I have taken them in all combinations: 1 cap, 2 caps, with food and without. I felt unsettled on an empty stomach but I found a way around it. By combining it with Glutamine and BCAA's, the stomach irritation is removed.
I prefer to take 1 cap to avoid the crash that two caps tend to provide.
In all, a very positive experience with this fat burner. Happy to see that caffeine isnt its first ingredient like most fat burner