My mother was diagnosed with Type II Diabetes about a decade ago. She's battled with her weight for the better part of her adult life, so I don't suppose this diagnosis should have been a surprise to anyone. Realize, however, that my mother was never one of those hugely obese people who ate entire chocolate cakes. Her BMI likely straddled the line between overweight and obese for many years until she lost 40 lbs when she was about 49 years old on a highly unhealthy diet (she ate nothing more than four shakes and a gallon of water per day) and dropped down to 135, which was within a healthy range for her height. Suffice it to say, she did not keep it off.
Since her diagnosis, Mom has managed her diabetes with a mix of diet, exercise, and oral medication. She tests her blood sugar when she should, and lives a reasonably healthy lifestyle.
Mom tells me that if she is ever diagnosed with any sort of painful and terminal illness, she will go out and eat an entire chocolate New York cheesecake. Death by chocolate, she calls it.