ADJUSTMENT FOR TOTAL-ENERGY INTAKE IN EPIDEMIOLOGIC STUDIES

In epidemiologic studies, total energy intake is often related to dise ase risk because of associations between physical activity or body siz e and the probability of disease. Ln theory, differences in disease in cidence may also be related to metabolic efficiency and therefore to t otal energy intake. Because intakes of most specific nutrients, partic ularly macronutrients, are correlated with total energy intake, they m ay be noncausally associated with disease as a result of confounding b y total energy intake. In addition, extraneous variation in nutrient i ntake resulting from variation in total energy intake that is unrelate d to disease risk may weaken associations. Furthermore, individuals or populations must alter their intake of specific nutrients primarily b y altering the composition of their diets rather than by changing thei r total energy intake, unless physical activity or body weight are cha nged substantially. Thus, adjustment for total energy intake is usuall y appropriate in epidemiologic studies to control for confounding, red uce extraneous variation, and predict the effect of dietary interventi ons. Failure to account for total energy intake can obscure associatio ns between nutrient intakes and disease risk or even reverse the direc tion of association. Several disease-risk models and formulations of t hese models are available to account for energy intake in epidemiologi c analyses, including adjustment of nutrient intakes for total energy intake by regression analysis and addition of total energy to a model with the nutrient density (nutrient divided by energy).