The most common thing we see is food allergies. If the allergy is consistent 365 days a year, then it's probably not fleas and it's probably not seasonal. I would approach illnesses that are related to food the same way.
If it's something that you're feeding—maybe it's a new additive that you added to the cat's diet or a new ingredient or perhaps even a new bag of food—and right at that point you see that your cat has been constantly ill with a variety of signs, it's a strong possibility that it's the food. If it began with the initiation of a new ingredient and it's consistent after the cat has been eating the new food, that is kind of a big red flag for me.

I would definitely monitor things like your cats stool. Sometimes if it is not the right nutrients for him, sometimes the stool can just be a little, not as solid. Also, it can be really foul smelling. Also if your cat's energy level decreases at all, or if the coat does not look as beautiful as before you started that diet. I think at that point, it's a good idea to chat with your veterinarian about switching diets.

Yeah, it's kind of a tough question, because what do we really mean when we say human food? There are certain things that we eat that cats most definitely eat; chicken and fish, things like that, absolutely. Do you want to depend just on those? Of course not.
It's always safest and, in my opinion, best, to feed them a well-balanced cat-formulated diet. Does that mean commercial foods are best? We can debate that when we have more time. But I think it's the simplest thing that provides, as I said, a well-balanced diet with all the vitamins and minerals that they need. So that's what I tend to stick with for my own animals.

I wouldn't recommend it. Reasons behind it are sometimes human food can be really fatty and actually cause harm to your cat. They can give them something called pancreatitis, which is inflammation of one of those digestive organs. Also, it can predispose them to developing obesity, which obesity in cats is associated with a lot of health conditions. So at this point I would just stick with the kitty food, which I think, my cat at least is very happy with his kitty food.

I think the safest bet is to look into various sites. I know for sure the ASPCA has a site that is fairly comprehensive, as far as foods and perhaps even more specifically human foods that can be toxic or make your animals ill. So I would probably reference a list like that to find out for sure.

So, it is hard. There's actually a way longer list than most clients think. I would recommend going on ASPCA, they have a great toxin section and just definitely looking at different plants that you can have in your household that can be toxic to cats. One of the big ones I can think of would be lilies, and also just looking at some of the household common spices, such as garlic, what those can be toxic for as well. And just trying to familiarize yourself with them, maybe printing out a list, putting it on your fridge, just to make sure that we're not giving your kitty anything that's going to harm them.