Playing Jeopardy, if I had to pose the question the study answers, maybe it'd be something like, "if you lowered either carbohydrate or fat in the diet in such a way that the difference between the two to fasting insulin was minimal, would there be a significant difference in weightloss?" The answer being no, not really. We don't really know what was done to postprandial insulin--but in the muddy middle, given the effect of dietary fat combined with substantial amounts of carbohydrate of increasing the amount of insulin needed to handle the given glucose load, there is no guarantee that swapping carbohydrate out for fat will lower postprandial insulin until the decrease in carbohydrate is substantial.

Eat a high carb, low fat meal, and the second meal effect can reduce the insulin needed to handle the next high-carb, low fat meal, and so on. It's clear that a very low carb diet will result in lower insulin levels vs. a high carb meal, fasting, postprandial, and twenty four hour. It's actually not clear that that would be the case in the sort of intervention used in this study.

edited; end of post not ready for prime time.