The obesity paradox: methodological considerations based on epidemiological and clinical evidence--new insights.

Despite the well-known association of obesity with increased mortality and the development of chronic diseases, an "obesity paradox" has been reported in several patient categories; i.e., overweight and obese patients have a better prognosis than normal or low-weight individuals. The present review aims to identify potential factors lying beneath the beneficial effect of overweight and obesity. In particular, the role of nutritional status, malnutrition and catabolic state, as well as intentional vs. unintentional weight loss and the possibility of a U-shape relationship between body mass index and survival will be examined. Furthermore, methodological considerations framing the obesity paradox will be presented and discussed.