Differences in calcium absorption and kinetics between black and white girls aged 5-16 years.

To assess racial differences in calcium (Ca) metabolism, we measured Ca absorption and kinetics in 89 girls (38 black and 51 white) aged 4.9-16.7 years using a dual-tracer stable isotope technique. We found significantly greater rates of fractional (0.44 +/- 0.13 vs. 0.25 +/- 0.08, p < 0.0001) and total calcium absorption (406 +/- 142 vs. 234 +/- 82 mg/day, p < 0.0003) in black than in white postmenarcheal girls. Fractional absorption of Ca was also greater in black than in white premenarcheal girls (0.39 +/- 0.14 vs. 0.30 +/- 0.10, p = 0.01). Fractional absorption of Ca was more closely correlated to Ca intake in white (r = -0.42, p = 0.002) than in black girls (r = -0.25, p = 0.14). Urinary Ca excretion was significantly lower in pre- but not postmenarcheal black girls than in white girls. Calcium kinetic values associated with bone calcium deposition were greater in black girls, indicating a greater rate of bone Ca deposition in both pre- and postmenarcheal black girls. These results suggest that the greater bone mass accumulated during childhood and adolescence in black than in white females is due, in part, to greater rates of Ca absorption in black girls.

Changes in calcium kinetics associated with menarche.

To evaluate the consequences of puberty on calcium (Ca) metabolism, we measured Ca kinetic parameters in 43 healthy girls 1-60 months post menarche. There was a close relationship between the logarithmic transform of the number of months post menarche and the bone Ca deposition rate (Vo +) (r = -0.90, P < 0.001). Using multiple regression analysis with the logarithmic transforms of chronological age and months post menarche as independent parameters, we found that the number of months post menarche was more significantly correlated with Vo + (t = -7.4, P < 0.0001) than with chronological age (t = -3.1, P = 0.003). A longitudinal study of 17 girls demonstrated a peak Vo + approximately 8 months before menarche, with a decrease in Vo + after menarche. These studies indicate that the peak time for bone Ca deposition is in the premenarcheal and perimenarcheal time period. The close correlation between Vo + and months post menarche demonstrates the importance of puberty in consideration of bone Ca metabolism in girls.

Serum leptin concentrations in Caucasian and African-American girls.

Because African-American girls are heavier, taller, and mature earlier than Caucasian girls, we hypothesized that the serum leptin concentration differs between the two groups. Serum leptin concentrations were measured by immunoassay in 12-h fasted blood samples collected from 79 Caucasian and 57 African-American girls between 8 and 17 yr of age. Body composition was measured by dual-energy x-ray absorptiometry, sexual maturity by physical examination, and physical fitness by treadmill testing. Serum leptin concentrations were positively correlated (P < 0.01) with maturation, body fatness, and insulin and were higher (6.6 ng/mL, P < 0.01) in the African-American girls after adjusting for age. The difference remained significant (P < 0.01) but was reduced to 3.2 ng/mL after controlling for differences in maturation, fat mass, and physical fitness. The higher serum leptin levels might play an important role in the accelerated growth and sexual maturation of African-American girls.

Pubertal African-American girls expend less energy at rest and during physical activity than Caucasian girls.

Between 1963 and 1991, the most dramatic increases in the prevalence of overweight in the United States have been reported in African-American girls. Lower basal energy expenditure and lack of physical activity are believed to be risk factors for excessive weight gain. We hypothesized that energy expenditure at rest and during physical activity are lower in pubertal African-American girls than in Caucasian girls. Basal metabolic rate and sleeping energy expenditure of 40 Caucasian and 41 African-American pubertal girls (matched for age, physical characteristics, body fat, and energy intake) were measured by whole-room calorimetry, energy expended for physical activity by the doubly labeled water method, sexual maturity by physical examination, body composition by dual-energy x-ray absorptiometry, physical fitness by treadmill testing, and energy intake by 3-day food record. After adjusting for soft lean tissue mass, the basal energy expenditure (1333 +/- 132 vs. 1412 +/- 132 kcal/day, P = 0.01) and energy expended for physical activity (809 +/- 637 vs. 1271 +/- 162 kcal/day, P < 0.01) were significantly lower in the African-American girls than in the Caucasian girls. The differences remained the same after controlling for differences in sexual maturity and/or physical fitness. The lower energy expenditure of the pubertal African-American girls suggests that they are at a higher risk of becoming overweight than their Caucasian counterparts.

