Diverticulosis is very common here in the US, and this is probably in part because of our diet (which is often low-fiber and highly refined) which can also lead to a chronic state of constipation. Most people with diverticulosis will not have any symptoms, but about 10-15 % will develop diverticulitis. Recurrence is not uncommon with diverticulitis.
I think that it is great that you have modified your diet and are consuming more fiber. These can definitely help. It is unknown whether or not anal sex can lead to episodes of diverticulitis, but I would avoid it. Anal sex is relatively traumatic to the anus and rectum, and since you are already predisposed to irritation and inflammation in the area, it is probably best to avoid any potential causes of or triggers of further episodes. Anal sex very well could be a trigger, but studies have not been done, so it cannot be said conclusively. Nevertheless, I think that it is certainly possible.
So I would avoid it. Hopefully this will help a bit, but if not, you may require more aggresive therapy to treat your diverticular disease; many people do. This would be something to discuss with your GI physician.
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