COMMENTARIES

Soy and Metabolic Syndrome

Leila Azadbakht, Ph.D., Assistant Prof. of Nutrition,
Department of Nutrition,
School of Health,
Isfahan University of Medical Sciences,
Isfahan,
Iran
Tel: 0311 7922791
E-mail: azadbakht@hlth.mui.ac.ir

Introduction

The metabolic syndrome is a heterogeneous condition accompanied by visceral adiposity, dyslipidemia, hypertension, and insulin resistance [1,2]. Elevated blood levels of inflammatory markers such as C-reactive protein (CRP), interleukin-2 (IL-2), interleukin-6 (IL-6), interleukin-18 (IL-18), and tumor necrosis factor-α (TNF-α), and endothelial dysfunction are associated with features of the metabolic syndrome [3-7]. Fat accumulation, a serious problem in the metabolic syndrome, is correlated with systemic oxidative stress in humans [8,9]. Oxidative stress may play critical roles in the pathogenesis of various features of the metabolic syndrome, via impairment of glucose uptake in muscle and fat and reduction in insulin secretion [10].

          Diet plays an important role in metabolic syndrome [11-13]. Soy contains fiber, polyunsaturated fat, and phytoestrogens, which are individually associated with lower levels of inflammatory markers and improved endothelial function [14,15].

Methods

In our study we examined the effect of soy nut and soy protein on the markers of inflammation and oxidative stress among 42 postmenopausal women with metabolic syndrome [16,17]. We conducted a randomized cross-over study with randomly assigned women to a control diet (red meat-Dietary Approaches to Stop Hypertension [DASH] diet), DASH diet with soy protein, or DASH diet with soy nut, each one for eight weeks. Each woman followed the three diets and had two wash-out periods (each wash-out for 4 weeks).

Results

Results showed that soy nut could improve some markers of inflammation and endothelial function such as C-reactive protein, IL-18, and E-selectin [16]. Both soy products significantly reduced malondialdehyde (MDA) [17] and controlled the glycemic indices and lipid profiles of the patients [18]. For nitric oxide levels, the difference from the control diet was +9.8% (p < 0.01) on the soy nut and -1.7 % (p = 0.10) on the soy protein diets. The difference from the control diet for E-selectin was -11.4% (p < 0.01) on the soy nut consumption and -4.7% (p = 0.19) on the soy protein diets. Soy nut consumption reduced interleukin-18 compared to the control diet (difference from the control diet: -9.2%, p < 0.01) but soy protein did not (difference from the control diet: -4.6%, p = 0.14). For C-reactive protein the difference from the control diet was -8.9% (p < 0.01) on the soy nut diet and -1.6% (p < 0.01) on the soy protein diet [16]. Significant differences between the end values of control diet, soy protein diet, and soy nut diet were seen for MDA (0.70, 0.64, and 0.63 µmol/L, respectively, global P < 0.01). The results also showed a significant difference between the end values for TAC (1.95, 2.03, and 2.11µmol/ml, respectively, P < 0.01). Difference from control for TAC was +4.5% (p < 0.01) in soy nut period and +5.8% (p < 0.01) in soy protein regimen. Both soy nut and soy protein decreased MDA significantly compared to control diet (difference from control: -7.9%, p < 0.01 in soy nut period and -9.4%, p < 0.01, in soy protein diet) [17]. Soy nut regimen decreased Homeostasis Model Assessment-Insulin Resistance (HOMA-IR) score significantly compared to the soy protein (difference in percent change: -7.4 ± 0.8, P < 0.01) or control diets (-12.9 ± 0.9, P < 0.01). Consumption of soy nut also reduced fasting plasma glucose more significantly than soy protein (-5.3 ± 0.5, P < 0.01) or control diets (-5.1 ± 0.6, P < 0.01). Soy nut regimen decreased LDL-C more than did soy protein period (-5.0 ± 0.6, P < 0.01) and control diet (-9.5 ± 0.6, P < 0.01). Soy nut consumption reduced serum C-peptide level compared to control diet (-8.0 ± 2.1, P < 0.01) but soy protein did not [18].

Conclusions

In most studies the phytoestrogens, amino acids, and fatty acid content of soy nut were suggested as possibly being responsible for its favorable effects. In our studies, soy nut intake had more beneficial effects on metabolic risks compared to soy protein intake. The combination of higher amounts of unsaturated fat and isoflavones in soy nut may synergistically provide optimum benefit. [16-18].

          Therefore, it seems that short-term soy nut consumption reduces some markers of inflammation. Moreover, both soy nut and soy protein reduces oxidative stress and controls glycemic indices and improves lipid profiles.

References

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  11.    Azadbakht L, Mirmiran P, Esmaillzadeh A, Azizi F. Dairy consumption is favorably associated with metabolic syndrome in Tehranian adults. Am J Clin Nutr 2005;82:523-30.
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  14.    Esposito K, Giugliano D. Diet and inflammation: a link to metabolic and cardiovascular diseases. Eur Heart J 2006;27:15-20.
  15.    King DE. Dietary fiber, inflammation, and cardiovascular disease. Mol Nutr Food Res 2005;49:594-600.
  16.    Azadbakht L, Kimiagar M, Mehrabi Y, Esmaillzadeh A, Hu FB, Willett WC. Soy consumption, markers of inflammation, and endothelial function: a cross-over study in postmenopausal women with the metabolic syndrome. Diabetes Care 2007;30:967-73.
  17.    Azadbakht L, Kimiagar M, Mehrabi Y, Esmaillzadeh A, Hu FB, Willett WC. Dietary soya intake alters plasma antioxidant status and lipid peroxidation in postmenopausal women with the metabolic syndrome. Br J Nutr 2007 May 17;:1-7 [Epub ahead of print].
  18.    Azadbakht L, Kimiagar M, Mehrabi Y, et al. Soy inclusion in the diet improves features of the metabolic syndrome: a randomized crossover study in postmenopausal women. Am J Clin Nutr 2007;85:735-41.

 

 

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