I recently posted on the forum that my cat Romeo has just been diagnosed with diabetes. For a couple of years I noticed the same behaviour you are describing. Romeo would eat a lot and then throw up--once or twice a week. We feed him wet and dry food, so when we gave him the wet food we took away the dry food until we felt he had digested the wet. But this didn't always work. While he continued to eat a lot he started losing weight. The vet thinks this behaviour may have been the early stages of the diabetes. I know you said your cat is healthy, but it may be worth getting his glucouse checked just to be sure. Good luck!