**Background:** The 2021 Lancet Commission on adolescent nutrition emphasised the need to eliminate adolescent malnutrition to unlock human capital and break the intergenerational malnutrition trap. Adolescence is a period of peak nutritional requirements, with 50% of adult weight and 20% of overall height acquired during this phase. In India, limited nationally representative data have previously restricted analysis of the roles of dietary diversity and individual-level hygiene practices in adolescent malnutrition. The present study aimed to assess the prevalence of stunting, thinness, and anaemia among Indian adolescents and to evaluate the contributions of socioeconomic factors, dietary diversity, and hygiene behaviour to these outcomes.
**Methods:** The study used data from the Comprehensive National Nutrition Survey (CNNS 2016–18), a nationally representative cross-sectional survey covering children and adolescents (0–19 years) across 29 states and the Union Territory of Delhi. A multistage stratified cluster sampling design with probability proportionate to size was employed. The analytical sample included 35,830 adolescents aged 10–19 years for anthropometric outcomes (stunting and thinness) and 14,669 for anaemia. Stunting was defined as height-for-age z-score below -2 SD from the WHO 2007 growth reference; thinness as BMI-for-age z-score below -2 SD. Anaemia was classified per WHO age-sex-specific criteria (haemoglobin <11.5 g/dL for ages 10–11 years, <12 g/dL for ages 12–14 years, <13 g/dL for males 15–19 years, and <12 g/dL for females 15–19 years). Dietary diversity was assessed using a score based on FAO guidelines, with a cut-off of ≥4 indicating adequate diversity. Two hygiene behaviour indexes (general and critical) were constructed from ten questions on handwashing practices. Bivariate and multivariable logistic regression models were applied with appropriate sampling weights.
**Key Results:** The prevalence of stunting, anaemia, and thinness among Indian adolescents was 27.2%, 28.5%, and 24.1%, respectively. Stunting was more prevalent among females (29.9%) than males (25.4%), and anaemia was markedly higher among females (39.6%) compared with males (17.7%). Rural adolescents had higher rates of stunting (28.8% vs. 22.0%), thinness (25.3% vs. 20.5%), and anaemia (29.1% vs. 26.9%) than urban adolescents. The highest prevalence of stunting (35.6%) and anaemia (37.6%) was observed among Scheduled Tribes. Only 11.4% of adolescents had adequate dietary diversity (score ≥4). In multivariable analysis, the likelihood of stunting was significantly higher among late adolescents (OR 1.26, 95% CI 1.20–1.33), females (OR 1.19, 95% CI 1.14–1.26), those with low dietary diversity (OR 1.14, 95% CI 1.05–1.24), and those with no compliance on critical hygiene behaviour (OR 1.20, 95% CI 1.08–1.33). Adolescents from the poorest wealth quintile had substantially higher odds of stunting (OR 2.83, 95% CI 2.54–3.17), thinness (OR 1.83, 95% CI 1.63–2.04), and anaemia (OR 1.66, 95% CI 0.99–1.35, though this was not statistically significant in the adjusted model). Scheduled Tribe adolescents had higher odds of stunting (OR 1.43, 95% CI 1.30–1.58) and anaemia (OR 1.62, 95% CI 1.40–1.87). Muslim adolescents were more likely to be stunted (OR 1.37, 95% CI 1.18–1.59), anaemic (OR 1.46, 95% CI 1.17–1.83), and thin (OR 1.44, 95% CI 1.23–1.70) compared with other religious groups. Adolescents not attending school had higher odds of stunting (OR 1.21, 95% CI 1.09–1.34) and anaemia (OR 1.24, 95% CI 1.03–1.48).
**Clinical Implications:** The study demonstrates that adolescent undernutrition and anaemia remain substantial public health challenges in India, with marked disparities by sex, caste, wealth, and region. The strong association between low dietary diversity and stunting underscores the need to improve the quality and diversity of adolescents' diets. School-based feeding programmes (PM-POSHAN) could be expanded to higher classes and made more nutritious. The finding that poor hygiene compliance is independently associated with stunting and anaemia highlights the importance of behaviour change communication beyond infrastructure provision (e.g., toilet ownership). The Swachh Bharat Mission should emphasise sustained hygiene practices. Targeted interventions for the poorest households, Scheduled Tribes, and Muslim communities are needed to address the large socioeconomic gradients in malnutrition. The persistent gender gap in anaemia (females three times more likely than males) calls for continued focus on adolescent girls' nutrition, including iron supplementation and delayed age at first pregnancy.