The morbidity and mortality associated with overweight and obesity in adulthood: a systematic review.

Background: Overweight and obesity are generally thought to elevate morbidity and mortality. New data call this supposed association into question.
Methods: The Cochrane, Pubmed, and other databases were systematically searched for a combination of relevant terms and subject headings. Meta-analyses and cohort studies based on the German population were evaluated for possible associations between overweight/ obesity and adult morbidity and mortality. Case-control and cross-sectional studies were excluded.
Results: A total of 27 meta-analyses and 15 cohort studies were evaluated. The overall mortality of overweight persons (body mass index [BMI] 25-29.9 kg/m(2)) is no higher than that of persons of normal weight (BMI 18.5-24.9 kg/m(2)), but their mortality from individual diseases is elevated, diminished or unchanged, depending on the particular disease. The overall morbidity is unknown. Both obesity (BMI >30 kg/m(2)) and overweight are associated with increased disease-specific morbidity for some diseases, but decreased or unchanged for others. In general, obesity confers a higher risk than overweight. Morbidity and mortality are markedly influenced by the patient's age, sex, ethnic origin, and social status. The external validity of the comparative predictive performance (c-statistic) of BMI, waist circumference, and ratio of waist to hip circumference cannot be determined from the available analyses.
Conclusion: The prevailing notion that overweight increases morbidity and mortality, as compared to so-called normal weight, is in need of further specification. Obesity, however, is indeed associated with an elevated risk for most of the diseases studied.