9 Key SIBO Weight Gain & Symptoms Facts

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Medically reviewed by, Russell Braun RPH

Bloating, abdominal pain, diarrhea seem to be part of the norm for you? Trying various medications but still dealing with these issues is frustrating. Now you wonder if those few pounds you put on have come as a result of these symptoms. If this sounds familiar, could SIBO be causing your symptoms and weight gain?

SIBO also known as Small Intestinal Bacterial Overgrowth is a common cause of weight gain and most people do not realize it.

Picture of bacteria

There are billions of bacteria and fungus that live in your gut, known as normal flora. These bacteria interact with your body and work in a synergistic way. It is an everybody wins scenario. You provide the bacteria a place to live and they help protect your intestines from bad bacteria, fungus and toxins.

When you eat food it goes in through your mouth, down the esophagus and into the stomach. Acid is secreted from the stomach to help you digest the food. Afterward the stomach allows the food to pass into the small intestine. That is where most nutrients are absorbed. Once food reaches the colon (aka large intestine) it is exposed to your normal flora that feed off the food remains and help further break it down.

What Is SIBO?

The colon (also known as large intestine) is the place where the normal flora live. However, when SIBO occurs bacteria get into the small intestine where nutrient absorption is normally occurring. As colon bacteria start migrating into the small intestine they break down food as they normally do in the large intestine.

That is a problem because the small intestine is not equipped for fermentation. That leads to a production of methane or hydrogen gases and SIBO symptoms are the result.

Another thing to remember is that certain types of bacteria are found in various areas of the colon and small intestines naturally. With SIBO certain bacteria overgrow and this throws off the natural balance of the GI tract.

What Causes SIBO?

Finding the cause of SIBO is not always straightforward. This frustrates many patients because it may take several trips to the doctor to confirm a diagnosis of SIBO. One commonality is that all the causes are from stress on the body. These stresses which could be physical or emotional slow the passage of food through the digestive tract.

That slowdown in movement through the GI tract (aka peristalsis) allows for bacteria to overgrow. The table below lists the most common causes of SIBO.

StressorWhy it leads to SIBOExample
Chronic stressStress causes the body to go into fight or flight mode. During fight or flight your body diverts blood away from the gut.Stress from family, friends or work
TraumaBody expends energy on healing instead of digestion.Surgery
Antibiotic useKills off good bacteria that normally protect the gut and allows other bad bacteria to take over.Amoxicillin for an ear ache
Viral or parasitic infectionInfections can cause the balance of bacteria to be altered.Lyme disease
HypothyroidismLow thyroid function slows down digestion and the movement of food through the gut.Hashimotos disease
DiabetesDiabetes can damage nerves including the nerves that stimulate the GI tract. This slows down digestion.Type II diabetes
Immune suppression70% of the immune system is found around the gut. When the immune system is suppressed bad bacteria can take over.Taking medications that suppress the immune system
Decreased stomach acidWith less acid coming from the stomach certain bacteria can overgrow in small intestine.Using acid blocking drugs
High estrogen levelsEstrogen stops bile salts from being secreted by the liver. These bile salts prevent bacterial growth.Plastics in the environment can obesity can lead to high estrogen levels.
Gut scar tissueScar tissue from bowel disease slows down digestion.Crohn’s disease

What Does SIBO Feel Like?

SIBO can lead to a variety of symptoms. Unfortunately, many people just think digestive problems are a part of life. They may suffer with symptoms and try to use medications to mask the symptoms. This never gets the root of the problem.

SIBO GI symptoms

Decreased appetiteDiarrheaBelching
HeartburnAbdominal pain & gasFeeling of fullness

When people think about SIBO they may only be focused on digestive symptoms. While SIBO does cause several stomach issues it can affect the entire body.

SIBO Non GI symptoms

As bacteria grow in the small intestine they create gas byproducts, hydrogen and methane. In addition to GI symptoms these gases cause problems with other body functions as well. Two issues lead to the non GI symptoms.

