An increase in BMI may also increase the risk for many diseases. The results of BMI may differ between young adults, seniors, men and women. On average, women usually have a higher percentage of body fat then men of the same BMI, and older adults have a higher percentage than younger adults.Results also vary for those adults that are very muscular. For example, a bodybuilder will have a high percentage of muscle and a low percentage of fat.n increase in BMI may also increase the risk for many diseases. The results of BMI may differ between young adults, seniors, men and women. On average, women usually have a higher percentage of body fat then men of the same BMI, and older adults have a higher percentage than younger adults.