I have tried this. Thing is, the substitution rate has to be very slow and steady. I also know how to cook, and my woman loves to cook as well. I almost always sneak extra calories in by replacing any given ingredient with one with higher calories. At first, she revolted against the gain, but it only took a few months to coax her into being a "foodee"--a very mainstream hobby for millions of folks. She accepted the weight gain, but neither of us is into feederism, per se. I like her larger size, and she is accepting of it--that is the extent of it. Feederism is a real turn-off for her, but gaining weight "just as it comes" is something she can accept.