Physical fitness and academic performance in youth: A systematic review.

Physical fitness (PF) is a construct of health- and skill-related attributes which have been associated with academic performance (AP) in youth. This study aimed to review the scientific evidence on the association among components of PF and AP in children and adolescents. A systematic review of articles using databases PubMed/Medline, ERIC, LILACS, SciELO, and Web of Science was undertaken. Cross-sectional and longitudinal studies examining the association between at least one component of PF and AP in children and adolescents, published between 1990 and June 2016, were included. Independent extraction of articles was carried out by the two authors using predefined data fields. From a total of 45 studies included, 25 report a positive association between components of PF with AP and 20 describe a single association between cardiorespiratory fitness (CRF) and AP. According to the Strengthening the Reporting of Observational Studies in Epidemiology guidelines: 12 were classified as low, 32 as medium risk, and 1 as high risk of bias. Thirty-one studies reported a positive association between AP and CRF, six studies with muscular strength, three studies with flexibility, and seven studies reported a positive association between clustered of PF components and AP. The magnitude of the associations is weak to moderate (ß = 0.10-0.42 and odds = 1.01-4.14). There is strong evidence for a positive association between CRF and cluster of PF with AP in cross-sectional studies; and evidence from longitudinal studies for a positive association between cluster of PF and AP; the relationship between muscular strength and flexibility with AP remains uncertain.

Forage-based dairying in a water-limited future: use of models to investigate farming system adaptation in southern Australia.

The irrigated dairy industry in southern Australia has experienced significant restrictions in irrigation water allocations since 2005, consistent with climate change impact predictions for the region. Simulation models of pasture growth (DairyMod), crop yield (Agricultural Production Systems Simulator, APSIM), and dairy system management and production (UDDER) were used in combination to investigate a range of forage options that may be capable of sustaining dairy business profitability under restricted water-allocation scenarios in northern Victoria, Australia. A total of 23 scenarios were simulated and compared with a base farm system (100% of historical water allocations, grazed perennial ryegrass pasture with supplements; estimated operating surplus $A2,615/ha at a milk price of $A4.14/kg of milk solids). Nine simulations explored the response of the base farm to changes in stocking rate or the implementation of a double cropping rotation on 30% of farm area, or both. Five simulations explored the extreme scenario of dairying without any irrigation water. Two general responses to water restrictions were investigated in a further 9 simulations. Annual ryegrass grazed pasture, complemented by a double cropping rotation (maize grown in summer for silage, followed by either brassica forage crop and annual ryegrass for silage in winter and spring) on 30% of farm area, led to an estimated operating surplus of $A1746/ha at the same stocking rate as the base farm when calving was moved to autumn (instead of late winter, as in the base system). Estimated total irrigation water use was 2.7ML/ha compared with 5.4ML/ha for the base system. Summer-dormant perennial grass plus double cropping (30% of farm area) lifted operating surplus by a further $A100/ha if associated with autumn calving (estimated total irrigation water use 3.1ML/ha). Large shifts in the forage base of dairy farms could sustain profitability in the face of lower, and fluctuating, water allocations. However, changes in other strategic management policies, notably calving date and stocking rate, would be required, and these systems would be more complex to manage. The adaptation scenarios that resulted in the highest estimated operating surplus were those where at least 10 t of pasture or crop DM was grazed directly by cows per hectare per year, resulting in grazed pasture intake of at least 2 t of DM/cow, and at least 60% of all homegrown feed that was consumed was grazed directly.

CD4+ T cells cause multinucleated giant cells to form around Cryptococcus neoformans and confine the yeast within the primary site of infection in the respiratory tract.

The possible mechanisms by which CD4+ T cells prevent the dissemination of Cryptococcus neoformans from the primary site of infection in the respiratory tract were examined. It was found that even before fungicidal mechanisms are fully induced in the lungs, the host generates a CD4+ T cell-dependent inflammatory response that sequesters yeast within the pulmonary alveoli. This confinement is evident histopathologically and demonstrable objectively as a rapid decline in the ability to dislodge yeast from the lungs by bronchopulmonary lavage. One striking component of this response is the enclosure of cryptococci within multinucleated giant cells in granulomas. Studies in severe combined immunodeficient mice that were engrafted with selected lymphocyte subpopulations show that B cells, and hence anti-Cryptococcus antibodies, are not necessary for the CD4+ T cell-dependent responses that isolate and subsequently destroy this opportunistic pathogen in the lung parenchyma.

