Age patterns in overweight and wasting prevalence of under 5-year-old children from low- and middle-income countries

Global nutrition agendas have expanded from undernutrition to all forms of malnutrition, including childhood overweight and obesity. Despite targets such as the WHO Global Target to halt increases in childhood overweight by 2025 and SDG indicator 2.2.2 on wasting and overweight, no country is on track. In 2019, an estimated 38.2 million under-5 children (5.6%) were overweight/obese, with higher prevalence in upper-middle- and high-income settings amid nutrition transition. While overweight is known to increase with age after 5 years, there has been little evidence on age patterns under 5 across multiple countries; the authors initially expected overweight to increase with age within under-5s. Wasting affected 47 million children (6.9%) in 2019, concentrated in low-income contexts and especially South Asia. Though classically considered most common in the second year of life, newer evidence indicates higher wasting among younger children. Given heterogeneity by socio-demographics and the double burden of malnutrition in LMICs, and the SDG’s call for age-disaggregated data, the study aims to describe overweight and wasting prevalence by age in years among under-5 children in LMICs.

The paper situates the study within evidence that: (1) childhood overweight is rising globally, driven by nutrition transition, urbanization, and dietary shifts toward ultra-processed, energy-dense foods; (2) overweight prevalence tends to be higher in more affluent settings; (3) wasting remains prevalent in LMICs, notably South Asia, linked to food insecurity, poor diet, and disease; (4) prior research emphasizes stunting inequalities by age, with less attention to age gradients in wasting and particularly overweight under age 5; and (5) the double burden of malnutrition coexists in many LMICs. Classical views place wasting peaks in the second year, but recent studies suggest younger children are more at risk. There was no prior multicountry analysis of under-5 age patterns in overweight and wasting using standardized surveys.

Study design and data sources: Secondary analyses of nationally representative DHS and MICS surveys conducted in LMICs between 2010 and 2019 (most recent post-2010 survey per country). These cross-sectional surveys use multistage cluster sampling to select women 15–49 years and children under 5, with standardized, face-to-face questionnaires and anthropometry by trained fieldworkers. Data were harmonized by the International Center for Equity in Health. Inclusion required valid anthropometric and age data for children under 5. Measurement: Children 0–23 months had supine length; 24–59 months had standing height, measured with ShorrBoards, SECA, or local boards; weight measured using portable SECA 874 U electronic scales. WHZ (weight-for-length/height Z-score) used 2006 WHO Child Growth Standards, with valid WHZ in −5 to +5. Overweight defined as WHZ > +2 SD; wasting as WHZ < −2 SD (WHO standards use medians to account for asymmetric weight distribution). Data quality assessment: Standard deviation (SD) of WHZ assessed by age; WHO suggests WHZ SD outside 0.85–1.1 may indicate measurement issues. The number of countries with age-specific SDs outside this range was tabulated. Additional classification: For ages 2–5 years, overweight was also estimated using IOTF age- and sex-adjusted BMI cut-offs corresponding to adult BMI 25 and 30 kg/m² (results in Supplementary Materials). Age groups: 0–11, 12–23, 24–35, 36–47, 48–59 months. Analytic approach: Descriptive national estimates of overweight, wasting, mean WHZ, and WHZ SD stratified by age in years. Logistic regression tested within-country linear trends across full-year age groups for overweight and wasting separately. Chi-square tests compared prevalence across five age groups, overall and by World Bank income groups, yielding heterogeneity p-values. Graphical outputs included bar graphs of prevalence by age and income group, boxplots of WHZ means and SDs, and scatter plots relating mean WHZ to overweight/wasting prevalence; fractional polynomials fitted regression curves. All analyses were weighted by each country’s under-5 population (median survey year 2014) and accounted for complex survey design (sampling weights, clustering). Supplementary analyses used local polynomial smooths of mean WHZ by continuous age with under-5 population weights. Software: Stata 16.0 and Microsoft Excel. Ethical approvals were obtained by implementing institutions for each survey.

