SIBO, IBS, FODMAP: what’s in a name?

Maybe you’ve seen these acronyms before. Or maybe like me, they have become a familiar part of your life. But what do they all have in common? How are these related? Here’s everything you wanted to know (or didn’t) about gut acronyms. Let’s start at the beginning…

Your Gut 101

The small intestine receives digested food from the stomach and breaks it down so that the body can absorb vitamins, minerals, proteins, carbohydrates, and fats. Once everything has been absorbed and broken down, your muscles begin a series of contractions called peristalsis that pushes the leftovers into the large intestine through the ileocecal valve (think of it as an open and shut valve that connects the two pipes).

So what does the gut have to do with bacteria? Gut flora, or microflora, is the name given to the bacteria colony that lives in our intestines. It plays an important role in proper digestion, the immune system, and maintains the balance needed in the gut. What blows my mind is that a baby is actually born with a sterile system which begins colonizing after he swallows bacteria from Mom on the way out (gross)! By the 3rd day of life your microflora develops based on how you’re fed (breast milk vs. formula) and by age 3 your gut is functioning similar to an adult.

The balance of bacteria in your gut is largely personalized and determined by your diet and environment. And it can change. Allergies, inflammatory bowel diseases, immune deficiencies, functional bowel disorders, and chronic diseases can be attributed to a flora imbalance. So when my pediatrician gave me a shot of penicillin at 10 days old or multiple rounds of antibiotics by year 1, my gut was already destroyed. Bye-bye healthy gut. Hello allergies, autoimmune disease, and SIBO.

SIBO: Small Intestine Bacterial Overgrowth

The first of the gut-related acronyms. The small intestine is relatively sterile, but when the gut flora is off balance, bacteria – either pathogenic or from the large intestine – can set up camp and quickly take over. SIBO is a chronic bacterial infection of the small intestine that can lead to all sorts of problems. Instead of your small intestine digesting food, the bacteria feasts on the undigested food and steals your nutrients. They then produce toxic waste which causes large amounts of gas and bloating within the intestines and can lead to distention of your bowels and abdominal muscles causing pain. Your intestinal wall has tight junctions, think of bouncers at a club, guarding the barrier and controlling who gets through. But over time, the increasing amount of bacteria and toxic waste can do wear and tear on your mucosal lining. Intestinal permeability can develop, allowing larger food particles, proteins, and bacteria to enter your bloodstream (leaky gut) which can trigger an immune attack.

SIBO can be long-term and symptoms can develop slowly over time as bacteria multiplies and crowds out the good bacteria. Symptoms include: bloating, gas, abdominal pain, constipation, diarrhea, heartburn, nausea, fatigue, weight loss. As time goes on, malabsorption and nutrient deficiency becomes a problem as your body is unable to absorb what it needs. All the healthy eating in the world won’t do you much good if the bacteria is eating it all. Long term you could start experiencing other symptoms like chronic fatigue syndrome, joint pain, headaches, food sensitivities, allergies, skin rashes, asthma, and autoimmune responses. This is the stage I find myself in.

Though easily tested, discovering you have SIBO may take some digging since your symptoms can be mistaken for other things. SIBO has been found in patients with IBS (50%), Crohn’s (25%), and Celiac Disease, among others. Treatment with the antibiotic Rifaximin has shown significant improvement along with diet (fodmap) control.

IBS: Irritable Bowel Syndrome

This is a functional disorder of the gut, usually affecting the large intestines. Its symptoms are almost identical to SIBO: abdominal pain, bloating, gas, constipation or diarrhea. Not to be confused with Irritable Bowel Disease like Crohn’s and ulcerative colitis, which actually damage the tissue. IBS symptoms can come and go, get better or worse, without much of an explanation. Mayo Clinic sites as many as 1 out of 5 Americans struggle with IBS.

Until recently, doctors have recommended treatment by adjusting lifestyle, stress, and diet. Some doctors even prescribe antidepressants for the condition, thinking it’s due to anxiety.  Now that SIBO is being seen as a likely factor, IBS may have a brighter future ahead. And thanks to Australian research, doctors in the US are finally starting to give the Fodmap Diet its rightful place in symptom relief.

FODMAP: Fermentable Oligo-Di-Monosaccharides and Polyols

Seriously, what kind of name is this? What does it even mean? When I tell someone I’m on a low-fodmap diet, I get blank stares and awkward silence, which I usually follow up with, “It’s complicated”.