Intrapulmonary growth and dissemination of an avirulent strain of Cryptococcus neoformans in mice depleted of CD4+ or CD8+ T cells.

The contribution of T lymphocyte subpopulations to intrapulmonary and systemic resistance against an opportunistic strain of Cryptococcus neoformans was examined. It was found that C. neoformans was destroyed when introduced into the lungs of normal mice, but disseminated to the brains of mice treated with an antibody that depleted them of CD4+ T cells. Depletion of either CD8+ or CD4+ T cells impaired the ability of the host to clear the yeast from the lung. These results, together with the observation that CD8+ T cells accumulate in the lungs of CD4+ T cell-deficient mice, suggest that CD8+ T cells play an important role in resistance to C. neoformans infection acquired via the respiratory tract.

Elimination of CD4+ suppressor T cells from susceptible BALB/c mice releases CD8+ T lymphocytes to mediate protective immunity against Leishmania.

This study examined the capacity of BALB/c mice that had been depleted of T cell subpopulations to generate a protective immune response to Leishmania major. Thymectomized mice were depleted of either L3T4+ (CD4+) T lymphocytes, Ly2+ (CD8+) T lymphocytes, or both, by treatment with appropriate mAbs. It was found that susceptible mice were rendered resistant to Leishmania by an intravenous infusion of anti-L3T4 mAb. These mice generated an immune response that destroyed the parasite in the primary lesion and in visceral metastatic foci. CD4+ cell-depleted mice also acquired a capacity to mount a sustained delayed-type hypersensitivity (DTH) response to parasite antigens, indicating that DTH, per se, is not a disease-promoting mechanism in the susceptible murine host as has been suggested. Depleting BALB/c mice of CD8+, as well as CD4+ T cells, left them highly susceptible to Leishmania infection, thereby indicating that CD8+ lymphocytes are key protective cells. Our results can be interpreted as showing that the susceptibility of BALB/c mice is due to the generation of CD4+ cells that suppress either the generation or expression of CD8+ T cell-mediated antiLeishmania immunity.

Weight-loss maintenance in successful weight losers: surgical vs non-surgical methods.

OBJECTIVE: As large weight losses are rarely achieved through any method except bariatric surgery, there have been no studies comparing individuals who initially lost large amounts of weight through bariatric surgery or non-surgical means. The National Weight Control Registry (NWCR) provides a resource for making such unique comparisons. This study compared the amount of weight regain, behaviors and psychological characteristics in NWCR participants who were equally successful in losing and maintaining large amounts of weight through either bariatric surgery or non-surgical methods. DESIGN: Surgical participants (n=105) were matched with two non-surgical participants (n=210) on gender, entry weight, maximum weight loss and weight-maintenance duration, and compared prospectively over 1 year. RESULTS: Participants in the surgical and non-surgical groups reported having lost approximately 56 kg and keeping > or =13.6 kg off for 5.5+/-7.1 years. Both groups gained small but significant amounts of weight from registry entry to 1 year (P=0.034), but did not significantly differ in magnitude of weight regain (1.8+/-7.5 and 1.7+/-7.0 kg for surgical and non-surgical groups, respectively; P=0.369). Surgical participants reported less physical activity, more fast food and fat consumption, less dietary restraint, and higher depression and stress at entry and 1 year. Higher levels of disinhibition at entry and increased disinhibition over 1 year were related to weight regain in both groups. CONCLUSIONS: Despite marked behavioral differences between the groups, significant differences in weight regain were not observed. The findings suggest that weight-loss maintenance comparable with that after bariatric surgery can be accomplished through non-surgical methods with more intensive behavioral efforts. Increased susceptibility to cues that trigger overeating may increase risk of weight regain regardless of initial weight-loss method.

Environmental contributions to the obesity epidemic.

The current epidemic of obesity is caused largely by an environment that promotes excessive food intake and discourages physical activity. Although humans have evolved excellent physiological mechanisms to defend against body weight loss, they have only weak physiological mechanisms to defend against body weight gain when food is abundant. Control of portion size, consumption of a diet low in fat and energy density, and regular physical activity are behaviors that protect against obesity, but it is becoming difficult to adopt and maintain these behaviors in the current environment. Because obesity is difficult to treat, public health efforts need to be directed toward prevention.

Ion binding by synthetic macrocyclic compounds.

