Sleep duration, physical activity, and caloric intake are related to weight status in Mexican American children: a longitudinal analysis.

BACKGROUND: Obesity is a serious issue, spanning all ages, and, in the U.S., disproportionately affects Latinos and African Americans. Understanding sleep, physical activity and dietary behaviors that may predict childhood obesity can help identify behavioral intervention targets. METHODS: Data were drawn from a U.S. cohort study of 323 Mexican American 8-10-year-old children and their mothers, who participated in a longitudinal study over a 2-year period. Measures were collected at baseline (BL; child mean age = 8.87, SD = 0.83), year 1 (FU1) and year 2 (FU2). Mothers reported on household income and acculturation at BL. Child height and weight were collected and BMI z-scores (BMIz) were calculated for weight status at BL, FU1, and FU2. Accelerometer-estimated sleep duration (hours) and moderate-to-vigorous physical activity (MVPA; minutes) were collected across 3 days at BL, FU1, and FU2. Two 24-h dietary recalls were performed at each time point; from these, average energy intake (EI, kcals/day) was estimated. Cross-lagged panel analysis was used to examine behavioral predictors on BMIz at each time point and across time. RESULTS: At BL and FU1, longer sleep duration (ß = - 0.22, p < 0.001; ß = - 0.17, p < 0.05, respectively) and greater MVPA (ß = - 0.13, p < 0.05; ß = - 0.20, p < 0.01, respectively) were concurrently related to lower BMIz. At FU2, longer sleep duration (ß = - 0.18, p < 0.01) was concurrently related to lower BMIz, whereas greater EI (ß = 0.16, p < 0.01) was related to higher BMIz. Longer sleep duration at BL predicted lower BMIz at FU1 (ß = - 0.05, p < 0.01). CONCLUSIONS: Longer sleep duration was concurrently related to lower weight status at each time point from ages 8-10 to 10-12. Higher MVPA was concurrently related to lower weight status in earlier childhood (ages 8-10 and 9-11) and higher EI was concurrently related to higher weight status toward the end of childhood (ages 10-12 years). Furthermore, longer sleep in earlier childhood was protective of children's lower weight status 1 year later. These findings suggest that sleep duration plays a consistent and protective role against childhood obesity; in addition, MVPA and healthy EI remain important independent factors for obtaining a healthy weight.

Temporal associations between circadian sleep and activity patterns in Mexican American children.

OBJECTIVE: This study aimed to examine the relationship between circadian sleep and activity behaviors (sedentary time [SED], light-intensity physical activity [LPA], and moderate- to vigorous-intensity physical activity [MVPA]) across 3 consecutive days. METHODS: This study included 308 Mexican American children aged 8-10 years from the San Francisco Bay Area. Minutes of sleep duration, SED, LPA, and MVPA were estimated using hip-worn accelerometers from Wednesday night to Saturday night. A cross-lagged panel model was used to estimate paths between sleep duration the prior night and subsequent behaviors, and paths between behaviors to subsequent sleep duration across the 3 days. We adjusted for child age, sex, body mass index, and household income. RESULTS: Overall, children were 8.9 (SD 0.8) years old; the weighted average for weekday and weekend combined was 9.6 (SD 0.7) hours per night in sleep duration, 483 (SD 74) min/d SED, 288 (SD 61) min/d LPA, and 63 (SD 38) min/d MVPA. Cross-lagged panel analyses showed that, over 3 days, for every 1-hour increase in sleep duration, there were an expected 0.66-hour (40-minute) decrease in SED, 0.37-hour (22-minute) decrease in LPA, and 0.06-hour (4-minute) decrease in MVPA. For every 1-hour increase in LPA, there was an expected 0.25-hour (15-minute) decrease in sleep duration. CONCLUSION: An additional hour of sleep the night before corresponded to an hour decrease in combined SED and LPA the next day in Mexican American children. For every hour of LPA, there was an associated 15-minute decrease in sleep. Encouraging longer sleep may help to reduce SED and LPA, and help offset LPA's negative predictive effect on sleep.

