JP,
  High levels of protein can be a risk. Typically they bring along
higher levels of phosphorus which is a risk factor in cats with
undetected renal failure. Since we presently cannot test a cat and
determine if renal failure is present, until over 70% of the kidney is
destroyed and the disease bis unstoppable, there is a risk in feedidng
excessive levels protein. Renal failure is the number two cause of
death in cats and should never be taken lightly.
 There is a risk in feeding excessive levels of anything. There are
two competing schools of thought. The traditional tried and true
method eliminates the risk of undetected renal failure by maintaining
sufficient protein and reducing calories by lowering fat content.
Typically these foods contain higher levels of fiber to increase
satiety (feeling full). Most obesity diets do contain a bit more
protein than normal typical diets, part of this is to insure that lean
body tissue (muscle mass) is not lost while fat tissue is lost. These
diets have been proven for forty years and have an excellent track
record of success when fed properly.
  Another school of thought that has recently emerged tends to blame
every disease know to cats on carbohydrates, never mind there is no
data to support those claims, merely hypothesis and supposition. This
school of thought seeks to move cats into a state of metabolic
ketosis. This is not the same as ketoacidosis so don't think of
metabolic ketosis as being "bad". By this process some cats can lose
weight much like some humans lose weight on the Adkins type diets -
pretty much the same philosophy. There are several diets on the market
that work in this manner.
  The right choice is one you need to make in consultation with your
veterinarian who can assess any risk factors that your individual cat
may have and make a determination of which diet philosophy will work
best and safest.