How Do You Get SIBO? 

If you’ve just tested positive for SIBO, you’re probably wondering how and why you got it. SIBO symptoms like diarrhoea, constipation and bloating are no fun. You probably eat the same things as your family and friends, so why did you end up with SIBO while they didn’t? 

Gut health is incredibly complex, and it’s crucial to find out exactly what you’re dealing with before you get any treatment. If you want to shine a light into the wonderful world of your gut, you can start your journey by taking one of our evidence-based gut health tests. If you want to find out how you might have got SIBO, read on.

What is SIBO? 

SIBO stands for small intestinal bacterial overgrowth. Like it sounds, it’s an overgrowth of bacteria in your small intestine. It happens when bacteria that are normally present in your large intestine (or colon) start to grow in your small intestine. ⁠

We need more research here, but it appears that SIBO isn’t always just a numbers game. It could be caused by the ‘wrong’ types of bacteria living in your small intestine, rather than just too many: a ‘normal’ amount of the ones that actually belong in your colon. However, we do know that most often it’s a case of too many in the wrong place: Unlike your large intestine, your small intestine has relatively few bacteria due to your body’s natural preventative measures, like bile, digestive enzymes and the movements that speed your food through it.

SIBO happens when those mechanisms go wrong. It can also happen after surgery. When food and waste products don’t move quickly enough through your small intestine, it creates a breeding ground for bacteria. The gases and toxins those bacteria produce can cause symptoms both inside your gut and outside it, causing weight loss (or gain) and prevent you from absorbing all the nutrients in your diet. 

What are the first signs of SIBO? 

The first signs of small intestinal bacterial overgrowth are usually digestive symptoms like diarrhoea, constipation and bloating. There’s a big crossover between IBS and SIBO, so a lot of the people we see at IBS Clinics have been diagnosed with IBS by their doctor. Some experts even think that IBS and SIBO are the same thing, but there’s evidence that some people with SIBO don’t have any symptoms at all. There are also people with IBS symptoms who test negative for SIBO, although current research suggests that most test positive.

Small Intestinal Bacterial Overgrowth can also present with upper gastrointestinal symptoms that don’t fall under the IBS umbrella, like reflux and burping.

Some of the most common symptoms of SIBO are:

• Abdominal pain⁠
• Bloating and distension⁠
• Burping
• Diarrhoea/constipation⁠
• Excess flatulence/wind
• Reflux ⁠

 SIBO symptoms 

Although SIBO is best known for the symptoms it causes in your gut, research is revealing links between it and more and more conditions outside of your gut.

Because SIBO is a relatively ‘new’ disorder, we don’t have many conclusions. We know that it happens at the same time as a long and growing list of conditions, but we don’t know whether it causes them, or it’s the result of them. In other words, we don’t know what comes first, the SIBO or the condition.

The below is just a small selection of chronic diseases now associated with SIBO:

• Acne 
• Anaemia 
• Anxiety
• Autism
• Brain fog 
• Chronic fatigue syndrome 
• Gallbladder disease 
• Hypochloridia (low stomach acid) 
• Leaky gut 
• Multiple sclerosis 
• Osteoporosis 
• Psoriasis 
• Rheumatoid arthritis 
• Rosacea 

Because the symptoms of SIBO can all be symptoms of other conditions, or conditions in their own right, a doctor or other healthcare professional is unlikely to diagnose you with it without a test.

The good news is that you don’t need to wait for a diagnosis. You can order a SIBO breath test through us at IBS Clinics or any other online provider and get a test kit delivered to your door. 

If you’re unsure if it’s worth taking the test, there are a number of ‘clues’ that you might have SIBO. While there’s no evidence to back them up as diagnostic criteria, we see them as pointers that can turn us in the right direction.

The top 10 signs of SIBO

You have IBS

Research has shown that up to 85% of people with IBS have SIBO. That’s why if someone comes to us with IBS symptoms like bloating, flatulence, diarrhoea and/or constipation, we usually recommend a SIBO test.

You have diarrhoea

If you have persistent diarrhoea for over 3 months, your doctor will usually diagnose you with IBS. If your diarrhoea comes and goes, you may not get a diagnosis of IBS, but it’s still a sign that you could have SIBO. Hydrogen-dominant SIBO often comes with diarrhoea.

