For example, although the BMI is associated with fat mass in obese people, there is little or no association with that of normal or underweight individuals. At any given BMI score, fat mass varies widely, and other variables, such as gender or age, further distort findings, with greater increases in fat mass per BMI unit seen in women and in the elderly.
但是，最近的研究成果质疑了体重指数的价值。比方说，尽管体重指数与肥胖人群的脂肪量相关，但与正常或体重偏低者的脂肪量却没有多大关系。任何给定体重指数评分的脂肪量都差别甚大，而且性别或年龄等其他变量也进一步扭曲了研究结果，显示妇女和中老年人的单位体重指数脂肪量有较大的增加。