รำข้าวโอ๊ตและรำข้าวเต็มไขมันคล้ายลด Hypercholesterolemia ใน Humans1, 2Ann L. Gerhardt3 และ Noreen บีกอลโล+ เข้าสังกัดผู้เขียนกรมการแพทย์ มหาวิทยาลัยแคลิฟอร์เนีย ศูนย์การแพทย์ Davis และซัท สถาบันหัวใจ แซคราเมนโต CA 95819 1 ส่วนถัดไปบทคัดย่อScientific studies support recommendations to increase dietary soluble fiber as part of hyperlipidemia treatment. Rice bran contains minimal soluble fiber, but rice bran oil has a hypolipidemic effect. Full-fat rice bran was compared with oat bran and a rice starch placebo in hyperlipidemic humans to see if it might have a role in the treatment of hyperlipidemia. Moderately hypercholesterolemic (5.95–8.02 mmol/L), nonsmoking, nonobese adults were studied in a 6-wk, randomized, double-blind, noncross-over trial. Three groups added 84 g/d of a heat-stabilized, full-fat, medium-grain rice bran product (n = 14), oat bran product (n = 13) or rice starch placebo (n = 17) to their usual low-fat diet. Serum cholesterol, triglycerides, HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), apoA1 and apoB were measured before and at the end of the supplementation period. Serum cholesterol decreased significantly (P ≤ 0.05) by 8.3 ± 2.4% and 13.0 ± 1.8% in the rice bran and oat bran groups, respectively, but there was no change in the rice starch group. This change was attributable to LDL-C, which decreased by 13.7 ± 2.8% in the rice bran group and 17.1 ± 2.4% in the oat bran group (P ≤ 0.05). Serum apoB decreased proportionately. There was no consistent effect on triglycerides within each group and HDL-C and apoA concentrations did not change. The LDL-C:HDL-C ratio decreased significantly in the rice bran and oat bran groups. Stabilized, full-fat rice bran or oat bran, added to the prudent diet of hyperlipidemic adults, similarly reduced cholesterol and LDL-C and improved lipid ratios in 78% of these individuals. Rice bran, as well as oat bran, should be included in the prudent diet of individuals with hyperlipidemia.cholesterol hyperlipidemia rice bran fiber humanHypercholesterolemia is an established major risk factor for coronary artery disease. Lifestyle modification is the preferable form of treatment for most types of hyperlipidemia (National Cholesterol Education Program 1993). The American Heart Association guidelines for treating hypercholesterolemia and most studies concerning dietary modification have focused on dietary cholesterol and fat reduction (American Heart Association, 1984).Including water-soluble fiber in the diet was shown to be an additional, important component of cholesterol reduction efforts (Anderson et al. 1990). Oat gum, guar gum and pectin, all soluble fibers, have hypocholesterolemic effects in animals (Anderson et al. 1984, Matheson et al. 1995, Todd et al. 1990). The addition of beans, oat bran, locust bean gum, guar gum, psyllium or pectin to human diets reduces elevated cholesterol levels by 3–20%, depending on study design (Anderson et al. 1984, 1991, Everson et al. 1992, Judd and Truswell 1982, Kay and Truswell 1977, Zavoral et al. 1983). Water-insoluble fiber does not affect cholesterol levels (Anderson et al. 1990, 1991, 1994, Jenkins et al. 1993, Miettinen and Tarpila 1989).The mechanism by which soluble fiber reduces serum cholesterol is not definitively established. The most likely postulate is that intestinal bile salt adsorption by fiber prevents bile salt reabsorption with or without dietary cholesterol absorption (Arjmandi et al. 1992; Ebihara and Schneeman 1989; Miettinen and Tarpila 1989). This leads to increased bile salt synthesis (Everson et al. 1992; Matheson et al. 1995) and low-density lipoprotein (LDL) receptor upregulation and enhanced LDL catabolism, and there is evidence supporting this (Fernandez et al. 1995; Miettinen and Tarpila 1989).
Rice bran contains less total dietary fiber (6–14.4 vs. 15–22 g/100 g), and less soluble fiber (1.8–2.7 vs. 5.3–8.4 g/100 g) than oat bran (Marlett, 1993; Saunders, 1985). Based on its soluble fiber content alone, rice bran should have less hypolipidemic effect than other sources of fiber. However, rice bran is 12–23% oil, a relatively high percentage compared to most other bran sources, and the oil has an unusually high unsaponifiable matter concentration (4.2%) (Saunders 1985; Sugano and Tsuji 1997). This fraction includes tocotrienols, γ-oryzanol, β-sitosterol and unsaturated fatty acids, all of which may contribute to cholesterol reduction (Saunders 1985; Sharma and Rukmini 1987; Sugano and Tsuji 1997; Yoshino et al. 1989). Rice bran oil, possibly because of this unsaponifiable fraction or its fatty acid content, lowers cholesterol levels in hamsters, rats, humans and nonhuman primates (Kahlon et al. 1992; Nicolosi et al. 1991; Purushutharma et al. 1995; Seetharamaiah and Chandrasekhara 1989; Sharma and Rukmini 1986).
