The Effects of Goami No. 2 Rice, a Natural Fiber-Rich Rice, on Body Weight and Lipid Metabolism

Authors


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Department of Endocrinology and Metabolism, Ajou University School of Medicine, San-5 Wonchon Dong, Yongtong Gu, 443-721, Suwon, Republic of Korea. E-mail: LKW65@ajou.ac.kr

Abstract

Objective: Increased intake of dietary fiber reduces the risk of obesity and type 2 diabetes. We assessed the effects of a fiber-rich diet on body weight, adipokine concentrations, and the metabolism of glucose and lipids in non-obese and obese subjects in Korea, where rice is the main source of dietary carbohydrates.

Research Methods and Procedures: Eleven healthy, non-obese and 10 obese subjects completed two 4-week phases of individual isoenergetic food intake. During the control diet phase, subjects consumed standard rice; during the modified diet phase, subjects consumed equal proportions of fiber-rich Goami No. 2 rice and standard rice. We used a randomized, controlled, crossover study design with a washout period of 6 weeks between the two phases.

Results: After the modified diet phase, body weight was significantly lower in both the non-obese and obese subjects (non-obese, 57.0 ± 2.9 vs. 56.1 ± 2.8 kg, p = 0.001; obese, 67.7 ± 2.1 vs. 65.7 ± 2.0 kg, p < 0.001 for before vs. after). The BMI was significantly lower in obese subjects (26.9 ± 0.5 vs. 26.0 ± 0.6 kg/m2, p < 0.001). The modified diet was associated with lower serum triacylglycerol (p < 0.01), total cholesterol (p < 0.01), low-density lipoprotein cholesterol (p < 0.05), and C-peptide (p < 0.05) concentrations in the obese subjects.

Discussion: These results indicate that fiber-rich Goami No. 2 rice has beneficial effects and may be therapeutically useful for obese subjects.

Introduction

Type 2 diabetes is 3 to 7 times more prevalent in obese adults than in adults of normal weight (1). Therefore, strategies that improve nutrition and increase physical activity are essential to stem the obesity epidemic. Several studies have shown that a high rate of intake of fiber-rich carbohydrates is beneficial for weight management (2), and recent reports have revealed a correlation between increased intake of dietary fibers and a lower incidence of cardiovascular disease (3, 4), type 2 diabetes (2, 5, 6), stroke (7), and colorectal cancer (8).

In 1976, Trowell et al. (9) defined dietary fiber as a collection of lignin and non-starch or non-α-glucan polysaccharides. Dietary fibers absorb water, form gels, exchange positive ions, relieve constipation, lower serum cholesterol levels, improve insulin resistance, and absorb toxic organic metabolites (10, 11). Dietary fibers (soluble fibers, in particular) are highly viscous and are broken down by intestinal microbacteria into absorbable, short-chain fatty acids (12).

With the increased interest in dietary fiber, the genetics and breeding division of the National Institute of Crop Science under the Korean Rural Development Administration developed a natural fiber-rich rice called Goami No. 2. Physicochemical analysis revealed that Goami No. 2 rice has unusually high amylose content, a β-type starch crystallinity, and a remarkably low proportion of short chains in the glucan chain fraction of debranched starch, all of which contribute to the unsuitability of Goami No. 2 as a replacement for ordinary rice. In addition, the ultrastructure of Goami No. 2 rice in situ in fractured whole grain and isolated starch preparations is strikingly different from that of ordinary rice. The relatively higher rigidity, lower swelling power, and poorer gelatinization of Goami No. 2 rice has been attributed to the presence of high amounts of starch granule-associated protein and embraced lipid (13, 14).

To assess the effects of Goami No. 2 rice on body weight management and obesity, we compared the effects of the intake of this fiber-rich rice with the effects of a diet of standard rice on several metabolic markers of glucose metabolism, lipid metabolism, and adipokine concentrations in non-obese and obese subjects. We used a randomized, controlled, crossover study design.

Research Methods and Procedures

Subjects

Eleven healthy, non-obese subjects (two men and nine women) and 10 obese subjects (two men and eight women) volunteered for this study. Before the diet phase of the study (i.e., at baseline), the obese subjects had a BMI of at least 25 kg/m2. New criteria for the definition of overweight and obesity for Asians in the Asia-Pacific region were proposed in 2000 by the World Health Organization as BMI ≥ 25 kg/m2 (15). None of the subjects had evidence of acute or chronic illness or recent changes in body weight, and none was taking medication. All subjects provided written informed consent that was approved by the institutional Medical Ethics Committee.

