- Must be of normal weight with a body mass index (BMI) ≤ 25. The correlation between the BMI number and body fatness is fairly strong; however it varies by sex, race, and age. These variations include the following examples: At the same BMI, women tend to have more body fat than men; at the same BMI, older people, on average, tend to have more body fat than younger adults; highly trained athletes may have a high BMI because of increased muscularity rather than increased body fatness; source at http://www.cdc.gov/healthyweight/assessing/bmi/adult_BMI/index.html. Therefore, subjects with a BMI > 25 can be enrolled at the discretion of the PI in writing.