Generational trends in the transition to womanhood in lowland rural Nepal: Changes in the meaning of early marriage.

OBJECTIVE: In South Asia, studies show secular trends toward slightly later women's marriage and first reproduction. However, data on related biological and social events, such as menarche and age of coresidence with husband, are often missing from these analyses. We assessed generational trends in key life events marking the transition to womanhood in rural lowland Nepal. METHODS: We used data on 110 co-resident mother-in-law (MIL) and daughter-in-law (DIL) dyads. We used paired t-tests and chi-squared tests to evaluate generational trends in women's education, and mean age at menarche, marriage, cohabitation with husband, and first reproduction of MIL and DIL dyads. We examined norms held by MILs and DILs on a daughter's life opportunities. RESULTS: On average, MIL was 29 years older than DIL (60 years vs. 31 years). Both groups experienced menarche at average age 13.8 years. MIL was married at average 12.4 years, before menarche, and cohabitated with husbands at average 14.8 years. DIL was simultaneously married and cohabitated with husbands after menarche, at average 15 years. DIL was marginally more educated than MIL but had their first child on average 0.8 years earlier (95% CI -1.4, -0.1). MIL and DIL held similar norms on daughters' education and marriage. CONCLUSION: While social norms remain similar, the meaning of "early marriage" and use of menarche in marriage decisions has changed in rural lowland Nepal. Compared to DIL, MIL who was married earlier transitioned to womanhood more gradually. However, DIL was still married young, and had an accelerated trajectory to childbearing.

Patterns of childhood body mass index (BMI), overweight and obesity in South Asian and black participants in the English National child measurement programme: effect of applying BMI adjustments standardising for ethnic differences in BMI-body fatness associations.

BACKGROUND: The National Child Measurement Programme (NCMP) records weight and height and assesses overweight-obesity patterns in English children using body mass index (BMI), which tends to underestimate body fatness in South Asian children and overestimate body fatness in Black children of presumed African ethnicity. Using BMI adjustments to ensure that adjusted BMI was similarly related to body fatness in South Asian, Black and White children, we reassessed population overweight and obesity patterns in these ethnic groups in NCMP. METHODS: Analyses were based on 2012-2013 NCMP data in 582 899 children aged 4-5 years and 485 362 children aged 10-11 years. Standard centile-based approaches defined weight status in each age group before and after applying BMI adjustments for English South Asian and Black children derived from previous studies using the deuterium dilution method. FINDINGS: Among White children, overweight-obesity prevalences (boys, girls) were 23% and 21%, respectively, in 4-5 year olds and 33% and 30%, respectively, in 10-11 year olds. Before adjustment, South Asian children had lower overweight-obesity prevalences at 4-5 years (19%, 19%) and slightly higher prevalences at 10-11 years (42%, 34%), whereas Black children had higher overweight-obesity prevalences both at 4-5 years (31%, 29%) and 10-11 years (42%, 45%). Following adjustment, overweight-obesity prevalences were markedly higher in South Asian children both at 4-5 years (39%, 35%) and at 10-11 years (52%, 44%), whereas Black children had lower prevalences at 4-5 years (11%, 12%); at 10-11 years, prevalences were slightly lower in boys (32%) but higher in girls (35%). INTERPRETATION: BMI adjustments revealed extremely high overweight-obesity prevalences among South Asian children in England, which were not apparent in unadjusted data. In contrast, after adjustment, Black children had lower overweight-obesity prevalences except among older girls. FUNDING: British Heart Foundation, NIHR CLAHRC (South London), NIHR CLAHRC (North Thames).

Body mass index adjustments to increase the validity of body fatness assessment in UK Black African and South Asian children.

