The name says it all: small intestinal bacterial overgrowth, aka, SIBO. Your small intestine is supposed to be relatively sterile, meaning, not having a lot of bacteria or other microbes that live there. Contrast this with the large intestine, where an abundant and diverse microbiome is considered a marker of good health.
When bacteria (hydrogen and/or hydrogen-sulfide-predominant SIBO), archaea (methane-predominant SIBO, aka methanogen bloom), or yeast (fungal SIBO, aka SIFO) set up shop in your small intestine, they interfere with normal digestion by stealing your food (carbs), creating excess intestinal gas, and damaging your GI tract.
The most common symptoms are bloating, diarrhea, constipation, and/or abdominal pain, to name a few. These symptoms overlap quite a bit with some other GI disorders. In fact, it is estimated that 60-70% of IBS cases are caused by SIBO, which means that it could affect up to 10% of the US population.
Some of the most prominent names in SIBO research hypothesize that the majority of cases are caused by a poorly-functioning migrating motor complex, or MMC. Essentially the MMC is responsible for sweeping your small intestines clean after every meal.
Previous cases of food poisoning can permanently damage the MMC, which causes food to sit for longer than it should in the small intestines, making it easier for microbes to take up residence where they don't belong. There are also structural abnormalities and other predisposing factors that can impair underlying MMC function, leading to chronic SIBO, but these are not as common as food poisoning.
SIBO is chronic for approximately two-thirds of patients, and the main goal for chronic cases is to maximize the amount of time that SIBO is in remission. There is a lot of research being done to better understand and treat the condition.
For more information on the condition, Wikipedia and SIBO Info are good places to start. Also check out the Resources section.
I am not a medical professional.
Having suffered from SIBO for over a decade myself, I know how miserable it can be. I want to help others avoid the same fate by sharing what I've learned along the way. In doing so, I've aimed to include only information and recommendations where there appears to be some level of consensus among SIBO experts, steering clear of personal bias and interpretation as much as possible.