Association between low-carbohydrate diet score and childhood obesity: a national population-based study

Abstract Background Aimed to investigate the association between a low-carbohydrate diets (LCD) score and the prevalence of obesity in a large, nationally representative sample of children and adolescents in the United States. Methods This cross-sectional study utilized data from participants aged 2–17 years from the National Health and Nutrition Examination Survey (NHANES) spanning 2003 to 2018. The exposure of interest was an LCD score, calculated based on the relative intake of carbohydrates, proteins, and fats from the mean of two 24-hour dietary recalls. The primary outcome was obesity, defined as a body mass index at or above the 95th percentile for age and sex. Multivariable logistic regression analysis with three progressive models, restricted cubic spline (RCS) analysis, and subgroup analyses were performed. Results A total of 12,684 participants were included in the final analysis, including 7,392 with obesity and 11,679 without obesity. After comprehensive adjustment for demographic, socioeconomic, and dietary covariates (including total energy intake), a higher LCD score was positively associated with the odds of obesity. When treated as a continuous variable, each one-unit increase in the LCD score corresponded to a 2% increase in the odds of obesity (OR = 1.02, 95% CI: 1.01–1.03, P < 0.001). When categorized into quartiles, participants in the highest quartile (Q4) had 40% higher odds of obesity compared to those in the lowest quartile (Q1) (OR = 1.40, 95% CI: 1.17–1.68, P < 0.001). The RCS analysis confirmed a significant non-linear association between the LCD score and the odds of obesity (P for non-linearity = 0.001). Furthermore, subgroup analyses indicated that the association varied across strata; for instance, a significant positive association was observed in children aged 12 years and younger but not in older adolescents, and was stronger in males than in females, though formal tests for interaction were not statistically significant. Conclusion In this nationally representative sample of U.S. children and adolescents, a higher LCD score was associated with increased odds of obesity. This finding suggests that a dietary pattern characterized by a lower proportion of carbohydrates and higher proportions of fat and protein may reflect poor overall dietary quality rather than a structured, health-promoting diet, which is associated with higher obesity prevalence. Clinical trial number Not applicable.