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American Journal of Clinical Nutrition, Vol. 87, No. 1, 79-90, January 2008
© 2008 American Society for Nutrition

ORIGINAL RESEARCH COMMUNICATION

The effects of a whole grain–enriched hypocaloric diet on cardiovascular disease risk factors in men and women with metabolic syndrome1,2,3

Heather I Katcher, Richard S Legro, Allen R Kunselman, Peter J Gillies, Laurence M Demers, Deborah M Bagshaw and Penny M Kris-Etherton

1 From The Huck Institutes of the Life Sciences (HIK and PMK-E) and the Departments of Nutritional Sciences (HIK, DMB, and PMK-E) and Pathology, Core Endocrine Laboratory (LMD), Pennsylvania State University, University Park, PA; the Departments of Obstetrics and Gynecology (RSL) and Public Health Sciences (ARK), Pennsylvania State University College of Medicine, Hershey, PA; and DuPont Central Research & Development, Wilmington, DE (PJG)

2 Supported by the General Mills Bell Institute of Health and Human Nutrition, grants no K24 HD01476 and M01 RR10732 from the National Institutes of Health, and construction grant no. C06 RR016499 (to the General Clinical Research Center of The Pennsylvania State University).

3 Reprints not available. Address correspondence to PM Kris-Etherton, Department of Nutritional Sciences, 126 South Henderson Bldg, University Park, PA 16802. E-mail: pmk3{at}psu.edu.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Background: Whole-grain foods are associated in observational studies with a lower body mass index and lower cardiovascular disease (CVD) risk. However, few clinical trials have tested whether incorporating whole grains into a hypocaloric diet increases weight loss and improves CVD risk factors.

Objective: The aim of this study was to determine whether including whole-grain foods in a hypocaloric (reduced by 500 kcal/d) diet enhances weight loss and improves CVD risk factors.

Design: Obese adults (25 M, 25 F) with metabolic syndrome were randomly assigned to receive dietary advice either to avoid whole-grain foods or to obtain all of their grain servings from whole grains for 12 wk. All participants were given the same dietary advice in other respects for weight loss.

Results: Body weight, waist circumference, and percentage body fat decreased significantly (P < 0.001) in both groups over the study period, but there was a significantly (P = 0.03) greater decrease in percentage body fat in the abdominal region in the whole-grain group than in the refined-grain group. C-reactive protein (CRP) decreased 38% in the whole-grain group independent of weight loss but was unchanged in the refined-grain group (P = 0.01 for group x time interaction). Total, LDL, and HDL cholesterol decreased in both diet groups (P < 0.05). Dietary fiber and magnesium intakes increased in the whole-grain but not the refined-grain group (P = 0.007 and P < 0.001, respectively, for group x time interaction).

Conclusions: Both hypocaloric diets were effective means of improving CVD risk factors with moderate weight loss. There were significantly (P < 0.05) greater decreases in CRP and percentage body fat in the abdominal region in participants consuming whole grains than in those consuming refined grains.

Key Words: Whole-grain foods • metabolic syndrome • weight loss • fiber • C-reactive protein • CRP • insulin resistance


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
In 2004, the Centers for Disease Control and Prevention (CDC) estimated that as many as 64 million Americans, or 27% of the United States population, have metabolic syndrome (1). Metabolic syndrome is characterized by a cluster of cardiovascular disease (CVD) risk factors, including abdominal obesity, elevated blood glucose, dyslipidemia, and high blood pressure, and it carries a greater risk of type 2 diabetes and CVD (2-4). Lifestyle changes such as diet, weight loss, and exercise are the first line of treatment for metabolic syndrome (5); however, the optimal diet composition is debated (6).

