My toy poodle Honey has had fits since she was about 6 - will be 15 in August and is not on medication. Her average now is maybe about 2 in 3 months.
The longest between fits has been 8 months - just after we got our other dog - so definately think diet plays a big part - she was eating dry puppy food as well as hers, and we changed to ceramic bowls for food and water, due to the puppy taking the plastic ones.
I mainly feed fresh cooked food. I have heard that fish oil is good for them, which she gets also to help her arthritis.