The existence of synthetic macrocyclic molecules with hydrophilic cavities containing multiple binding atoms and with hydrophobic exteriors gives rise to extraordinary possibilities with respect to the design and synthesis of molecules with specific cation and anion binding properties. The preparation of many new macrocyclic compounds has recently been reported, but few practical applications for them have been suggested. From the information available, it is becoming clear that it should be possible to synthesize macrocycles that will have specified, or selected, ion binding properties. Cavity size can be varied to accommodate only those cations or anions within a specified narrow band of sizes. Numbers and types of coordinating atoms can be chosen to give essentially electrostatic or covalent bonding or a combination of the two in a metalmacrocycle complex. The metal ligand bond appears to be predominantly ionic in the case of the cyclic polyethers but the covalent character increases on substitution of sulfur or nitrogen for oxygen donor atoms. The essential hydrophobic exteriors of the macrocycles can be modified by the addition of side chains and groups to facilitate the solution of anions and cations in organic solvents. The structures of many macrocycles can be made to approximate naturally occurring molecules, that is, cyclic polyethers similar to macrocyclic antibiotics of the valinomycin and nonactin types and cyclic polyamines similar to porphyrins. Macrocycles are also useful as model compounds for the study of metal interactions with biological systems. The synthetic macrocycles thus represent an intriguing new area of coordination chemistry, the systematic study of which should lead to many interesting and useful chemical applications in the field of metal complexation in solution.

PROCEED: Prospective Obesity Cohort of Economic Evaluation and Determinants: baseline health and healthcare utilization of the US sample.

AIM: To summarize baseline characteristics, health conditions, resource utilization and resource cost for the US population for the 90-day period preceding enrolment, stratified by body mass index (BMI) and the presence of abdominal obesity (AO). METHODS: PROCEED (Prospective Obesity Cohort of Economic Evaluation and Determinants) is a multinational, prospective cohort of control (BMI 20-24.0 kg/m(2)), overweight (BMI 25-29.9 kg/m(2)) and obese (BMI >or= 30 kg/m(2)) subjects with AO and without AO [non-abdominal obesity (NAO)], defined by waist circumference (WC) >102 and 88 cm for males and females, respectively. Subjects were recruited from an Internet consumer panel. Outcomes were self-reported online. Self-reported anthropometric data were validated. Prevalence of conditions and utilization is presented by BMI class and AO within BMI class. Differences in prevalence and means were evaluated. RESULTS: A total of 1067 overweight [n = 474 (NAO: n = 254 and AO: n = 220)] and obese [n = 493 (NAO: n = 39 and AO: n = 454)] subjects and 100 controls were recruited. Self-reported weight (r = 0.92) and WC (r = 0.87) were correlated with measured assessments. Prevalence of symptoms was significantly higher in groups with higher BMI, as were hypertension (p < 0.0001), diabetes (p < 0.0001) and sleep apnoea (p < 0.0001). Metabolic risk factors increased with the BMI class. Among the overweight class, subjects with AO had significantly more reported respiratory, heart, nervous, skin and reproductive system symptoms. Overweight subjects with AO reported a significantly higher prevalence of diabetes (13%) compared with overweight subjects with NAO (7%, p = 0.04). Mean healthcare cost was significantly higher in the higher BMI classes [control ($456 +/- 937) vs. overweight ($1084 +/- 3531) and obese ($1186 +/- 2808) (p < 0.0001)]. CONCLUSION: An increasing gradient of symptoms, medical conditions, metabolic risk factors and healthcare utilization among those with a greater degree of obesity was observed. The independent effect of AO on health and healthcare utilization deserves further study with a larger sample size.

Effects of consuming a high-protein diet with or without soy protein during weight loss and maintenance: a non-inferiority, randomized clinical efficacy trial.

OBJECTIVE: This 12-month randomized, non-inferiority clinical trial sought to determine the impact of consuming soy protein as part of an energy-restricted, high-protein diet on weight loss, body composition and cardiometabolic health. METHODS: Seventy-one adults (58 female) with overweight or obesity (body mass index: 32.9 ± 3.6 kg m-2) were randomly assigned to consume three servings of soy (S) or non-soy (NS) protein foods per day for 12 months. All participants completed a group-based behavioural weight loss program lasting 4 months (M4), and follow-up assessments were completed at month 12 (M12). RESULTS: Body weight was reduced in both groups at M4 (S: -7.0% ± 5.2%, NS: -7.1% ± 5.7%) and M12 (S: 3.6% ± 5.1%, NS: -4.8% ± 7.3%). Body weight reductions (mean difference [90% confidence interval]) were not different between S and NS at either time point (M4: -0.16% [-1.4, 3.6], P = 0.90; M12: 1.1% [-1.4, 3.6], P = 0.44). Differences in body fat mass loss were not different between S and NS at M4 (0.29 ± 0.84 kg, P = 0.73) or M12 (0.78 ± 1.5 kg, P = 0.59). Weight loss-induced improvements in cholesterol, triglycerides and blood pressure did not differ between S and NS. CONCLUSION: These results indicate that soy-based protein foods can be effectively incorporated into an energy-restricted, high-protein diet for improving body weight, body composition and cardiometabolic health.