BACKGROUND/OBJECTIVES: Body mass index (BMI) (weight per height2) is the most widely used marker of childhood obesity and total body fatness (BF). However, its validity is limited, especially in children of South Asian and Black African origins. We aimed to quantify BMI adjustments needed for UK children of Black African and South Asian origins so that adjusted BMI related to BF in the same way as for White European children. METHODS: We used data from four recent UK studies that made deuterium dilution BF measurements in UK children of White European, South Asian and Black African origins. A height-standardized fat mass index (FMI) was derived to represent BF. Linear regression models were then fitted, separately for boys and girls, to quantify ethnic differences in BMI-FMI relationships and to provide ethnic-specific BMI adjustments. RESULTS: We restricted analyses to 4-12 year olds, to whom a single consistent FMI (fat mass per height5) could be applied. BMI consistently underestimated BF in South Asians, requiring positive BMI adjustments of +1.12 kg m-2 (95% confidence interval (CI): 0.83, 1.41 kg m-2; P<0.0001) for boys and +1.07 kg m-2 (95% CI: 0.74, 1.39 kg m-2; P<0.0001) for girls of all age groups and FMI levels. BMI overestimated BF in Black Africans, requiring negative BMI adjustments for Black African children. However, these were complex because there were statistically significant interactions between Black African ethnicity and FMI (P=0.004 boys; P=0.003 girls) and also between FMI and age group (P<0.0001 for boys and girls). BMI adjustments therefore varied by age group and FMI level (and indirectly BMI); the largest adjustments were in younger children with higher unadjusted BMI and the smallest in older children with lower unadjusted BMI. CONCLUSIONS: BMI underestimated BF in South Asians and overestimated BF in Black Africans. Ethnic-specific adjustments, increasing BMI in South Asians and reducing BMI in Black Africans, can improve the accuracy of BF assessment in these children.

Body shape and size in 6-year old children: assessment by three-dimensional photonic scanning.

BACKGROUND: Body shape and size are typically described using measures such as body mass index (BMI) and waist circumference, which predict disease risks in adults. However, this approach may underestimate the true variability in childhood body shape and size. OBJECTIVE: To use a comprehensive three-dimensional photonic scan approach to describe variation in childhood body shape and size. SUBJECTS/METHODS: At age 6 years, 3350 children from the population-based 2004 Pelotas birth cohort study were assessed by three-dimensional photonic scanner, traditional anthropometry and dual X-ray absorptiometry. Principal component analysis (PCA) was performed on height and 24 photonic scan variables (circumferences, lengths/widths, volumes and surface areas). RESULTS: PCA identified four independent components of children's body shape and size, which we termed: Corpulence, Central:peripheral ratio, Height and arm lengths, and Shoulder diameter. Corpulence showed strong correlations with traditional anthropometric and body composition measures (r>0.90 with weight, BMI, waist circumference and fat mass; r>0.70 with height, lean mass and bone mass); in contrast, the other three components showed weak or moderate correlations with those measures (all r<0.45). There was no sex difference in Corpulence, but boys had higher Central:peripheral ratio, Height and arm lengths and Shoulder diameter values than girls. Furthermore, children with low birth weight had lower Corpulence and Height and arm lengths but higher Central:peripheral ratio and Shoulder diameter than other children. Children from high socio-economic position (SEP) families had higher Corpulence and Height and arm lengths than other children. Finally, white children had higher Corpulence and Central:peripheral ratio than mixed or black children. CONCLUSIONS: Comprehensive assessment by three-dimensional photonic scanning identified components of childhood body shape and size not captured by traditional anthropometry or body composition measures. Differences in these novel components by sex, birth weight, SEP and skin colour may indicate their potential relevance to disease risks.

Height, adiposity and hormonal cardiovascular risk markers in childhood: how to partition the associations?

OBJECTIVE: Obesity is associated with rapid growth during childhood. There is uncertainty over how to adjust for body size, when using adiposity as a proxy for cardiovascular risk. We studied associations of height, body composition (by dual-energy X-ray absorptiometry) and cardiovascular risk markers (insulin resistance (IR), leptin) in children. METHODS: Using partial correlations in 172 children aged 7-12 years, we investigated associations of (a) fat mass with IR or leptin, adjusting for height or lean mass, and (b) height or lean mass with IR or leptin, adjusting for fat mass. Analyses were conducted both cross-sectionally at each age, and for changes between 7 and 12 years. RESULTS: Height, fat mass, lean mass, IR and leptin were all inter-correlated at all ages. Although fat mass was strongly associated with IR and leptin, height was independently negatively associated with leptin (whole sample, adjusting for age: boys r=-0.12, girls r=-0.13; P<0.001). Independent of adiposity, height was also associated with insulin IR (whole sample, adjusting for age: boys r=0.11, girls r=0.20; P<0.001). When analysed by year of age, these associations tended to remain significant at older ages. Change in height from 7 to 12 years was also associated with change in IR (boys: r=0.18, P<0.05; girls: r=0.34, P<0.01), independently of change in adiposity, with similar findings for lean mass. CONCLUSIONS: During childhood, markers of cardiovascular risk have a complex profile, associated with growth as well as fat accumulation. Taller and faster-growing children have elevated risk markers, independently of their adiposity. These findings have implications for the interpretation of pediatric indices of adiposity that aim to adjust for body size. Adiposity indices that perform best at summarizing metabolic risk may not be those that perform best at understanding the developmental aetiology of risk.

