I tend to be an advocate of HIT-like low volume but a few months ago tried training twice a day as an experiment. I was dieting too(Eventually hitting 1500kcal at a bodyweight of 200lbs. Dumb.) Surprisingly it worked pretty well for me. Not staggeringly better than once a day, but I didn't shrivel to the size of Woody Allen as I was expecting. I basically did a low-volume, low-rep workout in the morning and repeated the same workout with high-reps in the evening. I had to sleep about 10hours a day, plus an hour nap, because I was so utterly exhausted by this schedule. And every two weeks I had to take one week where I trained only once a day when I felt overtraining coming on. I also ended up concluding that training legs twice a day was too much, and typically skipped the 2nd session for them. I just couldn't squat in the morning to failure and come back in the evening for high rep squats and lift any kind of intensity. I wouldn't necessarily recommend training 2x a day to anyone else, but just thought I share my experiences.(I'm natural btw.) I might well try doing this again when not dieting, just to see what happens.