Dietary Intake, Attitudes toward Healthy Food, and Dental Pain in Low-Income Youth.

Few studies have examined the relation between food consumption and related attitudes and dental pain among children. The objective of this study is to examine the associations of healthy and unhealthy food items, attitudes toward healthy food, and self-efficacy of eating healthy with dental pain among children. A cross-sectional analysis was performed using child survey data from the Texas Childhood Obesity Research Demonstration (TX CORD) project. Fifth-grade students ( n = 1,020) attending 33 elementary schools in Austin and Houston, Texas, completed the TX CORD Child Survey, a reliable and valid survey instrument focused on nutrition and physical activity behaviors. All nutrition questions ask about the number of times food and beverage items were consumed on the previous day. Dental pain was reported as mouth or tooth pain in the past 2 wk that made their mouth hurt so much that they could not sleep at night. Mixed-effects logistic regression models were used to test the association between 10 unhealthy food items, 9 healthy food items, 2 health attitudes, and self-efficacy with dental pain. All models controlled for sociodemographic variables. In total, 99 (9.7%) students reported dental pain. Dental pain was associated with intake of the following unhealthy items: soda, fruit juice, diet soda, frozen desserts, sweet rolls, candy, white rice/pasta, starchy vegetables, French fries/chips, and cereal (adjusted odds ratio [AOR], 1.27-1.81, P < 0.01). The intake of other vegetables (AOR, 1.56; P < 0.01), a healthy item, and the attitude that healthy food tastes good (AOR, 1.59; P = 0.04) were also positively associated with dental pain. The attitude of eating healthier leads to fewer health problems (AOR, 0.50) and self-efficacy for healthy eating (AOR, 0.44) were negatively associated with dental pain ( P < 0.01). Interventions should focus on improving oral health by reducing intake of unhealthy foods and educating children and families on the importance of diet as a means of reducing dental caries. Knowledge Transfer Statement: The results of this study can be used to inform researchers on potential food items and psychosocial measures to examine in low-income, minority populations for longitudinal research. These results would also be useful to educators who could incorporate oral health care and nutrition education into school curriculums.

Brain-derived neurotrophic factor in human subjects with function-altering melanocortin-4 receptor variants.

BACKGROUND: In rodents, hypothalamic brain-derived neurotrophic factor (BDNF) expression appears to be regulated by melanocortin-4 receptor (MC4R) activity. The impact of MC4R genetic variation on circulating BDNF in humans is unknown. OBJECTIVE: The objective of this study is to compare BDNF concentrations of subjects with loss-of-function (LOF) and gain-of-function (GOF) MC4R variants with those of controls with common sequence MC4R. METHODS: Circulating BDNF was measured in two cohorts with known MC4R sequence: 148 subjects of Pima Indian heritage ((mean±s.d.): age, 15.7±6.5 years; body mass index z-scores (BMI-Z), 1.63±1.03) and 69 subjects of Hispanic heritage (10.8±3.6 years; BMI-Z, 1.57±1.07). MC4R variants were characterized in vitro by cell surface expression, receptor binding and cyclic AMP response after agonist administration. BDNF single-nucleotide polymorphisms (SNPs) rs12291186, rs6265 and rs7124442 were also genotyped. RESULTS: In the Pima cohort, no significant differences in serum BDNF was observed for 43 LOF subjects versus 65 LOF-matched controls (age, sex and BMI matched; P=0.29) or 20 GOF subjects versus 20 GOF-matched controls (P=0.40). Serum BDNF was significantly associated with genotype for BDNF rs12291186 (P=0.006) and rs6265 (P=0.009), but not rs7124442 (P=0.99); BDNF SNPs did not interact with MC4R status to predict serum BDNF. In the Hispanic cohort, plasma BDNF was not significantly different among 21 LOF subjects, 20 GOF subjects and 28 controls (P=0.79); plasma BDNF was not predicted by BDNF genotype or BDNF-x-MC4R genotype interaction. CONCLUSIONS: Circulating BDNF concentrations were not significantly associated with MC4R functional status, suggesting that peripheral BDNF does not directly reflect hypothalamic BDNF secretion and/or that MC4R signaling is not a significant regulator of the bulk of BDNF expression in humans.

