Here's an article I saw this week about the dearth of Omega-3's and overabundance of Omega-6's in the American diet.
Hence, we have more than double the linoleic acid in our body fat as do our parents' generation, and fatty acid turnover in adipose tissue can take years. So you may feel the health effects of your diet from the past year or two, even if you switch to a healthier diet.
Besides the importance of supplementing with Omega-3's (preferably eating Omega-3 rich foods before turning to supplements), the point about the "delay" in your healthier habits taking hold reinforces the idea that you just have to give things time. The body doesn't repair itself overnight. Major health changes through behaviour change are not easy, and the rewards don't come quickly, but they will pay off with consistent effort over time.
How about some Omega-3 Powerhouse Muffins?