Comparisons of conventional and novel anthropometric obesity indices to predict metabolic syndrome among vegetarians in Malaysia

Metabolic syndrome (MetS), a cluster of risk factors for cardiovascular diseases and type 2 diabetes, is a growing global health concern. Its prevalence varies significantly across populations, with Malaysia exhibiting a high rate (42.5%). Obesity is a major contributor to MetS, and identifying early diagnostic tools is crucial. Advanced imaging techniques like DXA and CT scans are effective but costly and time-consuming, limiting their use in large-scale epidemiological studies. Anthropometric indices offer a cost-effective alternative, but their predictive power and optimal cut-off values may vary across populations and sexes. While conventional indices like BMI and WHtR are widely used, novel indices such as LAP and VAI offer potential advantages by considering visceral adiposity. Previous research has examined these indices in different populations, but their effectiveness among vegetarians, a group with potentially different body composition and metabolic profiles, requires investigation. This study aimed to compare the ability of both conventional and novel anthropometric indices to predict MetS among Malaysian vegetarians and establish sex-specific optimal cut-off values for MetS prediction, acknowledging potential differences between vegetarians and the general population, as well as between sexes.

Numerous studies have investigated the use of anthropometric indices to predict MetS. Body Mass Index (BMI), while widely used, fails to distinguish between muscle and fat mass and doesn't accurately reflect abdominal fat distribution. Body fat percentage (BF%), measured using techniques like bioelectrical impedance analysis (BIA), provides a more direct measure of adiposity but is still less specific to abdominal fat. Waist-to-height ratio (WHtR) has emerged as a potentially better predictor, as it considers both waist circumference and height, offering advantages over BMI in identifying central obesity, a key factor in MetS. However, WHtR does not differentiate between subcutaneous and visceral fat. Novel indices like the lipid accumulation product (LAP) and visceral adiposity index (VAI) address this by incorporating blood lipid parameters to better reflect visceral adiposity. LAP has shown a strong correlation with MetS, while VAI is considered an indicator of adipose distribution and cardiometabolic risk. However, both LAP and VAI require blood lipid measurements, making them less practical for large-scale surveys. Body shape index (ABSI) and body roundness index (BRI) were proposed as cost-effective alternatives to assess abdominal obesity without blood tests. However, their effectiveness in predicting MetS has yielded inconsistent results across studies. Vegetarian diets have been associated with a lower risk of MetS compared to non-vegetarian diets. However, the prevalence of MetS among vegetarians is not insignificant, and there is a need for a tailored approach to MetS prediction in this population.

This cross-sectional study involved 273 adult Malaysian vegetarians (96 men and 177 women) recruited from Buddhist and Hindu community centers in Kuala Lumpur and Selangor. Ethical approval was obtained. Participants were included if they were aged 18 or older, had practiced vegetarianism for at least two years, were not pregnant or lactating, and were not taking medication for dyslipidemia, diabetes, or hypertension. Anthropometric measurements (height, weight, waist circumference, body fat percentage) and blood pressure were taken using standard protocols. Blood samples were collected to determine fasting blood glucose, triglycerides, and HDL cholesterol. Seven anthropometric indices were calculated: BMI, BF%, WHtR, LAP, VAI, ABSI, and BRI. Metabolic syndrome was defined according to the Joint Interim Statement 2009 criteria. Receiver operating characteristic (ROC) curve analyses were performed to assess the ability of each index to predict MetS, separately for men and women. The area under the curve (AUC), sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. Optimal cut-off points were determined using Youden's index. Statistical analyses were conducted using IBM SPSS version 24.0 and NCSS statistical software.

The overall prevalence of MetS among the study participants was 24.2% (29.2% in men, 21.5% in women). All conventional anthropometric indices (BMI, BF%, WHtR) and novel indices (LAP, VAI) except for ABSI and BRI in males, and BRI in females, showed significant associations with MetS. WHtR demonstrated the highest AUC among conventional indices, and LAP exhibited the highest AUC among the novel indices in both sexes. Paired design ROC curve analysis revealed that LAP had a significantly larger AUC than WHtR in both men and women. Sex-specific optimal cut-off values were determined for WHtR (0.541 for men, 0.532 for women) and LAP (41.435 for men, 21.743 for women). These cut-off points were generally higher than those reported in previous studies conducted on non-vegetarian populations.

This study's findings highlight the effectiveness of LAP and WHtR in predicting MetS among Malaysian vegetarians. LAP's superior performance might be attributed to its inclusion of triglycerides, a key component of MetS. However, WHtR's simplicity and cost-effectiveness make it a practical alternative for large-scale epidemiological surveys. The sex-specific optimal cut-off values identified in this study offer valuable guidance for health professionals working with vegetarian populations in Malaysia. The observed differences in prevalence and optimal cut-off values compared to previous studies in non-vegetarian populations underscore the importance of considering dietary patterns when assessing metabolic risk.

This study demonstrates that LAP is the best predictor for MetS among Malaysian vegetarians, but WHtR is a practical alternative for large-scale studies due to its cost-effectiveness. Sex-specific optimal cut-off values for WHtR and LAP are provided to aid in MetS diagnosis among this population. Future research should explore the applicability of these findings to other vegetarian populations and compare them to non-vegetarian groups to further refine MetS prediction tools.

The cross-sectional design limits the establishment of causality between anthropometric indices and MetS. The study focuses solely on Malaysian vegetarians, limiting the generalizability of findings to other populations and dietary patterns. Sample size limitations prevented stratification by ethnicity within sexes. Future longitudinal studies should address these limitations to enhance our understanding of MetS prediction in diverse populations.