Many patients who have been given the non-descript diagnosis of irritable bowel syndrome (IBS) routinely notice that eating healthy foods such as many different types of vegetables and fruits, causes an increase in their symptoms - abdominal bloating, abdominal discomfort, burping, flatulence, heartburn, nausea, and poor quality bowel movements. Whole grains, although not considered healthy for many people, also seem to cause an increase in these symptoms.
Some patients believe it’s just their unique circumstance that leads to the poor reaction to these foods. Many times chalking it up to digestive enzyme deficiencies, low stomach acid production, or food intolerances/sensitivities. However, the bacteria that over grow in the small intestines, leading to SIBO, are by far the number one reason why specific kinds of vegetables, fruits, and whole grains create such digestive havoc.
The majority of bacteria living within our intestinal tract feed and thrive on a few specific constituents of food – fibre and most sugars. A large variety of vegetables, fruits, and whole grains contain high levels of these constituents.
We do not have enzymes that can break fibre down into smaller components, and therefore, fibre is a non-absorbable substance. This means that fibre will proceed down the entire length of the small intestines and then travel throughout the entire length of the large intestine, being a super food for our large intestinal bacteria. This is why fibre is considered very beneficial for our large intestinal health.
However, if SIBO is present, now as the fibre travels along the small intestines, copious amounts of bacteria begin to feed on it. As this feeding occurs, the bacteria produce high levels of hydrogen gas (aka hydrogenic SIBO), leading to expansion of the intestines, and therefore, symptoms such as abdominal bloating, abdominal discomfort, burping, flatulence, heartburn, and even nausea in some cases. This is the reason why so many IBS/SIBO patients feel worse when eating high fibre foods or taking fibre supplements.
Sugars, which can come in the form of glucose, sucrose, lactose, or fructose, also lead to worsening IBS symptoms if SIBO is present. In the same sense as fibre, an overgrowth of bacteria also feed on these sugars, leading once again to copious amounts of hydrogen gas being produced within the small intestines. The reason why many fruits trigger significant IBS/SIBO symptoms, is because not only are some of them high in fibre, but they are also high in fructose. This combination of bacteria feeding constituents can provide a “nuclear bomb” of sorts in regards to digestive symptoms. If a patient has a condition called Fructose Malabsorption, it leads to fruits creating extremely significant symptoms if SIBO is present. In this condition, the fructose is not being absorbed into circulation from the small intestines, and therefore, all of it remains in the presence of the bacterial overgrowth and provides even more of a feast.
Lactose is a naturally occurring sugar in most dairy products, and is a favourite food of the bacteria found in our intestinal tract. Many SIBO patients end up with a diagnosis of Lactose Intolerance many years before they receive their diagnosis of SIBO. In many of these patients, it is not actually a deficiency of the lactase enzyme leading to lactose intolerance, but instead, a case of SIBO mimicking lactose intolerance symptoms. The symptoms that arise in both lactose intolerance and SIBO are abdominal bloating, abdominal discomfort and pain, burping, flatulence, heartburn, nausea, and loose stool/diarrhea. It is easy to see why many patients receive the diagnosis of lactose intolerance when they tell their doctor that they get these symptoms after eating or drinking certain dairy products. However, if they have SIBO, they will get the same symptoms after ingesting the same dairy products. Many patients who have SIBO diagnosed and treated, can once again eat lactose containing dairy products without experiencing the debilitating symptoms.
Therefore, fibre and sugars lead to excess hydrogen production, which is seen in hydrogenic SIBO. What about other form of SIBO – methagenic SIBO? The M.smithii bacteria that produces methane gas and can overgrow in the small intestines doesn't actually feed on fibre and sugars. This bacterium instead feeds on the hydrogen that is produced by the hydrogen-producing bacteria in the small intestines. It takes the hydrogen and combines it with carbon dioxide as its primary fuel sources. Therefore, fibre and sugar does not directly create methane production, but very easily indirectly causes it as the hydrogen bacteria feed on them. The end result is methane gas production, which leads to all of the same IBS/SIBO symptoms that excess hydrogen production leads to. One major difference is that high methane production is very much correlated with constipation, where as high hydrogen production is more correlated with loose stool and diarrhea.
A note should be made about a very well known diet that has been studied and implemented in many cases of IBS - the Low FODMAP diet. FODMAP stands for Fermentable Oligosaccharides Disaccharides Monosaccharides and Polyols. A diet low in all of these carbohydrate constituents and sugar alcohols has been shown to reduce the symptoms of many IBS patients. However, even though a very specific diet has been formulated that seems to work, the reason why it works lies in the fact that when you avoid foods high in FODMAPs, you are essentially avoiding foods high in fibres and specific sugars that feed SIBO. And because we know SIBO is causing up to 84% of IBS cases, it makes sense that the low FODMAP diet works in most cases of IBS. An important note is that a low FODMAP diet was not designed as a diet specific to SIBO, therefore, some of the food recommendations will still make symptoms worse in SIBO patients.
If you are perplexed to why many healthy foods make your IBS worse, then it is in your best interest to be evaluated by a qualified SIBO doctor who can test for and efficiently treat SIBO.
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