You have constipation

Unrelenting constipation for over three months normally means a doctor will diagnose you with IBS. However, occasional constipation is still a sign all is not well with your gut, and if you’ve tried the usual drinking more water and eating more fibre to no avail, SIBO may be the cause of your constipation. Research has proven that methane-dominant SIBO contributes towards constipation.

 Fibre makes your symptoms worse 

If your IBS symptoms get worse when you eat more fibre, SIBO may be at play. While you need fibre to feed the good bacteria in your gut, if those bacteria are in the wrong place, they do more harm than good. There are two main types of fibre: soluble and insoluble, and either, or both, could affect you. 

Your symptoms get worse with probiotics

Well-meaning health experts everywhere advise us to supplement our diets with fermented foods like kefir or kombucha, but if you have SIBO, that can be a disaster. Probiotic foods and supplements often lead to more diarrhoea, constipation or bloating. Probiotics are helpful for most people, but when you have too many bacteria living in your small intestine, you’re adding fuel to an existing fire.

Alcohol makes your symptoms worse

Sadly, alcohol is one of the worst things for SIBO because it contains both yeast and sugar, which bacteria love. Alcohol also damages the lining of your gut, causes leaky gut, and slows down the movements that push your food through your intestines. The slower the food moves through your gut, the longer it hangs around feeding SIBO bacteria.

You feel full easily

If you feel uncomfortably full after a normal-sized meal, you might have low stomach acid. Stomach acid is a powerful antibacterial substance that stops harmful bacteria from getting past your stomach into the rest of your gut. Without enough stomach acid,  bacteria can overgrow in your small intestine.

You have Crohn’s disease or ulcerative colitis

Having ulcerative colitis or Crohn’s disease makes you more susceptible to SIBO in a number of ways. For instance, they both cause strictures and narrowing of your intestines, slowing down the movement of food through your gut, and the disordered immune system that accompanies both the disorders makes SIBO more likely to happen.

You’ve taken a lot of antibiotics

While we don’t have any evidence, a lot of people who test positive for SIBO have a history of taking multiple courses of antibiotics. Because most antibiotics wipe out beneficial bacteria as well as the bacteria you’re trying to get rid of, you can end up with dysbiosis (an imbalance of the microbial communities in your gut). Less helpful types can take over, perhaps setting the scene for SIBO.

You have an underactive thyroid

If you have Hashimotos (an autoimmune thyroid disease) or a slow or malfunctioning thyroid, it can slow the motility of your gut, causing constipation and creating an ideal scenario for SIBO. 

SIBO stools 

As we’ve already explained, there’s a big overlap between IBS and SIBO, so a lot of people with SIBO have constipation or diarrhoea. However, not everybody with SIBO has IBS symptoms.

Some people with SIBO have trouble digesting fats, resulting in severe diarrhoea or steatorrhea (light-coloured, soft, bulky, greasy, and unusually foul-smelling stool).

SIBO pain location 

SIBO itself doesn’t really cause pain, but the gases the bacteria produce can build up, get trapped and cause pain in your abdomen. Most people with SIBO don’t suffer from pain, but if bloating is one of your complaints, you could feel pain anywhere from the top of your small intestine to the end of your large intestine (your anus).

If you have bloating or discomfort shortly about two hours after breakfast, it’s a clue you could have SIBO. Because breakfast is your first meal of the day, you know that discomfort is down to what you’ve just eaten, not a meal before it.

Food usually takes around two hours to reach your small intestine, and around six to reach your large intestine. It’s quite normal to feel food move through your gut straight after a meal, but that’s down to something called your gastrocolic reflex, which makes your gut move after you’ve eaten. What you feel is actually an earlier meal moving its way along.

What causes SIBO? 

SIBO doesn’t happen in a vacuum: it’s always part of a much larger picture of the health of the rest of your gut and body. There are many reasons why bacteria can overgrow in your small intestine, or why the tiny microbiome there becomes unbalanced. 

If you don’t know what caused your SIBO, it will be difficult to get rid of it for good, because without treating the cause, any treatment will only address it temporarily. Your body has inbuilt mechanisms to keep your small intestine free of excess bacteria. If you have SIBO, one or more of them has gone ‘wrong’.