Whole-grain foods are recommended for prevention of CVD because they contain many cardioprotective compounds, including dietary fiber, trace minerals, phytoestrogens, and antioxidants (7). In observational studies, a greater intake of whole-grain foods is associated with less frequent development of metabolic syndrome (8) and lower mortality due to CVD (9). Greater whole-grain consumption also is inversely related to CVD risk factors including body weight, abdominal obesity, and insulin resistance (10-12). On the basis of evidence that dietary patterns high in whole-grain products and fiber are associated with greater diet quality and lower risk of CVD, the American Heart Association now recommends that at least half of a person's grain intake come from whole grains (13). Similar recommendations are made in the 2005 dietary guidelines for Americans (14) and by the American Diabetes Association (15).

Although numerous groups have made recommendations to increase whole-grain intake, there is limited information from randomized, clinical trials on whether the inclusion of whole grains in a hypocaloric diet increases weight loss. Whole grains are believed to have a beneficial effect on body weight because they are usually less energy-dense and more satiating than are refined-grain foods (10). However, a recent study by Melanson et al (16) reported similar reductions in body weight in overweight and obese men and women after a 24-wk hypocaloric diet with or without whole-grain cereals. Changes in other CVD risk factors were not examined.

The aim of the present study was to determine whether including whole-grain foods in a hypocaloric diet enhances weight loss and improves CVD risk factors. We hypothesized that there would be a greater reduction in body weight and greater improvement in CVD risk factors in persons consuming whole grains. The free-living design of this study better predicts whether a diet high in whole grains will reduce CVD risk in the general population.


   SUBJECTS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Participants
Fifty obese adults (25 M, 25 F; age range: 20–65 y) with metabolic syndrome were recruited to participate. Men and women were eligible if they had a body mass index (BMI; in kg/m2) ≥ 30 and met ≥3 of 5 National Cholesterol Education Program Adult Treatment Panel III criteria for metabolic syndrome (17). These criteria were defined as 1) triacylglycerol concentrations ≥ 150 mg/dL, 2) HDL-cholesterol concentrations < 40 mg/dL in men or < 50 mg/dL in women, 3) fasting glucose concentrations ≥ 100 mg/dL, 4) systolic blood pressure ≥ 130 mm Hg or diastolic blood pressure ≥ 85 mmHg (or both), and 5) waist circumference ≥ 102 cm in men or ≥ 88 cm in women. Participants were excluded if they had been diagnosed with type 1 or 2 diabetes, CVD, cancer, or any other serious medical condition or if they were using any medications known to affect glucose, insulin, cholesterol, or reproductive hormones. Also excluded were persons who smoked, drank >2 alcoholic beverages/d, or consumed a diet high in whole grains (>3 servings/d) or who were pregnant or lactating.

All participants gave written informed consent. The study was conducted in accord with the guidelines of the Institutional Review Board of The Pennsylvania State University.

Study design
We used a randomized, open-label, parallel-arm study design in which patients received dietary advice either to avoid whole-grain foods (the refined-grain group) or to obtain all of their grain servings each day from whole-grain foods (the whole-grain group) for 12 wk. Participants were assigned to either a whole-grain or refined-grain hypocaloric diet with the use of a stratified randomization scheme. The stratification factors used in the randomization were sex (male or female) and BMI status (BMI < 40 or ≥ 40). The study opened to accrual in September 2005 and completed enrollment in August 2006.

A registered dietitian met individually with each participant at baseline to discuss the dietary intervention; she also provided educational materials to facilitate understanding and adherence. Participants in the whole-grain group were given a target number of daily whole-grain servings—4, 5, 6, or 7 servings/d—based on the number of grain servings recommended in the 2005 dietary guidelines for Americans for their energy needs (15). Energy needs were calculated by using the Mifflin equation (18) with an activity factor of 1.3, and subtracting 500 kcal to account for the calorie deficit needed to achieve weight loss. Participants in the whole-grain group were given a list and description of whole-grain foods to help them identify foods to include in their diet, and they were encouraged to select foods for which a whole grain is listed as the first ingredient. To ease the transition, participants in the whole-grain group were advised to consume 3 daily servings of whole-grain foods for the first 2 wk of the study and then to increase to their target number of daily whole-grain servings for the remaining 10 wk. Participants in the refined-grain group also were given a list of whole-grain foods and were asked not to consume any of these foods during the study period.

