just look at Cathy Freeman, who would have thought an atheist would get it huh? But GD is often treated with diet and exercise anyway, so I guess for me, maintaining those two things is a good thing to do.
Diabetes is very high in the aboriginal community, it didn't surprise me that she would get it, her Mum probably had it as did her Elders all most likely not diagnosed.

You are very right, a good diet and excersise is one of the tricks. My GF had it in her 3rd pregnancy, she was the same build as you (definitely not overweight!) and hers was treated with diet and excerise.

If your comfortable with your decision, that is all that matters