varies with the rate of growth, which occurs unevenly in spurts and periods of slower growth. The growth that occurs during adolescence is significant and comparable to the growth that occurs during the first year of life. During adolescence, nutrition needs are higher than during any other period of the lifecycle. Puberty is when adolescents gain approximately 50 percent of their adult body weight, accumulate an estimated 40–45 percent of skeletal muscle mass, and achieve the final 15–20 percent of their linear growth (Shils et al., 1999; Story et al., 2003).
National dietary recommendations and guidelines established for the American population have been used to assess the diets of children and youth. These recommendations and guidelines collectively include the Dietary Reference Intakes (DRIs), the Dietary Guidelines for Americans, and the Food Guide Pyramid (FGP) and MyPyramid.
The DRIs is a term used for a set of distinct, nutrient-based reference values that are based on scientifically grounded relationships between nutrient intake and indicators of good health and chronic disease prevention (IOM, 1997, 1998, 2001, 2002–2005, 2005a). The DRIs, which replaced the former Recommended Dietary Allowances in the United States (NRC, 1989), include values for the following:
Estimated Average Requirement (EAR), which is the nutrient intake level estimated to meet the requirements of half the healthy individuals in a given life stage and gender group for a specific indicator or outcome; it is the median of a distribution and can be used to estimate the prevalence of inadequacy in a group;
Recommended Dietary Allowance (RDA), which is a nutrient intake level estimated to meet the needs of nearly all individuals (97.5 percent) within a given life stage and gender group, and is calculated as two standard deviations above the EAR;
Adequate Intake (AI),6 which is a nutrient intake level based on observed or experimentally derived estimates of nutrient intake of healthy
Mean usual intake at or greater than the AI is equated with a low prevalence of inadequate nutrient intakes, especially when the AI is based on the mean intake of a healthy group. Unlike an EAR, an AI value cannot be used to estimate the prevalence of nutrient inadequacy in a population. If at least 50 percent of the gender or age group has intakes greater than the AI, then the prevalence of inadequacy should be low. If less than 50 percent have intakes greater than the AI, then no conclusion can be drawn about the prevalence of nutrient inadequacy in a population group.