Dissimilar Associations Between Stunting and Low Ponderosity Defined Through Weight for Height (Wasting) or Body Mass Index for Age (Thinness) in Under-Five Children

Background: Wasting and stunting commonly coexist, supposedly due to biological and social mechanisms. In under-five children, low-ponderosity is defined as <–2SD of WHO standards for either weight for height (wasted) or body mass index for age (thin) metrics. Unlike body mass index for age, weight for height ignores physiological changes in ponderosity with age, resulting in overestimation of wasting in comparison to thinness in under-5 populations with high stunting prevalence. This suggests a plausible statistical explanation for the wasting-stunting association. Aim: To test the null hypothesis that wasting-stunting (WaSt) and thinness-stunting (ThSt) associations are similar. Methods: Demographic Health Survey datasets (2010-2020) from South and South-East Asia (7 countries) and Sub-Saharan Africa (13 countries) were evaluated. WaSt and ThSt associations were estimated as odds ratio (OR) for individual datasets, which was pooled (random-effects meta-analysis). Stratified analyses were done for sex, age and region. Results: Young infants (0-6 months) comprised 8-14% of underfive children, with equal representation of boys and girls. Participants, especially Asians, were mostly shorter with lower ponderosity than WHO standards. WaSt prevalence was higher than ThSt in the 6-59 months age group, but lower in young infants. Pooled WaSt estimates were not significant: Asia (OR 0.95; 95% CI 0.75-1.14), Africa (1.17; 0.95-1.40), and combined (1.09; 0.93-1.24). In contrast, pooled ThSt associations were significantly negative: Asia (0.63; 0.50-0.76), Africa (0.82; 0.68-0.96), and combined (0.75; 0.65-0.85). In girls, these associations were attenuated for WaSt (0.96; 0.8-1.1), but enhanced for ThSt (0.6; 0.5-0.7). Conclusion: WaSt and ThSt associations are dissimilar. This suggests a primary statistical explanation for the reported wasting-stunting association, originating from ignoring physiological changes with age.