Adiposity in children and adolescents: correlates and clinical consequences of fat stored in specific body depots.

The 2011 Pennington Biomedical Research Center's Scientific Symposium focused on adiposity in children and adolescents. The symposium was attended by 15 speakers and other invited experts. The specific objectives of the symposium were to (i) integrate the latest published and unpublished findings on the laboratory and clinical assessment of depot-specific adiposity in children and adolescents, (ii) understand the variation in depot-specific adiposity and related health outcomes associated with age, sex, maturation, ethnicity and other factors and (iii) identify opportunities for incorporating new markers of abdominal obesity into clinical practice guidelines for obesity in children and adolescents. This symposium provided an overview of important new advances in the field and identified directions for future research. The long-term goal of the symposium is to aid in the early identification of children and adolescents who are at increased health risk because of obesity and obesity-related conditions.

Genome-wide scan revealed genetic loci for energy metabolism in Hispanic children and adolescents.

OBJECTIVE: Genome-wide scans were conducted in search for genetic locations linked to energy expenditure and substrate oxidation in children. DESIGN: Pedigreed data of 1030 Hispanic children and adolescents were from the Viva La Familia Study which was designed to investigate genetic and environmental risk factors for the development of obesity in Hispanic families. A respiratory calorimeter was used to measure 24-h total energy expenditure (TEE), basal metabolic rate (BMR), sleep metabolic rate (SMR), 24-h respiratory quotient (24RQ), basal metabolic respiratory quotient (BMRQ) and sleep respiratory quotient (SRQ). Protein, fat and carbohydrate oxidation (PROOX, FATOX and CHOOX, respectively) were also estimated. All participants were genotyped for 384 single tandem repeat markers spaced an average of 10 cM apart. Computer program SOLAR was used to perform the genetic linkage analyses. RESULTS: Significant linkage for TEE was detected on chromosome 1 near marker D1S2841, with a logarithm of the odds (LOD) score of 4.0. SMR, BMRQ and PROOX were associated with loci on chromosome 18, 17 and 9, respectively, with LOD scores of 4.88, 3.17 and 4.55, respectively. A genome-wide scan of SMR per kg fat-free mass (SpFFM) peaked in the same region as SMR on chromosome 18 (LOD, 5.24). Suggestive linkage was observed for CHOOX and FATOX. Several candidate genes were found in the above chromosomal regions including leptin receptor (LEPR). CONCLUSION: Regions on chromosomes 1, 9, 17 and 18 harbor genes affecting variation in energy expenditure and substrate oxidation in Hispanic children and adolescents.

Linkage analysis of circulating levels of adiponectin in Hispanic children.