Feeding hamsters, mice, chicks and pigs rice bran containing the oil significantly reduces serum cholesterol (Hundemer et al. 1991; Kahlon et al. 1992; Marsono et al. 1993; Newman et al. 1992); rat studies show conflicting results (Anderson et al. 1994; Topping et al. 1990). Studies of rice bran in humans failed to show lipid reduction using defatted rice bran or brown rice (Kestin et al. 1990; Miyoshi et al. 1986; Sanders and Reddy 1992), but rice bran oil does produce an effect (Lichtenstein et al. 1994; Raghuram et al. 1989). Thus full-fat rice bran might reduce cholesterol more in humans than defatted rice bran and other sources of insoluble fiber.
We describe here the results of a randomized, double-blind, placebo-controlled, non-cross-over trial comparing the hypolipidemic effects of stabilized, full-fat rice bran, oat bran and rice starch (placebo) in moderately hyperlipidemic humans.
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METHODS
Subjects.
Healthy subjects of both sexes were recruited through community advertising. The protocol was approved by the Sutter Community Hospitals Institutional Review Board and informed consent was obtained. Fifty-two subjects were enrolled and randomly assigned to groups. They were predominantly middle-class Caucasians. They were nonsmokers, average age 51.7 ± 1.5 y (range 32–64 y), and 85–125% of ideal body weight (Metropolitan Life Insurance Company 1979). The average body mass index was 23.05 and 25.82 kg/m2 for males and females, respectively. None had experienced weight change of >4.5 kg in the preceding 6 mo.
Subjects were excluded if they were taking medication that might affect serum lipids (thyroid or steroid hormones, beta blockers, prednisone or diuretics) or had diabetes mellitus, uncontrolled hypertension (systolic blood pressure >140 mm Hg or diastolic blood pressure >90 mm Hg), symptomatic coronary or vascular disease, thyroid disease, hepatic abnormality or renal disease. The health status of prospective subjects was verified by physical examination and fasting blood chemistry.
Screening serum lipid levels were measured twice in each prospective subject, ≥1 wk apart, before the onset of the study. Those with consistent cholesterol concentrations between 5.95 and 8.02 mmol/L and a fasting triglyceride level <4.48 mmol/L were included in the study.
Materials.
A heat-stabilized, full-fat rice bran product, processed from California medium grain rice and containing a small amount of pectin-free apple juice concentrate (Vitafiber, Pacific Rice Products, Woodland, CA), was used. Oat bran product was obtained from Grain Millers Inc., Bellevue, WA. The rice starch placebo consisted of rice flour, sugar, salt and malt extract (202 Crisp Rice, Pacific Rice Products). Each was presented in a crisp form that could be sprinkled on or mixed into other food. The macronutrient and selected micronutrient content of each product is detailed in Table 1.
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Table 1.
Rice bran, oat bran and rice starch products composition
Protocol.
In this randomized, double blind, noncross-over study, subjects were assigned to receive rice bran product, oat bran product or rice starch placebo. There was no significant difference among groups in age, body mass index or male:female ratio. Subjects were given 84 g product per day to eat in addition to their regular diet for 6 wk. They continued to consume their usual diets and perform their customary exercise. At weekly visits the week's supply of product packets (3/d of 28 g each) was distributed, any unused packets from the previous week were collected and counted, blood pressure and weight were measured, food records were collected and symptoms and exercise were reviewed. Venous blood for measurement of serum cholesterol, triglycerides, high-density lipoprotein-cholesterol (HDL-C)2 and apolipoproteins was drawn at weeks 0, 3 and 6.
Weekly food records were analyzed by computer using Food Processor II (R) software (ESHA Research, Salem, OR). Analysis confirmed that there was no change in the baseline diet during the study period. Product was not included in this analysis.
Chemical analysis.
Cholesterol in finger-stick blood samples (used for screening potential subjects) was measured by Reflotron reflectance photometer (Boehringer Mannheim Diagnostics, Indianapolis, IN). Comprehensive chemistry panels were performed on a Technicon SMAC analyzer (Maclin and Yang 1986) at Physicians Clinical Laboratory, Sacramento, CA. Serum lipid levels were assayed by the Associated Regional and University Pathologists, Inc., Salt Lake City, Utah, using the following methods: total cholesterol and triglycerides were measured by Boehringer Mannheim enzymatic assays (Allain et al. 1974; Wahlefeld 1974). HDL-C was assayed after phosphotungstate precipitation of LDL and very low density lipoprotein (VLDL) (Burstein et al. 1970). LDL cholesterol (LDL-C) was calculated by Friedwald's formula (Friedewald et al. 1972). Apolipoproteins (apoA and apoB) were measured by rate nephelometry (Maciejko et al. 1987) with an ICS A
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