The effects of black and brown rice on lipid metabolism and antioxidant enzyme activities

Abstract

비만은 전 세계적으로 가장 흔한 영양장애 중의 하나로서, WHO 통계자료에 의하면 현재 2억 5천만여 명의 인구가 비만 환자로 분류되며, 20년 후에는 약 3억의 인구가 비만으로 고통 받을 것으로 예측된다. 최근 국내 통계자료에 의하면 성인 4명 중 1명이 체질량지수가 25이상의 비만인으로 보고 되고 있다. 비만은 외형적인 문제뿐 아니라 각종 성인병의 발병과 매우 깊은 관련을 갖는다. 본 연구에서는 동물실험과 임상시험을 통해 곡류의 섭취가 체내 지질대사와 항산화 효소의 활성에 어떠한 영향을 미치는지 함께 살펴보았다. 동물실험에서는 12주령 수컷 흰쥐 50마리를 대상으로 American Institute of Nutrition-93 Growth (AIN-93 G) diets를 기본으로 실험식이를 제조하여 8주간 섭취시켰다. 탄수화물 급원은 옥수수 전분대신 곡물 가루로 대체하였고, WR diet는 500 g/kg의 백미 (WR group, n=10), WRBR diet는 250 g/kg 백미와 250 g/kg 현미 (WRBR group, n=10), WRBL diet는 250 g/kg 백미와 250 g/kg 흑미 (WRBL group, n=10), BRBL diet 는 250 g/kg 현미와 250 g/kg 흑미 (BRBL group, n=10), WH diet 는 500 g/kg 밀가루를 사용하였다. 장통과시간은 BRBL군이 가장 짧았고 WRBL, WRBR, WR, WH군 순이었다. 혈중지질농도는 곡류 조성에 따라 각 군에서 유의적인 차이를 보였는데 BRBL군이 다른 군에 비해 TG, TC, LDL-C 수준이 유의적으로 가장 낮았고 HDL-C 수준이 가장 높았다. 대동맥 벽의 두께는 BRBL군이 다른 군에 비해 유의적으로 낮게 나타났다. 관상동맥의 동맥 경화증은 혈관의 구조적 변형에 따라 내막-중막이 두꺼워지는 것과 밀접한 관련이 있다. 대동맥벽 두께는 두꺼워지고 내강은 더 넓어진다고 보고되고 있다. 지질과산화물인 TBARS 농도는 WR군이 가장 높았고 WH, BRBL, WRBL, BRBL군 순이었다. 반면 항산화 효소인 SOD와 CAT의 활성은 유의적인 차이를 보이지 않았지만 BRBL군에서 GSH 농도와 GPx 활성이 다른 군들에 비해 유의적으로 높았다. 본 연구의 임상실험은 2005년 3월 23일 한양대학교 병원 제176회 임상연구위원회 심의에서 승인되었으며, 총 연구기간은 6주로 처음 2군으로 나누어 각각 대조군(백미군)과 실험군(혼합미군)으로 식사 대체식을 제공하였다. 본 연구에 사용되는 식이는 대조군으로 백미군은 백미를 탄수화물 급원으로 하고 실험군으로 혼합미군은 동물실험에서 가장 큰 체중감량 효과를 보인 현미 50%와 흑미 50%를 혼합하여 탄수화물 급원으로 이용한다. 탄수화물 급원 외에 두류, 채소류, 해조류, 버섯류 등을 사용하여 균형 있는 식이가 되도록 하고 실험식이 1포(50g, 180kcal)는 우유 1팩(200ml, 120kcal)이나 두유 1팩(200ml, 118kcal)에 섞어서 아침, 점심, 저녁에 섭취하도록 하고 6주간 진행한다. 실험식이 외에 간식으로 야채와 과일을 각각 1회 섭취하도록 하여 하루 총 열량 섭취가 약 1074kcal-1081kcal 내외가 되도록 하였다. 두 군 모두 체중, BMI, 체지방량, 허리둘레, 엉덩이둘레, 허리둘레/엉덩이둘레가 3주째, 6주째에 유의적으로 감소하였다. 그러나 변화량에서는 두 군간의 차이는 체중과 BMI, 체지방량에서 변화량에서 유의적으로 더 크게 나타났다. 혈중지질, 총콜레스테롤은 두군 모두에서 3주째, 6주째에 감소 하였고 두 군 사이에서는 유의적이지는 않았지만 혼합미군이 약간 더 큰 감소를 보였다. 지질과산화물 농도에서는 백미군은 유의적으로 3주째, 6주째 증가하였으나 혼합미군은 감소하였다. 한편, 항산화 효소에서는 SOD가 백미군에서 유의적으로 감소하였으나 혼합미군에서는 차이를 보이지 않았다. 변화량에서도 두군 간의 차이가 없었다. GPx 활성에서는 혼합미군에서 유의적으로 증가하였고 백미군에서는 유의적이지는 않았지만 약간 증가하는 추세를 보였다. 결론적으로 본 연구의 동물실험과 임상시험의 결과들을 살펴보았을 때, 현미와 흑미는 백미와 밀가루에 비해 체중감량과 혈중 지질 패턴을 유익한 방향으로 개선하는데 효과적이고 항산화 효소의 활성을 높여 지질과산화물의 농도 축적을 방지한다는 것을 알 수 있었다.; The treatment of cardiovascular disease (CHD) with rice diets was suggested several decades ago. More than 50 years ago, it was reported that consumption of white rice decreased blood pressure and lowered hypercholesterolemia in human. The most common type for human consumption is white rice, and the rest is brown and black rice. In the refining process, however, the bran and germ are separated from the starch endosperm, which is ground to flour. When the bran is removed in refining, important disease-preventing nutrients and phytochemicals (such as lignans, tocotrienols, and phenolic compounds), and antinutrients (including phytic acid, tannins, and enzyme inhibitors) are removed as well. In this study, diet combinations were not combined to maintain total amount of energy equally but to make equal diet compositions except rice powders to evaluate functional differences of various grains. The present study was carried out to evaluate the nutritional quality of brown rice and black rice, particularly with respect to fiber and antioxidant components. In animal study (part 1), gut transit time, plasma lipid parameters, hepatic enzyme activities, and thickness of the aortic wall in rats fed with different combinations of grains were evaluated and compared with white rice and wheat flour. Fifty male rats were divided into five groups and raised for eight weeks with diets containing white rice (WR), white rice and brown rice (WRBR), white rice and black rice (WRBL), brown