Food Allergies and dermatitus in cats

One of my cats seems to have a food allergy. His skin condition isn't getting better with the new foods I'm trying...Holistic, natural, no grain formulas. He is breaking out with red bumps and red scabs and scratching.

Below are two great articles on food allergy and intolerance. Has anyone had the same problems and what have you tried?

Food allergies account for about 10% of all the allergies seen in cats and dogs. It is the third most common cause after flea bite allergies and atopy (inhalant allergies) Food allergies account for 57% of the causes of itching and scratching in cats. For full article: http://www.peteducation.com/article.cfm?c=1+1332&aid=142

Omega fatty acids: Sources, Effects and Therapeutic uses in Cats:  http://www.peteducation.com/article.cfm?c=1+1400&aid=665