  1. Nutrients are not able to be absorbed. Eventually deficiencies in nutrients can lead to disease like anemia and neurologic problems.
  2. Leaky gut (also known as increases permeability in the gut) allows bacteria to be absorbed. When this occurs the immune system starts to fight them. This happens in the bloodstream and leads to inflammation in many other places in the body.


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These two processes lead to other secondary symptoms of SIBO such as:

AnxietyFatigueMood swingsIrritability
Weight gainWeight lossDepressionAcne
MalnutritionFood cravingsNasal congestionAsthma

Why Does SIBO Cause Weight Gain?

SIBO causes weight gain due to the methane gas that is produced. Higher methane levels have a direct impact on the small intestines normal digestion processes. Specifically, methane causes the following issues that lead to weight gain:

  1. It slows down the speed with which food is moved through the small intestine. The food sits in the small intestine and begins to rot, while bacteria feed on it and make more methane.
  2. Methane decreases the strength of muscle contractions in the small intestine. This results in a decreased ability to move the food along so it can be excreted in the stool.

You literally will have food staying in the body longer than it normally would. This means more calories will be absorbed and leading to weight gain. The bacteria which feed off of sugars also make you crave sweets. This factor alone can lead to overeating due to these urges.

Changes in the types of bacteria

Another factor is the type of bacteria that are commonly seen in people with SIBO. Specifically the balance of bacteria is affected. The two bacteria listed below are found to have overgrown in SIBO.

Stool tests of patients with SIBO confirm these bacteria being overgrown. High quantities of these bacteria have also linked to weight gain.

When the natural balance of bacteria in your gut are thrown off losing weight becomes more of a challenge. Bacteria in the gut actually impact hormones that your body releases. This has a direct effect on weight due the effect of these hormones on energy storage.

Is It Hard to Lose Weight With SIBO?


SIBO bacteria have a direct impact on the beta cells of the pancreas that release insulin.

The direct impact is that less insulin is secreted in response to a meal. This means that the blood sugar from the food can’t be taken up by cells in the body. Insulin is required for that to occur. When the levels are low the sugar stays in the bloodstream.

In addition SIBO may cause insulin resistance. More inflammatory bacteria get absorbed from the gut. This inflammation leads to insulin resistance.


Leptin is a hormone that is secreted by your fat cells. Leptin works as a gauge for your brain to help balance food intake based on energy your using.

It acts in the brain to stimulate hunger and is the key part of the reward center in the brain. Specifically it helps drive reward sensations tied to eating.

The toxins that are produced by the SIBO bacteria lead to an increase in leptin sensitivity. Thus leading to an increased desire to eat.

These hormone malfunctions make it difficult to curb appetite and resist food cravings. The sugary foods that lead to more reward responses are the ones that allow SIBO bacteria to thrive. This is a powerful combination of hormonal influences that are leading to more and more people suffering with SIBO.

A link Between SIBO And Obestiy

Studies have shown a that SIBO is twice as likely in obese patients vs non obese. The jury is still out on which one typically presents first. The scary thing is the incidence jumped to three times as likely for people on the SAD (Standard American Diet) typically seen in the western world.

The difference in SIBO with Hydrogen vs Methane

Not all cases of SIBO will have weight gain. In fact, weight gain or loss seems to result based on the primary symptom. Those with constipation seem to gain weight versus those with diarrhea may lose weight.

A study looked at this and found a primary difference. The type of gas produced is based on the primary bacteria present. It appears that hydrogen production seemed to have diarrhea and weight loss. This was in contrast with people with constipation who seemed to produce methane gas.

Recently, a new term has arisen for this difference in hydrogen vs methane producers. Technically the organisms that make methane are not bacteria. Instead they are an atypical organism called archaea, but are a normal resident of the gut.


IMO = Intestinal Methanogen Overgrowth produces CH4 gas, also called methane.

