Abstract: Serum lipid abnormalities are an established risk factor for cardiovascular disease in hyperlipidemic patients. Because of the side effect of long-term medications in these patients, soy protein, as a part of healthy diet, may improve their lipid profile. The purpose of this study was to determine the effect of soy protein with low-calorie diet on lipid profiles in hyperlipidemic patient. Fifty two hyperlipidemic patients of both sex and age range of 25-65 years were participated. The patients received low-calorie diet based on 1400 kcal energy 18% protein, 24% fat and 58% carbohydrate per day for 4 weeks. The treatment group received low-calorie diet including (30 g day-1) of soy protein. Blood samples were obtained after an overnight (12 h) fasting period before the study and in the last day of the intervention period. Anthropometric indices and levels of serum triacylglycerol, total cholesterol, low-density lipoprotein and high-density lipoprotein were measured before and after the intervention. In groups, weight, body mass index, waist and hip circumferences were significantly reduced (p<0.05) after four weeks. In comparison with control group, the results of treatment of soy protein with low-calorie diet showed that at the end of 4th week serum low-density lipoprotein was significantly (p<0.05) decreased while an insignificant reduction was seen in total cholesterol. This study suggest that soy protein with low calorie diet for 4 weeks treatment may be safe and effective alternative therapy for diminished the cardiovascular risk factors in hyperlipidemic patients.
INTRODUCTION
The morbidity and mortality associated with Cardio Vascular Disease (CVD) make it a major public health problem. Mortality from all heart disease increases with age in all races and both sexes (Thom et al., 2006). The importance of non-pharmacological control of plasma lipids is increasing along with the number of subjects whose plasma lipid levels are non-optimal. Consumption of soy protein as a nutritional intervention may prevent cardiovascular disease (Poli et al., 2008).
Soybeans contain all of the essential amino acids necessary for human nutrition and have been grown harvested for thousands of years. Soy is well tolerated and because it is a complete source of protein (Wansink and Cheong, 2002), can be substitution for higher-fat animal products (Michelfelder, 2009). Consumption of a diet with soy protein induced a decrease in the plasma level of Total Cholesterol (TC) and Low-Density Lipoprotein (LDL) in hypercholestrolemic subjects (Hoie et al., 2005; Blachier et al., 2010), in obese adults (Liao et al., 2007) in hyperlipidemic postmenopausal women (Shidfar et al., 2009; Hanachi and Golkho, 2008) and also in rat model (Oboh, 2006; Anosike et al., 2008) but there was no significant effect on plasma triacylglycerols (TAG) (Teixeira et al., 2000; Hoie et al., 2005). However, a 24 weeks, diet supplemented with soy protein in hypercholesterolemic subjects showed no significant changes in plasma TC, LDL and TAG (Dent et al., 2001; Hermansen et al., 2005). Moreover, in a recent study in mildly hypercholestrolemic subjects, a dietary intervention of soy protein for ten weeks was reported had no significant effects on LDL and high-density lipoprotein (HDL) (Thorp et al., 2008).
Result from different studies on the effect of soy protein on lipid profile is inconsistent and there are few data focusing on the effect of soy protein with a low-calorie diet on blood lipids in hyperlipidemic patients. Hence, the objective of this study was to investigate the effect of soy protein with low-calorie diet on blood lipids TAG, TC, LDL and HDL in hyperlipidemic patients.
Since, for primary prevention of coronary artery disease, physicians and patients often wish to avoid pharmacologic therapy of elevated cholesterol concentrations. The use of adjuncts to diet such as soy protein may allow target lipid concentrations to be reached without the use of drugs.
MATERIALS AND METHODS
Patients: This randomized clinical trial was conducted on 52 hyperlipidemic patients who were healthy in other respects and were recruited from nutrition and diet therapy clinic in Boalisina Hospital, Qazvin University of Medical Science, Iran in 2010. The inclusion criteria required the age of 25-65 years. The inclusion criteria required all subjects were between 25-65 years old. They had at least one of blood lipid indices including TC≥200, HDL≤40, LDL≥130 and TAG≥150 mg dL-1. Exclusion criteria included pregnancy and lactation, smoking, steroid therapy, taking lipid-lowering drugs, hormone and a personal history of nephropathy, cardiovascular disease, diabetes and other chronic disease.
Protocol: Fifty-two subjects (45 female and 7 male) participated in this study. They were randomly divided into treatment (n = 26) and control (n = 26) groups. All subjects received a low calorie diet based on 1400 kcal energy per day for 4 weeks, including 24% fat, 18% proteins and 58% carbohydrate from registered dietitian.
Treatment group received the low-calorie diet including (30 g day-1) soy protein. Soy protein was prepared by Shaddasht Soy Protein Company, Qazvin, Iran. The soy protein was used had national quality control certificate number 4935. The low calorie diet with soy protein was well tolerated and accepted overall cases. Oral and written instructions for recording foods were given to all subjects by the clinical nutritionist.