Study Design

The study comprised two randomly ordered 4-week diet phases that were separated by a 6-week washout period. The total length of the study was 14 weeks. During each diet phase, the subjects consumed either a control diet (standard refined rice) or a modified diet (a 1:1 ratio of standard and Goami No. 2 rice). Total daily calorie intake was determined using the 24-hour recall method and the Computer Aided Nutritional Analysis program (CAN-pro version 1.0, Seoul, Republic of Korea) developed by the Korean Nutrition Society, which took into account the eating habits, BMI, and level of physical activity of each subject. In addition, snacking habits were considered to determine the frequency and amount of snacks (e.g., milk, fruit, and crackers) consumed by each subject. All meals including snacks were provided by the investigator. The total daily calories provided by the control and modified diets per subject were equal to those of the subjects’ usual diets. The average amount of rice per meal was 76 grams. The control and modified dietary macronutrient composition was 60% carbohydrate, 20% protein, and 20% fat (16). The subjects consumed their usual diet of standard refined rice during the washout period. Subjects were evaluated using anthropometric, biochemical, and hormonal measurements at baseline and on the last day of each dietary phase. Waist circumference was measured at the midpoint between the lower rib margin and the iliac crest. Body fat content was measured using a bioimpedance analyzer (BIA 101S; RJL Systems, Clinton Township, MI). Fasting blood samples were drawn to measure the concentrations of glucose, insulin, C-peptide, free fatty acids, lipids [total and high-density lipoprotein (HDL)1-cholesterol and triacylglycerol], and adipokines (leptin, resistin, and adiponectin). Postprandial (30, 60, and 120 minutes) blood samples were drawn to measure the concentrations of glucose, insulin, C-peptide, free fatty acids, and triacylglycerol. All subjects consumed 76 grams of standard rice for the postprandial test during the control diet phase and 36 grams each of standard and Goami No.2 rice during the modified diet phase. The area under the curve was estimated.

Before the study, individual habits and lifestyles of the subjects were recorded, including medical and family histories. We required that all boiled rice and >80% of the side dishes were consumed during a meal. All participants kept a diary in which they recorded food intake. Compliance was monitored by clinical dietitians through one-on-one interviews with each subject every day. All subjects were advised to maintain their usual level of physical activity. We confirmed that physical activity remained unchanged by administering a questionnaire at baseline and on the last day of the study.

Biochemical Parameters

The following biochemical parameters were measured. Glucose concentrations were measured by the glucose oxidase method. Insulin and C-peptide concentrations were measured by radioimmunoassay. Cholesterol and triacylglycerol concentrations were measured enzymatically. Low-density lipoprotein (LDL)-cholesterol concentrations were estimated indirectly using the Friedewald formula (LDL = total cholesterol − [HDL + (triacylglycerol/5)]) for subjects in whom the serum triacylglycerol concentration was <4.52 mM (17). LDL-cholesterol concentrations were measured directly if the serum triacylglycerol concentration was >4.52 mM. Insulin resistance was calculated using the homeostasis model of insulin resistance [HOMA-IR; insulin resistance = [fasting insulin concentration (microunits per milliliter) × fasting glucose concentration (millimolar)]/22.5] (18). Serum used to measure adipokine concentrations was stored at −70 °C. Plasma leptin concentrations were measured by immunoradiometric assay (human leptin immunoradiometric assay, DSL-23, 100; Diagnostic System Laboratories, Inc., Webster, TX). Serum resistin and total adiponectin concentrations were measured using radioimmunoassay kits (resistin, Phoenix Pharmaceuticals, Inc. Belmont, CA; adiponectin, HADP-61HK; Linco Research, St. Charles, MO).

Comparative Analysis of Nutrients in Standard and Goami No. 2 Rice

In standard rice, the proportions of crude fiber, insoluble dietary fiber, and soluble dietary fiber were 0.1, 1.8, and 0.1 grams per 100 grams, respectively. In Goami No. 2 rice, the proportions of the same types of fiber were 0.8, 3.4, and 0.6 grams per 100 grams, respectively. The protein and lipid contents were 6.9 and 0.5 grams per 100 grams, respectively, in standard rice and 8.9 and 0.8 grams per 100 grams, respectively, in Goami No. 2 rice. The fatty acid content was 3.5 mg per 100 grams in standard rice and 6.8 mg per 100 grams in Goami No. 2 rice.

