Considering that fiber intake has other known health benefits, such as promoting regularity of bowel movements and maintaining a healthy gut bacteria, it makes sense to recommend a high-fiber diverticulitis diet.
Additionally, today most people only consume half of the recommended amount. Women should aim to get at least 25 grams per day, while the average man should have at least 38 grams per day (
16,
17).
However, with that said, there is no reliable evidence that a high-fiber diet improves symptoms or prevents complications in diagnosed cases of diverticulitis.
A recent review of 19 studies (9 looking at dietary fiber, 10 at fiber supplements) was unable to make any firm conclusions because each study varied so greatly in how they were conducted, the type and amount of fiber used, among other things (
27).
The authors’ conclusions were:
“The presence of substantial methodological limitations, the heterogeneity of the therapeutic regimens employed, and the lack of ad hoc designed studies, did not permit a summary of the outcome measure. Thus, the benefit of dietary or supplemental fiber in SUDD (symptomatic uncomplicated diverticular disease) patients still needs to be established.”
So there is no definite answer, which helps explain why the Danish and Polish guidelines recommend fiber supplements, whereas the Italian guidelines argue somewhat the opposite (
28).
Basically fiber supplements are an option, as is a high-fiber diet, but unfortunately a bit of trial and error is the only way to see what sits better with you. Many people report doing better on a low fiber diverticulitis diet, which overlaps heavily with a low FODMAP diet (more on that below).
And as mentioned above, a low-fiber diet is definitely recommended following a flare-up. After a few days on a clear fluids diet, you can progress to boiled and soft foods, including cooked fruits and vegetables (without skins), as you slowly increase your fiber intake.