Overview of why we recommend high protein diets to cats.

In cats, we don't change metabolism we just take advantage of the cats normal metabolism. High protein/low carbohydrate diets don't have the profound benefit for dogs that they do for cats. That is because of 2 key factors. 1) Cats don't metabolize serum glucose in the same way dogs do 2) cats [as obligate carnivores] constantly burn protein for glucose through the Krebs's cycle and they cannot stop doing this [another difference from dogs].
        1) Cats phosphorolate glucose inside their cells with the enzyme Hexokinase. This enzyme works slowly and steadily at the same pace regardless of the amount of the postprandial glucose spike. In dogs, the enzyme Glucokinase that up regulates to meet demand manages the large rise in serum glucose after eating. A dog can eat a single large meal and efficiently store glucose in cells for later use through more efficient phosphorolation. Cats phosphorolate what they can and dump the rest into the urine when presented with more serum glucose than they can manage at the time.
        2) Cats use a large amount of dietary protein for energy [Gluconeogenesis] in addition to all the other valuable things that protein does in the body [maintain lean body mass, build supporting tissue, make antibodies, and many more examples]. Dogs can store their daily caloric needs more easily from fats and CHOs [through cell storage for later] and do well on lower protein diets. The current rule of thumb is that dogs require 1 Gm of protein/ lb of BW daily, while a cat requires 2 Gm/ lb BW. Falling below these levels requires the dog or cat to catabolize body proteins to meet daily needs.
Dietary trials in both dogs and cats show that high protein/reduced calorie weight loss formulas lead to saving lean body mass, and more loss of body fat, than low calorie diets alone.

Neutered Kittens

It is a lot easier to keep it off a cat than to take it off after it's on so overeating in kittens should be controlled. Calories restriction seems to be the key to weight control. Convenience feeding of primarily dry food down all the time contributes to overeating. A GENERAL rule of thumb is that a 10 lb mature adult, intact cat needs 30 Kcal/lb/day. Neutered would be 15-25% or less considering daily activity or lack thereof. Only 300 Kcal for a 10 lb intact cat or 200-150 Kcal for a neutered cat are needed for an adult cat.
Since huge difference in both calorie content and protein content are found in different brands of cat food. For example one can of DM or 2 cans of OM has about 194 Kcal, so a 10 lb neutered cat needing 20 Kcal/lb/day should do well on 1/2 can AM and PM of DM or 1can AM and PM of OM. Smaller cans of higher protein food such as Fancy Feast have about 90 calories per can.
In dry the owner will have to use a measuring cup to actually measure cups/day based on the calories/cup of THAT formula. Some dry foods approach 600 Kcal/cup and some have 250- that's a HUGE difference in the amount of food that cat gets/day. If they are not overweight many AFFCO adult trialed kitten formulas are out there that will give them the high protein, adequate calories, and are palatable and affordable for the client- Friskies and Fancy Feast have hundreds of flavors that the client can feel like they are giving their cat something at least "interesting" that day.
Excessive food is not love. Most cats given the variables of intact or not, and breed related size differentials, need somewhere between 200 and 400 Kcal/day. Why give them more unless you have that legitimate 14-16 lb Manx? The hormonal changes associated with neutering and with obesity are becoming better understood and complicate the problem