IBS is a common set of symptoms. IBD is short for inflammatory bowel disease, and it's an umbrella term for Crohn's disease and ulcerative colitis (UC).
My point seems to have flown over your head. Obviously it's a given that I know that, I'm a histologist. My point was that IBD is marked by histological changes within gut epithelial tissue that suggest chronic inflammation and elevated TNF-a and cytokine activity. However, it doesn't mean that the causative agent of IBD is the same for everyone.
If this was the case, and IBD was a purely genetic illness with no environmental component, then it would be literally impossible to study it. In labs we force mice to ingest dextran sodium sulfate (DSS) which produces persistent colitis by degrading the gut mucosa. It's impossible to really tell without sequencing someone's entire genome whether their IBD comes from genetic factors or environmental factors.
Both IBD and IBS respond to changes in diet, as both diseases involve degradation of the gut mucosa. Obviously IBD is marked with inflammation as well, while IBS is marked only by dysbiosis and abdominal discomfort.
IBS is a common set of symptoms. IBD is short for inflammatory bowel disease, and it's an umbrella term for Crohn's disease and ulcerative colitis (UC).