But it’s not really that complicated once you understand the premise. Fodmaps are short chain carbohydrates that are poorly absorbed in the small intestine. The low-fodmap diet has been scientifically proven to show significant improvement for SIBO and IBS patients. It was created by Monash University in Australia which has done extensive research on how certain foods, particularly fodmaps, affect the gut. They discovered that by restricting foods high in fodmaps, one can control symptoms and perhaps even heal the gut from functional disorders. Monash continues ongoing research on fodmaps and functional gut disorders.

Here are a few important concepts I’m learning as I become a fodmapper:

Carbohydrates are fermented by bacteria. This includes grains, fruits, vegetables, dairy, legumes, nuts, etc. If your problem is excessive bacteria that is fermenting undigested carbs, then your goal becomes “starving” the bacteria by feeding the host (you) but denying them the food they need to survive and multiply. Some suggest avoiding carbs completely. But if your diet is very low in carbohydrates, the bacteria will start to ferment protein instead because there’s an insufficient amount of carbs. Not cool.

It’s a delicate battle between you and the bacteria, which is why the antibiotic for SIBO gives you a jumpstart by destroying a large amount of the bad bacteria upfront. The low-fodmap diet specifies which carbs are more likely to be fermented by bacteria. Restricting these carbs while allowing others that are low in fodmaps gives you the best of both worlds.

Insoluble Fiber cannot be fermented by bacteria. These include foods like certain seeds, nuts, bell peppers, brown rice, zucchini, tomatoes, carrots, cucumbers, green beans, dark leafy vegetables, etc. All which are allowed on the fodmap diet.

Fructans and Oligos are the most common fodmap to cause IBS symptoms. The “O” in fodmaps, no one is actually able to fully digest these. The biggest offenders are onions, garlic, and wheat products. If that makes you sad, there are a few substitutions you can use for flavor such as garlic-infused oil or chives and the green part of scallions. I was all about the garlic-infused oil until I discovered the very high risk of botulism that accompanies even store-bought products. Weighing the taste of garlic vs. the risk of possible hospitalization or paralysis was a no brainer. I think I’ll stick to other flavors, thank you very much!

Low-fodmap diet is not the same as a gluten-free or dairy-free diet. It does restrict gluten and lactose but for different reasons. A gluten-free diet is generally followed by those with celiac disease who react to the protein, gluten. A fodmap diet primarily focuses on removing the fructan, not the protein, found in wheat based products like breads, cereals, and pastas. Therefore, small amounts of wheat and gluten are generally tolerable. A fodmap diet restricts the undigested sugar lactose, but still allows for dairy products. Did you know that you can be lactose intolerant but still eat cheese? Hard, aged cheeses like swiss, cheddar, etc. have virtually no lactose. The same is true of butter, sour cream, and small amounts of cream cheese.

Fodmaps are cumulative. One type of fodmap may not invoke many symptoms but eat an entire meal of fodmaps and combined they can cause a flare up. Paying attention to the dose and amount is crucial to understanding and following a low-fodmap diet.

So what do I eat? fodmapappYou can find lots of lists and charts online but a lot of them seem to be contradictory, leaving you feeling frustrated. I prefer to go directly to the source. Monash University has an app for purchase that lists foods based on a high, moderate, and low scale. It also comes with recipes and a shopping guide. I find this to be the most accurate and resourceful list as they continue to update it with new research findings. And it’s easy to have “on the go”, pulling it out when you’re picking up groceries or eating out.

No really, what do I eat? Following a low-fodmap diet can be a little challenging. I always say if someone could just put a meal plan together and cook for me, this would be a breeze! But since I’m the cook and the planner, finding other resources like The Low Fodmap Diet Cookbook can be a time saver. Not only does it outline the entire diet to help you understand the principles, it provides recipes and a food journal to keep track of your symptoms.


Stage 1 of the diet is to eliminate all fodmap categories from your diet, avoiding those foods that are high in fodmaps. This is where the app comes in handy. Many suggest doing this phase for an initial 1-2 months while monitoring your symptoms for signs of improvement. This phase would also start immediately following antibiotic treatment for SIBO. As you transition, make sure you are getting an adequate amount of calories each day!

Stage 2 of the fodmap diet is to reintroduce one fodmap category at a time in small doses after the initial elimination phase. By watching your symptoms, you should be able to tell which group of fodmaps or which foods cause flare ups. Because IBS triggers are individual, it is recommended that you customize your diet based on what works for you.

Fodmapping is not for life. This diet is intended to “starve” and reduce the bacteria causing your symptoms in order to help you gain control over your gut. If you can better understand what has caused your gut flora imbalance in the first place (long term antibiotics, slow motility, ileum issue, etc.) your gut will have a better chance at healing long term!



Disclaimer: I am not a medical professional. Everything you read I have learned through my own hours of research. Please discuss any dietary changes or medical concerns with your physician.

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