9 months after the first treatment. There are many diets that claim to stop SIBO from coming back. But there is little evidence to support their use. In fact, following a restrictive diet over a long period of time could make it harder to sustain a healthy balance of gut bacteria.
Probiotics and SIBO
Probiotic supplements are often claimed to benefit digestive health. Some studies suggest that probiotics may limit bacterial overgrowth, lower scores on the hydrogen breath test, and reduce abdominal pain with SIBO. However, a 2021 systematic review concluded that large, high-quality studies are needed to understand the effects of probiotics on SIBO. Some experts believe probiotics could make SIBO worse. Before making any changes to your diet or implementing new treatment, discuss the risks with your doctor or dietitian.
Targeted probiotic therapy may also increase the effectiveness of antibiotic treatment and regulate bowel movements.
SIBO and IBS: A Complex Relationship
Small intestinal bacterial overgrowth (better known as SIBO) is gaining more and more attention as a potential cause of gut symptoms in at least a subset (4-78%) of IBS patients. Research suggests that SIBO may play a significant underlying factor in irritable bowel syndrome (IBS).
The SIBO-IBS relationship remains elusive - further research is required to determine better and more accurate ways to diagnose SIBO and set standards for what is ‘normal’ and ‘abnormal’ when it comes to bacteria in the small intestine (both the number and species present).
Diagnostic Challenges
Whilst jejunal aspirate is the most accurate diagnostic test for SIBO, it is quite invasive, so is rarely used in clinical practice. Hydrogen breath testing is an alternative, non-invasive method for identifying SIBO that is now popular in clinical practice. Two different types of breath tests for SIBO are available (glucose or lactulose), however both methods have considerable diagnostic limitations. Unfortunately, both of these tests lack sensitivity and specificity, meaning that there is considerable chance of getting a false positive or false negative result.
Current and Future Treatments
Currently, the antibiotic rifaximin appears to be the most effective treatment for SIBO, however more high quality research is needed to determine how best to use this medication.
The majority of studies to date have investigated the use of different antibiotics to treat SIBO, with variable results. The most promising antibiotic therapy studied so far seems to be rifaximin, which is a non-absorbable drug that works predominantly in the gut. Probiotic formulations have also been studied as a treatment for IBS patients with evidence of SIBO, however so far only a handful of high quality studies are available with variable results. A low FODMAP diet is also sometimes recommended following antibiotic treatment for SIBO in order to prevent re-occurrence. This is based on the idea that a low FODMAP diet reduces consumption of fermentable carbohydrates, essentially helping to ‘starve out’ any excess bacteria that may take up residence in the small intestine. Unfortunately, studies are not yet available to either confirm or deny this theory.
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