COMMENTARIES

The Effects of a Whole Grain-Enriched Hypocaloric Diet on Cardiovascular Disease Risk Factors in Men and Women with Metabolic Syndrome

Heather I. Katcher¹, Ph.D., R.D., Penny M. Kris-Etherton¹, Ph.D., R.D., and Richard S. Legro², M.D., ¹Department of Nutritional Sciences, Pennsylvania State University, University Park, PA, U.S.A. and ²Department of Obstetrics and Gynecology, Pennsylvania State University College of Medicine, Hershey, PA, U.S.A.

Many health benefits have been ascribed to whole grains, especially in recent years [1-3]. A 30% reduced risk of coronary artery disease and ischemic heart disease has been observed in observational studies (the Nurse’s Health Study [4], the Iowa Women’s Health Study [5], and the Atherosclerosis Risk in Communities Study [6]) in individuals who consume three or more servings of whole grains per day. Several studies have demonstrated a lower BMI and reduced weight gain over time in individuals who consume more whole grains [7]. Whole grains are a good source of dietary fiber (both soluble and insoluble), which favorably affects many physiological processes such as lowering cholesterol and glucose levels, and increasing satiety [8,9]. In addition to fiber, whole grains deliver a package of many bioactive components to the diet including antioxidants, phytochemicals, vitamins, and minerals [9].

Despite the abundance of observational studies and single food studies (e.g. oatmeal), there have been few clinical trials designed specifically to evaluate the effects of whole grains on health outcomes. Two controlled clinical trials have reported improved insulin sensitivity when whole grains were substituted for refined grains [10,11]. However, these studies did not evaluate the effects of whole grains on cardiovascular disease risk factors or weight loss. Thus, we recently published a controlled clinical study designed to assess whether whole grains favorably affect body weight and cardiovascular disease risk. Our objective was to determine whether, indeed, whole grains have a causal effect on CVD risk factors and weight loss, as suggested by the observational studies.

Our study enrolled 50 men and women with metabolic syndrome and a body mass index ³ 30 kg/m² [12]. Study participants were randomly assigned to receive dietary advice either to avoid whole grain foods or to consume all of their grain servings (4-7 servings/day) from whole grains for twelve weeks. Aside from the advice on whole grain servings, participants in both groups met with a dietitian bi-weekly, where they were given the same dietary advice to achieve weight loss. The weight loss goal for all participants was 0.5 to 0.9 kg/week and they were encouraged to exercise at least 30 minutes, three times per week.

Despite our hypothesis that participants in the whole grain group would have a greater amount of weight loss, we observed no significant difference in weight loss between groups: both diet groups lost 4-5 kg. The similar amount of weight loss in both groups likely reflects the fact they made similar dietary changes to facilitate weight loss, such as decreasing total fat and calorie intake and eating more fruits and vegetables.

Of note, there were differences between the whole grain and refined grain groups in some risk factors independent of weight loss. A key finding was that participants in the whole grain group had a 38% reduction in C-reactive protein (CRP) compared with no change in the refined grain group. Both groups had similar levels at baseline. CRP was significantly correlated with BMI at baseline (r = 0.46, p < 0.01), but the change in CRP did not correlate with weight loss (r = -0.07, p = 0.66). Although changes in CRP generally are related to weight loss, our findings agree with the previous study by Esposito et al. [13] that observed a decrease in CRP independent of weight loss in participants consuming a Mediterranean diet high in whole grains, fruit, vegetables, nuts, and olive oil. The reduction in CRP could be due to lower day-long glucose concentrations, decreased oxidative stress produced by antioxidants intrinsic to whole grains, or from reduced release of inflammatory cytokines from adipose tissue.

In support of the latter, we observed a greater reduction in percent fat in the abdominal region in participants consuming whole grains compared with those consuming refined grains (-2.2 ± 2.2% versus -0.9 ± 1.8%). Although both groups had similar reductions in total percent body fat (-1.2 ± 1.3% versus -1.0 ± 1.6%), the whole grain group had a significantly greater reduction in abdominal fat. That whole grains decreased abdominal fat is a novel finding, and agrees with a recent study by Kallio et al. [14] that reported a 21% reduction in adipocyte size in persons with metabolic syndrome consuming a rye-pasta diet with a low postprandial insulin response. Interestingly, there was an increase in expression of genes related to inflammation, oxidative stress, and interleukin cytokines when participants switched to an oat-wheat-potato diet with a high postprandial insulin response.

This study is one of the first clinical trials to demonstrate that whole grain foods have a beneficial effect on CVD risk factors independent of weight loss. Moreover, in our study the benefit of maintaining a whole-grain enriched diet on CRP was comparable to the effects of some statins [15-17]. It is important to recognize that this was a relatively small study (n = 50), over a short period of time (3 months), and that participants in both groups were making other diet and lifestyle changes that may have affected the outcomes we reported. However, since the study was conducted in a free-living population with metabolic syndrome, the results easily translate to persons at risk of CVD who want to include whole grains in their diet and lose weight.