In addition to the instructions about whole-grain servings, participants in both groups were asked to eat, daily, 5 servings of fruit and vegetables, 3 servings of low-fat dairy products, and 2 servings of lean meat, fish, or poultry, as recommended in the 2005 dietary guidelines for Americans. The target macronutrient composition for all participants was 55% of energy as carbohydrate, 30% of energy as fat (with an emphasis on unsaturated fats), and 15% of energy as protein. All participants were encouraged to engage in moderate physical activity for 30 min per session ≥3 times/wk and were instructed to avoid dietary supplements throughout the study period. Participants in both groups were told that their aim was to lose ≥1 pound/wk during the study.

To increase compliance, participants were instructed to keep track of their daily food intake and exercise in a diary log that was provided and to record their weight at home weekly. Every other week, participants visited the study site and reviewed their diet records with a dietitian on a one-on-one basis. During this time, the dietitian presented an educational lesson that explained the rationale for the dietary guidelines used in the study and offered nutritional guidance, encouragement, and suggestions for improvement. The participant's weight, blood pressure, and waist circumference were recorded at each visit. At the end of each visit, each participant selected to take home 2 foods containing either refined grains or whole grains, depending on the participant's randomized assignment. On the weeks that participants did not come in for a study visit, a dietitian contacted them by telephone or E-mail to discuss their progress and address any concerns or questions. A fasting blood draw, 2-h oral-glucose-tolerance test (OGTT), dual energy X-ray absorptiometery (DXA) scan, and biometric measurements were done at the beginning and end of the 12-wk diet period at The Pennsylvania State University General Clinical Research Center (GCRC) at University Park, PA.

Dietary assessment
At baseline and every 4 wk, participants kept a detailed, 3-d diet record. A dietitian reviewed the 3-d diet record with each participant and shared the diet analysis with him or her at the next biweekly visit. Diet records were analyzed with NUTRITION DATA SYSTEM for RESEARCH software (NDS, version 2005; Nutrition Coordinating Center, University of Minnesota, Minneapolis) by a dietitian trained in using the NDS software. If a whole-grain food was not listed in the NDS database, an appropriate whole-grain substitution with a similar macronutrient and dietary fiber content was selected. Grain servings were defined according to the 2005 dietary guidelines for Americans as 1 slice of bread, 1 ounce (28 g) of ready-to-eat cereal, and 1/2 cup (120 mL) of cooked cereal, rice, or pasta. A grain product was identified as a whole grain if a whole grain was listed as the first ingredient on the food label.

A validated diet satisfaction questionnaire was administered at baseline, at week 4, and at the end of the 12-wk study period (19). This 45-item questionnaire evaluated 7 issues that affect diet satisfaction, including ease of meal planning and preparation, convenience, cost, effect on family dynamics, sense of having a healthy lifestyle, presence of negative feelings such as deprivation or embarrassment, and preoccupation with food. The available responses to questions were arranged on a 5-point Likert scale from 1 ("strongly disagree") to 5 ("strongly agree"). A score for each of the 7 sections and a global score for overall diet satisfaction were calculated by averaging the responses to the questions in the respective sections.

Clinical measurements
Waist circumference was measured according to guidelines of the National Heart, Lung, and Blood Institute (NHLBI) (20). Weight was measured while subjects were wearing light clothing and no shoes by using an electronic scale (model CN20; Cardinal/Detecto, Webb City, MO). Blood pressure was measured with the use of an automatic blood pressure monitor (Omron Healthcare Inc, Milton Keynes, United Kingdom). Participants remained comfortably seated with their legs uncrossed for ≥5 min before blood pressure was measured. Three blood pressure measurements were taken ≥1 min apart, and the second and third readings were averaged. DXA scans were performed at baseline and at the end of the study to assess changes in body composition (QDR-4500W; Hologic Corp, Waltham, MA). Each participant underwent a total-body scan using fan-beam mode at baseline and at the end of the study. The percentage body fat (%BF) in the abdominal area (R1 area) was calculated as the %BF in the 50-cm2 area around the central point of the midline between the lateral iliac crests and the lowest rib margins at the end of normal expiration (21). Proper operation of the X-ray subsystem was verified daily by using a spine phantom, and tissue composition calibration was performed 1 time/wk on a tissue equivalent phantom.