Is regular exercise an effective strategy for weight loss maintenance?

Weight regain after weight loss is one of the most significant challenges to successful obesity treatment. Regular exercise has long been touted as a strategy for weight loss maintenance, but the lack of clear evidence in clinical trials has caused some to question its effectiveness. In this review, we present the arguments both questioning and in support of exercise as an obesity therapeutic. Our purpose is to bring clarity to the literature, present a unified perspective, and identify the gaps in knowledge that need to be addressed in future studies. Critical questions remain including sex differences, individual variability and compensatory behaviors in response to exercise, exercise adherence, the role of energy flux and the molecular mechanisms mediating the beneficial effects of exercise after weight loss and during weight regain. Future research should focus on these critical questions to provide a more complete understanding of the potential benefits of exercise on weight loss maintenance.

The role of public policy in treating the epidemic of global obesity.

Given the powerful forces promoting population weight gain, the obesity epidemic cannot be reversed solely by promoting individual behavior change. Policy initiatives might lessen the impact of the biological and economical forces promoting weight gain or provide motivation to resist these forces. Unfortunately, there is little information to adequately evaluate the many policies that have been suggested. The intent of this review is to discuss the potential use of policy to stem the global epidemic of obesity.

The association between obesity and academic performance in youth: a systematic review.

Previous studies have found that obesity could influence academic performance. The aim of this study was to systematically review the scientific evidence on the association between obesity and academic performance in school children. A systematic review of English articles was undertaken by using databases PubMed/Medline, ERIC, LILACS, SciELO and Web of Science. Cross-sectional and longitudinal studies examining the association between obesity and academic performance in children and adolescents, published between January 1990 and December 2016, were included. Risk of bias was assessed by using Strengthening the Reporting of Observational Studies in Epidemiology. Thirty-four studies (23 cross-sectional and 11 longitudinal) matched all inclusion criteria and were included. Seven studies were classified as low risk of bias, 23 as medium risk and four as high risk. After controlling for covariates such as socio-economic status, parental education and physical activity, the association between obesity and academic performance becomes uncertain for most of the studies (55.9%). Therefore, at present, there is insufficient evidence to support a direct link between obesity and poor academic performance in school age children. In order to clarify this issue, we need more longitudinal studies with adequate sample sizes and that control for potential confounders.

The association of change in physical activity and body weight in the regulation of total energy expenditure.

BACKGROUND/OBJECTIVES: The limited success in addressing the current obesity epidemic reflects the insufficient understanding of the regulation of energy balance. The present study examines the longitudinal association of body weight with physical activity (PA), total daily energy expenditure (TDEE) and total daily energy intake (TDEI). SUBJECTS/METHODS: A total of 195 adults (52% male) between 21 and 35 years of age with no intention for weight loss were followed over a 2-year period. Body weight, fat mass and fat-free mass were measured every 3 months. Participants were stratified into three groups based on change in body weight using a 5% cutpoint. TDEE and time spent in different PA intensities were determined via a multisensor device at each measurement time. TDEI was calculated based on change in body composition and TDEE. RESULTS: At 2-year follow-up, 57% of the participants maintained weight, 14% lost weight and 29% gained weight. Average weight change was -6.9±3.4 and 7.1±3.6 kg in the weight-loss and weight-gain groups, respectively. Average TDEE and TDEI did not change significantly in any weight change group (P>0.16). Moderate-to-vigorous PA, however, increased significantly in the weight-loss group (35±49 min/day; P<0.01) and decreased in the weight-gain group (-35±46 min/day; P<0.01). CONCLUSIONS: Results of this observational study indicate an inverse association between body weight and PA to maintain a stable TDEE and allow for a stable TDEI over time. Sufficient PA levels, therefore, are an important contributor to weight loss maintenance.