Calcium metabolism in girls: current dietary intakes lead to low rates of calcium absorption and retention during puberty.

We evaluated the effects of self-selected diets on calcium absorption and calculated retention in girls during pre-, early, and late puberty. Dietary calcium absorption was measured in 51 girls aged 4.9-16.7 y by using a dual-tracer stable-isotope technique. We found that calcium intake was similar among girls of all ages and all degrees of pubertal development and was below the recommended dietary allowance (1200 mg/d) for 21 of 25 girls aged > or = 11 y. The early pubertal period was associated with a higher percent of dietary calcium absorption (34.4 +/- 11.9%) than was the prepubertal (27.7 +/- 8.2%) or late pubertal periods (25.9 +/- 7.8%). Calculated calcium retention averaged 132 +/- 83 mg/d in prepubertal girls, 161 +/- 88 mg/d in early pubertal girls, and 44 +/- 91 mg/d in late pubertal girls. Peak calcium retention during early puberty was far below that previously reported after higher calcium intakes. We conclude that peak periods for calcium retention for girls are in the pre- and early pubertal periods. The current calcium intake of American girls during the pubertal growth period may not enable maximal mineral retention; therefore, increased calcium intakes should be considered.

Effect of maternal diet and body composition on lactational performance.

Milk production, dietary intake, and body composition of 45 lactating women were monitored for 4 months postpartum to examine the interrelationships of these maternal variables. A 3-day dietary record, 24-h test-weighing for determination of milk production, 24-h milk collection, anthropometric measurements, and water displacement for estimation of body fat were performed monthly. The overall mean (SD) energy intake was 2186 (463) kcal/day. Milk production (g/day) averaged 751 (130), 725 (131), 723 (114), and 740 (128) during the 4 sequential months. Weight postpartum was 64.6 (9.1) kg and was 59.3 (10.5) kg at 4 months. Body fat determined by water displacement averaged 28 (7)% at 1 month and 26 (8)% at 4 months. Estimations of body fat from skinfold thickness ranged from 28 (5)% postpartum to 27 (5)% at 4 months. Energy balance calculations based on the energy available from the diet plus the energy derived from tissue mobilization, minus the caloric equivalent of the milk, indicated sufficient energy available for maintenance and activity needs. Thus, it appears that successful lactation is compatible with gradual weight reduction and attainable with energy intakes less than current recommendations.

PIP: Milk production, dietary intake, and body composition of 45 lactating women were monitored for 4 months postpartum to examine the interrelationships of these maternal variables. A 3-day dietary record, 24-hour test-weighting for determination of milk production, 24-hour milk collection, anthropometric measurements, and water displacement for estimation of body fat were performed monthly. The overall mean (SD) energy intake was 2186 (463) kilocalories/day. Milk production (grams/day) averaged 751 (130), 725 (131), 723 (114), and 740 (128) during the 4 sequential months. Weight postpartum was 64.6 (9.1) kilograms (kg) and was 59.3 (10.5) kg at 4 months. Body fat determined by water displacement averaged 28 (7)% at 1 month and 26 (8)% at 4 months. Estimations of body fat from skinfold thickness ranged from 28 (5)% postpartum to 27 (5)% at 4 months. Energy balance calculations based on the energy available from the diet plus the energy derived from tissue mobilization, minus the caloric equivalent of the milk, indicated sufficient energy available for maintenance and activity needs. Thus, it appears that successful lactation is compatible with gradual weight reduction and attainable with energy intakes less than current recommendations.

Estimating body fat in African American and white adolescent girls: a comparison of skinfold-thickness equations with a 4-compartment criterion model.