Adjustment of directly measured adipose tissue volume in infants.

BACKGROUND: Direct measurement of adipose tissue (AT) using magnetic resonance imaging is increasingly used to characterise infant body composition. Optimal techniques for adjusting direct measures of infant AT remain to be determined. OBJECTIVES: To explore the relationships between body size and direct measures of total and regional AT, the relationship between AT depots representing the metabolic load of adiposity and to determine optimal methods of adjusting adiposity in early life. DESIGN: Analysis of regional AT volume (ATV) measured using magnetic resonance imaging in longitudinal and cross-sectional studies. SUBJECTS: Healthy term infants; 244 in the first month (1-31 days), 72 in early infancy (42-91 days). METHODS: The statistical validity of commonly used indices adjusting adiposity for body size was examined. Valid indices, defined as mathematical independence of the index from its denominator, to adjust ATV for body size and metabolic load of adiposity were determined using log-log regression analysis. RESULTS: Indices commonly used to adjust ATV are significantly correlated with body size. Most regional AT depots are optimally adjusted using the index ATV/(height)(3) in the first month and ATV/(height)(2) in early infancy. Using these indices, height accounts for<2% of the variation in the index for almost all AT depots. Internal abdominal (IA) ATV was optimally adjusted for subcutaneous abdominal (SCA) ATV by calculating IA/SCA(0.6). CONCLUSIONS: Statistically optimal indices for adjusting directly measured ATV for body size are ATV/height(3) in the neonatal period and ATV/height(2) in early infancy. The ratio IA/SCA ATV remains significantly correlated with SCA in both the neonatal period and early infancy; the index IA/SCA(0.6) is statistically optimal at both of these ages.

Shifts in population dietary patterns and physical inactivity as determinants of global trends in the prevalence of diabetes: an ecological analysis.

BACKGROUND AND AIMS: The worldwide epidemiology of diabetes is rapidly changing as a result of the spreading of westernised nutritional and lifestyle habits. We conducted an ecological analysis to identify dietary, lifestyle and socio-economic factors associated with global diabetes prevalence. METHODS AND RESULTS: Country-specific estimates of diabetes prevalence were obtained. Data were then matched to year- and country-specific food and energy availability for consumption, and to year-specific information on obesity, physical inactivity, urbanisation, gross domestic product (GDP), and smoking. Data were obtained from publicly available databases compiled by the Food Agricultural Organisation (FAO), World Health Organisation (WHO) and World Bank. Cluster analysis was used to derive dietary patterns of global food consumption. The association with diabetes prevalence was evaluated. Stepwise multiple regression analysis was conducted to identify predictors associated with worldwide diabetes prevalence. 96 countries were eligible for inclusion in the analysis. The average diabetes prevalence was 7.0% and the highest rate was observed in the Middle-Eastern region (13.1%). The worldwide prevalence of obesity and physical inactivity was 15.1% and 36.1%, respectively. Diabetes prevalence was associated with age and physical inactivity prevalence in a fully adjusted multiple regression model. Three dietary patterns (agricultural, transitional and westernised) were identified by the cluster analysis. Diabetes prevalence showed a direct dose-response association with the degree of exposure to a westernised dietary pattern. CONCLUSIONS: The adoption of sedentary lifestyle and westernised dietary patterns appears to be closely linked to the global rise in diabetes prevalence.

There is an obstetrical dilemma: Misconceptions about the evolution of human childbirth and pelvic form.

