Why is the feeding advice for cats for Unique Protein (Rabbit) | UPR without the use of a carbohydrate source?

As an exception to the Unique Protein range, for cats in the Unique Protein (Rabbit) variant it is recommended to use this product without adding a carbohydrate source. For cats, following the feeding advice with only Unique Protein (Rabbit), an optimal protein / energy ratio is achieved. Adding a carbohydrate source, in addition to the recommended amount of Unique Protein (Rabbit) will cause an energy intake which is too high.