Weaning and stunting affect nitrogen and carbon stable isotope natural abundances in the hair of young children.

Natural abundances of stable nitrogen and carbon isotopes (δ15N and δ13C) can vary with both dietary intake and metabolic (specifically catabolic) state. In low-income countries, weaning is a period of dietary transition from milk to plant-based foods and a high-risk period for malnutrition. We explored how diet and malnutrition impact hair δ15N and δ13C in young children by an observational, cross-sectional study in Cox's Bazar District, Bangladesh [255 children, 6-59 months with 19.6% wasted (7.1% severely) and 36% stunted (9.8% severely)]. Hair δ15N and δ13C exhibited exponential decreases with age, with the loss of one trophic level (3.3‰ and 0.8‰, respectively) from 6 to 48 months, which we associate with the shift from exclusive breastfeeding to complete weaning. After adjustment for age and breastfeeding status, hair isotopic values were unaffected by wasting but lower in severe stunting (-0.45‰ to -0.6‰, P < 0.01). In this population of young children, whose isotopic values in hair primarily depended on age, we failed to observe any effect of wasting, likely due to opposite, compensating effects between dietary and metabolic changes involved. In contrast, we evidenced low δ15N and δ13C values in severely stunted children that likely indicate chronic exposure to diets low in animal products.