INTRODUCTION: Adiponectin, a hormone produced exclusively by adipose tissue, is inversely associated with insulin resistance and proinflammatory conditions. The aim of this study was to find quantitative trait loci (QTLs) that affect circulating levels of adiponectin in Hispanic children participating in the VIVA LA FAMILIA Study by use of a systematic genome scan. METHODS: The present study included extended families with at least one overweight child between 4 and 19 years old. Overweight was defined as body mass index (BMI) 95th percentile. Fasting blood was collected from 466 children from 127 families. Adiponectin was assayed by radioimmunoassay (RIA) technique in fasting serum. A genome-wide scan on circulating levels of adiponectin as a quantitative phenotype was conducted using the variance decomposition approach. RESULTS: The highest logarithm of odds (LOD) score (4.2) was found on chromosome 11q23.2-11q24.2, and a second significant signal (LOD score=3.0) was found on chromosome 8q12.1-8q21.3. In addition, a signal suggestive of linkage (LOD score=2.5) was found between 18q21.3 and 18q22.3. After adjustment for BMI-Z score, the LOD score on chromosome 11 remained unchanged, but the signals on chromosomes 8 and 18 dropped to 1.6 and 1.7, respectively. Two other signals suggestive of linkage were found on chromosome 3 (LOD score=2.1) and 10 (LOD score=2.5). Although the region on chromosome 11 has been associated with obesity and diabetes-related traits in adult populations, this is the first observation of linkage in this region for adiponectin levels. Our suggestive linkages on chromosomes 10 and 3 replicate results for adiponectin seen in other populations. The influence of loci on chromosomes 18 and 8 on circulating adiponectin seemed to be mediated by BMI in the present study. CONCLUSION: Our genome scan in children has identified a novel QTL and replicated QTLs in chromosomal regions previously shown to be linked with obesity and type 2 diabetes (T2D)-related phenotypes in adults. The genetic contribution of loci to adiponectin levels may vary across different populations and age groups. The strong linkage signal on chromosome 11 is most likely underlain by a gene(s) that may contribute to the high susceptibility of these Hispanic children to obesity and T2D.

Skeletal muscle energetics assessed by (31)P-NMR in prepubertal girls with a familial predisposition to obesity.

OBJECTIVE: To determine whether skeletal muscle energetics, measured by in vivo (31)P-nuclear magnetic resonance spectroscopy during plantar flexion exercise, differ between multiethnic, prepubertal girls with or without a predisposition to obesity. DESIGN: Cross-sectional study. SUBJECTS: Girls (mean age and body fat+/-s.d.=8.6+/-0.3 y and 22.6+/-4.2%) were recruited according to parental leanness or obesity defined as follows: LN (n=22), two lean parents, LNOB (n=18), one lean and one obese parent; and OB (n=15), two obese parents. MEASUREMENTS: A 3 min, rest-exercise-recovery plantar flexion protocol was completed. Work was calculated from the force data. Spectra were analyzed for inorganic intracellular phosphate (P(i)), phosphocreatine (PCr), P(i)/PCr (ratio of the low and high energy phosphates indicating the bioenergetic state of the cell), intracellular pH, and adenosine triphosphate (ATP). Magnetic resonance imaging was used to determine calf muscle volume. RESULTS: BMI was lower in the girls in the LN group (15.9+/-1.5 kg/m(2)) compared to the OB group (16.7+/-1.3 kg/m(2)) of girls (P<0.05), with no difference with the LNOB group (16.7+/-1.9 kg/m(2)). Adjusted for muscle volume and cumulative work, no differences in P(i), PCr, P(i)/PCr, pH, or ATP were observed among the LN, LNOB and OB groups at rest, the end of exercise, and after 60 and 300 s of recovery. From rest to the end of exercise, P(i) and P(i)/PCr (mean+/-s.d.: 0.2+/-0.1 vs 1.5+/-1.0) increased, whereas PCr and pH (7.04+/-0.06 vs 6.95+/-0.10) decreased (all P<0.001). By 60 s of recovery, P(i) and P(i)/PCr decreased, whereas PCr and pH increased (all P<0.001). CONCLUSIONS: Skeletal muscle energetics, specifically P(i)/PCr and pH measured during plantar flexion exercise, do not differ between prepubertal girls with or without a familial predisposition to obesity.

Body composition in prepubertal girls: comparison of six methods.