Blood samples were collected in the morning after a 12-h fast. A nurse inserted an intravenous catheter into a vein, and a fasting blood sample was drawn into 10-mL syringes and transferred into Vacutainer tubes (VWR Scientific Products, West Chester, PA). An OGTT was then performed with a 75-g oral glucose challenge. Blood samples were taken at 30-min intervals for 2 h for measurement of glucose and insulin concentrations. Serum and plasma were separated by centrifugation for 15 min at 1465 x g (3200 rpm) and 4 °C and aliquoted into 0.5–2.0-mL cryovials and stored at –80 °C until they were analyzed.

Biochemical analysis
Glucose was measured by the glucose oxidase technique using a glucose analyzer (model 2300; Yellow Springs Instruments, Yellow Springs, OH). Insulin was measured by radioimmunoassay (Linco, St Charles, MO), as described by Legro et al (22). Total and HDL cholesterol and triacylglycerol were measured by Quest Diagnostics (Chantilly, VA) with the use of an automated chemistry analyzer (AU-5400; Olympus Optical Co, Tokyo, Japan). LDL-cholesterol concentrations were calculated by using the Friedewald equation (23). Measurements of mass concentrations of LDL-cholesterol subfractions were performed by analytic ultracentrifugation as described elsewhere (24). Nondenaturing polyacrylamide gradient gel electrophoresis with lipid staining of plasma was performed as described previously for determination of peak LDL particle diameter (25). Interleukin-6 (IL-6) and tumor necrosis factor-{alpha} (TNF-{alpha}) were measured by using high-sensitivity (hs) enzyme-linked immunosorbent assays (ELISAs; R&D Systems, Minneapolis, MN). The hs-CRP was measured by using an ELISA developed by the Cytokine Core Laboratory of the Pennsylvania State University GCRC (26). Plasminogen activator inhibitor 1 (PAI-1) was measured by using the Zymutest PAI-1 Antigen ELISA (Hyphen BioMed, Neuville-sur-Oise, France). Apolipoprotein (apo) A-I and apo B were measured by using immunoturbidometric assays (25). All of the immunoassays used had interassay CVs <10% at the median level.

Statistical analysis
The study was designed to detect a 2-kg difference in weight loss between the 2 hypocaloric diet groups at the end of the 12- wk trial. We assumed a dropout rate of 20% and a common SD of 1.8 kg, which resulted in a standardized effect size of 2/1.8 = 1.1. On the basis of these assumptions, to detect a 2-kg difference between the 2 hypocaloric diets at the end of the 12-wk trial, we needed to enroll 50 participants for the study to have a power of 92% for a 2-sided test with a type I error rate of 0.05. The area under the glucose and insulin curves during the OGTT were calculated by using the trapezoidal rule (22). An insulin sensitivity index (ISI) was calculated according to the method of Matsuda and DeFronzo (28).