Compared to other primates, modern humans face high rates of maternal and neonatal morbidity and mortality during childbirth. Since the early 20th century, this "difficulty" of human parturition has prompted numerous evolutionary explanations, typically assuming antagonistic selective forces acting on maternal and fetal traits, which has been termed the "obstetrical dilemma." Recently, there has been a growing tendency among some anthropologists to question the difficulty of human childbirth and its evolutionary origin in an antagonistic selective regime. Partly, this stems from the motivation to combat increasing pathologization and overmedicalization of childbirth in industrialized countries. Some authors have argued that there is no obstetrical dilemma at all, and that the difficulty of childbirth mainly results from modern lifestyles and inappropriate and patriarchal obstetric practices. The failure of some studies to identify biomechanical and metabolic constraints on pelvic dimensions is sometimes interpreted as empirical support for discarding an obstetrical dilemma. Here we explain why these points are important but do not invalidate evolutionary explanations of human childbirth. We present robust empirical evidence and solid evolutionary theory supporting an obstetrical dilemma, yet one that is much more complex than originally conceived in the 20th century. We argue that evolutionary research does not hinder appropriate midwifery and obstetric care, nor does it promote negative views of female bodies. Understanding the evolutionary entanglement of biological and sociocultural factors underlying human childbirth can help us to understand individual variation in the risk factors of obstructed labor, and thus can contribute to more individualized maternal care.

Body shape by 3-D photonic scanning in Thai and UK adults: comparison of national sizing surveys.

BACKGROUND: Body mass index (BMI) cut-offs associated with increased risk of diabetes and cardiovascular disease differ between European and Asian populations, and among Asian populations. Within-population and ethnic variability in body shape has likewise been linked with variability in cardiovascular risk in western settings. OBJECTIVES: To explore differences between Thai and White UK adults in body shape and its associations with height, age and BMI. METHODS: Data on weight and body shape by 3-D photonic scanning from National Sizing Surveys of UK (3542 men, 4130 women) and Thai (5889 men, 6499 women) adults aged 16-90 years, using a common protocol and methodology, were analysed. RESULTS: Thai adults in both sexes had significantly smaller body girths than UK adults after adjusting for age and height. Matching for BMI, and adjusting for height and age, Thais in both sexes tended to have similar or greater limb girths, but significantly smaller torso girths (especially waist and hip) than UK individuals. These results were replicated within narrow BMI bands at ∼20 and ∼25 kg m(-2). Shape-age associations also differed between the populations. DISCUSSION: Young Thai adults have a significantly slighter physique than White UK adults, with a less central distribution of body weight. However these differences reduce with age, especially in males. The 3-D photonic scanning provides detailed digital anthropometric data capable of monitoring between- and within-individual shape variability. The technology merits further application to investigate whether variability in body shape is more sensitive to metabolic risk than BMI within and between-populations.

Maternal and infant factors associated with neonatal adiposity: results from the Tasmanian Infant Health Survey (TIHS).

OBJECTIVE: To examine the maternal and neonatal factors associated with offspring adiposity and the role of birth and placental weight as potential mediators in such associations. DESIGN: The Tasmanian Infant Health Survey was a prospective cohort study conducted between 1988 and 1995 in Australia to investigate the cause of Sudden Infant Death Syndrome. This large infant cohort provides measurement of skinfolds on 7945 mothers and their offspring. SUBJECTS: Participants included singletons born ≥37 weeks gestation who were at high risk of sudden infant death syndrome identified through a composite score that included birth weight, maternal age, neonatal gender, season of birth, duration of second-stage labor and intention to breastfeed. MEASUREMENTS: Neonatal adiposity was assessed from skinfold measurements of the subscapular (SSF) and triceps folds (TSF) taken at birth. Maternal early-pregnancy body mass index (BMI) was calculated from self-reported height and weight. Neonatal data were extracted from birth records. Data relating to other environmental exposures were obtained from questionnaires administered when neonates were ∼4-days old. RESULTS: In multivariable models, higher maternal adiposity, increasing maternal age, gestation age, delivery by Caesarian section and female gender were associated with larger SSF independent of placental and birth weight (P<0.001). Maternal age and delivery by Caesarian section were significantly associated with larger TSF, whereas gestational age and male gender were associated with thinner TSF independent of placental and birth weight. Higher early-pregnancy BMI, maternal weight gain, maternal age, parity and gestational age were significantly associated with larger placental and birth weight. Smoking during pregnancy was associated with smaller birth weight but not with placental weight. CONCLUSION: In addition to birth weight, maternal adiposity and placental weight were important additional factors associated with neonatal adiposity.

Family-based behavioural treatment of childhood obesity in a UK National Health Service setting: randomized controlled trial.

