Cat food has more protein than dog food. Cats need more protein. Dogs do not.
So, you will want to take away his access to the cat food completely.
Let me know if you need more help.
Dogs simply do not need that much protein. So, you might see him gaining weight, which predisposes them to cancer, thyroid issues and liver and renal problems.
You might also see urinary problems like stones and urinary tract infections.
There is a really simple fix for this, though. Just feed the cat up high, like on top of the dryer or on a bathroom counter. That way, she can still eat and the nosy dog will stay out.
Let me know if you want to discuss this more.