rice and black rice (BRBL), or wheat flour (WH), respectively. Gut transit time decreased by diet in the following order: BRBL, WRBL, WRBR, WR and WH. Plasma lipid profiles differed significantly according to grain combination. The BRBL group had the lowest levels of triglycerides (TG), total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) and the highest plasma high-density lipoprotein cholesterol (HDL-C) concentration among all groups. Aortic wall thickness was also thinner in BRBL fed rats. The level of thiobarbituric acid reactive substance (TBARS) in liver is shown higher in rats by the order of those fed WR, WH, WRBR, WRBL and BRBL. While superoxide dismutase (SOD) and catalase (CAT) activities did not differ among the five groups, glutathione (GSH) and glutathione peroxidase (GPx) in BRBL were significantly higher than in other groups. In human study (part 2), the physiological consequences of meal replacements using white rice or mixed rice were evaluated in overweight Korean women (BMI≥25kg/m2) over a period of 6 weeks. Meal replacements, in the form of a shake reconstituted from powder and providing about 1000 kcal/day, have been used in several weight-loss trials. Two forms of the meal replacement were compared, one composed of white rice and the other a mixture of brown and black rice for their effects on weight, body mass index (BMI), body fat (%) and blood lipid levels and antioxidant activities. Forty women between 20 and 35 years old of age were randomly divided into two groups who consumed one of two low calorie meal replacements containing either white rice (WR group) or mixed rice (BRBL group). The subjects were not allowed to have any food other than the low calorie meal replacement 3 times a day and snacks provided by the researcher. The changes of anthropometric indices and blood parameters such as lipid levels and antioxidant activities were measured every 3 weeks during the dietary intervention. The subjects showed a significant reduction in weight, BMI and body fat (%) during the experimental period, with the BRBL group exhibiting levels of all three parameters significantly lowered than that of the WR group. The levels of TC and TG decreased gradually and significantly after intervention in both groups, with no significant difference between the groups. HDL-C was significantly elevated in the BRBL group, but not in the WR group. SOD activity was not affected by dietary intervention, but GPx activity in the BRBL group was higher than in the WR group, and the level of TBARS was lower in the BRBL group compared to the WR group. The major finding of this study is that rats fed brown and black rice diets (BRBL group) had dramatically lower plasma TC, TG and LDL-C concentrations, increased antioxidant activities (GSH, GPx) and also had thinner in aortic walls compared with the rats fed other grain combinations. In human study, it was also demonstrated that a mixture of brown and black rice was effective in weight control and improving antioxidant enzyme activities compared to white rice. The benefits of brown and black rice likely result from it containing dietary fiber, flavonoids, zinc, selenium and rice bran oil (RBO). Corresponding to these results, a low-calorie meal replacement containing brown and black rice was advisable for diet therapy in obese women. In conclusion, this study has demonstrated that the brown and black rice had a cardioprotective effect. This effect was related to several mechanisms that corresponded to lowering plasma TC, TG and LDL-C, decreasing TBARS and increasing antioxidant activities. The incorporation of dietary fiber and phytochemicals in grain products would enhance their nutritional and physiological properties.