Person:

Reiches, Meredith

Adolescence is a life history transition of individual and evolutionary importance: the body begins to allocate energy available above maintenance costs away from somatic growth and towards reproductive function. This study investigates how both distal, intergenerational effects and proximal, seasonal changes in energy availability impact the way adolescent female bodies allocate energy among linear growth, fat and lean mass, activity, and metabolic function. The research follows up on a prenatal supplementation study conducted by the British Medical Research Council in rural Gambia between 1989 and 1994. Pregnant women were randomized to receive daily supplements of 1015 kcal either from week 20 of pregnancy until delivery or during the first 20 weeks of lactation. The 67 adolescent daughters included in the follow up study were born to women in both groups during the rainy agricultural season, the period of the year associated with weight loss, poor perinatal outcomes, and high impact of the pregnancy supplement on birth weight. Anthropometry, body composition, daily saliva, weekly serum, and weekly fasting urine samples for C-peptide of insulin were collected during one month each in the 2009 rainy agricultural season, the 2010 dry harvest season, and the 2010 rainy agricultural season. Participant heart rates were calibrated to oxygen consumption each season, and 24-hr accelerometer and heart rate data were recorded to estimate free-living energy expenditure. It was found that pregnancy supplementation status did not predict infant or adolescent phenotype in the study sample. Maternal postpartum weight, however, was a powerful positive distal predictor of adolescent size. The daughters of heavier mothers produced less leptin per unit fat mass. Under conditions of high energy expenditure and low intake, adolescent women who were growing in height mobilized adipose stores and acquired lean mass, while developmentally older women maintained fat stores at the expense of lean mass. Married adolescents in the sample were older, had lower fasting C-peptide of insulin, had higher absolute energy expenditure, and spent more of their total energy budgets in activity than did unmarried peers.

Background and objectives: Life history theory predicts a shift in energy allocation from growth to reproductive function as a consequence of puberty. During adolescence, linear growth tapers off and, in females, ovarian steroid production increases. In this model, acquisition of lean mass is associated with growth while investment in adiposity is associated with reproduction. This study examines the chronological and developmental predictors of energy allocation patterns among adolescent women under conditions of energy constraint. Methodology: Fifty post-menarcheal adolescent women between 14 and 20 years old were sampled for weight and body composition at the beginning and end of 1 month in an energy-adequate season and 1 month in the subsequent energy-constrained season in a rural province of The Gambia. Results: Chronologically and developmentally younger adolescent girls gain weight in the form of lean mass in both energy-adequate and energy-constrained seasons, whereas older adolescents lose lean mass under conditions of energetic stress (generalized estimating equation (GEE) Wald chi-square comparing youngest tertile with older two tertiles 9.750, P = 0.002; GEE Wald chi-square comparing fast- with slow-growing individuals for growth rate 19.806, P < 0.001). When energy is limited, younger adolescents lose and older adolescents maintain fat (GEE Wald chi-square for interaction of age and season 6.568, P = 0.010; GEE Wald chi-square comparing fast- with slow-growing individuals for interaction of growth rate and season 7.807, P = 0.005). Conclusions and implications: When energy is constrained, the physiology of younger adolescents invests in growth while that of older adolescent females privileges reproductively valuable adipose tissue.

We present a critique of a paper written by two economists, Quamrul Ashraf and Oded Galor, which is forthcoming in the American Economic Review and which was uncritically highlighted in Science magazine. Their paper claims there is a causal effect of genetic diversity on economic success, positing that too much or too little genetic diversity constrains development. In particular, they argue that “the high degree of diversity among African populations and the low degree of diversity among Native American populations have been a detrimental force in the development of these regions.” We demonstrate that their argument is seriously flawed on both factual and methodological grounds. As economists and other social scientists begin exploring newly available genetic data, it is crucial to remember that nonexperts broadcasting bold claims on the basis of weak data and methods can have profoundly detrimental social and political effects.

Abstract Background and objectives: The human immune system is an ever-changing composition of innumerable cells and proteins, continually ready to respond to pathogens or insults. The cost of maintaining this state of immunological readiness is rarely considered. In this paper we aim to discern a cost to non-acute immune function by investigating how low levels of C-reactive protein (CRP) relate to other energetic demands and resources in adolescent Gambian girls. Methodology: Data from a longitudinal study of 66 adolescent girls was used to test hypotheses around investment in immune function. Non-acute (under 2 mg/L) CRP was used as an index of immune function. Predictor variables include linear height velocity, adiposity, leptin, and measures of energy balance. Results: Non-acute log CRP was positively associated with adiposity (β = 0.16, P < 0.001, R2 = 0.17) and levels of the adipokine leptin (β = 1.17, P = 0.006, R2 = 0.09). CRP was also negatively associated with increased investment in growth, as measured by height velocity (β = −0.58, P < 0.001, R2 = 0.13) and lean mass deposition β = −0.42, P = 0.005, R2 = 0.08). Relationships between adiposity and growth explained some, but not all, of this association. We do not find that CRP was related to energy balance. Conclusions and implications: These data support a hypothesis that investment in non-acute immune function is facultative, and sensitive to energetic resources and demands. We also find support for an adaptive association between the immune system and adipose tissue.