Wrangell-Wrong on so many points.
First no one should be doing HIIT 5x a week. If you are doing correct HIIT (which what you are describing is not) it is WAY to taxing on the CNS and would burn someone out to quickly.
Well, I disagree....though I concede frequent HIIT isn't for everyone.
If you are taking in enough calories, keeping your total HIIT session time short enough, managing your work and rest intervals properly, you've got a solid aerobic base , doing HIIT 5X a week isn't an issue IMO. Mind you it IS serious training and should be spread out over 7 days. And you're right, it depends on how you define HIIT and whether you focus on issues of VO2max, MHR, and interval times to guide your training. For example, I don't think the interval protocols used in the Tabata or Tremblay studies translate well to everything when it comes to sports or the average gym rat trying to lose weight ( fat ). For example, during my time in university hockey we did a lot of pre-season HIIT sessions at 1;1, 1:2 or 1:3 ratios at 85% MHR 5X a week ( i.e over 7 days ).
As far as post workout nutrition while refilling glycogen stores are a concern
Well, it isn't a concern is this persons' case ( assuming he is eating properly and frequently ) as he isn't coming anywhere close to depleting his glycogen stores by doing very low intensity LISS of 20 minutes and weight training.
there are so many other factors in to why post workout nutrition is important immediately following a workout ranging from muscle repair
I already touched on that. If he is eating properly throughout the day or even has a snack before his work out he has ample amino acids in his system to deal with any issues of " muscle repair " post workout. Again, he can have a shake after a workout if he wants to, but if he his getting his .9 grams of protein per pound of body weight throughout the day, there is no amino acid issue at play that says he HAS to. That is my point.
less chance for DOMS, better CNS function and neurological read, etc.
DOMS usually occurs for most gym rats due to over-training or using muscles that have not been in use for awhile etc. - neither of which seem to be an issue in this case. In any event, my point is, the sky is not going to fall - DOMS or otherwise - in if there isn't a shake taken immediately after a workout
If you don't not have a fast acting simple sugar, you don't have the boat to carry the repair, understand?
You need carbs for tissue synthesis - correct, and if you eat properly throughout the day you meet most of your needs in this regard.
Gags-As far as HIIT burning into your muscle, well that is a bizarre concept being that it is better protecting of muscle as far as aerobic training is concerned than LISS. I would likely believe more that these sessions were burning more calories then you were accounting for and your overall daily caloric intake was to low, there for causing you to eat into some of your muscle.
Bottom line-
-Cardio is not the answer to fat loss, nutrition is really going to be your big player at this point of body fat.
-Hit Those weights hard and don't do those splits anymore
-Get in, go hard, repair right, and really stick to a program. IF you don't give yourself over to a program and trust it, you aren't going to get anywhere with it, you are just going to be another A.D.D fat loss victim.
Again, I would simpy add cardio to the mix you mentioned above.
I would say the key to " optimal fat loss " is achieved through a combo of diet / nutrition, weight training and cardio.