The body mass index, based on weight and height, is not an accurate measure of body fat content, two U.S. researchers say. Those who are obese are predisposed to diabetes, heart diseases, sleep apnea, cancer and other diseases. Although several studies have shown an increase in mortality in obese people, recent research suggests obesity can protect against death from all causes, including chronic diseases such as diabetes, heart failure and stroke, Dr. Rexford Ahima and Dr. Mitchell Lazar of the Perelman School of Medicine at the University of Pennsylvania say. This so-called \"obesity-mortality\" paradox suggesting a beneficial influence of obesity has generated a lot of controversy, Ahima said. \"There is an urgent need for accurate, practical and affordable tools to measure fat and skeletal muscle, and biomarkers that can better predict the risks of diseases and mortality,\" Ahima said in a statement. \"Advances to improve the measurement of obesity and related factors will help determine the optimal weight for an individual, taking into account factors such as age, sex, genetics, fitness, pre-existing diseases, as well novel blood markers and metabolic parameters altered by obesity.\" The researchers noted in an article published in the journal Science that the true impact of obesity might not be appreciated because population studies often describe associations of BMI and health and mortality risks without assessing how intentional or unintentional weight loss or weight gain affect these outcomes. \"Future research should be focused more on molecular pathways, especially how metabolic factors altered by obesity change the development of diabetes, heart diseases, cancer and other ailments, and influence the health status and mortality,\" Lazar said.