Well, we could discuss this for days, but in a way she's right, and in a way she's wrong.
She's right because all cat foods (and other pet foods) have to meet certain standards, no matter what they put in them. The AAFCO standards provide a set of values for adult foods, and one for kitten/growth/lactation foods. All foods have to meet or exceed these values. This makes the nutritional profile of most pet foods fairly similar. So, you'll see that most dry cat foods tend to run around 30-33% protein, and the other numbers will be similar across the board, varying by only a few percentage points.
Also, most manufacturers are drawing from the same available pool of ingredients. If you're making a dry food, you will be getting your animal proteins (chicken meal, meat and bone meal, by-product meal, etc.) from a rendering facility, such as Griffin Industries or Darling or Tyson Chicken. There's just so much of each thing available across the country at any one time. The meal will be guaranteed just as you see on the pet food bag: protein, moisture, and fat content will be specified.
Then she becomes wrong, because it definitely makes a difference in terms of biologic quality, palatability, digestibility, and bioavailability by exactly what went into those meals and how it was processed. If you're buying chicken meal from Tyson, you'll get a very consistent product in terms of the amino acid profile of the chicken meat, and the cuts you receive, done by machine, will be similar.
But if you were over at Tyson or Darling or Griffin, you would have your choice of "high grade" by-product meal, which costs $xx per ton, or "feed grade" by-product meal, costing a lot less. Depending on your company's orders, you may pick either one. There is a huge difference in nutrient content and quality between the two. Same ingredient name on the package, but the high grade meal may have had heads, feathers and feet excluded from the batch, at the request of your company, so there is more usable parts (hearts, kidneys, spleens, lungs, intestines, etc.) of a higher quality in that batch. Guess where these now extra, leftover heads, feathers and feet go? Right--into the feed grade product. So even though they both say legally and quite rightly say "chicken by-product meal" on the bag, the difference in quality can be vast.
There's a lot more to it than that, of course. And it's true that companies adding things like cranberries, blueberries, uva ursi, and kiwi fruit to the pet food are using these things primarily as a marketing tool, to appeal to you, the consumer. The dog or cat could care less how many uva ursi berries are in that bowl! :wink: Although the manufacturer will also rightly claim that these fruits and herbs are known to have certain positive effects on, say, the urinary tract. They do, but are they in the food in a suffient amount to make a difference? Probably not. So, you have to learn to read the label with a cautious (one might say jaundiced) eye, and try to figure out what's important, what's real, and what's window dressing.
COINCIDENTALLY

, I just happen to have an article on this very topic in my free article library,
http://www.littlebigcat.com/index.php?a ... w&item=004. :lol: I will be revising it soon, so please check back now and then, and enjoy the rest of the articles in the library while you're there!
Cheers,
Dr. Jean