Obese cat WITH struvite crystals

I have been readings threads upon threads about cats with struvite crystals. My male rescue, approx 6 years old, was rushed to the ERhey only to find he had a huge blockage. Now they're recommending Purina UR  or RC Urinary S/O for 4-6 weeks and then a urine test, as most vets typically do from what I've seen.

I'm more than happy to do that, but am hugely concerned because my cat is quite large. We've been on weight management food (nutro/evo) for a while now, but I am worried that these canned urinary foods are the opposite of what he needs to lose weight. 

We have 4 other rescues at home so I am already facing a tough battle ahead with making sure he doesn't eat from their bowls. But I was wondering if anyone else has any insight into the best thing to do for struvite crystals in an overweight cat. The vet says portion control is key, but I am worried that with the huge grain focus in the RX food, he will not be getting the nutrients he needs on smaller portions + he'll still feel hungry.

I don't want to play god here so I'm happy to keep him on the RX food for a while, but the unhealthiness in terms of nutrients for him is concerning.

I'm also in Canada so it's even tougher to order food online.

Have you considered raw? Check out www.catinfo.org. Dr. Pierson has a section on urinary troubles and has saved these cats which were severely obese and had urinary troubles.

My cat(female) had to have surgery to remove a bladder stone and was put on a RX diet . I thought the quality of the food was inferior with poor ingredients so after researching and reading Lisa Pierson site i switched her to all canned food ( Weruva,Earthborn) and give her the vermont Pet naturals UT support chews which she loves. She doesn't have any more bloody drainage and has lost weight to a more healthy size and looks better than she ever did. She pees soooo much more from the extra liquid in her diet of canned food and that helps keep her system flushed. No dry food at all is very much the key. She also had accupuncture for inflammation and anxiety and the calming chews from V.P.Naturals helped as well. I transitioned her from the dry food gradually and had my vets approval before discontinuing the Royal Canin RX. She gets periodic xrays to make sure no stones but this condition is not as critical in a female. I also have little water pumps in my cats water bowls( get a large METAL or Ceramic bowl) and they drink more water Don't get the plastic fountains cause they get slimy quickly and hard to keep clean. You can get a replacement pump for one of those fountains and just put it in a big dog feeding dish(non plastic. Clean the pump with vinegar once a month.

 Raw food will not dissolve struvite crystals. Some cats have very high ph levels which cause the crystals to form.  My cat is one of those cats who has to have either a prescription food for LIFE or methionine added to his diet to keep his urine ph low.   If you pull him off of the script food his urine ph gets too high and he starts getting crystals again.

My cat's natural urine ph on a high meat diet is 8.0, instead of 6.2. So if the vet recommends a script food, go with what the vet says!

You need to separate your cats when you feed them.  My cats get fed in their cages and are let out after they are done. None of them are overweight.  Cats are not meant to be free choice feeders.  In the wild they would get one meal, and go hungry for 2 days.

If the vet says it is okay to take him off the prescription stuff, be sure to get another urinalysis done in 4 weeks. If his ph is too high, he may need to stay on the prescription diet.

You can try adding methionine to his regular food, but the dosage can be tricky and it requires you to get ph strips and monitor the urine ph yourself.  Plus if you accidently overdose, it would be bad!