IBD Cats develop an intolerance for common meats they eat regularly - like chicken

They  may do better with less common ones like duck and venison.
Go offers some helpful options, they have a variety of  meats to choose from.  Hounds & Gatos have a variety as well.

If you prefer to feed your cat raw food to constipated cats.

With some cats, constipation is made worse by foods with ground bones  - most raw recipes have ground bones in them.  When that is the case, then you could make homemade raw food with one of these complete supplements.

Please keep in mind that cats can die without enough of certain key nutrients so you need to follow very specific instruction if you want to start a homemade raw diet.

Current Supplement for making homemade cat food:

Alnutrin Supplement:  A good supplement and recipe for bone-free homemade cat food.  You can request a free sample and they will include the recipe.

Feline Instincts Supplement:  They provide a recipe and nutrient supplement, which makes if easy t make  - sure your cat gets what they need.

Natural cat food picks for cats with IBS/IBD Symptoms

Mainstream vet medicine often puts cats with IBS/IBD symptoms on manufactured  hypoallergenic foods like Hill's Z/D, but these odds are often high in carbohydrates (fattening) and low in quality protein..  And according to some like myself and DVM, these food do not always work either  - at least not for long.

For mild cases of IBD, grain -free canned diets are helpful.

For tougher cases, a raw diet of ground meat with cat-appropriate vitamin and essential-fatty acid supplements mixed in is a complete cure ( my opinion.)

I have seen cats ( two of mine) that have done well with food that have a lot of ingredients, even fruits and vegetables.

First Choice:

My first choice of natural cat food with the most simple, digestive-friendly formulas are:

Hounds & Gatos, canned.  One of the higher quality choices out there.  Several different meat formulas. 

Pure Vita canned.  Simple ingredients, grain free  and low carb.

Tiki Cat Koolina Lua and Puka Puka Luau canned.  Very simple recipes, but the only option is chicken.

What Are Feline IBD and IBS?

Inflammatory Bowel Disease (IBD) is an inflammatory immune-reaction syndrome in the gastrointestinal tract.  We know healing has been possible for many humans and cats, but the roots of the condition have not been well understood , so doctors have not had reliable solutions.

The symptoms are regular bouts of diarrhea, constipation, or vomiting.  You may also see mucous or blood in the stool.  In some cats the only symptom i weight loss.  Some may stop using the litter box because it reminds them of a painful experience.

IBD has similar symptoms to IBD and  I believe it is a precursor to IBD.  The difference is that IBD is so inflammatory that it causes damage to the intestines.  Besides making everyone miserable, the scary thing about IBD is it can be deadly because:

. a cat can actually starve from a very serious case of IBD
. some experts believe the inflammation it causes can to to the intestinal lymphoma which has
become so common in cats.

By the way sometimes what you think are frequent hairballs are actually IBD symptoms.  If you
have a cat who gags or throws up hairballs more than once a month, consider it suspicious.