The sharpest wedge
A tin at 11% protein beats a bag at 30%.
Pet labels print a “Guaranteed Analysis” that is
not comparable between products: four fifths of the tin is
water, and the percentages are of the pack. Nobody does that arithmetic in an
aisle, and almost nobody knows it needs doing.
So the Laboratory carries a second bench that puts up to four pet foods on one
scale. When the pack that looks highest in protein isn’t the one
that is, the screen says so in a sentence — that is a fact about the
arithmetic, not an opinion about the food. It also offers grams per 100 kcal,
because an animal eats to its calorie need, and carbohydrate by difference,
which no pet food label prints anywhere.
Every figure is divided out of numbers printed on the pack. No model is asked,
nothing missing is estimated, and any of it can be checked by hand in front of
the tin. A pack that doesn’t print its moisture is left off the scale
rather than given a typical value for its form. Nothing is ranked: more protein
is not better for a cat in renal failure.