I'm secretly making my wife plump
Are you trying to make her fat?
Yes and I'm never going to tell her.
You are a feeder, no doubt. What you are doing is still related to abuse, because you are making her health worse and worse for some pointless gain. Do you really want her to die an early death?
You are wrong! This is fine as long as I don't say it to a third party. She wants me to do it!
Even if she's okay with it, it's wrong to harm her health like that no matter what. You should be encouraging her to eat healthy and maintain a normal weight.