Equivalent reductions in body weight during the Beef WISE Study: beef's role in weight improvement, satisfaction and energy.

OBJECTIVE: The objective of this randomized equivalence trial was to determine the impact of consuming lean beef as part of a high protein (HP) weight-reducing diet on changes in body weight, body composition and cardiometabolic health. METHODS: A total of 120 adults (99 female) with overweight or obesity (BMI: 35.7 ± 7.0 kg m-2) were randomly assigned to consume either a HP diet with ≥4 weekly servings of lean beef (B; n = 60) or a HP diet restricted in all red meats (NB; n = 60) during a 16-week weight loss intervention. RESULTS: Body weight was reduced by 7.8 ± 5.9% in B and 7.7 ± 5.5% in NB (p < 0.01 for both). Changes in percent body weight were equivalent between B and NB (mean difference: 0.06%, 90% confidence interval: (-1.7, 1.8)). Fat mass was reduced in both groups (p < 0.01; B: 8.0 ± 0.6 kg, NB: 8.6 ± 0.6 kg), while lean mass was not reduced in either group. Improvements in markers of cardiometabolic health (total cholesterol, low-density lipoprotein cholesterol, triglycerides and blood pressure) were not different between B and NB. CONCLUSION: Results of this study demonstrate that HP diets - either rich or restricted in red meat intakes - are effective for decreasing body weight and improving body composition and cardiometabolic health.

Model for predicting and phenotyping at normal weight the long-term propensity for obesity in Sprague-Dawley rats.

Tests were conducted to determine whether weight gain or nutrient intake measures during the first week of exposure to a macronutrient diet can accurately predict an animal's long-term propensity towards obesity. In multiple groups of normal-weight Sprague-Dawley rats (n=35-70/group), daily weight gain during the first 5 days on a high-fat diet (45-60% fat) was found to be strongly, positively correlated (r=+0.71 to r=+0.82) with accumulated body fat in 4 dissected depots after 4-6 weeks on the diet. This measure consistently identified obesity-prone (OP) rats which, relative to the obesity-resistant (OR) rats, were only slightly heavier (+15 g, 4%) and hyperphagic (+9 kcal, 8%) after 5 days but markedly heavier (+70g) with up to 2-fold greater fat mass after several weeks on the diet. Other dietary conditions and measures revealed weaker relationships to ultimate body fat accrual. The OP rats identified by their 5-day weight-gain score exhibited at this early stage clear disturbances characteristic of markedly obese rats. These included elevated leptin, insulin, triglycerides and glucose, along with increased lipoprotein lipase activity (LPL) in adipose tissue and galanin expression in the paraventricular nucleus. Most notable were significant reductions in muscle of LPL activity and ratio of beta-hydroxyacyl-CoA dehydrogenase to citrate synthase activity, indicating a decline in lipid transport and capacity of muscle to metabolize lipids. By occurring early with initial weight gain, these hypothalamic and metabolic disturbances in OP rats, favoring fat storage in adipose tissue over fat oxidation in muscle, may have causal relationships to long-term accumulation of body fat.

Initial weight loss goals: have they changed and do they matter?

OBJECTIVE: Nearly 20 years ago, participants in behavioural weight loss programmes reported goals that greatly exceeded the amount of weight typically produced by these programmes. Whether having unrealistic weight loss goals impacts weight loss or attrition is unclear. The intent of the current study was to revisit current weight loss goals and examine whether goals impact outcomes. METHODS: Adults (N = 308, BMI = 33.7 ± 4.2 kg/m2) participated in a 12-month behavioural weight management programme and completed questionnaires about their goals. RESULTS: Participants' weight loss goal was 19.8 ± 7.9% of their body weight, and 90.4% selected a goal ≥10%. Weight goals were not associated with weight loss at 3 (p = 0.75) or 12 months (p = 0.47), or from 3 to 12 months (p = 0.55). Weight loss goals were not related to attrition at 3 (p = 0.91) or 12 months (p = 0.86). Participants believed that weight reduction would positively impact their health and psychosocial functioning. CONCLUSION: Weight loss goals have decreased, but still greatly exceed what can be expected by most. Unrealistic goals, however, had no impact on weight loss or attrition. These results question the utility of counseling people with obesity to set more realistic weight loss goals, which is typically practiced in behavioural weight management.

The effects of experimentally manipulated social status on acute eating behavior: A randomized, crossover pilot study.

