Here’s a practical, vet‑based overview of limited‑ingredient diets (LIDs) for cats with inflammatory bowel disease (IBD), what works, how to run a trial, and important cautions.

1. What “limited‑ingredient” means and the two common approaches

• Novel‑protein (single‑source) LIDs: use a protein your cat has probably never eaten (rabbit, venison, duck, kangaroo, etc.). Many commercial LID foods are sold over the counter.
• Hydrolyzed protein diets: proteins are broken into very small peptides that are less likely to trigger an immune/food reaction. These are typically sold as prescription diets and are commonly used for GI or skin food‑sensitivity problems. Hydrolyzed diets are often recommended when you want to eliminate dietary antigenicity completely. (onlinelibrary.wiley.com)

2. Evidence and which to try first

• Both hydrolyzed and novel‑protein LIDs can help cats with food‑responsive enteropathy (a subset of IBD). Studies and clinical reviews show hydrolyzed diets can resolve signs in many cats and are a reasonable first‑line dietary trial. Commercial novel‑protein diets also help some cats. Choice often depends on prior exposures, palatability, availability and whether you need a prescription product. (pubmed.ncbi.nlm.nih.gov)

3. How to run an elimination/limited‑ingredient diet trial (practical steps)

• Be strict: feed ONLY the trial food and water — no treats, flavored medications, chewable supplements or table scraps. If there are other pets in the house, keep feeding controlled so the trial cat cannot access different food. Contamination invalidates the trial. (academy.royalcanin.com)
• Transition slowly over ~7–14 days to avoid vomiting or anorexia.
• Trial length: plan for at least 8 weeks and ideally up to 10–12 weeks (some cats improve earlier, but full response can take 10–12 weeks). If you see improvement, maintain the diet; if you want to confirm food‑responsiveness, carefully reintroduce the original food (challenge) and watch for recurrence. (academy.royalcanin.com)

4. Monitoring and concurrent care

• Track clinical signs (vomit, stool consistency, appetite), body weight and body condition. If the cat loses weight or refuses the trial food, contact your veterinarian—you may need an appetite stimulant, appetite‑support wet food alternative, or bloodwork.
• Test serum cobalamin (B12) when IBD is suspected; many cats with chronic enteropathy are hypocobalaminemic and benefit from parenteral B12 supplementation (commonly 250 µg SC q7 days × ~6 weeks, then tapered/reevaluated). Correcting B12 can speed recovery. (pmc.ncbi.nlm.nih.gov)

5. Home‑cooked LID diets — important cautions

• Homemade or “cook at home” single‑ingredient diets are sometimes used, but most published homemade recipes are nutritionally incomplete for cats (risk of taurine, vitamin/mineral deficiencies). If you plan a long‑term home‑prepared LID, work with a board‑certified veterinary nutritionist (ACVN/DAVN) to provide a balanced recipe and supplements. For short emergency bland feeding a few days is usually safe, but not as a long‑term solution without professional formulation. (tuftscatnip.com)

6. Practical product notes (how owners and vets typically choose)

• If you’ve never tried a novel protein, a commercial single‑source LID can be tried first (many brands are available). If the cat has severe signs, prior exposure to many proteins, or if a food reaction is suspected but a novel protein fails, a hydrolyzed prescription diet is commonly used next. Many clinics start with a hydrolyzed diet for moderate–severe cases because it minimizes antigen exposure. Always confirm whether a product requires a veterinary prescription in your area. (pubmed.ncbi.nlm.nih.gov)

7. When to escalate (no improvement)

• If there’s no meaningful improvement after an appropriate, strict 8–12 week trial (and appropriate supportive care such as B12 correction), further diagnostics (abdominal ultrasound, GI biopsy/endoscopy, fecal testing, trial of antibiotics or immunosuppressive therapy) are commonly pursued. Your primary care vet or a specialist (internal medicine) can advise next steps. (onlinelibrary.wiley.com)

Bottom line (recommended plan)

• Start with a strict elimination: either a novel‑protein single‑ingredient commercial LID (if truly novel for your cat) or a hydrolyzed prescription diet. Feed exclusively for 8–12 weeks, monitor weight and signs, and check serum cobalamin (supplement if low). Use a board‑certified veterinary nutritionist for any long‑term homemade diet. If the cat doesn’t improve with a well‑run trial, pursue further diagnostics with your veterinarian/specialist.

If you want, I can:

• Suggest example prescription and OTC LID/hydrolyzed diets commonly used in the U.S. (with pros/cons), or
• Draft a checklist you can print/share with your vet to run an elimination trial correctly (transition schedule, strict‑feeding rules, monitoring log).

Which would you prefer?