OBJECTIVE: To compare estimates of fat mass (FM), fat-free mass (FFM) and percentage body fat (%fat) by six different methods in prepubertal girls. DESIGN: Cross-sectional study. SUBJECTS: Normal-weight, multi-ethnic, prepubertal girls (age=8.5+/-0.4 y, n=101). MEASUREMENTS: Body composition was measured in each child by anthropometry (skinfold thickness using Slaughter equation), dual-energy X-ray absorptiometry (DXA), total body potassium (TBK), isotope dilution for total body water measurement (TBW), multifrequency bioelectrical impedance spectroscopy (BIS), and total body electrical conductivity (TOBEC). RESULTS: TOBEC and skinfold thickness yielded the lowest values of FM followed by DXA, TBK, TBW and BIS, with BIS giving the highest value of FM. All methods were significantly different for FFM, FM and %fat (P<0.001), except FFM by DXA and TBK. The Bland-Altman limits of agreement among the methods reveal that they are not directly interchangeable for FM, FFM, or %fat. The largest mean difference for FM was between TOBEC and BIS (-2.90 kg), whereas the smallest mean difference was between TOBEC and skinfold thickness (-0.14 kg). For FFM, the largest mean difference was also between TOBEC and BIS (2.83 kg), but the smallest mean difference for FFM was between DXA and TBK (-0.03 kg). For %fat, the mean differences were larger, -10.5% for TOBEC and BIS and+9.7% for skinfold thickness and BIS. The closest two techniques for %fat were TOBEC and skinfold thickness (mean difference of -0.62%) and DXA and TBK (-1.81%). CONCLUSIONS: We found that estimates of body composition in prepubertal 8-y-old girls are highly method-dependent and that the six methods studied (DXA, TBK, TBW, TOBEC, BIS and anthropometry) are not directly interchangeable.

Familial resemblance of body composition in prepubertal girls and their biological parents.

BACKGROUND: Heritability estimates for body mass index (BMI; in kg/m(2)) in children generally have been derived from twin and adoption studies. However, BMI does not reflect total or regional body composition. OBJECTIVE: We evaluated the familial resemblance of body composition between prepubertal girls of normal weight and body fatness and their parents by using state-of-the-art technology. DESIGN: The subjects were 101 girls [mean age: 8.5 +/- 0.4 y; percentage body fat (%BF): 12-30%] and their biological parents. Weight, height, and body composition [fat mass (FM), fat-free mass (FFM), and %BF] were measured with dual-energy X-ray absorptiometry (DXA) and total body potassium (TBK). RESULTS: Weight, height, and BMI showed low-to-moderate similarity between the girls and both their parents (r = 0.29-0.44, P < 0.01). The girls' FM, FFM, and %BF were significantly related to both parents' body composition. Cross-generational equations were developed for DXA, eg, child's %BF = 12.4 + (0.158 paternal %BF) + (0.145 maternal %BF) (adjusted r(2) = 0.16, P < 0.001). Regional analysis with DXA showed that the adjusted r(2) values for the arm, trunk, and leg regions, respectively, were 0.17, 0.33, and 0.31 for lean tissue mass and 0.11, 0.14, and 0.09 for FM. TBK showed a similar relation between parents and girls (r = 0.28-0.47, P < 0.01). Significant heritability (h(2) +/- SE) was detected for BMI (0.35 +/- 0.17, P = 0.03) and %BF measured with DXA (0.50 +/- 0.12, P = 0.0001). CONCLUSION: The body composition of prepubertal girls of normal weight and body fatness is significantly related to the body composition of both biological parents.

Glucose production, gluconeogenesis, and insulin sensitivity in children and adolescents: an evaluation of their reproducibility.

The prevalence of overweight and obese children has doubled, and the incidence of type 2 diabetes in children (0-19 y) has increased 4-fold during the past several decades. As a result we can anticipate an increased number of metabolic studies in children. There are few data on measures of glucose metabolism in normal children, and virtually none relating to their reproducibility. The aims of this study were 1) to provide new data on energy expenditure and glucose, lipid, and protein metabolism in nonobese, healthy children and adolescents; 2) to evaluate their reproducibility; and 3) on the basis of these data, to perform power calculations for metabolic studies. Eight nonobese subjects (8-16 y) were studied on two occasions, preceded by 7 d of a diet with identical energy content and macronutrient distribution. Gluconeogenesis, measured by deuterium oxide, accounted for 50% of glucose production. Insulin sensitivity, measured by the labeled minimal model, averaged 4.9 x 10(-4) mL(mU x min)(-1). Glucose appearance rate was significantly higher (p < 0.01) in the children than in the adolescents. Furthermore, we demonstrated that for energy intake and expenditure, plasma concentrations of glucose and C-peptide, and rates of appearance of glucose and leucine, a 10% difference can be detected in fewer than five subjects with a power of 80% and a type I error of 5%. Insulin concentration, gluconeogenesis, insulin secretory indices, insulin sensitivity, and glucose effectiveness were more variable, but with the above power a difference of 25% could be detected in 7-11 subjects using a paired study design.

