I doubt they'll ever really expand beyond small studies in that field. There's certain groups that routinely do meta-analyses of nutritional (and other) studies, like the Cochrane Collaboration. E.g., Effect of cocoa on blood pressure: http://www.cochrane.org/CD008893/HTN_effect-of-cocoa-on-bloo...

That's really the only way to be confident, short of setting up a massive (expensive) randomized controlled trial.