BACKGROUND: Although skinfold-thickness equations are widely used to estimate body fat, their accuracy in a biracial population of female adolescents has not been established. OBJECTIVE: We undertook this study to determine the agreement between 8 widely used skinfold-thickness equations and a 4-compartment criterion model in predicting the percentage body fat of 72 white and 40 African American girls aged 13.0 +/- 1.9 y. DESIGN: The biceps, triceps, suprailiac, subscapular, thigh, calf, and abdominal skinfold thicknesses of the subjects were measured with skinfold calipers and the buttocks circumference with a metal tape. The percentage fat mass (%FM) predicted by using each skinfold-thickness equation was compared with the criterion value calculated by the 4-compartment model on the basis of measurements of body density, body water, and bone mineral content. RESULTS: When the racial groups were analyzed separately, the Bland-Altman analysis indicated that the quadratic equations agreed most closely with the 4-compartment model's measurement of %FM. Agreement of the other equations varied with body fatness. CONCLUSIONS: The quadratic equation of Slaughter et al is recommended for population studies in female adolescents because of its accuracy and simplicity. However, an individual %FM can be over- or underestimated by approximately 10% when this skinfold-thickness equation is used.

A comparison of dietary methods in nutritional studies.

Dietary intakes of 40 lactating women were measured by a 7-day record (7DR) and compared with results using a 1-day record (1DR), 3-day record (3DR), and a newly developed food frequency form. The estimated intakes of energy, protein, calcium, phosphorus, and iron were used in the comparison. The subjects ranged from 3 wk to 6 months postpartum and all were totally breast-feeding their infants at the time of the study. The 7DR was recorded by the subjects and random days were chosen to provide 1DR and 3DR. The food frequency form is a method developed to estimate nutrient intakes based on the consumption of 105 food items. Intraclass correlation coefficients used to compare methods indicated good, moderate, and poor agreement for 3DR/7DR, 1DR/7DR, and food frequency form/7DR comparisons, respectively. Regression analysis was used to assess further the agreement between 3DR and 7DR. This analysis indicated that the 3DR cannot provide good individual estimates of nutrient intakes, but can provide a reasonable estimate of the general quality of the diet. Intakes also were classified as high (greater than 1 1/3 Recommended Daily Allowance), medium (2/3 to 1 1/3 Recommended Daily Allowance), or low (less than 2/3 Recommended Daily Allowance), and Cohen's kappa was used to measure agreement between methods. None of the intakes was found to agree with the 7DR classification. Intraindividual variation was found to be greater than interindividual variation.

Cholesterol-lowering effect of soy protein in normocholesterolemic and hypercholesterolemic men.

Cardiovascular heart disease is a major health problem in the United States. Elevated blood cholesterol has been shown to significantly increase the risk of cardiovascular heart disease. The National Cholesterol Educational Program (NCEP) Step I diet, which restricts fat and cholesterol intakes, is usually recommended as the initial treatment to lower blood cholesterol. Soy protein has been shown to be hypocholesterolemic, particularly in hypercholesterolemic subjects. However, the hypocholesterolemic effect of soy protein in subjects with a blood total cholesterol concentration <5.17 mmol/L is not clear. To determine whether soy protein could enhance the hypocholesterolemic effect of the NCEP Step I diet, 13 normocholesterolemic and 13 hypercholesterolemic men aged 20-50 y were enrolled in a randomized, 2-part, crossover study. Subjects were fed either an NCEP Step I soy-protein diet or an NCEP Step I animal protein diet for 5 wk. After a washout period of 10-15 wk, the subjects were fed the alternate diet for 5 wk. The hypocholesterolemic effect of soy protein was found to be independent of age, body weight, pretreatment plasma lipid concentrations, and sequence of dietary treatment. Regardless of plasma lipid status, the soy-protein diet was associated with a statistically significant decrease in the plasma concentrations of LDL cholesterol (P = 0.029) as well as the in the ratio of plasma LDL cholesterol to HDL cholesterol (P = 0.005). Our results indicate that soy protein enhances the hypocholesterolemic effect of the NCEP Step I diet in both normocholesterolemic and hypercholesterolemic men.