BACKGROUND: The best outcomes for treating childhood obesity have come from comprehensive family-based programmes. However there are questions over their generalizability. OBJECTIVE: To examine the acceptability and effectiveness of 'family-based behavioural treatment' (FBBT) for childhood obesity in an ethnically and socially diverse sample of families in a UK National Health Service (NHS) setting. METHODS: In this parallel group, randomized controlled trial, 72 obese children were randomized to FBBT or a waiting-list control. Primary outcomes were body mass index (BMI) and BMI s.d. scores (SDSs). Secondary outcomes were weight, weight SDSs, height, height SDSs, waist, waist SDSs, FM index, FFM index, blood pressure (BP) and psychosocial measures. The outcomes were assessed at baseline and after treatment, with analyses of 6-month data performed on an intent-to-treat (ITT) basis. Follow-up anthropometric data were collected at 12 months for the treatment group. RESULTS: ITT analyses included all children with baseline data (n=60). There were significant BMI SDS changes (P<0.01) for the treatment and control groups of -0.11 (0.16) and -0.10 (1.6). The treatment group showed a significant reduction in systolic BP (-0.24 (0.7), P<0.05) and improvements in quality of life and eating attitudes (P<0.05), with no significant changes for the control group. However the between-group treatment effects for BMI, body composition, BP and psychosocial outcomes were not significant. There was no overall change in BMI or BMI SDSs from 0-12 months for the treatment group. No adverse effects were reported. CONCLUSIONS: Both treatment and control groups experienced significant reductions in the level of overweight, but with no significant difference between them. There were no significant group differences for any of the secondary outcomes. This trial was registered at http://www.controlled-trials.com/ under ISRCTN 51382628.

Prenatal and postnatal programming of body composition in obese children and adolescents: evidence from anthropometry, DXA and the 4-component model.

BACKGROUND: Low-birth weight has been proposed to programme central adiposity in childhood. However, there is little information on associations between fetal weight gain and fat distribution within obese individuals. OBJECTIVES: To investigate associations between birth weight and postnatal weight gain with body composition in a sample of obese children and adolescents. SUBJECTS AND METHODS: Body composition was measured using anthropometry, dual-emission X-ray absorptiometry and the 4-component model in 45 male and 76 female obese individuals aged 5-22 years. General linear models were used to investigate associations between birth weight standard deviation score (SDS), or change in weight SDS between birth and follow-up, and body composition, adjusting for age, pubertal status, height and gender. RESULTS: Birth weight SDS ranged from -1.86 to 3.46, and was inversely associated with current weight SDS after adjustment for height SDS. Birth weight SDS was weakly associated with waist and hip girths, but not waist-hip ratio or trunk fat, after adjusting for age, height, pubertal status and gender. Change in weight SDS was strongly associated with total and central adiposity. CONCLUSIONS: Despite incorporating substantial variability, birth weight SDS was only a weak predictor of tissue masses and their distribution in obese children. Variability in central adiposity was more strongly associated with the magnitude of postnatal growth, which in turn was weakly inversely associated with birth weight SDS. In a population uniformly characterised by excess body weight, postnatal weight gain exerted the dominant impact on adiposity and fat distribution.

Digit ratio (2D:4D) and rowing ergometer performance in males and females.

Fetal and adult testosterone may be vital in the establishment and maintenance of sex-dependent abilities associated with male physical competitiveness. It has been shown that digit ratio (2D:4D) is negatively associated with prenatal testosterone, and it is also negatively associated with ability in sports such as football, skiing, middle distance running, and endurance running, which are dependent upon an efficient cardiovascular system. The relationship between digit ratio and sports requiring high power (physical strength) output in addition to well-developed cardiovascular systems has not been defined. This study investigated this association in male and female young adult rowers. Participants (77 male and 70 female) were student rowers encompassing a range of abilities from the University of Cambridge. Bilateral digit measurements were taken blind from each subject using Mitutoyo vernier calipers. Rowing performance over 2,000 m was assessed using the Concept 2 rowing ergometer. Significant negative correlations were observed between 2,000 m ergometer performance and male digit ratios, which persisted following adjustment for rowing experience and height. However, no such significant association was found in females despite a comparable sample size. Our data indicate that digit ratio is a predictor of ability in rowing, a sport which requires both cardiovascular efficiency and high power output, in males but not females. This in turn suggests that fetal testosterone exposure has long-term effects on traits associated with physical power in males but not females, suggesting a sex-difference in the capacity to respond to such exposures.

