Varying Associations Between Carbohydrates and Metabolic Syndrome Across Populations: findings from surveys in UK and Jiangsu Province of China

Objective: Low-carbohydrate diets have gained considerable popularity, but its association with metabolic syndrome (MetS) remains contradictory. Therefore, the aim of this study was to investigate the relationship between dietary macronutrient intake and MetS. Methods: We conducted the cross-sectional analysis of data from UK Biobank (UKB, 2006-2010), and Jiangsu Nutrition Survey (JNS, 2021), encompassing 104,665 (age from 40 to 69 years old) and 7,464 (age≥40 years old) participants, respectively. Multivariate logistic regression was utilized to estimate the odds ratio (OR) and 95% confidence interval (95%CI) for the association between dietary macronutrient intake and MetS. The restricted cubic spline (RCS) was used to analyze the linear or nonlinear relationship between macronutrient intake and MetS Results: The prevalence of MetS was 34.73% (95%CI: 34.08%-35.38%) in Jiangsu Province of China and 25.4% (95%CI: 25.1%-25.6%) in UK. The relationship between dietary macronutrient and MetS varied among different populations. In UKB (2006-2010), we found a positive association between higher-carbohydrate intake and MetS (compared to Q1, OR = 1.35, 95% CI: 1.28-1.42, P < 0.001). From the RCS plots, it is also apparent that the OR of MetS increases with a higher-carbohydrate intake. In JNS (2021), we found that higher-carbohydrate intake was negatively associated with MetS (compared to Q1, OR = 0.76, 95% CI: 0.64-0.89, P < 0.001), while higher-fat intake was positively associated with MetS (compared to Q1, OR = 1.24, 95% CI: 1.05-1.46, P = 0.010). We observed a decreasing trend in the prevalence of MetS with increasing carbohydrate intake, while the opposite was true for fat intake from the RCS. Conclusion: MetS is prevalent and its relationship with macronutrient intake varies among populations. In the middle-aged and elderly population of Jiangsu, higher-carbohydrate intake is negatively associated with MetS, whereas in the UK population, it shows a positive association. These findings are particularly relevant given the current phenomenon of carbohydrate “phobia” in the Chinese population. More prospective studies are needed to validate these findings and to further explore the complex relationship between macronutrient intake and MetS.