Sources of variance in milk and caloric intakes in breast-fed infants: implications for lactation study design and interpretation.

Between-individual variation (BIV) and day-to-day variation (DDV) of total caloric and human milk intakes were examined in 17 infants. Nine were studied at months 5 and 6; 8 at months 6 and 7. All 17 were exclusively breast-fed for 5 full mo after which solid foods were added to the diet. Each infant was studied for five consecutive 24-h periods during which serial measurements were made of milk intake (test weighing) and solid food intake (pre- and postfeeding jar weighing). Total daily caloric intakes (kcal/day) were (mean +/- SD) 492 +/- 57, 547 +/- 70, and 567 +/- 98 at months 5, 6, and 7, respectively. Estimates of caloric intakes (kcal/kg/day) adjusted for body weight were 65.9 +/- 6.7, 72.6 +/- 11.2, and 70.9 +/- 13.0 at months 5, 6, and 7, respectively. Milk intakes (g/day) were 735 +/- 85, 640 +/- 106, and 562 +/- 214 at months 5, 6, and 7, respectively. BIV of milk intake increased after the introduction of solid foods. DDV (expressed as coefficient of variation) of caloric intake was nearly constant at each monthly observation and BIV increased from 8.8 at month 5 to 14.6 at month 7. The numbers of 24-h periods and subjects required for estimates of known precision of caloric and milk intakes of older breast-fed infants can be determined from these estimates of variance.

PIP: Between-individual variation (BIV) and day-to-day variation (DDV) of total caloric and human milk intakes were examined in 17 infants at the Lactation Program of the Children's Nutrition Research Center in Houston, Texas. 9 were studied at months 5 and 6; 8 at months 6 and 7. All 17 were exclusively breast-fed for 5 full months after which solid foods were added to the diet. Each infant was studied for 5 consecutive 24-hour periods during which serial measurements were made of milk intake (test weighing) and solid food intake (pre- and postfeeding jar weighing). Total daily caloric intakes (kcal/day) were (mean + or - SD) 492 + or - 57, 547 + or - 70, and 567 + or - 98 at months 5, 6, and 7, respectively. Estimates of caloric intakes (kcal/kg/day) adjusted for body weight were 65.9 + or - 6.7, 72.6 + or - 11.2, and 70.9 + or - 13.0 at months 5, 6, and 7, respectively. Milk intakes (g/day) were 735 + or - 85, 640 + or - 106, and 562 + or - 214 at months 5, 6, and 7, respectively. BIV of milk intake increased after the introduction of solid foods. DDV (expressed as coefficient of variation) of caloric intake was nearly constant at each monthly observation and BIV increased from 8.8 at month 5 to 14.6 at month 7. The numbers of 24-hour periods and subjects required for estimates of known precision of caloric and milk intakes of older breast-fed infants can be determined from these estimates of variance.

Are basal metabolic rate prediction equations appropriate for female children and adolescents?

The basal metabolic rate (BMR), which accounts for 50-70% of total energy expenditure, is essential for estimation of patient and population energy needs. Numerous equations have been formulated for prediction of human BMR. Most equations in current use are based on measurements of Caucasians performed more than four decades ago. We evaluated 10 prediction equations commonly used for estimation of BMR in 76 Caucasian and 42 African-American girls between 8 and 17 yr of age against BMR measured by whole-body calorimetry. The majority of the prediction equations (9 of 10) overestimated BMR by 60 +/- 46 kcal/day (range, 15-176 kcal/day). This overestimation was found to be significantly greater (P < 0.05) for African-American (77 +/- 17 kcal/day) than for Caucasians (25 +/- 17 kcal/day) in six equations, controlling for age, weight, and sexual maturity. We conclude that ethnicity is an important factor in estimation of the BMR and that the current prediction equations are not appropriate for accurate estimation of the BMR of individual female children and adolescents.

