please refer to
http://bodybuilding.com/fun/beast11.htm
Personally I don't take 10+ grams. I usually only shoot for 4-5 grams in the am before fasted cardio. Also taking Leucine is not to "engender significant fat burning", it is to prevent muscle catabolism; I take DCP in addition to do that. Also my fasted am cardio is mostly moderate pace (45 minutes at ~130 HR) with some HIIT mixed in (usually 10-15 minutes in the above 45 minutes - heart rate approximately up to 150+).
my bad, I didn't exactly explain myself too clearly. supposing Leucine is ketogenic, what I meant by "fat burning" was that Leucine would help set off a signal in the body to burn more adipose tissue. what i am saying is that i doubt Leucine's ability to do this on its own, w/o first seeing some clinical studies proving this true.
grant it, a couple grams before morning cardio will not hurt to prevent muscle catabolism. but my basic argument is that one should not be so worried about muscle breakdown during a "light-moderate" fasted cardio, as long as the sessions are kept to a minimum (i.e. 15-20 min max) and you ingest a well-balanced, complete breakfast directly afterward. BCAAs would really only serve a significant purpose if one is doing HIIT or fast-paced cardio, where the fuel provided by the BCAAs would prevent significant muscle catabolism during that highly intensive w/o period. although, in this context, you're better off eating some kind of carbohydrate for fuel
BCAAs serve a purpose. i just think they're overrated in terms of using them to "quickly blunt catabolism dead in its tracks" so to speak. research shows that if you supplement with a modest amount of BCAAs pre workout, they will help reduce protein breakdown within muscles. by the same token during PWO, it stands to reason, they will also help expedite recovery.
if you use them at any other time they're just extra cals that you're likely to piss out