Statistical Analyses

All data in the text are presented as the mean ± SE. Statistical analyses were carried out using SPSS for Windows (version 11.0; SPSS Inc., Chicago, IL). To compare non-parametric data between groups, we used a Wilcoxon signed rank test. Changes in the values of parameters after the modified diet vs. the control diet were evaluated using a Wilcoxon signed rank test and the net differences of values for each diet. We defined the net difference as the difference between values for the 1st and final day of the diet phase. We took p < 0.05 to be statistically significant.

Results

Compared with the non-obese subjects, obese subjects had a greater body weight, BMI, body fat content, and waist circumference (body fat content, 15.8 ± 1.2 vs. 23.0 ± 0.6 kg; waist circumference, 71.5 ± 2.2 vs. 80.9 ± 2.1 cm; p < 0.01); higher fasting concentrations of plasma C-peptide and adiponectin (p < 0.05 for each); and greater insulin resistance (p < 0.01) at baseline (Table 1).

Table 1. . Changes in BMI and concentrations of hemoglobin A1c, leptin, adiponectin, and resistin before and after the 4-week dietary phase*
 Control dietModified diet 
 D1D28D1D28p
  • D1, 1st day of diet phase; D28, final day of diet phase; HDL, high-density lipoprotein; LDL, low-density lipoprotein; HOMA-IR, value of homeostasis model of insulin resistance; SEM, standard error of the mean.

  • *

    Values are the mean ± SEM.

  • p < 0.05 for net difference vs. control diet phase for each subject.

  • p < 0.01 vs. D1.

  • §

    p < 0.05 vs. D1.

Healthy controls (n = 11)     
 Weight (kg)56.7 ± 2.856.8 ± 2.857.0 ± 2.956.1 ± 2.8§0.041
 BMI (kg/m2)21.9 ± 0.722.0 ± 0.722.0 ± 0.721.8 ± 0.6§0.047
 Total cholesterol192.6 ± 10.4181.4 ± 10.4176.1 ± 10.4184.5 ± 11.90.033
 HDL-cholesterol58.2 ± 3.853.9 ± 4.451.0 ± 3.551.7 ± 4.00.041
 LDL-cholesterol115.2 ± 9.8111.4 ± 9.6104.4 ± 9.4113.5 ± 9.80.155
 Triacylglycerol (mg/dL)96.1 ± 10.080.5 ± 8.4103.6 ± 12.696.5 ± 14.00.424
 Adiponectin (μg/mL)5.27 ± 0.624.92 ± 0.815.94 ± 1.178.01 ± 1.830.374
 Leptin (ng/mL)10.56 ± 1.6410.33 ± 1.349.67 ± 1.349.04 ± 1.280.857
 Resistin (ng/mL)53.43 ± 5.9360.02 ± 4.1058.63 ± 6.1360.05 ± 3.031.000
 HOMA-IR1.15 ± 0.061.27 ± 0.111.29 ± 0.111.54 ± 0.160.790
Obese subjects (n = 10)     
 Weight (kg)67.3 ± 2.266.9 ± 2.267.7 ± 2.165.7 ± 2.00.074
 BMI (kg/m2)26.7 ± 0.526.5 ± 0.526.9 ± 0.526.2 ± 0.60.037
 Total cholesterol193.9 ± 14.7180.5 ± 12.0187.4 ± 9.5162.9 ± 8.8§0.139
 HDL46.1 ± 3.143.5 ± 1.645.1 ± 2.444.1 ± 2.40.959
 LDL112.2 ± 13.3107.7 ± 10.4111.3 ± 6.897.0 ± 7.90.203
 Triacylglycerol (mg/dL)140.6 ± 23.5146.4 ± 27.7153.0 ± 35.3108.8 ± 21.1§0.059
 Adiponectin (μg/mL)6.73 ± 1.046.42 ± 1.238.39 ± 1.167.11 ± 1.440.878
 Leptin (ng/mL)16.88 ± 2.5215.91 ± 2.3314.92 ± 2.0815.16 ± 2.110.203
 Resistin (ng/mL)56.81 ± 5.1255.50 ± 3.8653.55 ± 3.3050.21 ± 3.460.169
 HOMA-IR2.32 ± 0.172.87 ± 0.312.26 ± 0.182.72 ± 0.190.799

