There is a school of thought that these categories are drawn too simplistically. I don't have a reference right now, but I read an article on this last year. Essentially the argument is that the 25-29 in general have better health outcomes than the apparent 'ideal weight' group. For this reason, labelling it as 'overweight' seems incorrect. I'm interested in this personally as I have never been able to get to the bottom of the 25-29 group in my life despite many lifestyle changes, exercise regimes and diets. Lumping people with BMI 39 with those on 30 makes no sense either as BMI 39 is borderline seriously obese. It seems to be an area where social or cultural bias determines what is normal rather than strictly scientific metrics on health.