The proportion who developed type 2 diabetes was lowest in the group which reported the highest wholegrain consumption, and increased for each group which had eaten less wholegrain. In the group with the highest wholegrain intake, the diabetes risk was 34 percent lower for men, and 22 percent lower for women, than in the group with the lowest wholegrain intake.
“It is unusual to be able to investigate such a large range when it comes to how much wholegrain people eat,” says Rikard Landberg. “If you divided American participants into 4 groups, the group that ate the most wholegrain would be the same level as the group that ate the least wholegrain in Denmark. In Europe, Scandinavia eats the most, Spain and Italy the least.”
Additionally, the study was uncommonly large, with 55,000 participants, over a long time span — 15 years.
My source article is here and the study abstract can be found here.