Association between infant correlates of impulsivity--surgency (extraversion)--and early infant growth.

Increasing evidence suggests that rapid postnatal weight gain is associated with increased risks of being overweight or obese later in life and of co-morbidities, such as diabetes, the metabolic syndrome and cardiovascular disease. In children as young as two years of age, as well as in adults, an appetitive system-linked impulsivity trait has been demonstrated to be linked with increased overweight, and postulated to act via increased food intake, through greater responsiveness to food and lower self-inhibitory control skills. In this study, we hypothesized that growth in infancy, a critical window for metabolic programming, would be predicted by measures of infant surgency/extraversion, assessed using the Rothbart Infant Behaviour Questionnaire (revised version). Anthropometry was measured at birth and at 3, 6 and 12 months, and weight gains expressed as increases in standardized scores, allowing for adjustment for gender and age, including gestational age. We used conditional weight (CW), a residual of current weight regressed on prior weights, to represent deviations from expected weight gains, from 0 to 3, 3 to 6 and 6 to 12 months. Controlling for significant sociodemographic correlations, multiple regression analyses showed significant prediction of CWs at 3 months but not of CWs at 6 or 12 months by surgency/extraversion. These pilot findings of association between infant growth, during a critical period, and surgency/extraversion, early correlates of impulsivity, warrant further investigation, to ascertain implications for childhood and later weight and body composition.

Fluctuating asymmetry as a predictor for rowing ergometer performance.

Fluctuating asymmetry (FA) can be defined as an organism's deviation from perfect bilateral symmetry. FA has been of interest to evolutionary biologists as it may be indicative of the ability of an individual to express its genotype in a stable manner. Asymmetry has been shown to correlate with success in both intra- and inter-sexual selection in various species, including humans. A growing body of knowledge is emerging concerning the relationship between asymmetry and sporting ability. This study seeks to expand upon understanding of developmental stability and athletics by investigating the association between asymmetry and performance in rowers. Both male and female competitors from a range of abilities were tested (76 males and 70 females), with asymmetry being determined through bilateral digit measurements and performance through personal best time over 2000 m on the Concept 2 indoor rowing ergometer. Significant negative correlations were observed between asymmetry and 2000 m ergometer performance in both males and females. The relationship remained significant after adjustment for rowing experience and height. These results suggest that asymmetry may serve as a predictor of potential ability in the sport of rowing. The cause for the association between asymmetry and sporting performance has yet to be identified.

First-borns have a higher metabolic rate and carry a higher metabolic risk in young women attending a weight loss clinic.

BACKGROUND: Birth order has been associated with variability in early life growth and subsequent obesity risk, but the consequent metabolic risks have not been assessed. OBJECTIVE: To quantify the metabolic risk in young adulthood of being first-born relative to those born second or subsequently. METHODS: Body composition, resting metabolic rate and metabolic risk were assessed in 383 women, aged 18-35 years, from a clinical setting in southern Italy. RESULTS: First-borns had increased body mass index, adiposity and metabolic risk (p<0.05) and increased resting metabolic rate adjusted for fat-free mass (p<0.05) in the Italian women. CONCLUSION: First-born status is associated with significantly elevated metabolic risk in a clinical population of overweight and obese young women attending a weight loss clinic. If these findings are confirmed in other studies, they may suggest that the prevalence of the metabolic syndrome worldwide may increase as a function of the trend to smaller family size.

Evaluation of DXA against the four-component model of body composition in obese children and adolescents aged 5-21 years.

BACKGROUND: Body composition is increasingly measured in pediatric obese patients. Although dual-energy X-ray absorptiometry (DXA) is widely available, and is precise, its accuracy for body composition assessment in obese children remains untested. OBJECTIVE: We aimed to evaluate DXA against the four-component (4C) model in obese children and adolescents in both cross-sectional and longitudinal contexts. DESIGN: Body composition was measured by DXA (Lunar Prodigy) and the 4C model in 174 obese individuals aged 5-21 years, of whom 66 had a second measurement within 1.4 years. The Bland-Altman method was used to assess agreement between techniques for baseline body composition and change therein. RESULTS: A significant minority of individuals (n=21) could not be scanned successfully due to their large size. At baseline, in 153 individuals with complete data, DXA significantly overestimated fat mass (FM; Delta=0.9, s.d. 2.1 kg, P<0.0001) and underestimated lean mass (LM; Delta=-1.0, s.d. 2.1 kg, P<0.0001). Multiple regression analysis showed that gender, puberty status, LM and FM were associated with the magnitude of the bias. In the longitudinal study of 51 individuals, the mean bias in change in fat or LM did not differ significantly from zero (FM: Delta=-0.02, P=0.9; LM: Delta=0.04, P=0.8), however limits of agreement were wide (FM: +/-3.2 kg; LM: +/-3.0 kg). The proportion of variance in the reference values explained by DXA was 76% for change in FM and 43% for change in LM. CONCLUSIONS: There are limitations to the accuracy of DXA using Lunar Prodigy for assessing body composition or changes therein in obese children. The causes of differential bias include variability in the magnitude of tissue masses, and stage of pubertal development. Further work is required to evaluate this scenario for other DXA models and manufacturers.

