The present study compared the effect of rice-eating patterns on MetS. We categorized the subjects into four rice-eating groups: white rice alone, rice with beans, rice with multi-grains, and mixed group. We analyzed the effects of rice-eating patterns by gender because the prevalence of MetS and reported risk factors differ by gender [5, 26]. We found that the risk for metabolic disorders was lower in the rice with beans and rice with multi-grains groups compared with the white rice group, particularly in postmenopausal women. The characteristics such as lifestyle habits, nutrient consumption, and metabolic indices differed according to rice-eating patterns.
The one of main characteristics of Korean diet is high proportion of carbohydrate intake because rice is the staple food. Korean eats rice only or with other foods such as beans or other grains. White rice can be characterized as a refined grain because it is polished during processing and the bran and germ are entirely removed. The rice with beans group showed some features of bean consumption, and the rice with multi-grains group showed the benefits of whole grain. The third Korea National Health and Nutrition Examination Survey (KNHANES III) reported grains such as barely, sorghum, glutinous rice, Job’s tears, oats, millet and glutinous millet .
We found reduced risks for central obesity, dyslipidemia, and MetS in participants in the rice with multi-grains group compared with those in the white rice group. The rice with beans diet showed a beneficial effect on waist circumference and fasting glucose control. However, we could not find the BP lowering effect of rice with bean diet.
The most distinctive result was about central obesity. Means of WC of men in rice with multi-grains group and mixed group were higher than that of white rice group and odds ratio for central obesity was also elevated. However, means of WC in women were not significantly different among rice-eating groups, ORs for WC in rice with beans group and rice with multi-grains group were reduced. Especially in rice with beans group, both pre and post menopause women had low risk for central obesity.
We believe that the reduced ORs for MetS and the MetS components observed in rice with beans and multi-grains groups were the effect of soy protein and/or isoflavones in the beans group and cereal fibers and various components of unpolished grains in the rice with multi-grains group. The presence of dietary fiber, vitamins and minerals, phenolic acid, and phytoestrogen may contribute to the protective effect of whole grains . Whole grain intake is associated with a reduction in the risk for metabolic disease [28–31].
Soybean provides protein, fiber, and isoflavones. Clinical trials have shown positive effects of soy and soyfoods on total cholesterol, low-density lipoprotein (LDL) cholesterol, HDL cholesterol, and improvement in glycemic control [32–34]. Several studies have shown that soy isoflavones reduce the risk of coronary heart disease or cardiovascular disease by controlling blood lipid levels [33, 35, 36].
The study had some unavoidable weaknesses. Because we use baseline data, this study had a limitation of a cross-sectional study. This kind of study cannot provide information of changes over time and explain the causal relationship between risk factor and outcome. However, as cohort study is going on, disease outcomes would be ascertained. It provides the chance to investigate the risk of not only long term effect of mass carbohydrate consumption but also dietary pattern related to socio-psychological tendency for health and diseases.
Food frequency questionnaire had a limitation of ingredient assuming . We supposed that ‘rice with multi grains’ have whole grain effect but amount and kind of grains must be assumed in the ‘rice with multi grains’ item of food frequency questionnaire. The amount of beans was also estimated. These might have the association between diet and disease weakened.
The strength of this study was that metabolic risk factors were compared by rice-eating pattern in large scale data. And we could show the positive effects on health by rice eating with beans and multi-grains even in high carbohydrate consuming population.
We applied strict inclusion criteria in the present study to clearly identify the effect of rice-eating patterns on MetS. To avoid misclassification, the subjects themselves indicated their rice-eating patterns. It could clarify the feature of each pattern group. Furthermore, because disease may alter eating habits or lifestyle, we also excluded subjects with a diagnosis of a major disease. This reduces the available data but can make the effect of exposure in cross-sectional study relatively clearer.
The effect of rice-eating pattern on the metabolic components of MetS differed according to gender. We found a benefit of eating rice with beans or multi-grains in women; however, little difference in metabolic variables was observed among the rice-eating patterns in men. Because trends of nutrient intake by rice-eating pattern were similar in men and women (Table 2) and life-style factors were statistically controlled, gender difference of metabolic risks is due to intrinsic factor like hormone.
This finding is consistent with that of Kim et al.  who reported differences between men and women in their study on dietary carbohydrate and MetS, and with suggestion of Sun et al.  that genetic and/or hormonal influences may cause sexual dimorphism. Moreover, the effect of rice-eating patterns differed between pre- and postmenopausal women in the Kim et al. study . The primary metabolic symptom in postmenopausal women is central obesity, which is likely associated with changes in the androgen-to-estrogen ratio after menopause . Our results indicated that the beneficial effects of beans and multi-grains were the greatest in postmenopausal women, who lack protective hormones.
The results of this study suggested a desirable rice eating style. Rice is a main food in Asian countries and rice consumption is increasing in US . Eating rice with beans or other grains can provide the variety on rice consumption and apply to increase whole grains consumption rather than refined grains as a partly replacement method in western countries.