The median weights and heights of those under 19 years of age were taken from Hamill et al. (1979) (see pp. 16–17). The use of these figures does not imply that the height-to-weight ratios are ideal. c Retinol equivalents. 1 retinol equivalent ¼ 1 mg of retinol or 6 mg of b-carotene. See text for calculation of vitamin A activity of diets as retinol equivalents. d a-Tocopherol equivalents. 1 mg of d-a tocopherol ¼ 1 a-TE. See text for variation in allowances and calculation of vitamin E activity of the diet as a-tocopherol equivalents.

For a large majority of girls in the USA, the bone mass achieved during this adolescent period is considered to be less than optimal because of limited selections of nutrient-dense foods and preferences for low nutrient-dense foods. Figure 1 illustrates the declining consumption of milk and the increasing intake of soft-drink beverages over the last two decades in the USA. Concern has arisen that girls, and possibly boys, are not getting sufficient calcium and other essential nutrients from milk and related dairy products, because so many of these nutrients are essential for the growth of skeletal tissue, and also that adolescent females may be consuming excessive amounts of phosphorus, which alters the calcium:phosphorus ratio in a deleterious way (see Calcium and Phosphorus sections).

As a consequence, the changes in sympathetic activity, BAT hypertrophy and hyperplasia, mitochondrial proliferation, guanosine diphosphate binding and UCP concentration in rats exhibiting DIT are smaller than those seen in cold-adapted rats. However, these changes in BAT function are sufficient to account for up to 80% of the diet-induced changes in thermogenic capacity seen in hyperphagic rats. By contrast, BAT is usually atrophied and relatively inactive in obese rodents, although it will respond to exogenous noradrenaline, and the animals retain the capacity to adapt to the cold and exhibit NST.