Primary symptom = Constipation

SIBO = Small Intestinal Bacterial Overgrowth produces H2 gas, also known as hydrogen.

Primary symptom = Diarrhea

What Happens If SIBO Is Left Untreated?

Long term SIBO will lead to the effects mentioned above that are present throughout the body. As bacteria overgrow, they start to eat up nutrients from the food you eat. This leads to malnutrition even though you eat a normal amount of food.

Additionally your food will not be broken down as part of normal digestion. That also leads to less nutrients being absorbed. Malnutrition combined with increased leaky gut leading to inflammation can lead to some or all of the following:

  • Mental health problems
  • Skin problems
  • Breathing issues
  • Inflammatory diseases
  • Osteoporosis
  • Decreased absorption of fat soluble vitamins A,D,E & K

How Do You Know If You Have SIBO?

The good news is that you can test to find out if you have SIBO or not. The test is a simple breath test that monitors for hydrogen and methane production. The test is non-invasive, meaning there is nothing probing your body.

Prior to the test you must drink a sugar solution that the bacteria will feed off of and produce gas. The presence of hydrogen or methane in the breath after 90 minutes is considered a positive test. The idea is that it would take a full two hours for the liquid to reach the normal bacteria which may produce this gas in the large intestine.

There is the potential for a false positive if you move liquid through the GI tract quickly. The test also does not have a well established range for the amount of gas expected in the breath.

North American Consensus on Hydrogen and Methane Breath Tests

  • Test with either 10 grams of lactulose or 75 grams of glucose
  • Hydrogen >20 parts per million at 90 minutes is positive
  • Methane >10 parts per million at 90 minutes is positive

You should work with your doctor or someone who specializes in SIBO to ensure you get a good test. It is relatively simple and can help clarify if your symptoms are due to SIBO or another problem.

Can a Stool Test Detect SIBO?

You may see claims that SIBO can be tested with a stool sample. That is simply not the case. The large intestine comes after the small intestine. It is the area where your stool is formed and is home to billions of bacteria.

That makes it pretty easy to understand why a stool test would not be able to tell you about the bacteria in your small intestine. There would be no way to differentiate it from those coming from the large intestine.

What Is The Fastest Way to Cure SIBO?

SIBO did not come on quickly and to treat it effectively you need to be prepared that this is not a quick fix. Working with a doctor trained in SIBO will go a long way. Many doctors may just try antibiotics to kill the offending bacteria. The problem with that approach is it can wipe out good bacteria too leaving you open for other infections in the future.

Most treatment plans consist of three components.

  1. Diet
  2. Supplements or antibiotics
  3. Probiotics and probiotics

Timing each of the components is important as well. For instance you want to start out by starving the bacteria via your diet. That means cutting our sugars that the bacteria thrive on, which will weaken them. Then antibiotics or supplements can be tried to help eliminate the bacteria. Finally, giving probiotics to repopulate any that were lost due to antibiotic use is critical.

1. Diet

Limiting sugars is critical to success in treating SIBO. That is why the low FODMAP diet was created. FODMAP means Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols. These are all type of sugars that fall under the macronutrient of carbohydrates.

The sugars listed by the FODMAP name are all hard for your body to absorb. Therefore, they cause digestive symptoms seen with SIBO.

FODMAP is a very restrictive diet and is not intended to become a way of life. Rather it is a tool you use to help you weaken and eliminate the bacteria that take over your small intestine. The diet includes three phases:

  1. Stop eating the FODMAP sugars.
  2. Slowly reintroduce foods that have the sugars… SLOWLY!
  3. See which foods make you have symptoms and then look to limit those foods in the future.

When being treated for SIBO you will be on a very limited diet with no sugars for about two weeks. Then you can start to reintroduce certain foods at a rate of one every three days or so. After the two weeks you can also begin to take some antibiotics or supplements that can help eliminate the starving bacteria from your intestines.