The role of breastfeeding in obesity.

Most studies examining the effects of breastfeeding on later obesity have found an insignificant effect. Breastfeeding was positively associated with later body fatness in two studies. A protective effect of breastfeeding on childhood obesity was seen in four studies. An effect of breastfeeding on later obesity, if any, is probably weaker than genetic and other environmental factors. Also, an observed association between breastfeeding and later obesity does not prove causality. Controlling for confounders in an attempt to minimize the effects of differences between breastfeeding and formula-feeding mothers was done to a varying extent across studies. In several of the later studies, adjustment for confounders obliterated the effect of breastfeeding. Whether all the pertinent confounding factors have been measured and whether the differences between mothers who chose to breastfeed and mothers who chose to formula-feed have been controlled for adequately are always questionable. The dose response observed with the duration of breastfeeding is consistent with a causal association, but confounders associated with breastfeeding also may covary in a graded response. Although a highly provocative concept, the protective effect of breastfeeding on later obesity remains controversial.

Energy requirements of lactating women derived from doubly labeled water and milk energy output.

Instead of using an incremental approach to assess the energy requirements of lactation, a more comprehensive approach may be taken by measuring total energy expenditure (TEE), milk energy output and energy mobilization from tissue stores. The latter approach avoids assumptions regarding energetic efficiency and changes in physical activity and adiposity. The purpose of this study was threefold: to assess the energy requirements of lactation; to compare these estimates with energy requirements in the nonpregnant, nonlactating state and to test for energetic adaptations in basal metabolic rate (BMR) and physical activity during the energy-demanding process of lactation. Milk production and composition, body weight and composition, TEE, BMR and physical activity levels were measured in 24 well-nourished women during exclusive breastfeeding at 3 mo postpartum and after the cessation of breastfeeding at 18 or 24 mo postpartum. TEE was measured by the doubly labeled water method, milk production by 3-d test-weighing, milk energy by bomb calorimetry on a 24-h milk sample, body composition by dual-energy x-ray absorptiometry and BMR by room respiration calorimetry. TEE, BMR and physical activity level (physical activity level = TEE/BMR) did not differ between the lactating and nonlactating state (TEE 10.0 +/- 1.5 versus 10.6 +/- 2.1 MJ/d). Mean milk energy output was equivalent to 2.02 +/- 0.33 MJ/d. Total energy requirements were greater during lactation than afterward (12.0 +/- 1.4 versus 10.6 +/- 2.1 MJ/d, P: = 0.002). Energy mobilization from tissue stores (-0.65 +/- 0.97 MJ/d) resulted in net energy requirements during lactation of 11.4 +/- 1.8 MJ/d. Because adaptations in basal metabolism and physical activity were not evident in these well-nourished women, energy requirements during lactation were met primarily from the diet and only partially by mobilization of tissue stores.

Energy requirements derived from total energy expenditure and energy deposition during the first 2 y of life.