Insufficient evidence to support separate BMI definitions for obesity in children and adolescents from south Asian ethnic groups in the UK.

Re-evaluation of adult obesity thresholds in some ethnic groups has led to the questioning of childhood obesity thresholds. An expert group was convened to examine the representativeness of childhood obesity definitions, evidence for ethnic differences in body composition in UK children and the extent of misclassification of adiposity by current body mass index (BMI) thresholds in south Asian and black groups. The group concluded that the current International Obesity Task Force (IOTF) definitions remained the most appropriate for use in the United Kingdom, but further research was needed on the relationship of body shape, fat mass, metabolic markers and ethnicity in children and adolescents.

Thrift: a guide to thrifty genes, thrifty phenotypes and thrifty norms.

There is a growing interest in evolutionary models of human adiposity. Frequent reference has been made to 'thrifty genes' or 'thrifty phenotypes', referring to a variety of metabolic or behavioural traits that in one or the other way imply frugality in the expenditure or storage of energy. However, there is confusion over how the strategy of thrift has been incorporated into human biology. At the broadest level, humans represent a thrifty species relative to other mammals, indicating that metabolic adaptations had a crucial role in the emergence of the Homo lineage, in particular in buffering reproduction from ecological stochasticity. In contemporary humans, some variability in adiposity may be attributable to genotypes systematically favoured in certain ecological settings. Genetic variability is also present within populations, and may be considered bet hedging (distributing risk across offspring to increase parental fitness). Bet hedging is an alternative to genetic drift for accounting for genetic variability in the absence of strong selective pressures. Contrasting with genetic variability emerging over the long-term, thrifty phenotypes represent a response to short-term ecological variability. Physiological plasticity allows the emergence of variability across the life course in response to ecological cues experienced directly or by very recent ancestors. Finally, cultural norms or individual preferences allow voluntary behavioural manipulation of thrift in individuals. Overall, there is a range of factors and processes both favouring and opposing thrifty genes, which may reflect moderate bet hedging rather than systematic adaptation. Plasticity protects the genome from selective pressures by tailoring the organism to ongoing ecological conditions. The fact that obesity can occur in different individuals through different genotypes, life histories and behaviours indicates that different treatments are also likely to be required.

The contribution of psychosocial stress to the obesity epidemic: an evolutionary approach.

The Thrifty Gene hypothesis theorizes that during evolution a set of genes has been selected to ensure survival in environments with limited food supply and marked seasonality. Contemporary environments have predictable and unlimited food availability, an attenuated seasonality due to artificial lighting, indoor heating during the winter and air conditioning during the summer, and promote sedentariness and overeating. In this setting the thrifty genes are constantly activated to enhance energy storage. Psychosocial stress and sleep deprivation are other features of modern societies. Stress-induced hypercortisolemia in the setting of unlimited food supply promotes adiposity. Modern man is becoming obese because these ancient mechanisms are efficiently promoting a positive energy balance. We propose that in today's plentifully provisioned societies, where sedentariness and mental stress have become typical traits, chronic activation of the neuroendocrine systems may contribute to the increased prevalence of obesity. We suggest that some of the yet unidentified thrifty genes may be linked to highly conserved energy sensing mechanisms (AMP kinase, mTOR kinase). These hypotheses are testable. Rural societies that are becoming rapidly industrialized and are witnessing a dramatic increase in obesity may provide a historical opportunity to conduct epidemiological studies of the thrifty genotype. In experimental settings, the effects of various forms of psychosocial stress in increasing metabolic efficiency and gene expression can be further tested.