Relative validity and reproducibility of a quantitative FFQ for assessing nutrient intakes of vegetarians in Taiwan.

OBJECTIVE: To assess the relative validity and reproducibility of the quantitative FFQ used in the Tzu Chi Health Study (TCHS). DESIGN: The reproducibility was evaluated by comparing the baseline FFQ with the 2-year follow-up FFQ. The validity was evaluated by comparing the baseline FFQ with 3 d dietary records and biomarkers (serum folate and vitamin B12). Median comparison, cross-classification and Spearman correlation with and without energy adjustment and deattenuation for day-to-day variation were assessed. SETTING: TCHS is a prospective cohort containing a high proportion of true vegetarians and part-time vegetarians (regularly consuming a vegetarian diet without completely avoiding meat). SUBJECT: Subsets of 103, seventy-eight and 1528 TCHS participants were included in the reproducibility, dietary record-validity and biomarker-validity studies, respectively. RESULTS: Correlations assessing the reproducibility for repeat administrations of the FFQ were in the range of 0·46-0·65 for macronutrients and 0·35-0·67 for micronutrients; the average same quartile agreement was 40%. The correlation between FFQ and biomarkers was 0·41 for both vitamin B12 and folate. Moderate to good correlations between the baseline FFQ and dietary records were found for energy, protein, carbohydrate, saturated and monounsaturated fat, fibre, vitamin C, vitamin A, K, Ca, Mg, P, Fe and Zn (average crude correlation: 0·47 (range: 0·37-0·66); average energy-adjusted correlation: 0·43 (range: 0·38-0·55); average energy-adjusted deattenuated correlation: 0·50 (range: 0·44-0·66)) with same quartile agreement rate of 39% (range: 35-45%), while misclassification to the extreme quartile was rare (average: 4% (range: 0-6%)). CONCLUSIONS: The FFQ is a reliable and valid tool to rank relative intake of major nutrients for TCHS participants.

Taiwanese vegetarians and omnivores: dietary composition, prevalence of diabetes and IFG.

INTRODUCTION: Vegetarian diets have been shown to improve glucose metabolism and reduce risk for diabetes in Westerners but whether Chinese vegetarian diets have the same benefits is unknown. METHODS: We evaluated the association between diet and diabetes/impaired fasting glucose (IFG) among 4384 Taiwanese Buddhist volunteers and identified diabetes/IFG cases from a comprehensive review of medical history and fasting plasma glucose. RESULTS: Vegetarians had higher intakes of carbohydrates, fiber, calcium, magnesium, total and non-heme iron, folate, vitamin A, and lower intakes of saturated fat, cholesterol, and vitamin B12. Besides avoiding meat and fish, vegetarians had higher intakes of soy products, vegetables, whole grains, but similar intakes of dairy and fruits, compared with omnivores. The crude prevalence of diabetes in vegetarians versus omnivores is 0.6% versus 2.3% in pre-menopausal women, 2.8% versus 10% in menopausal women, and 4.3% versus 8.1% in men. Polytomous logistic regression adjusting for age, body mass index, family history of diabetes, education, leisure time physical activity, smoking and alcohol, showed that this vegetarian diet was negatively associated with diabetes and IFG in men (OR for diabetes: 0.49, 95% CI: 0.28-0.89; OR for IFG: 0.66, 95% CI: 0.46-0.95); in pre-menopausal women (OR for diabetes: 0.26, 95% CI: 0.06-1.21; OR for IFG: 0.60, 95% CI: 0.35-1.04); and in menopausal women (OR for diabetes: 0.25, 95% CI: 0.15-0.42; OR for IFG: 0.73, 95% CI: 0.56-0.95). CONCLUSION: We found a strong protective association between Taiwanese vegetarian diet and diabetes/IFG, after controlling for various potential confounders and risk factors.