There was a significant difference in the mean amounts of nutrients ingested during the control and modified diet phases (vegetable protein, 45.8 ± 2.9 vs. 50.1 ± 3.5 g/d, p < 0.001; total fatty acids, 40.5 ± 4.2 vs. 47.3 ± 3.7 g/d, p < 0.001; and crude fiber, 12.2 ± 0.6 vs. 13.8 ± 0.6 g/d, p < 0.001). The obese subjects ingested a greater amount of total, saturated, and monounsaturated fatty acids than the non-obese subjects during the modified diet phase (total fatty acids, 49.5 ± 3.3 vs. 45.4 ± 3.1 g/d; p < 0.05) (Table 2). As shown in Table 3, serum glucose concentrations were not affected by diet. In the obese subjects, the serum triacylglycerol concentration was significantly lower after the modified diet phase than after the control diet phase only at 30 and 60 minutes.

Table 2. . Mean nutrient analysis of daily intake during the study*
 Healthy controls (n = 11)Obese subjects (n = 10)
Daily intake by typeControl dietModified dietControl dietModified diet
  • SFA, saturated fatty acid; MUFA, monounsaturated fatty acid; PUFA, polyunsaturated fatty acid; SEM, standard error of the mean.

  • *

    Values are mean ± SEM.

  • p < 0.01 vs. the control diet for the same group.

  • p < 0.05 vs. the control diet for the same group.

  • §

    p < 0.05 vs. healthy subjects for the same diet phase.

Energy (kcal)1832 ± 431839 ± 381943 ± 421964 ± 43
Protein (g)    
 Vegetable45.3 ± 0.949.2 ± 1.046.3 ± 0.951.1 ± 1.1
 Animal46.7 ± 0.946.2 ± 0.848.8 ± 1.048.8 ± 1.0
Lipids (g)    
 Vegetable30.0 ± 0.630.0 ± 0.130.1 ± 0.130.1 ± 0.1
 Animal19.8 ± 0.919.3 ± 0.821.9 ± 1.021.9 ± 1.0
Carbohydrate (g)256.4 ± 8.4255.6 ± 8.0275.2 ± 9.2275.2 ± 9.2
Crude fiber (g)12.3 ± 0.213.7 ± 0.212.2 ± 0.213.9 ± 0.2
Ash content (g)37.2 ± 0.338.5 ± 0.237.6 ± 0.439.3 ± 0.3
Cholesterol (mg)250.3 ± 3.1248.3 ± 2.7257.5 ± 3.6257.5 ± 3.6
Total fatty acids (g)39.5 ± 1.545.4 ± 0.941.6 ± 1.049.5 ± 1.1†,§
 SFA11.4 ± 0.813.6 ± 0.512.7 ± 0.715.9 ± 0.6‡,§
 MUFA12.2 ± 0.514.1 ± 0.312.7 ± 0.315.3 ± 0.3†,§
 PUFA15.9 ± 0.317.7 ± 0.216.1 ± 0.218.3 ± 0.3
Table 3. . Effects on postprandial (30, 60, and 120 minutes) serum glucose, free fatty acid, insulin, and C-peptide concentrations*
 Baseline30 Minutes60 Minutes120 Minutes
  • D1, 1st day of diet phase; D28, final day of diet phase; SEM, standard error of the mean.

  • *

    Values are mean ± SEM.

  • p < 0.01 vs. initial (baseline) value (D1) for each group.

  • p < 0.05 vs. initial (baseline) value (D1) for each group.

  • §

    p < 0.05 for net difference vs. control diet phase for each subject.