Nutrient intake and growth performance of older infants fed human milk.

STUDY OBJECTIVE: To determine whether the ad libitum addition of solid foods to the diet of exclusively human milk-fed infants will increase energy intake and reverse the decline in weight-for-age percentiles observed during the exclusive breast-feeding period. DESIGN: Weekly or biweekly measures of growth were made longitudinally on a cohort of infants from birth to 36 weeks of age, and monthly measures of nutrient intake were made from 16 weeks of age until 10 weeks after solid foods were introduced into the diet. SUBJECTS: Volunteer mother-infant pairs from middle and upper income groups who met entry criteria, including the intention to breast-feed exclusively for at least for 16 weeks; 58 pairs entered and 45 pairs completed the study. INTERVENTION: Solid foods were introduced at a time determined by the mother and the pediatrician; solid foods from controlled lot numbers were provided for each infant. MEASUREMENTS AND MAIN RESULTS: After solid foods were added, daily human milk intake declined at a rate of 77 gm/mo (p less than 0.001). Milk composition did not change during the observation period. Daily total energy intake increased 29 kcal/mo, but no changes were noted in energy intake when consumption was normalized for body weight. Weight (National Center for Health Statistics percentiles) at 28 weeks was 13 percentiles lower than that at birth, and length at 28 weeks was 1 percentile lower than at week 1. Weight and length percentiles at 28 weeks, when compared with peak values at 8 weeks, had dropped 19 and 14 percentiles, respectively. CONCLUSIONS: Energy intake of human milk-fed infants did not increase after solid foods were added to their diet but was maintained at approximately 20% below recommended levels. Energy intake appeared to reflect infant demands. These data suggest that the recommendations for the energy requirements of infancy should be reevaluated. The growth pattern of exclusively breast-fed infants differs from that of the National Center for Health Statistics reference population. These observations raise questions about the adaptive response of human milk-fed infants to different levels of energy intake and about the estimations of energy requirements based on the sum of basal metabolism, activity, growth, and diet-induced thermogenesis.

Absorption of calcium, zinc, and iron from breast milk by five- to seven-month-old infants.

Data are scarce regarding mineral bioavailability from human milk in older infants who may also be receiving solid foods (beikost). We measured the absorption of Ca, Zn, and Fe in 14 healthy, nonanemic 5-7-mo-old breast-fed infants whose mothers milk was extrinsically labeled with stable isotopes (44Ca, 70Zn, and 58Fe) of these minerals. In addition, Ca and Zn stable isotopes (46Ca and 67Zn) were administered i.v., and a second isotope of Fe (57Fe) was given orally without food as a non-meal dose. Subjects were not receiving any artificial infant formula or cow's milk, but most (10/14) were receiving beikost. Ca and Zn absorption was calculated using the urinary excretion of the isotopes during the 24 h after dosing (Ca) or their urinary ratio 72 h after dosing (Zn). Fe absorption was calculated using the red blood cell incorporation at 14 d. Fe absorption averaged 20.7 +/- 14.8% from the 58Fe given with human milk (geometric mean, 14.8%) and 17.7 +/- 15.1% (geometric mean, 11.0%) from the 57Fe non-meal dose. Ca absorption averaged 61.3 +/- 22.7% and Zn absorption (n = 10) averaged 49.5 +/- 18.5%. Absorption of Fe (natural logarithm) from the non-meal Fe dose (57Fe) but not from the human milk (58Fe) was significantly negatively correlated to serum ferritin (r = -0.70, p = 0.007 versus r = -0.35, p = 0.24). At the intake levels in this study, total daily Fe, Ca, and Zn intakes from beikost were not significantly correlated to their fractional absorption from breast milk, but Fe intake from beikost was significantly negatively correlated to absorption of Fe from the non-meal dose (r = -0.61, p = 0.021). We conclude that minerals are well absorbed from human milk in older infants after the introduction of beikost to the diet.

Comparison of hand- and electric-operated breast pumps.