Two-sample t tests were used to test for differences between the diet groups in subjects’ characteristics measured at baseline. Linear mixed-effects models were fitted to assess the effects of the 2 hypocaloric diet groups over the course of the 12-wk study on biometric, biochemical, dietary intake, and diet satisfaction values (29). The linear mixed-effects model is an extension of the traditional analysis of variance model that accounts for the within- and between-subject correlations inherent in longitudinal trials. If necessary to meet modeling assumptions such as normality, the outcome variable was logarithmically transformed. The df for the mixed-effects models was adjusted by using the method of Kenward and Roger (30). If the diet group x time interaction was significant for a given outcome of interest from a mixed-effects model, then the P values were adjusted by using Bonferroni's procedure to account for multiple testing. The linear relation between the change (postdiet – prediet) in any 2 continuous outcomes was quantified by using Pearson's correlation coefficient. Data were analyzed according to the intention-to-treat principle, and all hypotheses tests were 2-sided. All analyses were performed with SAS software (version 9.1; SAS Institute Inc, Cary, NC).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Twenty-five men and 25 women aged 24–63 y were randomly assigned to the whole-grain (12 M, 13 F) or the refined-grain (13 M, 12 F) group (Figure 1Go). The mean age of the participants in the whole-grain and refined-grain groups was 45.4 ± 8 and 46.6 ± 9.7 y, respectively, and the mean BMI was 35.5 ± 4.1 and 36.1 ± 4.9, respectively. Systolic blood pressure and the percentage of the LDL-III subclass were significantly (P = 0.03) higher at baseline in the refined-grain group than in the whole-grain group, but there were no other significant differences at baseline between the diet groups. Forty-eight participants self-classified as white, one as African American, and one as Hispanic. Forty-seven of the 50 participants (94%) completed the study. One male and one female in the refined-grain group withdrew because of a change in job schedule and family reasons, respectively. One female in the whole-grain group withdrew because of an inability to adhere to the diet.


Figure 1
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  		FIGURE 1.. Flow of participants through the study.

 
Participants in the whole-grain group increased their intake of whole-grain foods to {approx}5 servings/d, whereas participants in the refined-grain group decreased their intake to <0.2 servings/d (Figure 2Go). The primary source of whole-grain foods for participants in the whole-grain group was bread and rolls (2–2.5 servings/d); other sources were ready-to-eat cereal, brown rice, oatmeal, pasta, salty snacks (eg, crackers, snack chips, and popcorn), and snack bars (0.5–1 serving/d) (data not shown).


Figure 2
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  		FIGURE 2.. Mean (±SE) number of servings/d of whole-grain foods consumed by participants in the whole-grain ({blacksquare}; n = 24) and refined-grain ({square}; n = 25) groups at baseline and at weeks 4, 8, and 12. A linear mixed-model analysis with repeated measures showed that the group x time interaction for whole-grain intake was significant (P < 0.001). Pairwise comparisons with Bonferroni adjustment showed that consumption of whole-grain foods increased from baseline at weeks 4, 8, and 12 in the whole-grain group and decreased from baseline in the refined-grain group (P < 0.001 for both).

 
Body weight decreased significantly (P < 0.001) in the whole-grain and refined-grain groups over the 12-wk study period. The decrease was 3.7 kg or 3.6% in the whole-grain group and 5.2 kg or 4.9% in the refined-grain group (Figure 3Go). The group x time interaction for the change in body weight was not significant.


Figure 3
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  		FIGURE 3.. Mean (±SE) cumulative weight loss at each biweekly visit in the whole-grain and refined-grain groups (n = 25 for each). Body weight decreased significantly in both diet groups over the 12-wk study period (P < 0.001). However, the group x time interaction was not significant. Data were analyzed with linear mixed-model analysis with repeated measures.

 
CRP decreased 38% in the whole-grain group, but there was no significant change in CRP in the refined-grain group (Figure 4Go). CRP decreased in 18 (75%) of 24 participants who completed the study in the whole-grain group but in only 12 (52%) of 23 who completed the study in the refined-grain group. In a comparison of only the participants who had a reduction in CRP, the average percentage decrease in CRP was 45% in the whole-grain group and 26% in the refined-grain group (P < 0.01). Although CRP was significantly correlated with BMI at baseline (r = 0.46, P < 0.001), the change in CRP did not correlate significantly with weight loss (r = –0.07, P = 0.66).


Figure 4
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  		FIGURE 4.. Mean (±SE) concentrations of C-reactive protein (CRP) in participants in the whole-grain and refined-grain groups (n = 25 for each) at baseline ({square}) and week 12 ({blacksquare}). Concentrations decreased 38% in the whole-grain group but were unchanged in the refined-grain group (P = 0.01 for group x time interaction). Data were analyzed with linear mixed-model analysis with repeated measures. P values for pairwise comparisons were adjusted by using Bonferroni's procedure to account for multiple testing.

