['Total body potassium (TBK) is an index of fat-free mass. Data describing changes in TBK in African American, Asian, or Hispanic populations have not been reported.', 'The aim was to investigate possible sex and racial differences in TBK in adults over an age range of 70 y.', 'The study used longitudinal and cross-sectional data collected in a body-composition unit from 973 men and 1368 women of African American, Asian, white, and Hispanic race-ethnicity. Random coefficient models in which baseline weight and height were taken into account were applied to estimate sex-specific changes in TBK among the 4 racial-ethnic groups.', 'The ages of 30 and 31 y were identified for women and men, respectively, as the cutoffs after which TBK began to decline. Both sexes had similar racial-ethnic patterns for expected mean TBK at the age cutoffs: African Americans had the highest value, followed by whites, Hispanics, and Asians. After the age cutoffs, the decline in TBK differed by race and sex. In women, African Americans showed the most rapid decline, whereas Asians had the lowest. In men, Hispanics had the most rapid decline in TBK, followed by African Americans, whites, and Asians.'] Does total body potassium differ by sex and race across the adult age span?