Only a randomized, double-blind, placebo controlled, cross-over (with washout) study - using DEXA/Hydrostatic on a large N population could even begin to tell you this
I've posted this before: IMO you can lose 98% of all the fat you ever wanted to lose with Coffee, Yohimbine HCL Caps, and Bronkaid/Primatene with a kcal deficit. All this other stuff is worth *maybe* the other 2%. I have the discretionary funds, so I use it - but I wouldn't sweat not using it one iota. We're talking fractions of degrees of extra fat loss here I would say.