Both subjective and objectively measured social status has been associated with multiple health outcomes, including weight status, but the mechanism for this relationship remains unclear. Experimental studies may help identify the causal mechanisms underlying low social standing as a pathway for obesity. Our objective was to investigate the effects of experimentally manipulated social status on ad libitum acute dietary intakes and stress-related outcomes as potential mechanisms relating social status and weight. This was a pilot feasibility, randomized, crossover study in Hispanic young adults (n=9; age 19-25; 67% female; BMI ≥18.5 and ≤30kg/m(2)). At visit 1, participants consumed a standardized breakfast and were randomized to a high social status position (HIGH) or low social status position (LOW) in a rigged game of Monopoly™. The rules for the game differed substantially in terms of degree of 'privilege' depending on randomization to HIGH or LOW. Following Monopoly™, participants were given an ad libitum buffet meal and energy intakes (kcal) were estimated by pre- and post-weighing foods consumed. Stress-related markers were measured at baseline, after the game of Monopoly™, and after lunch. Visit 2 used the same standardized protocol; however, participants were exposed to the opposite social status condition. When compared to HIGH, participants in LOW consumed 130 more calories (p=0.07) and a significantly higher proportion of their daily calorie needs in the ad libitum buffet meal (39% in LOW versus 31% in HIGH; p=0.04). In LOW, participants reported decreased feelings of pride and powerfulness following Monopoly™ (p=0.05) and after their lunch meal (p=0.08). Relative to HIGH, participants in LOW demonstrated higher heart rates following Monopoly™ (p=0.06), but this relationship was not significant once lunch was consumed (p=0.31). Our pilot data suggest a possible causal relationship between experimentally manipulated low social status and increased acute energy intakes in Hispanic young adults, potentially influenced by decreased feelings of pride and powerfulness. Increased energy intake over time, resulting in positive energy balance, could contribute to increased risk for obesity, which could partially explain the observed relationship between low social standing and higher weight. Larger and longitudinal studies in a diverse sample need to be conducted to confirm findings, increase generalizability, and assess whether this relationship persists over time.

Modulation of the pattern of development of experimental disseminated leishmaniasis by Corynebacterium parvum.

BALB/c mice are extremely susceptible to Leishmania major. In this mouse strain, the parasite multiplies progressively and rapidly disseminates to distant visceral and cutaneous sites. The present studies show, however, that if BALB/c mice are infected with the L major as an admixture with formalin-killed Corynebacterium parvum, they rapidly acquire the capacity to restrain the multiplication of the parasite at the site of inoculation, and prevent its dissemination to distant visceral sites. Moreover, admixture-treated mice subsequently develop systemic resistance to reinfection. Although the ability of C parvum to activate nonspecific microbicidal mechanisms of macrophages may be involved, the requirement that the adjuvant be given with the parasite inoculum is interpreted to suggest that C parvum facilitates the development of a protective immune response to the parasite.

Gender and Tanner stage differences in body composition and insulin sensitivity in early pubertal children.

A cross-sectional analysis examining the impact of gender and early pubertal stage on insulin sensitivity (Si) and body composition was carried out as part of a longitudinal study to determine how Si relates to body composition changes during puberty. The study population consisted of 97 healthy children (age range, 9.7-14.5 yr; 28 Tanner stage 2 boys, 25 stage 3 boys, 22 Tanner stage 2 girls, and 22 stage 3 girls). Si was determined by the modified minimal model of Bergman. Body fatness was assessed by body mass index (BMI), skinfold thickness, hydrodensitometry, and bioelectrical impedance. Results showed that stage 3 girls and stage 2 boys had significantly more body fat than stage 2 girls and stage 3 boys. Si was significantly lower (P < 0.02) and insulin-like growth factor-I levels higher (P < 0.006) in stage 3 girls compared to those in the other 3 groups. The best predictor of Si in all subjects was BMI (r2 = -0.63; P < 0.0001). In a stepwise multiple regression analysis, Si was best predicted from BMI, gender, and Tanner stage. According to this model, Si decreased as BMI increased and was lower in girls and Tanner stage 3 children. In boys, Si was best predicted from total fat mass and Tanner stage. In girls, Si correlated inversely with BMI, parental obesity, and insulin-like growth factor-I levels. Neither testosterone nor estradiol levels were associated with Si. These results demonstrate that Si, like body composition, has gender-dependent changes during puberty. It is, thus, possible that these pubertal changes in Si relate to changes in body composition.