Comparison of Weight for Height and BMI for Age for Estimating Overnutrition Burden in Under-Five Populations With High Stunting Prevalence.

BACKGROUND: Overnourished under-five children are anthro-pometrically classified as either being at possible risk of over-weight, overweight or obese and defined so, when either weight for height or body mass index for age (BMI-for-age) are >1SD to 2SD, >2SD to 3SD and >3SD, respectively of the analogous World Health Organization standards. AIM: To compare weight for height and BMI for age definitions for quantifying overnutrition burden. METHODS: Theoretical consequences of ignoring age were evaluated by comparing, at varying height for age z-scores, the age- and sex-specific cutoffs of BMI that would define overnutrition with these two metrics. Overnutrition prevalence was then compared in simulated populations (short, intermediate and tall) and real-life datasets from India. RESULTS: In short (-2SD) children, the BMI cutoffs with weight for height criteria were lower in comparison to BMI for age till 7-8 months, but higher at later ages. In National Family Health Survey-4, India dataset (short population), overnutrition (>1SD) prevalence with weight for height was higher from 0-0.5 years (exclusive breastfeeding age), but lower at subsequent ages. The prevalence difference (weight for height - BMI for age) in 0.5-5 years was -2.26% (6.57% vs 8.83%); this attenuated in 0-5 years (-1.55%; 7.23% vs 8.78%). The discrepancy was maxi-mal for stunted children and was lower in girls. A similar pattern, of lower magnitude, was observed for overweight (>2SD) com-parison. In intermediate and tall populations, there were no meaningful differences. CONCLUSION: The two definitions produce cutoffs, and hence estimates of overnutrition, that differ with the age, sex, and height of under-five children. The relative invariance, with age and height, of BMI for age, favors its use.

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, sup-posedly 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 plausi- ble 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 asso-ciations were estimated as odds ratio (OR) for individual data-sets, which was pooled (random-effects meta-analysis). Strati-fied analyses were done for sex, age and region. RESULT: Young infants (0-6 months) comprised 8-14% of under-five 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 was-ting-stunting association, originating from ignoring physiological changes with age.

Weight-for-height is associated with an overestimation of thinness burden in comparison to BMI-for-age in under-5 populations with high stunting prevalence.

BACKGROUND: Thinness at <5 years of age, also known as wasting, is used to assess the nutritional status of populations for programmatic purposes. Thinness may be defined when either weight-for-height or body-mass-index-for-age (BMI-for-age) are below -2 SD of the respective World Health Organization standards. These definitions were compared for quantifying the burden of thinness. METHODS: Theoretical consequences of ignoring age were evaluated by comparing, at varying height-for-age z-scores, the age- and sex-specific cut-offs of BMI that would define thinness with these two metrics. Thinness prevalence was then compared in simulated populations (short, intermediate and tall) and real-life data sets from research and the National Family Health Survey-4 (NFHS-4) in India. RESULTS: In short (-2 SD) children, the BMI cut-offs with weight-for-height criteria were higher in comparison to BMI-for-age after 1 year of age but lower at earlier ages. In Indian research and NFHS-4 data sets (short populations), thinness prevalence with weight-for-height was lower from 0.5 to 1 years but higher at subsequent ages. The absolute difference (weight-for-height - BMI-for-age) for 0.5-5 years was 4.6% (15.9-11.3%) and 2.2% (19.2-17.0%), respectively; this attenuated in the 0-5 years age group. The discrepancy was higher in boys and maximal for stunted children, reducing with increasing stature. In simulated data sets from intermediate and tall populations, there were no meaningful differences. CONCLUSIONS: The two definitions produce cut-offs, and hence estimates of thinness, that differ with the age, sex and height of children. The relative invariance, with age and stature, of the BMI-for-age thinness definition favours its use as the preferred index for programmatic purposes.