Healthy controls (n = 11)    
 Glucose (mg/dL)    
  Control diet D186.1 ± 2.5135.8 ± 8.2119.5 ± 8.195.4 ± 4.3
   D2881.5 ± 2.5122.6 ± 6.4117.7 ± 6.3103.8 ± 6.7
  Modified diet D187.9 ± 1.8128.2 ± 4.6115.2 ± 7.297.0 ± 3.4
   D2884.9 ± 1.7120.9 ± 5.1109.8 ± 7.9100.0 ± 4.8
  p§0.4250.8390.5410.632
 Free fatty acids (uEq/L)    
  Control diet D1452.1 ± 52.6314.1 ± 37.8181.2 ± 28.492.1 ± 11.0
   D28452.5 ± 52.9342.9 ± 46.7193.1 ± 26.5115.8 ± 13.0
  Modified diet D1337.2 ± 44.0285.6 ± 48.5170.5 ± 33.298.8 ± 16.7
   D28425.9 ± 50.8316.0 ± 43.5194.0 ± 29.4114.7 ± 9.1
  p§0.5200.9500.6760.959
 Triacylglycerol (mg/dL)    
  Control diet D196.1 ± 10.090.0 ± 8.991.9 ± 8.693.7 ± 6.7
   D2880.5 ± 8.481.8 ± 6.981.5 ± 6.573.4 ± 7.1
  Modified diet D1100.5 ± 11.4107.0 ± 13.1104.5 ± 13.283.2 ± 10.6
   D2896.5 ± 14.090.9 ± 12.993.4 ± 13.284.6 ± 12.0
  p§0.4270.8010.7140.766
 Insulin (uIU/mL)    
  Control diet D15.49 ± 0.3248.85 ± 6.5141.17 ± 5.0725.95 ± 4.40
   D286.35 ± 0.5350.97 ± 6.5642.65 ± 5.7532.76 ± 5.23
  Modified diet D15.97 ± 0.4836.98 ± 3.4235.45 ± 4.9629.75 ± 5.64
   D287.46 ± 0.8339.80 ± 4.2135.97 ± 3.7723.06 ± 3.36
  p§0.6720.7550.9530.191
 C-peptides (ng/mL)    
  Control diet D11.76 ± 0.145.32 ± 0.496.11 ± 0.565.38 ± 0.61
   D281.51 ± 0.104.11 ± 0.505.31 ± 1.105.54 ± 1.60
  Modified diet D11.71 ± 0.154.86 ± 0.516.23 ± 0.795.06 ± 0.80
   D281.62 ± 0.123.89 ± 0.285.29 ± 0.783.78 ± 0.43
  p§0.5460.6880.9920.510
Obese subjects (n = 10)    
 Glucose (mg/dL)    
  Control diet D189.3 ± 2.2130.6 ± 4.3139.6 ± 7.5110.9 ± 7.1
   D2888.3 ± 1.4117.6 ± 3.0120.7 ± 5.3106.6 ± 5.2
  Modified diet D194.2 ± 3.0141.1 ± 7.3132.8 ± 10.495.7 ± 2.2
   D2888.5 ± 3.1125.3 ± 4.9116.2 ± 5.598.1 ± 2.8
  p§0.5770.9380.7480.376
 Free fatty acids (uEq/L)    
  Control diet D1389.9 ± 62.5342.6 ± 39.1209.2 ± 31.9142.6 ± 20.4
   D28547.6 ± 47.4456.3 ± 46.0261.6 ± 39.2153.1 ± 21.6
  Modified diet D1417.2 ± 67.5329.0 ± 48.4217.3 ± 40.2126.1 ± 20.5
   D28585.9 ± 47.0468.3 ± 36.7273.7 ± 33.3158.0 ± 19.3
  p§0.5970.4360.9540.590
 Triacylglycerol (mg/dL)    
  Control diet D1140.6 ± 23.5136.9 ± 22.2137.5 ± 22.6131.7 ± 22.7
   D28146.4 ± 27.7139.0 ± 26.0139.1 ± 25.5129.8 ± 24.1
  Modified diet D1153.0 ± 35.3155.0 ± 30.8150.5 ± 29.3136.8 ± 30.2
   D28108.8 ± 21.1102.6 ± 19.3105.1 ± 18.598.6 ± 19.2
  p§0.0630.0080.0130.073
 Insulin (uIU/mL)    
  Control diet D110.68 ± 0.8557.21 ± 5.9665.62 ± 7.5635.35 ± 5.05
   D2813.33 ± 1.5146.84 ± 6.5663.63 ± 10.5735.56 ± 3.71
  Modified diet D19.73 ± 0.5866.12 ± 10.1361.16 ± 10.3632.69 ± 5.06
   D2812.73 ± 1.0750.27 ± 5.1061.58 ± 9.7835.96 ± 4.48
  p§0.5760.8880.7770.925
 C-peptides (ng/mL)    
  Control diet D12.89 ± 0.375.79 ± 0.587.97 ± 0.606.10 ± 0.69
   D282.13 ± 0.243.71 ± 0.755.46 ± 0.775.96 ± 0.97
  Modified diet D12.75 ± 0.215.76 ± 0.617.33 ± 0.846.17 ± 0.62
   D281.83 ± 0.043.21 ± 0.384.95 ± 0.484.49 ± 0.46
  p§0.3090.6810.7980.381