BACKGROUND: Current recommendations for energy intake of children are derived from observed intakes. Deriving energy requirements on the basis of energy expenditure and deposition is scientifically more rational than is using the observational approach and is now possible with data on total energy expenditure (TEE), growth, and body composition. OBJECTIVES: The objectives of this study were 1) to define energy requirements during the first 2 y of life on the basis of TEE and energy deposition; 2) to test effects of sex, age, and feeding mode on energy requirements; and 3) to determine physical activity. DESIGN: TEE, sleeping metabolic rate, anthropometry, and body composition were measured in 76 infants. TEE was measured with doubly labeled water, sleeping metabolic rate with respiratory calorimetry, and body composition with a multicomponent model. RESULTS: Total energy requirements were 2.23, 2.59, 2.97, 3. 38, 3.72, and 4.15 MJ/d at 3, 6, 9, 12, 18, and 24 mo, respectively. Energy deposition (in MJ/d) decreased significantly over time (P: = 0.001) and was lower in breast-fed than in formula-fed infants (P: = 0.01). Energy requirements were approximately 80% of current recommendations. Energy requirements differed by age (P: = 0.001), feeding group (P: = 0.03), and sex (P: = 0.03). Adjusted for weight or fat-free mass and fat mass, energy requirements still differed by feeding group but not by age or sex. Temperament and motor development did not affect TEE. CONCLUSION: The TEE and energy-deposition data of these healthy, thriving children provide strong evidence that current recommendations for energy intake in the first 2 y of life should be revised.

Fat intake of children in relation to energy requirements.

The optimal fat intake for children is discussed in light of their energy requirements. Total energy requirements were estimated from doubly labeled water studies of total energy expenditure (TEE) and the energy cost of growth. Basal metabolic rates (BMRs) were calculated from weight by using the equations of Schofield et al or by indirect calorimetry. Activity energy expenditure and physical activity levels were calculated as TEE - BMR and TEE/BMR, respectively. Weight-specific energy requirements for maintenance and growth changed inversely to the increased energy needed for physical activity in healthy, active children. The total energy requirements of infants increased from 1.4 MJ/d at 1 mo to 4.0 MJ/d at 24 mo. The energy cost of growth decreased sharply from 37-38% to 2% of the total requirement during the first 24 mo of life. Energy requirements increased from 4 MJ/d at 2 y to 11 MJ/d at 18 y in girls and from 5 to 15 MJ/d in boys. The energy cost of growth varied between 1% and 4% of total energy requirements in childhood and adolescence. The current recommendation of 30% of energy from dietary fat for children aged >2 y is sufficient for adequate growth. Lower fat intakes may be associated with inadequate vitamin and mineral intakes and increased risk of poor growth. Diets higher in fat may lead to higher energy intakes and higher body fat, although available data for children are conflicting. Beyond infancy, children can meet their energy needs for maintenance, physical activity, and growth from a diet providing 30% of energy from fat.

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.

Relations of parental obesity status to physical activity and fitness of prepubertal girls.

OBJECTIVE: To determine whether physical activity and fitness differ among normal-weight-for-height, multiethnic, prepubertal girls whose parents are lean, obese, or both. SETTING: Conducted in Houston, Texas. STUDY PARTICIPANTS: Normal-weight white, black, and Hispanic prepubertal girls (mean age +/- standard deviation: 8.5 +/-.4 years) participated in this study. Girls were recruited according to parental leanness or obesity defined as follows: girls with 2 lean parents (LN group; n = 30); girls with 2 obese parents (OB group; n = 27); and girls with 1 lean and 1 obese parent (LNOB group; n = 44). Intervention. Each child wore a heart rate monitor for two 24-hour periods, underwent a treadmill exercise test, answered an activity questionnaire, and completed energy expenditure measurements by basal calorimetry and doubly labeled water. OUTCOME MEASURES: The amount of time spent above 125% and 150% of basal heart rate (BHR) was calculated during each 24-hour period (n = 84). Fitness (n = 97), habitual physical activity (n = 101), and physical activity level (PAL = total energy expenditure/basal metabolic rate; n = 101) were also measured. RESULTS: The times spent above 125% and 150% of BHR were similar among LN, LNOB, and OB groups. Black girls spent less time than did white girls on the weekend above 125% BHR and above 150% BHR. No significant familial or ethnic differences in peak oxygen consumption or habitual physical activity were observed. PALs were as follows: LN = 1.6 +/-.21; LNOB = 1.64 +/-.27; OB = 1.58 +/-. 20; white = 1.63 +/-.23; black = 1.58 +/-.24; and Hispanic = 1.65 +/-.25. PAL was related to time spent above 125% BHR and 150% BHR (r =.31,.39). CONCLUSIONS: Physical activity and fitness of normal-weight prepubertal girls predisposed to obesity did not differ from girls without a family history of obesity. obesity, children, energy metabolism, exercise, heart rate monitoring.