 
Baseline values and changes in biometric measurements, lipids and lipoproteins, glucose and insulin measures, and markers of inflammation and fibrinolysis are listed in Table 1Go. Waist circumference and %BF decreased significantly (P < 0.001) from baseline in both groups. However, the decrease in %BF in the abdominal region was significantly (P = 0.03) greater in the whole-grain group than in the refined-grain group. Total, LDL, and HDL cholesterol and PAI-1 decreased significantly (P < 0.05) from baseline in both diet groups. There were no significant changes in LDL particle size or in IL-6 or TNF-{alpha} over the 12-wk study period. The average percentage change in the area under the curve for insulin after the OGTT was 9.6% for participants in the whole-grain group and 2.0% for participants in the whole-grain group (Figure 5Go). There was a main effect of time for the change in the area under the curve for insulin and the ISI. However, the group x time interaction was not significant. The frequency of the metabolic syndrome criteria did not significantly change within or between diet groups (data not shown).


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  		TABLE 1. Changes ({Delta}) in values of assessed variables during the 12-wk diet period in participants in the whole-grain and refined-grain groups1

 

Figure 5
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  		FIGURE 5.. Mean (±SE) circulating concentrations of glucose (top) and insulin (bottom) during an oral-glucose-tolerance test in participants in the whole-grain (left) and refined-grain (right) groups (n = 25 for each) at baseline (—) and week 12 (• • •). Data were analyzed with a linear mixed-model analysis with repeated measures. The area under the curve for insulin decreased significantly over the 12-wk study period (P = 0.04). However, the group x time interaction for the change in the area under the curve for glucose and insulin was not significant.

 
Analyses of energy and nutrient intake from 3-d recalls administered at baseline and at weeks 4, 8, and 12 are shown in Table 2Go. Energy intake decreased significantly (P < 0.001) from baseline in both diet groups. However, on average, participants in the refined-grain group had a nonsignificantly greater decrease in energy intake. When the study began, with respect to the participants in the whole-grain group, greater emphasis was placed on their consuming all of their whole-grain servings than on their avoiding refined grains. The first 9 participants who completed the study in the whole-grain group averaged a 7-kcal deficit from baseline and a 1.0-kg weight loss. After the first cohort of participants completed the study, a greater emphasis was placed on an avoidance of refined grains and on consumption of only whole-grain foods. The subsequent 15 participants who completed the study in the whole-grain group averaged a 430-kcal deficit from baseline and a 5.3-kg weight loss.


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  		TABLE 2. Daily energy and nutrient intakes at baseline and at week 12 from 3-d food records of the study participants1

 
The percentage of energy from carbohydrate and protein increased significantly (P < 0.01) and that from fat decreased significantly (P < 0.001) in both diet groups compared with baseline. Participants in the whole-grain group increased their intake of total, insoluble, and soluble fiber by 50%, 52%, and 47%, respectively, and those in the refined-grain group increased their intakes by 7%, 5%, and 14%, respectively. Magnesium intake also was significantly (P < 0.001) higher throughout the study period in the whole-grain group than in the refined-grain group.

Ratings of diet satisfaction at baseline and week 12 are listed in Table 3Go. At week 12, participants in both groups had a significantly greater overall satisfaction with their diet, rated a significantly greater sense of having a healthy lifestyle, had a significantly lower preoccupation with food (P < 0.001 for all), and considered their families to be significantly (P < 0.001) more approving of their diet than at baseline. Participants in only the whole-grain group rated their meal planning and preparation as more difficult than at baseline (P = 0.04 for group x time interaction).


