Re: taurine in cat food, I have also been suspicious of posts that try to sell me things, but I saw one that talked about a lack of taurine potentially being the reason cats might frequently regurgitate undigested food, especially cats that have pâté wet food (with a higher fat content) in their diet.
Is there any truth to that, or is that a different issue altogether?
Taurine deficiency primarily causes blindness and dilated cardiomyopathy (cats usually get hypertrophic cardiomyopathy). It can cause GI issues because bile uses it, but that should not be causing vomiting shortly after eating.
Canned food often looks lower in protein proportionally because of the moisture. You need to calculate without that moisture to see how much of the solids of the food, the part with actual nutrition, the protein is. A can that is 10% protein and 80% moisture is similar to a diet that is 50% protein. Because if 20% of the total can is protein, fat, and ash and half of that is protein...
