I trained HIT for the 1st time not long ago, and what I found was good strength gains, but the size gains were a little disappointing.
Having said that, my diet was not as good as it should have been, so that no doubt affected my size gains.
Having said that, my diet was the same as it was when I was doing higher volume, once per week training.
My conclusion for myself, is that diet is probably more important for size results while doing HIT style training, than it is for lower frequency training where I had more recovery time.
Either way I understand I am selling myself short with any results by having a poor diet.