Significant decreases in body weight and BMI were observed in obese subjects after the modified diet phase (body weight, 67.7 ± 2.1 vs. 65.7 ± 2.0 kg, p < 0.001; BMI, 26.9 ± 0.5 to 26.0 ± 0.6, p < 0.001 for before vs. after). Total cholesterol (p < 0.05), LDL-cholesterol (p < 0.01), and triacylglycerol (p < 0.05) concentrations were significantly lower in the obese subjects after the modified diet phase. Baseline data for the control diet phase were no different from those for the modified diet phase, except for total and HDL-cholesterol in healthy subjects. The net difference in the BMI of obese subjects after the modified diet phase was significantly lower than that after the control diet phase (97.2 ± 3.0% vs. 99.2 ± 1.4%; p < 0.05). Comparison of the net differences after the control and modified diet phases revealed an increase in the concentration of total cholesterol (94.4 ± 8.7% vs. 105.1 ± 14.3%; p < 0.05) and HDL-cholesterol (92.8 ± 12.9% vs. 101.6 ± 11.2%; p < 0.05) in the non-obese subjects after the modified diet phase. As indicated in Table 1, serum adipokine (adiponectin, resistin, and leptin) concentrations and HOMA-IR values were not affected by diet.

Most subjects noted difficulty with digestion as a disadvantage of the fiber-rich diet, whereas a few subjects reported that improved taste was an advantage. Only one subject was excluded due to poor compliance. The remaining 21 subjects consumed all of the boiled rice and more than 80% of the side dishes during each meal. Overall, compliance was satisfactory. Individual levels of physical activity did not change during the study.

Discussion

The long-term efficacy of a dietary approach to weight control remains to be determined. The ingestion of dietary fiber has been reported to improve the glycemic response and circulating insulin concentrations both in healthy subjects and in patients with type 2 diabetes (19, 20). The effects of dietary fiber on dyslipidemia in insulin-resistant persons vary, but the consumption of 3 g/d soluble dietary fiber is associated consistently with a reduction in total cholesterol concentrations (21, 22, 23, 24, 25, 26, 27). In 2002, Nicola et al. (19) of the Framingham Offspring Study reported that a greater amount of fiber in the diet was correlated with a decrease in BMI, waist-to-hip ratio, total cholesterol concentrations, and concentrations of LDLs. In support of this finding, another study compared the effects of a diet that contained 24 g fiber/d (a relatively high proportion of dietary fiber) with the effects of a diet that contained 50 g fiber/d and revealed that the high-fiber diet improved glycemic control, reduced hyperinsulinemia, and decreased plasma lipid levels (27). It would seem, therefore, that the consumption of a large amount of fiber is necessary to confer a metabolic benefit.

In the present study, we found that the consumption of a high-fiber diet produced a greater decrease in the concentrations of dietary metabolites, BMI, and postprandial triacylglycerol concentrations in obese subjects than did the consumption of a diet of standard rice. Diet can affect body weight through multiple pathways, including the control of satiety and metabolic efficiency and modulation of the secretion and actions of insulin. In the present study, the difference between the standard and high-fiber diets was the quality of carbohydrates; both diets provided equal amounts of energy and macronutrients. In addition, we took into account the usual eating habits and physical activity patterns of individual subjects when quantitatively organizing the meal plan. We also took care to prevent any major changes to the usual lifestyle of the subjects during the study period.

According to the Korean National Health and Nutrition Survey of 2001, the average daily energy intake in Republic of Korea was 1975.8 calories. Protein, fat, and carbohydrates were consumed at rates of 71.6, 41.6, and 315 g/d, respectively, which were the equivalent of 14.9%, 19.5%, and 65.6% of the total daily energy intake, respectively. Fiber was consumed at a rate of 6.6 g/d. Before participation in the present study, the subjects’ usual meal contained 4.36 g crude fiber/1000 kcal energy consumed; this value was relatively low compared with the 6.47 and 7.27 g crude fiber/1000 kcal in the control and modified diet.