Here are some of the features of your digestive tract that work to keep you SIBO free:

• Your stomach acid is a powerful antimicrobial substance that kills almost all bacteria in your stomach on contact.
• Your MMC (migrating motor complex) is a downward propulsive movement that pushes your food along your digestive tract.
• Your bile (from your gallbladder) breaks down food and helps you to absorb the nutrients in it, preventing it from hanging around and becoming fuel for SIBO.
• Immunoglobulins secreted by your small intestine fight bacteria and other pathogens.
• Your ileocecal valve is a one-way door between your small intestine and your large intestine that should prevent food and waste from your large intestine from going backwards into your small intestine.

If any of these processes aren’t working optimally, bacteria can overgrow in your small intestine, resulting in SIBO.

Is SIBO contagious?

No, SIBO isn’t contagious. It’s an imbalance of bacteria in your gut, not an infection.

While you can catch gut infections like Salmonella or Campylobacter from infected food, water, or another person, SIBO is a completely different disease. The bacteria that cause acute illness are pathogenic, meaning that they’re potentially life-threatening.

SIBO is too many bacteria in the wrong place, but those bacteria are normal inhabitants of your gut that do important work keeping you healthy when they’re at the right levels in the right place.

Can you get SIBO for no reason? 

We need more research on SIBO before we can reach any conclusions on how or why you get it. For instance, we don’t have any studies looking into what happens in the small intestine after someone has their gallbladder removed. While we do have studies that show people who have had their gallbladders removed are a lot more likely to suffer from IBS symptoms afterwards, we can’t say for sure that SIBO is the cause.

It seems unlikely that you can get SIBO for no reason. As we explained before, your body has natural processes that keep your small intestine relatively free of bacteria. If something goes wrong in your body, there’s a reason why. We may not know that reason, but that doesn’t mean that there isn’t one.

What foods cause SIBO? 

Bacteria love to eat carbohydrates, and they like some more than others. However, that doesn’t mean that eating carbohydrates caused your SIBO. Plenty of people with a carbohydrate-rich diet don’t get SIBO.

It’s another area we need more research in, but it seems likely that the typical modern western diet, high in processed foods and sugar and lacking in whole foods and fibre, sets up the scene for SIBO. We know that this kind of diet depletes the microbiome in your large intestine, reducing diversity, so it’s logical that it would also affect the small intestine.

If you already have SIBO, though, we know that carbohydrates are likely to make it worse. Some carbohydrates, like sugar, grains, starch and ‘FODMAPs’ (an acronym for five groups of carbohydrate foods that ferment quickly in your gut) are much more likely to cause problems for SIBO sufferers than ‘gentler’ ones like leafy vegetables.

Interestingly, people without SIBO or IBS can usually eat FODMAP foods with no problems, suggesting that SIBO causes food intolerances, rather than the other way round, as some experts speculate.

SIBO testing 

SIBO tests work by measuring the hydrogen and methane gas that bacteria produce in your small intestine.

To take the test, after giving a baseline breath sample, you’ll drink a sugar solution. When the solution gets to your small intestine, the bacteria there will eat the sugars, giving off gases while they do it. While small amounts of gas are normal, amounts above certain levels mean there are  too many bacteria in your small intestine: SIBO.

It might seem strange to test bacteria in your gut with your breath, but 80% of this gas escapes through the walls of your intestines: It’s the other 20% that gets absorbed into your blood (and goes straight round to your lungs, where you breathe it out) that the test is measuring. By measuring the levels of gases in your breath, technicians in a lab can estimate the degree of bacterial overgrowth.

The SIBO test doesn’t measure the actual bacteria, but the levels of the gases they produce.. Because our bodies don’t produce the gases they’re measuring (hydrogen and methane)—only bacteria do—we know that levels on your breath test reflect levels of bacteria in your small intestine.

Some SIBO breath tests only measure hydrogen, but it’s better to measure hydrogen and methane to get a more accurate picture of potential overgrowth. 

If you’re thinking about ordering a SIBO test, or you’re just about to take one, you might be feeling a bit overwhelmed by all the prep. It’s actually quite a simple test if you read the instructions properly before you start.

