While sitting on the toilet this morning I was thumbing through Pimentelâ€™s book. I suddenly realized that Pimentel has two explanations for the cause of SIBO. One explanation is that there are bad bacteria in the gut. Letâ€™s call this the bad bacteria theory. The other explanation is that there are bacteria in a part of the gut where they should not be. Letâ€™s call this the bad location theory. These are two very distinct theories. I have only read Pimentelâ€™s book and abstracts of his papers. Perhaps in his journal articles he provides greater theoretical clarification of SIBOâ€™s etiology but I do not believe that the book distinguishes sufficiently these two hypotheses.In order to understand these theories, letâ€™s make some simplifying assumptions. First, assume that all bacteria can be classified. Letâ€™s use the letters of the alphabet to name the classes of bacteria. So some bacteria are in class A, others are in class B, all the way through Z. Second, assume that the gut is a simple tube that is 100 units long. The oral opening is at location 0 and the anal opening is at location 100. Assume the small intestine is located between 60 and 80 and the large intestine begins after the small intestine ends and goes to 100.The bad bacteria theory states that there are some types of bacteria--call them B, C, and Dâ€”-which we will call â€œbad bacteria.â€ The bad bacteria theory claims that if there are bad bacteria in the gut then the gut has IBS and if the gut has IBS then there are bad bacteria in the gut. Pimentel uses the bad bacteria theory when he makes references to travelerâ€™s diarrhea, campylobacter, and â€œheralding events.â€ These are cases where bad bacteria somehow enter the gut and cause an infection because of the nature of these bacteria.The bad location theory states that there are some locations in the gutâ€”namely 60 through 80â€”through which bacteria pass but in which they should not reside. The bad location theory states that if there are bacteria of any class (A-Z) residing in gut locations 60-80 then that gut has IBS, and if a gut has IBS then there are bacteria (of any class) residing in locations 60-80. Pimentel uses the bad location theory when he makes the claim that there are no such things as good bacteria or bad bacteria, merely bacteria in the right place and bacteria in the wrong place. He uses this theory when he suggests that IBS may be the consequence of a defective cleansing wave or housekeeping wave in the gut. Now we can combine these two theories as follows:1. If the gut has IBS then either bacteria of any class reside in locations 60-80 or bad bacteria reside at any location.2. If bacteria of any class reside in locations 60-80 or bad bacteria reside in any location then the gut has IBS.One explanation emphasizes the type of bacteria; the other explanation emphasizes the location of the bacteria. One explanation suggests that elimination of bad bacteria is sufficient to bring about remission. The other explanation suggests that motility problems lie at the core of SIBO.