"IBS-A is a distinct subtype from IBS-C and IBS-D there is no reason to expect that the mechanism underlying the three different subtypes need to be related."
Hold on a second though, there is very strong evidence they are relateed to a problem with serotonin or at least it is involved in causing the c/d or A and motility problems as well as the signals to the brain.
I don't think its likely fructose will end up being a cause of IBS, just like at first they thought lactose was, but now they know it isn't, but having commorbid issues are important.
Increasingly our understanding of IBS is that it is a heterogeneous disorder – that is, multiple factors contribute to the well defined symptoms of the disorder. One of these suspected underlying dysfunctions involves serotonin, which is a neurotransmitter or messenger to nerves. Most serotonin in the body is in cells that line the gut where it senses what is going on and through receptors signals nerves that stimulate a response. The serotonin must then be reabsorbed (a process called re-uptake) into cells. This process appears to be disrupted in people with IBS.
Serotonin and SERT How does serotonin affect gut function? An interview with Gary M. Mawe, PhD, Professor of Anatomy and Neurobiology, University of Vermont, Burlington, VT. Dr. Mawe is a basic scientist.