Although subject retention is often challenging in weight loss trials, the present study had a 94% completion rate (47/50) with participants attending 99% of their bi-weekly study visits. Participants in the whole grain group were able to incorporate whole grain foods into their diet (self report), and reported a greater overall diet satisfaction, sense of having a healthy lifestyle, and family support compared with baseline. Given these promising early results, healthcare professionals should counsel patients about a healthy dietary pattern and physical activity as factors that can achieve a significant reduction in CVD risk initially before prescribing pharmaco-therapy for weight loss or management of CVD risk factors.

References

1.    Liu S. 2002. Intake of refined carbohydrates and whole grain foods in relation to risk of type 2 diabetes mellitus and coronary heart disease. J Am Coll Nutr 21: 298-306.
2.    Jacobs DR, Jr., Gallaher DD. 2004. Whole grain intake and cardiovascular disease: a review. Curr Atheroscler Rep 6: 415-23.
3.    McKeown NM. 2004. Whole grain intake and insulin sensitivity: evidence from observational studies. Nutr Rev 62: 286-91.
4.    Liu S, Stampfer MJ, Hu FB, et al. 1999. Whole-grain consumption and risk of coronary heart disease: results from the Nurses' Health Study. Am J Clin Nutr 70: 412-19.
5.    Jacobs DR, Jr., Meyer KA, Kushi LH, Folsom AR.1998. Whole-grain intake may reduce the risk of ischemic heart disease death in postmenopausal women: the Iowa Women's Health Study. Am J Clin Nutr 68: 248-57.
6.    Steffen LM, Jacobs DR, Jr., Stevens J, Shahar E, Carithers T, Folsom AR. 2003. Associations of whole-grain, refined-grain, and fruit and vegetable consumption with risks of all-cause mortality and incident coronary artery disease and ischemic stroke: the Atherosclerosis Risk in Communities (ARIC) Study. Am J Clin Nutr 78: 383-90.
7.    Koh-Banerjee P, Rimm EB. 2003. Whole grain consumption and weight gain: a review of the epidemiological evidence, potential mechanisms and opportunities for future research. Proc Nutr Soc 62: 25-29.
8.    Weickert MO, Pfeiffer AFH. 2008. Metabolic effects of dietary fiber consumption and prevention of diabetes. J Nutr 138: 439-42.
9.    Slavin J. 2003. Why whole grains are protective: biological mechanisms. Proc Nutr Soc 62: 129-34.
10.    Pereira MA, Jacobs DR, Jr., Pins JJ, et al. 2002. Effect of whole grains on insulin sensitivity in overweight hyperinsulinemic adults. Am J Clin Nutr 75: 848-55.
11.    Jang Y, Lee JH, Kim OY, Park HY, Lee SY. 2001. Consumption of whole grain and legume powder reduces insulin demand, lipid peroxidation, and plasma homocysteine concentrations in patients with coronary artery disease: randomized controlled clinical trial. Arterioscler Thromb Vasc Biol 21: 2065-71.
12.    Katcher HI, Legro RS, Kunselman AR, et al. 2008. The effects of a whole grain-enriched hypocaloric diet on cardiovascular disease risk factors in men and women with metabolic syndrome. Am J Clin Nutr 87: 79-90.
13.    Esposito K, Marfella R, Ciotola M, et al. 2004. Effect of a Mediterranean-style diet on endothelial dysfunction and markers of vascular inflammation in the metabolic syndrome: a randomized trial. JAMA 292: 1440-46.
14.    Kallio P, Kolehmainen M, Laaksonen DE, et al. 2007. Dietary carbohydrate modification induces alterations in gene expression in abdominal subcutaneous adipose tissue in persons with the metabolic syndrome: the FUNGENUT Study. Am J Clin Nutr 85: 1417-27.
15.    Hanefeld M, Marx N, Pfutzner A, et al. 2007. Anti-inflammatory effects of pioglitazone and/or simvastatin in high cardiovascular risk patients with elevated high sensitivity C-reactive protein: the PIOSTAT Study. J Am Coll Cardiol 49: 290-97.
16.    Schaefer EJ, McNamara JR, Asztalos BF, et al. 2005. Effects of atorvastatin versus other statins on fasting and postprandial C-reactive protein and lipoprotein-associated phospholipase A2 in patients with coronary heart disease versus control subjects. Am J Cardiol 95: 1025-32.
17.    Mora S, Ridker PM. 2006. Justification for the Use of Statins in Primary Prevention: an Intervention Trial Evaluating Rosuvastatin (JUPITER)--can C-reactive protein be used to target statin therapy in primary prevention? Am J Cardiol 97: 33A-41A.