First, body mass index readings were utilized to classify patients as either normal weight , overweight or obese . Blood transfusions during medical procedures were stacked up against the weights of the individuals then. The research team discovered that when undergoing hip surgery, 35 % of the standard weight patients needed a blood transfusion. However, that figure dropped to about 28 % among overweight individuals just, and almost 22 % among obese patients. Similarly, during knee surgery the 17 % transfusion rate seen among normal weight sufferers dropped down to simply 11 % among overweight patients and just 8 % among obese individuals.