• Malnutrition has long been researched and addressed in two distinct silos, focusing either on chronic 2 or acute undernutrition, energy inadequacy and micronutrient deficiencies, or on overweight, obesity 3 and dietary excess. The contemporary reality of the double burden of malnutrition is different, making it 4 impossible to separate these issues, but also indicating shared opportunities to address them. 5 • Malnutrition harms health throughout the life-course, but its emergence early in life has particularly 6 pernicious consequences. A variety of physiological mechanisms propagate effects of early-life 7 malnutrition across the life-course, while adolescent and adult malnutrition can transmit effects to the 8 next generation. 9 • Different forms of malnutrition can interact through the life-course and across generations. In some 10 settings, early stunting may predispose to a more central distribution of adiposity at later ages, while 11 the extent to which maternal obesity adversely affects early growth and development of the offspring 12 may be exacerbated if the mother herself was under-nourished in early life. 13 • Life-course exposure to the double burden of malnutrition (early undernutrition followed by later 14 overweight) increases the risk of non-communicable disease, by imposing a high metabolic load on a 15 depleted capacity for homeostasis. The health costs of adult obesity are therefore exacerbated among 16 those who previously experienced undernutrition. In women, life-course exposure to the double burden 17 of malnutrition increases the risk of childbirth complications. 18 • Exclusive and appropriate breast-feeding protects infants against all forms of malnutrition, and 19 protects mothers against diabetes and breast cancer, in part through healthy-weight benefits. However, 20 maternal obesity, diabetes and micronutrient deficiencies alter the biology of lactation, and should be 21 addressed to maximise the success of breast-feeding. 22 • Exposure to the double burden of malnutrition can only be fully understood in the context of broader 23 societal drivers acting across culture, behaviour and technology. Various groups are at high risk of the 24 double burden through elevated exposure to these drivers, often exacerbated by biological 25 susceptibility. 26 • Developmental responses to malnutrition in early life are shaped by ecological factors, such as 27 pathogen burden and extrinsic mortality risk. An evolutionary perspective, focusing on how our 28 biological plasticity was shaped in ancestral environments to promote survival and reproduction, may 29 help design interventions that promote linear growth and lean tissue accretion rather than excess 30 adiposity. 31 • Inter-generational cycles of malnutrition have proven difficult to disrupt through public health 32 interventions. Major societal shifts are required regarding nutrition and public health, in order to 33 implement comprehensive change that is sustained over decades, and scaled up into the entire global 34 food system.

Background: Among contemporary human populations, rates of cesarean delivery vary substantially, making it difficult to know if the procedure is inadequately available, or used excessively relative to medical need. A much-cited evolutionary hypothesis attributed birth complications to an “obstetric dilemma,” resulting from antagonistic selective pressures acting on maternal pelvic dimensions and fetal brain growth during hominin evolution. However, the childbirth challenges experienced by living humans may not be representative of those in the past, and may vary in association with trends in ecological conditions. We hypothesized that variability in maternal phenotype (height and nutritional status) may contribute to the risk of cesarean delivery. In many populations, high levels of child stunting contribute to a high frequency of short adult stature, while obesity is also becoming more common. The combination of short maternal stature and maternal overweight or obesity may substantially increase the risk of cesarean delivery.Methods: Using data from two large Indian health surveys from 2005–6 to 2015–2016, we tested associations of maternal somatic phenotype (short stature, overweight) with the risk of cesarean delivery, adjusting for confounding factors such as maternal age, birth order, rural/urban location, wealth and offspring sex.Results: Secular trends in maternal body mass index between surveys were greater than trends in height. Maternal short stature and overweight both increased the risk of cesarean delivery, most strongly when jointly present within individual women. These associations were independent of birth order, wealth, maternal age and rural/urban location. Secular trends in maternal phenotype explained 18% of the increase in cesarean rate over 10 years.Conclusion: Our results highlight how the emerging dual burden of malnutrition (persisting short adult stature which reflects persistent child stunting; increasing overweight in adults) is likely to impact childbirth in low and middle-income countries.

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