Radishes are not toxic to cats and can be included as a small part of their diet, in moderation. However, they are not a necessary part of a cat's diet, and cats do not derive any significant nutritional benefits from eating radishes. Moreover, some cats may not like the taste or texture of radishes, and others may experience digestive upset if they consume them in large quantities. Therefore, while small amounts of radishes are not harmful to cats, it's not necessary to include them in their diet, and it's best to stick to a balanced and nutritionally complete cat food recommended by a veterinarian.