In the absence of hard CVD endpoints in the young, early structural changes within the heart and arteries - such as an increase in left ventricular mass or a thickening or stiffening of the major arteries - are often used in early prevention research as surrogate measures of early disease. Many studies have related changes in these phenotypes at a young age to increases in either BMI or body fat %, suggesting that excess adiposity at an early age may drive pathophysiological changes within the heart and vessels. Both of these are crude measures of adiposity, however, with the former unable to separate fat from lean mass, and the latter unable to quantify absolute levels of each tissue type. The extent to which these phenotypic changes are driven by fat mass per se rather than a combination of fat and lean mass remains equivocal.