TABLE 5-5 Accretion of Phosphorus (P) in Bone and Lean Tissue During Peak Adolescent Growth Spurt

Gender/Age (y)

Change in Weighta (g/y)

Change in Leanb (FFBM-osseous) (g/y)

Lean-Tissue Pc (g/y)

Osseous Pd (g/y)

Bone Pe (g/y)

Total P Gainf (mg/d [mmol/d])

Males

13.3

5,000

3,970

9.1

320

60.8

192 (6.2)

Females

11.4

5,000

3,750

8.6

240

45.6

149 (4.8)

Mean, both sexes

171 (5.5)

a See Table 1-3.

b Body fat values from Deurenberg et al., 1990.

c Assuming a phosphorus content of soft tissue of 0.23 percent.

d Martin et al., 1997.

e Assuming a phosphorus content of bone of 19 percent.

f Calculated from sum of accretion of P in lean and bone/year divided by 365.

lean and osseous tissue gains is required. Gains in lean mass were determined by subtracting fat from total weight gain. Percentage body fat for pubertal boys aged 13.2 (standard error [SE] 1.3) was 14.2 (95 percent confidence interval [CI] 13.0 to 15.4), and 20.2 (95 percent CI 19.3 to 21.1) for pubertal girls aged 10.5 (SE 1.6) (Deurenberg et al., 1990). Osseous tissue gains were based on a study of 228 children in Canada where mean peak bone mineral content velocity was 320 g/year in boys at age 13.3 years and 240 g/year in girls at age 11.4 years (Martin et al., 1997). The computations are summarized in Table 5-5. Assuming a phosphorus content of bone mineral of 19 percent and a phosphorus content of soft tissue of 0.23 percent (Pennington, 1994), daily phosphorus needs during peak growth would approximate 200 mg (6.5 mmol) for boys and 150 mg (4.8 mmol) for girls.

Similar to younger children, the value derived for phosphorus excretion was then employed in a factorial model to obtain the EAR. Urinary phosphate excretion rises linearly with phosphorus intake according to the equation derived by Lemann (1996) in adults. This approach was adopted here since no such relationship has been developed for adolescents. Using the equation: Purine = 1.73 + 0.512 × Pintake (in mmol/day), and an intake of 1,000 mg



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