This is good advice for those who have a genetic predisposition for diabetes.   Unfortunately, eating a healthy diet does little to change your genetic makeup.   An extremely strict diet will keep your weight down, exercise will increase your insulin sensitivity.  The latest research on metabolic memory however indicates that extremely aggressive treatment of this condition makes a huge difference down the road.  Unfortunately for most, when this is discovered, they have already had over an 80% reduction of their beta-cell mass, leading to elevated glucagon levels and increased liver production of glucose from glycogen.   Strict diet tremendously helps, but you cannot get your beta cells back (for the most part).   People who discover this early, and treat aggressively with diet, exercise and treatment with insulin-sensitizing medication can have a normal life-span. (See research on metabolic memory)