Volume, fat and energy contents were measured in human milk samples collected over 2 24-h periods with either an electric or hand-operated breast pump. The energy content was significantly higher and the variance for this measurement was significantly lower in samples obtained by the electric pump. The type of pump used is an important consideration when the content of energy and other nutrients associated with the fat compartment in human milk is to be evaluated. This observation is especially pertinent to cross-study comparisons, eg studies of well- and malnourished populations.

Calcium absorption and kinetics are similar in 7- and 8-year-old Mexican-American and Caucasian girls despite hormonal differences.

To assess the possibility of ethnic differences in mineral metabolism in prepubertal children, we compared measures of calcium metabolism in 7- and 8-y-old Mexican-American (MA) and non-Hispanic Caucasian (CAU) girls (n = 38) living in southeastern Texas. We found similar fractional calcium absorption, urinary calcium excretion, calcium kinetic values and total-body bone mineral content in the MA and CAU girls. In contrast, parathyroid hormone (PTH) concentrations were greater in MA girls (4.01 +/- 0.47 vs. 1. 96 +/- 0.50 pmol/L, P = 0.005) than in CAU girls. Serum 25-hydroxyvitamin D concentrations were lower in MA girls (68.9 +/- 7.7 vs. 109.4 +/- 8.4 nmol/L, P = 0.001) than in CAU girls, but 1, 25-dihydroxyvitamin D concentrations did not differ between groups. Seasonal variability was seen for 25-hydroxyvitamin D concentrations in girls of both ethnic groups, but values in all of the girls were >30 nmol/L (12 ng/mL). We conclude the following: 1) greater PTH levels in MA girls than CAU girls are present without evidence of vitamin D deficiency; and 2) differences in 25-hydroxyvitamin D and PTH concentrations between MA and CAU girls do not have a large effect on calcium absorption, excretion or bone calcium kinetics. These data do not provide evidence for adjusting dietary recommendations for mineral or vitamin D intake by MA girls.

Precise determination of the absorptive component of urinary calcium excretion using stable isotopes.

Some patients with hypercalciuria are thought to have enhanced enteric calcium absorption, with a major component of recent diet contributing to urinary calcium. This mechanism has been difficult to test with the usual calcium loading procedures. We employed dual stable calcium isotope tracers to quantitate the components of urinary calcium excretion in 38 healthy female children. The mean urinary calcium excretion in these girls was 2.4 mg/kg per day. The contribution of recent diet to this total was a mean of 0.2 mg/kg per day. The maximum dietary contribution to urinary calcium excretion was 0.86 mg/kg per day. Recent diet contributes a mean of 8% to total dietary calcium excretion. This novel method permits precise quantitation of the contributions of recent diet and tissue stores to urinary calcium excretion. In these healthy girls, the fraction of urinary calcium derived from diet is trivial.

Variables related to urinary calcium excretion in young girls.

The relations among dietary and calcium kinetic factors and 24-h urinary mineral excretion were evaluated in a group of 89 healthy girls (51 white and 38 black) aged 4.9-16.7 years. Nutrient intakes were calculated for each participant using a weighed intake of all food and beverage on the day of the 24-h urine collection study and two subsequent 24-h food records. A significant relation was noted between urinary calcium and sodium excretion (r = 0.55; p < 0.0001). No significant relations were found between urinary calcium and (a) calcium intake (r = 0.08), (b) protein intake (r = 0.14), or (c) phosphorus intake (r = 0.11). Urinary calcium was not significantly related to fractional calcium absorption (r = 0.03) or net calcium absorption (r = 0.11), but was significantly associated with the bone calcium deposition rate (r = 0.24; p < 0.03). Using a multiple regression model, both urinary sodium and the bone calcium deposition rate were independent predictors of urinary calcium excretion in this population (r = 0.57; p = 0.0001). A substantial number of the children in this population had urinary calcium excretion > 4 mg/kg/day (12%). The incidence of hypercalciuria differed between the racial groups and was markedly higher in the white than in the black children (17.6 vs. 5.3%). Over a range of usual calcium intakes, during the rapid-bone-growth period in childhood and early adolescence, urinary calcium appears relatively unaffected by calcium intake and is most strongly associated with urinary sodium levels.