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  		TABLE 3. Diet satisfaction ratings at baseline; week 4, and week 12 in participants in the whole-grain and refined-grain groups

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Because obesity and CVD are prevalent health problems around the world, researchers have been interested in the effectiveness of different dietary patterns to decrease body weight and improve other CVD risk factors. We hypothesized that persons who included whole grains in their diet would have a greater reduction in body weight and improvement in CVD risk factors. However, we observed a similar degree of weight loss in men and women with metabolic syndrome who consumed whole grains or refined grains. Despite these similar weight losses, there was a significantly (P = 0.01) greater reduction in CRP, an important predictor of cardiovascular events, in the whole-grain group than in the refined-grain group. Participants in the whole-grain group also significantly (P < 0.01) increased their intake of dietary fiber and magnesium from baseline and had a significantly (P = 0.03) greater reduction of %BF in the abdominal region than did participants in the refined-grain group.

Whole-grain foods are thought to have a beneficial effect on body weight due to their greater fiber content, which decreases energy intake and body weight when supplemented in clinical trials (31). The finding of equivalent weight loss when whole grains are incorporated into a hypocaloric diet is in agreement with a recent study by Melanson et al (16) that reported a similar degree of weight loss in overweight and obese men and women on 6-mo weight-management programs with and without whole-grain cereals. In that study, body weight decreased in the hypocaloric diet groups with and without whole-grain cereals by 5.6 kg and 6.2 kg, respectively, but weight loss between the 2 groups did not differ significantly. Because participants in our study and the study by Melanson et al were given additional advice to achieve weight loss (ie, increase their intake of fruit and vegetables, decrease their fat intake, and decrease portion sizes) beyond eating whole-grain foods, the results of neither study can establish a direct cause-and-effect relation between whole-grain intake and weight loss. A weight-loss study manipulating only the source of grains would be necessary to conclusively establish whether whole grains affect weight loss. Our results do indicate that people can lose weight with a whole grain–enriched diet, as they can while following a conventional hypocaloric diet with refined grains, while benefiting from a greater reduction in CRP.

CRP is an emerging CVD risk factor and independent predictor of cardiovascular events in persons with and without CVD (32). Although changes in CRP correlate with weight loss in clinical trials (33), participants following a whole grain–enriched diet in the present study study lowered their CRP concentration in a manner that did not correlate with weight loss. The magnitude of reduction in CRP concentrations in the whole-grain group was similar to that seen with statins (34-36). However, there were few or no changes in the other measured inflammatory markers, which suggested that the changes seen in CRP with a whole grain–enriched diet were not part of a systemic antiinflammatory event. The finding of lower CRP concentrations independent of weight loss is consistent with a study by Esposito et al (37), in which they compared a 2-y Mediterranean diet high in whole grains, fruit, vegetables, nuts, and olive oil with a prudent diet (50–60% carbohydrate, 15–20% protein, <30% fat) in 180 men and women with metabolic syndrome. In that study, CRP decreased in the Mediterranean diet group independent of weight loss, whereas there was no change in CRP concentrations in men and women who consumed a prudent diet. Although the study of Esposito et al showed a benefit of a Mediterranean diet on CRP, the specific effect of whole-grain foods was not studied.

Some (38, 39) but not all (40) clinical trials have reported that supplementation with dietary fiber does not affect CRP concentrations. Thus, the reduction in CRP in participants consuming whole grains could be due to lower day-long glucose concentrations as a result of their increased fiber intake (40). However, the reduction in CRP could also be due to decreased oxidative stress produced by the antioxidants intrinsic to whole grains, or it could result from reduced release of inflammatory cytokines by adipose tissue. In support of the latter, we observed a greater reduction in %BF in the central abdominal region in participants in the whole-grain group than in participants in the refined-grain group. This may represent a decrease in visceral fat (41). Likewise, a recent study by Kallio et al (42) reported a 21% reduction in adipocyte size in persons with metabolic syndrome consuming a rye-pasta diet with a low postprandial insulin response, whereas there was increased expression of genes related to inflammation, oxidative stress, and interleukin cytokines when participants switched to a wheat-potato diet with a high postprandial insulin response. Finally, the reduced CRP concentration could be due to other components or mechanisms of whole grains that are unknown.

