When I had the classes for Diabetes, the nutritionist there said to stop aiming for the "Normal" BMI, because most people just can't get there unless they start devoting their entire life to maintaining their weight. She said to aim for a loss of about 5-10% per year. And even just that 5%-10% is already very beneficial.
Of course, 10% for some people would be quite a lot already... but the more you have to lose, the easier it is to actually lose it (well, according to the nutritionist anyway).