- Coverage: 90 LMIC national surveys (2010–2019; median 2014) included, representing 87.1% of low-income, 70.6% of lower-middle-income, and 50.9% of upper-middle-income countries. Median under-5 sample per country: 5,920 (IQR 3,263–10,263). Median by age group: 0–11m N=1,101; 12–23m N=1,137; 24–35m N=1,151; 36–47m N=1,192; 48–59m N=1,079. - Overweight: Overall prevalence declined with age from 6.3% (0–11m) to 3.0% (48–59m); heterogeneity p=0.03. Declines were similar by sex and when using IOTF cut-offs (supplementary). By income group, overweight was lowest in low-income and highest in upper-middle-income countries at all ages. In low-income countries, overweight in 0–11m exceeded older ages by at least 3.8 percentage points (p<0.001); in lower-middle-income countries by at least 2.0 p.p. (p<0.001). In upper-middle-income countries, the decline was smaller and not statistically significant (p=0.082). Country ranges: 0–11m overweight 1.8% (Mauritania) to 23.3% (South Africa); 48–59m 0.1% (Madagascar) to 14.5% (Egypt). Within-country linear trends: significant declines in 65 countries; increases in 3 (El Salvador, North Macedonia, Thailand); no trend in 22. National overall overweight ranged from 0.9% (Senegal) to 18.1% (Bosnia and Herzegovina). - Wasting: Highest among infants with a slight decrease into the second year and little change thereafter; pattern consistent by sex. By income group: upper-middle-income countries had the lowest wasting (4.9% in infants to 1.7% at 36–47m), lower-middle-income countries the highest (19.0% in infants to 10.9% at 36–47m), and low-income countries intermediate (11.5% in infants to 5.2% at 36–47m). All income groups showed declines up to ~3 years with stability thereafter. Country ranges: 0.8% (Peru) to 28.9% (India) at 0–11m; 0.0% (Eswatini) to 22.5% (Timor-Leste) at 48–59m. Within-country linear trends: significant declines with age in 72 countries; increase only in Maldives; no trend in 17. - Normal WHZ band: Proportion with WHZ between −2 and +2 increased with age: approximately 78%, 85%, 88%, 89%, and 90% across the five age groups from youngest to oldest. - Mean WHZ and dispersion: Mean WHZ remained near constant by age overall; upper-middle-income countries had slightly positive mean WHZ across ages; low-income countries showed a decline between 0 and 12 months. Median WHZ SD decreased with age: 1.39 in infants to 1.09 in 4-year-olds (heterogeneity p<0.001). Data quality flags: of 90 surveys, WHZ SD for infants exceeded 1.1 in 86 surveys; exceeding counts for ages 1–4 were 71, 49, 44, and 41, respectively. - Mean WHZ vs prevalence: For any given mean WHZ, both overweight and wasting prevalence were higher among infants than older children, consistent with wider WHZ SDs in infants.

The study answers the question of how overweight and wasting vary by age under 5 in LMICs by showing consistent declines in both conditions from infancy to age 4, while mean WHZ remains stable. This paradox—higher tail prevalence at younger ages without shifts in mean—aligns with substantially larger WHZ standard deviations among infants and, to a lesser extent, 1-year-olds. Likely contributors include greater anthropometric measurement error in younger children (length/height more difficult to measure accurately; small errors can inflate WHZ variability and tail proportions) and biological growth dynamics such as rapid crossing of growth percentiles in infancy (less canalized growth), which would increase dispersion in cross-sectional distributions. The findings also reaffirm expected income-group gradients: overweight prevalence higher in more affluent LMICs, while wasting concentrates in lower-middle-income countries due to South Asia’s high burden. Implications include caution in interpreting age patterns of malnutrition from routine cross-sectional surveys; reliance on prevalence cutoffs in the distribution tails may be especially sensitive to data quality in infants. Mean Z-scores are less influenced by outliers and may offer complementary insights. The results inform SDG 2.2.2 tracking, indicating that combined malnutrition (WHZ outside ±2 SD) is substantially higher in infancy and declines with age, but part of this gradient may be artefactual.

Across 90 LMICs, overweight and wasting prevalences both decline from infancy to age 4, while mean WHZ remains stable. The apparent age gradients are plausibly driven by wider WHZ standard deviations among infants, attributable to anthropometric measurement challenges and/or rapid crossing of growth channels. Until these issues are resolved, firm inferences about true age-related variability in overweight and wasting from routine surveys are limited. Future research should include cohort and high-quality cross-sectional studies with rigorous anthropometry to accurately delineate age patterns in under-5 overweight and wasting and improve the reliability of SDG 2.2.2 monitoring.

- Uneven survey availability by World Bank income groups: coverage was higher in low-income (87.1%) than in lower-middle (70.6%) and upper-middle-income countries (50.9%). - Temporal currency: only surveys from 2010 onward were included (median 2014), so estimates for countries without recent surveys may be outdated. - Potential measurement error: Elevated WHZ standard deviations, particularly in infants, suggest residual anthropometric measurement issues that can bias prevalence estimates based on distribution tails.