At the end of the study period in the present study, there were no significant differences between groups in changes in biometric outcomes, lipids and lipoproteins, and glucose and insulin measures. However, there were improvements in many of these variables with weight loss, which is in agreement with the findings of other studies (43, 44). Total and LDL cholesterol decreased from baseline, which is in line with the Adult Treatment Panel III guidelines for management of metabolic syndrome and high blood cholesterol (17, 45). HDL cholesterol also decreased during the study period, which is an outcome often observed during weight loss. However, on the basis of previous findings, it is likely that HDL cholesterol will increase if the reduction in body weight is maintained (46).

To assess dietary intake throughout the study period in the present study, participants completed a 3-d recall at baseline and every 4 wk. On average, participants in the refined-grain group had a greater reduction in energy intake than did participants in the whole-grain group. This could be due to the fact that participants in the whole-grain group increased their caloric intake to consume their recommended number of whole-grain servings or to the fact that they ate refined grains in addition to the recommended number of whole-grain servings. As discussed previously, a lower calorie deficit in the first cohort of participants likely accounts for the lower caloric reduction in the whole-grain group.

Participants in both diet groups significantly improved their diet quality by reducing their intakes of saturated fat, cholesterol, sodium, and added sugar. In addition, participants in the whole-grain group increased their intake of dietary fiber to almost 14 g/1000 kcal, which is the amount recommended in the 2005 dietary guidelines for Americans (15) and which is associated with the lowest risk of coronary heart disease (47). Participants in the whole-grain group also significantly increased their intake of magnesium, which improves insulin action and glucose metabolism in patients with type 2 diabetes (48-51). Thus, because of an improved nutrient profile, the consumption of whole-grain foods would be expected to benefit other chronic diseases, including type 2 diabetes.

This study had a high completion and compliance rate, which suggests that both diets were well tolerated. Forty-seven of 50 participants completed the study, and these 47 participants attended 99% of their scheduled study visits. In support of this, ratings of overall diet satisfaction, a sense of having a healthy lifestyle, and family support of the diet increased in participants in both treatment groups. Participants in the whole-grain group—but not those in the refined-grain group—rated their meal planning and preparation as more difficult than at baseline, which indicates that convenience may be a limitation to incorporating whole grains into the diet.

A strength of the present study is that it was conducted in a free-living population with metabolic syndrome, so that the results easily translate to persons at risk of CVD who want to include whole grains in their diet with the goal of losing weight. A limitation, however, is that other behavioral changes in exercise and diet may account for the effects that we observed. The present study also had a small sample size and duration, which gave little power to detect differences between groups in secondary outcomes. However, given that a wide range of whole-grain foods are now available to consumers, the results of the present study are timely, because they show that a diet high in whole grains can improve CVD risk factors. Future studies examining larger cohorts for longer periods are necessary to determine the long-term health benefits of whole grains.


   ACKNOWLEDGMENTS
 
We thank Amy Ciccarella, Mary Lou Kiel, Kari Whitehead, and Kitti Halverson for their help with the dietary counseling; Ronald Krauss for his help with the measurement and analysis of LDL particle size; and Julie Ello-Martin for her help with the diet satisfaction questionnaire. We also thank the staff at the Pennsylvania State University GCRC and Core Endocrine Lab for their help with the clinical tests and laboratory assays. The study was conducted under ClinicalTrials.gov Identifier no. NCT00455065.

The authors’ responsibilities were as follows—HIK, ARK, DMB, RSL, and PMK-E: study design; HIK: recruiting, data collection, and manuscript preparation under the supervision of DMB, PMK-E, and RSL; ARK and HIK: data analysis; LMD: most of the laboratory tests; PJG: significant advice on the analysis and interpretation of the results; and all authors: review of the manuscript and provision of scientific and editorial input. None of the authors had a personal or financial conflict of interest.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
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Received for publication May 24, 2007. Accepted for publication September 4, 2007.




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