Coffee is a stimulant, so if you tend toward high stress and cortisol, it can cause problems with your weight loss.
However, the bodybuilding world knows their shiz about the science of fat loss, and the ECA or ephedrine (no longer legal) caffeine aspirin stack is a staple for losing fat. It may also cause many other problems though.
Coffee does have some very special properties that help aid fat loss:
It can raise adiponectin which is a hormone made in fat tissue. Generally you want your adiponetin to be up since low adiponectin is related to metabolic syndrome, cancer and heart disease.
It lowers resistin, which is another adipose hormone that you generally want to be low. When elevated it's correlated with the things that low adiponectin is.
It elevates the enzyme AMPK which some call the master switch that turns regular fat cells into fat burning cells. It is said that caffeine acts in the same way exerise excerise does to elevate AMPK.
Since coffee can lower blood sugar and cause a resulting cortisol spike, which would prolly stall weight loss, my one real piece of advice is make sure your coffee is not taken on an empty belly, after meals seems like a better idea.
Also, I am a stay at home mom with a PubMed problem, so I could be wrong about all of this.
