[1] is the closest thing I can find on the subject, which showed that high-frequency diets substantially reduced insulin levels in the blood. This seems to be the Ur-study from which the idea was spawned.
On the other hand, you have [2] which shows that even though glucose levels fluctuated more on 3-meal plans, resting metabolism and satiation were both higher, though there was no significant effect on fat oxidation.
[3] suggests that regular meals (as opposed to irregular meals) "have beneficial effects on fasting lipid and postprandial insulin profiles and thermogenesis."
Finally, [4] seems to sum up existing findings as "some for, some against, most neutral, tl;dr eat fewer calories".
[1] http://www.ncbi.nlm.nih.gov/pubmed/2674713
[2] http://journals.plos.org/plosone/article?id=10.1371/journal....
[3] http://ajcn.nutrition.org/content/81/1/16.short
[4] http://journals.cambridge.org/action/displayAbstract?fromPag...
I wish more studies and nutritionists would focus on satiation. "Eat fewer calories" isn't practical, in a lot of cases, since it involves actively fighting hunger. Ceteris parabis, the more satiating of two diets should lead to more weight loss.
The diet and exercise popular literature is a mess. A lot of it is either seventh hand knowledge repeated to the point of truth, or articles written for SEO purposes to capture readers wondering "will food X burn fat/increase gains"?
I hear it repeatedly on fitness forums, but haven't seen it tested. I do leangains myself, which is intermittent fasting + barbells. In the leangains community the idea is widely derided. Martin Berkhan, the man who made leangains, is pretty scrupulous with citing studies, so if something supported the six small meals idea I suspect he would have mentioned it.
I did a few google scholar searches, but I'm not familiar with any specialized terms that might be relevant. Are there studies I might be missing?