> How did a diet with lots of carbs (Ornish) reduce insulin levels more than
> the low-carb diets?

I don't think that the study methodology is particularly strong:
* participants advised to follow the diet "to the best of their
ability for two months," and, for the following 10 months, "to whatever
extent they wanted."
* the study "evaluated only the food program, not any additional lifestyle
modifications such as meditation or exercise,".  This is another way of
saying that the researchers failed to account for the role of meditation and
exercise in weight loss or improvements in blood lipid markers.
* "the drop-out rate for each diet was 22% at two months and by 12 months
half of
the volunteers assigned to Atkins or Ornish had dropped out, as had 35% of
those assigned to Weight Watchers or Zone diets".  Insulin levels were
measured in only 50% of the original group supposedly following the Ornish
diet.  This group represents the most motivated.
* only 20 people supposedly followed the Ornish diet for 12 months
(Atkins=21, Weight Watchers=26, Zone=26).  This is a relatively low number
of participants; I'm surprised that results were generally statistically
significant.

Rob