FODMAP Food List

Foods to eliminateFoods you can have
Dairy based products
(Milk, yogurt, ice cream)
Eggs and meats
(Preferably organic and grass fed)
Wheat based products
(Cereal, bread, crackers)
Certain cheeses
(Brie, cheddar, feta)
Beans and lentils
(Black beans, kidney beans)
Nut milk
(Almond milk, coconut milk)
Certain vegetables
(Artichokes, asparagus, onions)
Some grains
(Rice, quinoa, oats)
Some fruits
(Apples, cherries, pears, peaches)
(Potatoes, tomatoes, cucumbers, zucchini)
Berry fruits
(Strawberries, blueberries, blackberries)

In general it is a good idea to stay away from ultra processed foods. These foods have added sugars that can feed the SIBO bacteria and increase cravings. Try to each whole foods, which are typically found on the perimeters of the grocery store. The good news is that will also help you lose weight!


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2. Antibiotics and Supplements

Unfortunately, many doctors will jump right to antibiotics for treating suspected SIBO. Again, this will kill off both good and bad bacteria. That could set you up for trouble later. If you can find a doctor who specializes in SIBO treatment it might be worth the effort.

There several products that can be used to kill off SIBO bacteria.

RifaximinPrescription antibiotic that is not absorbed. It is effective at killing SIBO bacteria.
BerberineAn herb that has antibacterial properties.
Caprylic acidMade from coconut oil and increases acid levels in the stomach and small intestine to eliminate SIBO.
BetaineHelps increase stomach acid and improve movement of food through small intestine.

After two weeks of low FODMAP diet and 7-10 days of antibiotics, the final step in treatment begins.

3. Prebiotics and probiotics

Prebiotics are foods such as fiber that feed the healthy bacteria in your large intestine. These preboitoics ensure the bacteria can provide you with nutrients you need from their healthy metabolism. This ensures that good bacteria do not get outnumbered by overgrowth of bad bugs.

Whole foods are the best source of prebiotics. These consist of high amounts of insoluble fiber. Examples include:

  • Kefir
  • Nuts
  • Beans
  • Cauliflower
  • Sauerkraut
  • Kimichi
  • Kombucha

Probiotics are required because the low FODMAP diet can lead to a die off of bifidobacteria. This is a healthy bug that you want to make sure and reestablish in your gut. Keeping a high level of healthy bacteria that are well fed will greatly improve your overall health.

Make sure to look for a supplement that has a majority of bifidocateria on the ingredients label.

Prevent SIBO Recurrence

It is important to remember that stomach acid is vital to digestion. It seems everyone takes acid blocking drugs for heartburn these days. That is a recipe for the explosion of SIBO and other GI problems we see today.

Acid blocking drugs say right on the label that they should not be used for more than 14 days. However far too many people end up on them for a lifetime.

If you have SIBO you have to find a way to taper off these medications. The trick is you have to do it slowly or else your body will rebound and make high levels of acid.

Adding some acidic foods to your diet can help once you get off the medications. Examples include:

  • Lemon
  • Pickles
  • Sauerkraut
  • Apple cider vinegar

Final Verdict on Weight Gain Vs. Weight Loss

Gaining or losing weight due to SIBO will depend on the type of gas being produced. Regardless, weight changes are just one aspect of SIBO. Working with a doctor who is familiar with the problem is the best bet. That will ensure you don’t suffer the long term consequences.

Click here to get Dr. Jason Reed’s exclusive list of medication questions you MUST ask your doctor, for FREE!

Share Your Story

Do you have problems that sound like SIBO? Chime in below with your comments and thoughts.


Basseri, Robert et. al. Intestinal methane production in obese individuals is associated with a higher body mass index. Gastroenterol Hepatol. 2012 Jan;8(1): 22-28.

Li-hui, Yan et. al, Association between small intestinal bacterial overgrowth and beta-cell function of type 2 diabetes. J Int Med Res. 2020 Jul;7(48): 93-100.

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