Yup, mutual gaining refers to both participants gaining weight (though they technically may not fall under the feedee/feeder categories either). I'd say that it's decently common in total.
I am a gainer myself and appreciate fat on others. Whilst I am not looking to feed someone else, if someone close to me was receptive and wanted to gain, I think I would be very tempted to assist.
CustardCream: When we met, my wife and I were both feeders and feedees. Sadly my wife has to lose some weight, but my goal now is to gain what she loses!
That will work, until you start having issues like your wife.