We found that the fasting and postprandial serum concentrations of C-peptide were lower after the modified diet phase, whereas the fasting serum insulin concentration was elevated, and the HOMA-IR value was unchanged after the control and modified diet phases. Improved insulin sensitivity and reduced postprandial glycemia after the consumption of a high-fiber diet may be attributable to the gel-forming property of soluble fibers, which delays the rate at which carbohydrates are absorbed (10, 11, 12, 27, 28). In the present study, insoluble cereal fiber (rather than soluble fiber) was the predominant form of fiber that had a favorable effect on fasting insulin concentrations (19). This is supported by the findings of Max et al. (29), who reported in a meta-analysis of randomized controlled trials that guar gum (a soluble dietary fiber) did not reduce body weight. The amount of soluble fiber intake per meal was not analyzed in the present study. However, we found that crude fiber intake was lower during the control diet phase than during the modified diet phase. Nevertheless, the intake of crude fiber in both phases was below the recommended range (20 to 35 g/d). Therefore, we believe that dietary fiber might not be the only factor that resulted in the improved weight control and lipid profile observed in our study.

Whether the glycemic index of food is relevant to human health is controversial. In the literature, there is evidence that consumption of foods with a low glycemic index can improve several measures of carbohydrate metabolism and lipid profiles (30, 31). A recent study demonstrated that, compared with a diet of high-glycemic index food, a 4-week diet of low glycemic-index food improved both fasting glycemia and hemoglobin A1c levels, as well as whole-body glucose use in individuals with type 2 diabetes (32). We did not analyze the glycemic index of the foods used in the present study.

The higher rigidity, lower swelling power, and poorer gelatinization of Goami No. 2 rice relative to ordinary rice have been attributed to the high amount of starch granule-associated protein and embraced lipid within this rice. Previous physicochemical analysis of Goami No. 2 rice revealed unusually high amylose content, β-type starch crystallinity, and a markedly lower proportion of short chains in the distribution of the glucan chain fraction of debranched starch, all of which contribute to the unsuitability of Goami No. 2 rice as a replacement for normal rice. In addition, the ultrastructure of Goami No. 2 rice is strikingly different from that of normal rice in in situ, fractured whole grain, and isolated starch preparations (13, 14). Although Goami No. 2 rice was less palatable than ordinary rice, all subjects consumed most of the foods provided. In other words, the total daily intake of calories per subject during the control and modified diet phase was equal to that provided by the subjects’ usual diets. In addition, the usual level of physical activity remained unchanged throughout the study. The large amounts of protein, lipid, crude fiber, and ash material in Goami No. 2 rice and the ultrastructural differences between this rice and normal rice could account for the weight reduction observed in our subjects after the modified diet phase.

After the modified diet phase, both non-obese and obese subjects exhibited a significant decrease in body weight (on average, a 1.6% and 3.0% decrease in body weight in non-obese and obese subjects, respectively, compared with baseline values). However, plasma adipokine concentrations were unchanged. This result concurs with the findings of Antonios et al. (33), who reported that adiponectin and tumor necrosis factor-α concentrations in obese subjects on a protein-sparing, very low-calorie diet were unaffected despite a marked improvement in glucose, insulin, and triacylglycerol concentrations after 4 to 6 weeks of weight loss (7% on average). It is possible that substantial and sustained weight reduction is required to correct altered adipocyte function, which might be affected by increased concentrations of adiponectin. Antonios et al. (33) postulated that the lack of change in adiponectin concentrations reflected persistent adipocyte dysregulation despite the initiation of a rapid weight loss. These authors suggested that a critical amount of total adiposity must be lost before the adipocyte can resume a more balanced function (33).

In conclusion, weight loss in obese subjects was greater after 4 weeks on a high-fiber diet that included fiber-rich Goami No. 2 rice than after a diet of standard rice. The Goami No. 2 rice diet also contributed to a decrease in triacylglycerol concentrations in obese subjects. Therefore, the implementation of a sustained, long-term diet that includes Goami No. 2 rice or other foods that contain a high proportion of dietary fiber may improve health by decreasing the risk of cardiovascular disease.

Acknowledgement

This work was supported by 2003 Specific Research-Promoting Joint Projects, Rural Development Administration, and a grant from the Korean Health 21 R&D Project, Ministry of Health and Welfare (A050463), Republic of Korea (to K.W.L.).

Footnotes

  • 1

    Nonstandard abbreviations: HDL, high-density lipoprotein; LDL, low-density lipoprotein; HOMA-IR, homeostasis model of insulin resistance.

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