Over 34% of adults aged 20 years and older are obese, but there has been no significant change in the prevalence since 2003-2004. The increasing trend in obesity over the last 25 years is a result of a shift in the entire BMI distribution and an increase in the prevalence of those who are extremely obese. In addition, disparities continue to exist. Non-Hispanic black and Mexican-American women continue to experience a higher prevalence of obesity than their non-Hispanic white counterparts. Although approximately two-thirds of obese individuals have been told by a health care provider that they are "overweight," obesity is extremely difficult to treat and the prevalence of obesity is not declining. Nonetheless, even without reaching ideal weight, research has shown that a moderate amount of weight loss can be beneficial in terms of reducing risk factors, such as high blood pressure. Maintenance of weight loss, however, remains difficult.