Absorption by 1-year-old children of an iron supplement given with cow's milk or juice.

A paucity of data are available on toddlers for the evaluation of optimal strategies of Fe supplementation. In this study, we used a two-tracer stable isotope technique to determine Fe absorption from a 5-mg dose of stable isotopically enriched (57Fe or 58Fe) ferrous sulfate given with cow's milk (CM) compared with the same dose given with apple juice. Ten children (age 13 +/- 1 mo, weight 10.8 +/- 1.1 kg) who had recently discontinued formula feeding and begun on CM were studied. Red blood cell (RBC) iron incorporation of the isotope was determined 14 d after dosing with 57Fe and 58Fe. Fe absorption was calculated based on the assumption that 90% of absorbed Fe is incorporated into RBC. Absorption of Fe was significantly greater (13.7 +/- 6.4%) when given with juice than with milk (5.7 +/- 4.0%), p < 0.01 by paired t tests. Fe absorption from the dose given with juice was significantly negatively correlated with serum ferritin (n = 9, r = -0.70, p < 0.05). These results indicate that 1) a small supplement of Fe is better absorbed when given with juice than with CM, and 2) a large variability in Fe absorption exists in healthy 1-y-old infants, which is related to their existing Fe stores.

Estimation of body fat in Caucasian and African-American girls: total-body electrical conductivity methodology versus a four-component model.

BACKGROUND: Obesity has been increasing dramatically in recent years among children, particularly African-American girls. Total-body electrical conductivity (TOBEC) is a simple way to measure body fat with minimal risk. OBJECTIVE: This study compared the agreement between the percentage of fat mass (%FM) predicted using two TOBEC equations with %FM measured by a four-component model in 73 Caucasian and 41 African-American girls. DESIGN AND MEASUREMENTS: %FM predicted using the TOBEC equations was compared with %FM from the four-component model based on measurements of body density, body water and bone mineral content. RESULTS: Analyses by linear regression analysis and by the Bland and Altman methods comparison procedure showed that the equation using the square root of the TOBEC zero-order Fourier coefficient and the subject's height yielded more accurate and more reproducible %FM, regardless of race, than the TOBEC linear equation, which was based on the zero-, first- and second-order Fourier coefficients. The Bland and Altman comparison further revealed that the accuracy and limits of agreement of the TOBEC linear equation were related to body fatness among the Caucasian girls. The relationship, however, disappeared when prepubescent girls and a girl with low %FM were excluded from the analysis. CONCLUSIONS: The TOBEC square root equation with adjustment for body geometry and length is recommended for use in adolescent girls, as it yielded better agreement with the criterion method. However, further validation of the TOBEC instrumentation for estimating body fat in prepubescent children and children with low body fat is warranted.

Calcium absorption and metabolism in children with juvenile rheumatoid arthritis assessed using stable isotopes.

OBJECTIVE: To assess calcium intake, absorption, urinary excretion and the fraction of urinary calcium originating from bone and diet in patients with juvenile rheumatoid arthritis (JRA). METHODS: A dual tracer stable isotope technique was used to study 6 girls and 3 boys with JRA. RESULTS: Fractional absorption in the 6 girls, ages 4-9, with JRA was significantly lower than that in 10 similar, healthy girls (22.6 +/- 4.7% vs 30.4 +/- 8.4%, p = 0.033). Urinary calcium excretion tended to be higher in the girls with JRA than in controls, (2.9 +/- 1.5 vs 1.6 +/- 1.7, p = 0.15). The urinary calcium in patients with JRA was derived principally from bone, and there was no increase in diet derived urinary calcium. One of the boys with new onset JRA was markedly hypercalciuric and in negative calcium balance (-222 mg/day). CONCLUSION: Our data show that hypercalciuria in patients with JRA results from bone resorption, not hyperabsorption of dietary calcium and suggest that increases in calcium intake may benefit children with JRA.