However, be aware that you need to make sure of a few things in advance of doing the test:

• Four weeks before the test: finish taking any antibiotics, but you should never stop a course of antibiotics in order to take a test. Talk to your GP first.
• One week before the test: stop taking any laxatives. Again, ask your doctor first.
• One day before the test: eat only the foods you’re ‘allowed’ to as set out by the instructions. If you skip this part, you’ll skew your test results.
• Twelve hours before the test: fast and drink only water. Most people find it easy to do a SIBO breath test first thing in the morning, so they can do the fast automatically overnight.
• On the day of the test: avoid smoking and physical activity before and during the three-hour test period.

When you’ve finished the test, you’ll need to send your breath bags to the lab. You should get the results within 7-10 working days.

SIBO treatment 

Treating SIBO takes a multi-pronged approach, but the two main tools are diet and antimicrobials.

Follow a low carbohydrate diet

Carbohydrates feed bacteria. It’s a good idea to cut down on specific types of carbohydrates for six to eight weeks. 

There are several ways to do this, such as the low-FODMAP diet, the Specific Carbohydrate Diet and the Bi-Phasic Diet. It’s important you find the right one for you: everyone reacts differently to each one. 

Take antimicrobials

You can take pharmaceutical antibiotics to reduce your bacterial overgrowth, but studies have found certain herbs to be equally effective.

The specific herbs you need to take will depend on your type of SIBO: hydrogen, methane or hydrogen sulphide-predominant SIBO all respond differently to different ones. Oil of oregano, berberine, neem and garlic are all commonly used.

Because SIBO often recurs, it’s also important to work out the root cause of your SIBO and address the health of your whole gut and body to create an environment that keeps it away.

SIBO diet 

The diet with the most evidence behind it for tackling SIBO is the low-FODMAP diet, which restricts the fermentable carbohydrates bacteria love to eat. 

There are many diets that can work for SIBO, such as the elemental diet, the specific carbohydrate diet (SCD) and the GAPS diet. The low FODMAP diet is the most ‘famous’—probably because it was developed by a group of esteemed scientists at a university who knew how to get the research right. As a result, there are numerous studies that back up its positive effects on SIBO and IBS symptoms.

FODMAP is an acronym that describes the carbohydrates that some people have trouble digesting. The ‘F’ stands for fermentable.

The sugars are:

• Oligosaccharides 
• Disaccharides 
• Monosaccharides
• Polyols 

You will find you react to some FODMAP foods more than others, perhaps depending on the ‘type’ of FODMAP.

Here are some examples:

High FODMAP foods

• Artichoke
• Apple
• Garlic
• Leek
• Onion
• Mushrooms
• Cauliflower
• Wholemeal bread
• Rye bread
• Wheat pasta
• Kidney beans
• Split peas
• Falafels
• Baked beans
• Soft cheeses
• Milk
• Yoghurt

Low FODMAP foods

• Aubergine
• Beans (green)
• Bok choy
• Green pepper
• Carrot
• Cucumber
• Lettuce
• Potato
• Zucchini
• Orange
• Pineapple
• Almond milk
• Hard cheeses
• Lactose-free milk
• Eggs
• Meats/poultry/seafood
• Corn
• Oats
• Quinoa
• Rice
• Sourdough spelt bread
• Wheat/rye/barley free breads

The FODMAP diet can be difficult to navigate and it’s important to make sure you’re getting enough nutrients and calories, so we recommend you work with a health professional to guide you through it.

Conclusion 

We still don’t know enough about SIBO to say what causes it, but a number of factors appear to be at play. 

Your small intestine is designed to house a small, select group of bacteria. For a range of possible reasons, natural protective mechanisms in your small intestine go wrong, and bacteria build up. The overgrown bacteria then release gases that cause uncomfortable symptoms.

At IBS Clinics, we see SIBO as one part of the puzzle of your gut health. Looking for and addressing the root causes of SIBO, and maximising the health of your whole gut and body gives you the best chance of beating SIBO and keeping it away for good.

Author 

Alexandra Falconer MA (Dist) DipCNM mBANT is a Nutritionist and Registered Nutritional Therapist. After graduating from Brighton’s College of Naturopathic Medicine in 2018, she set up her nutrition practice specialising in gut health, IBS, IBD and related conditions.

Before becoming a nutritionist, Alex was a journalist and copywriter. Now, she combines her two great loves—words and natural medicine—to help bring vibrant health to everyone who needs it.

Reviewed by: Tracey Randell