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.

Carbohydrate and lipid metabolism in pregnancy: normal compared with gestational diabetes mellitus.

This article reviews maternal metabolic strategies for accommodating fetal nutrient requirements in normal pregnancy and in gestational diabetes mellitus (GDM). Pregnancy is characterized by a progressive increase in nutrient-stimulated insulin responses despite an only minor deterioration in glucose tolerance, consistent with progressive insulin resistance. The hyperinsulinemic-euglycemic glucose clamp technique and intravenous-glucose-tolerance test have indicated that insulin action in late normal pregnancy is 50-70% lower than in nonpregnant women. Metabolic adaptations do not fully compensate in GDM and glucose intolerance ensues. GDM may reflect a predisposition to type 2 diabetes or may be an extreme manifestation of metabolic alterations that normally occur in pregnancy. In normal pregnant women, basal endogenous hepatic glucose production (R(a)) was shown to increase by 16-30% to meet the increasing needs of the placenta and fetus. Total gluconeogenesis is increased in late gestation, although the fractional contribution of total gluconeogenesis to R(a), quantified from (2)H enrichment on carbon 5 of glucose (65-85%), does not differ in pregnant women after a 16-h fast. Endogenous hepatic glucose production was shown to remain sensitive to increased insulin concentration in normal pregnancy (96% suppression), but is less sensitive in GDM (80%). Commensurate with the increased rate of glucose appearance, an increased contribution of carbohydrate to oxidative metabolism has been observed in late pregnancy compared with pregravid states. The 24-h respiratory quotient is significantly higher in late pregnancy than postpartum. Recent advances in carbohydrate metabolism during pregnancy suggest that preventive measures should be aimed at improving insulin sensitivity in women predisposed to GDM. Further research is needed to elucidate the mechanisms and consequences of alterations in lipid metabolism during pregnancy.

Body composition during the first 2 years of life: an updated reference.

Normative body composition during the first 2 y of life was derived from a prospective study of 76 children. We present 1) fat free mass (FFM) and its components, and fat mass (FM), 2) incremental growth rates partitioned into chemical components, and 3) age-specific and gender-specific constants for converting chemical and physical components into FFM for children during the first 2 y of life. A multicomponent model based on measurements of total body water (TBW), total body potassium (TBK) and bone mineral content (BMC) was used to estimate FFM and FM at 0.5, 3, 6, 9, 12, 18, and 24 mo of age. TBW was determined by deuterium dilution, TBK by whole body counting, and BMC by dual energy x-ray absorptiometry. FFM was higher in boys than girls between 0.5-18 mo of age (p < or = 0.05). Percent FM increased on average from 13 to 31% between 0.5 and 3-6 mo, and then gradually declined. Percent FM was significantly higher in girls than in boys at 6 and 9 mo of age (p < or = 0.02). The components of FFM on a percentage basis changed with age (p = 0.001), but not gender. The protein content of FFM increased gradually with age, while TBW declined (p = 0.001). As a percentage of FFM, osseous mineral increased from 2.0 to 3.4% in boys and from 2.1 to 3.3% in girls between 0.5 and 24 mo (p = 0.001). Density and potassium content of FFM increased gradually with age (p = 0.001). These normative body composition data provide an updated reference upon which to assess normal growth and nutritional status of pediatric populations representative of mixed feeding groups during the first 2 y of life.