Royal Canin Sterilised 37 is a complete dry food for neutered cats between one and seven years old. The 37 in the name is the protein level — and that number is the whole point of the product.

Why the protein figure matters

The obvious way to stop a neutered cat gaining weight is to cut the calories. The problem is that a cat losing weight on a low-calorie diet does not only lose fat — it loses muscle too, and muscle is what keeps a cat's metabolic rate up. Strip it away and the cat becomes easier to overfeed than it was before, which is how weight-control diets sometimes make the problem worse over a few years.

Raising protein to 37% while holding fat at a moderate 12% is the answer to that. The cat gets enough protein to hold its lean mass while the energy density stays low enough to keep the weight steady. High protein, moderate fat — not simply less food.

• ✓37% protein. Sized to preserve muscle while calories are held down.
• ✓12% fat. Moderate energy density, so a normal-looking portion is not a large calorie load.
• ✓With L-carnitine. Royal Canin include it for its role in fat metabolism.
• ✓Mineral balance for the urinary tract. Neutered cats carry a higher risk of urinary stones; the formula is built with that in mind.
• ✓Kibble for daily grazing. Suits cats that prefer small meals through the day, and gives teeth something to work against.

Feeding it

The same formula exists as wet food in gravy. Many owners feed both — kibble for the teeth and for grazing, wet for the water it carries. If you do, use Royal Canin's combined feeding guide rather than a full ration of each.

This formula is intended up to seven years of age. Past that, a senior diet takes over, since an older cat's needs shift again.