'Obesity paradox' misunderstands the biology of optimal weight throughout the life cycle

The 'obesity paradox' refers to observations that run counter to the thesis that normal weight (BMI 18.5-24.9 kg/m(2)) provides the lowest mortality and higher weight is associated with greater mortality. We argue that the weight of lowest mortality is influenced by aging and chronic disease, with mortality advantage extending into the overweight and even class I obese ranges under some circumstances. A focus on quality nutrition, physical activity, fitness, and maintaining function in these weight ranges may be preferable to a focus on intentional weight loss, which has uncertain effects. The 'obesity paradox' is no 'paradox' if one defines and interprets 'ideal' weight appropriately.