Previous studies have suggested that being somewhat overweight or even slightly obese may not be associated with a shortened life span. Some studies have suggested that being a bit overweight might even be healthier than being at normal weight. This has been referred to as the "obesity paradox."

A recent analysis of data from the Nurses' Health Studies I and II and the Health Professionals Follow-up Study has helped bring clarity to this paradox. Researchers from the Harvard T.H. Chan School of Public Health and Boston University School of Public Health assessed the maximum body mass index (BMI) over 16 years for more than 190,000 postmenopausal women and 35,000 senior men. They then tracked who died over a follow-up period averaging 12 years. They found that people with a maximum BMI in the normal range (18.5 to 24.9 kg/m2) throughout life had the lowest risk of death. Those whose highest recorded BMI fell into the overweight or obese category were at elevated risk of dying from any cause, as well as dying specifically from cardiovascular disease, cancer, or respiratory disease, during the follow-up period.