Seven-day food records and main daily nutrient intake record, completed during the last week of the study by subjects. All these records were reviewed by the clinical nutritionist for checking the diet compliance. Subjects� compliance was assessed by analysing seven days diet records and was analyzed by using a computerized nutrient database (Dorosty Food Processor-DFP, version 2003, Shahid Beheshti University, Tehran, Iran), which is mainly based on the national nutrient composition data. Blood samples were obtained after an overnight (12 h) fasting period before the study and in the last day of the intervention period. Anthropometric indices and levels of serum TAG, TC, LDL and HDL were measured before and after the intervention. Serum total cholesterol and triacylglycerol concentration were measured by commercially available enzymatic reagents (Pars Azmoon, Tehran, Iran) adopted to Selectra autoanalyzer (Vital Scientific, Spankeren, Netherlands). HDL-cholesterol was measured after precipitation of the apolipoprotein B containing lipoproteins with phosphotungistic acids (Burstein et al., 1970). Inter- and intra-assay coefficients of variation were both less than 5% for all these measurements.
Measurements: Body weight was measured with minimally clothed, without shoes with Digital scales. Height was measured in a standing position, without shoes, using a tape meter while the shoulders were in a normal state. Waist circumference was measured to the nearest 0.1 cm at the narrowest level over light clothing, using an unstretched tape measure. During the study, participants were asked not to change their habitual physical activity levels. All patients gave informed consent for their participation in the study after reading the protocol of this experiment and receiving information about soy protein consumption. The study protocol was approved by the Research Council and Ethical Committee of Qazvin University of Medical Sciences.
Statistical analyses: Results are presented as Mean±Standard deviation. Data were analyzed with the SPSS Statistical analysis software and t-test was used for analysis of differences between the groups. Paired t-test was applied to determine the difference between before and after measurements. One sample t-test for decreasing of blood lipids. A probability value of p<0.05 was accepted as statistically significant for all tests. The reduction percent of blood lipids after intervention was calculated as:
where, X 1 is blood lipids before intervention and X 2 is blood lipids after intervention.
RESULTS
The mean age of subjects was 38.90±8.79 years and the average of weight, waist and hip were 85.87 ±14.42 kg, 107.60±15.04 cm and 113.62±10.54 cm, respectively. Body mass index (BMI) and waist-to-hip ratio (WHR) were 33.08±5.32 kg m-2 and 0.94±0.07, respectively (Table 1). Body mass index and waist-to-hip ratio in the treatment groups were 32.73±5.90 k g m-2 vs. 33.42±5.33 kg m-2 and 0.94±0.08 vs 0.95±0.07 at baseline, repectively (Table 2). There were no significant differences in age, weight, height, waist, hip, BMI, WHR, TC, TAG, LDL, HDL, LDL/HDL and Chol/HDL between the two groups (treatment and control) at the baseline). Total cholesterol and LDL in the treatment and the control groups were 216.69±28.91 mg dL-1 vs 228.50±30.87 mg dL-1 and 129.29±22.22 mg dL-1 vs. 135.98±28.47 mg dL-1 at baseline, respectively. Weight, BMI, waist and hip circumferences were significantly reduced (p<0.05) after 4 weeks in both groups (Table 3). There were no significant differences at the beginning of dietary intervention (baseline) between plasma lipid concentrations. A low-calorie diet including soy protein intervention resulted in significantly lower levels of LDL than baseline 129.29±22.22 mg dL-1 versus 111.81±20.92 mg dL-1, (p<0.05).
| Table 1: | Characteristics of patients |
| Values are Mean±SD; LDL: Low-density, lipoprotein; HDL: High-density lipoprotein; WHR: waist to hip ratio; BMI: Body mass index | |
| Table 2: | Baseline characteristics of patients |
| Values are Mean±SD, LDL: Low-density lipoprotein, HDL: High-density lipoprotein, SD: WHR: waist to hip ratio, BMI: Body mass index | |
Soy protein with low-calorie diet was associated with a significant reduction in serum LDL (p<0.05). Intervention diet significantly decreased Total cholesterol and Triacylglycerol compared with the baseline 216.69±28.91 mg dL-1 versus 187.79±27.53 mg dL-1 and 205.73±138.18 mg dL-1versus 168.69±136.40 mg dL-1, respectively (p<0.05) but compared with the control group, these changes were insignificant. No significant change occurred in HDL, LDL/HDL and Chol/HDL. Lipid profile before and after intervention, in both groups, are summarized in Table 3.
DISCUSSION
Treatment with diet including soy protein for 4 weeks resulted in a significant decrease in LDL cholesterol by 7.3%. However, insignificant change occurred in other lipid profile. More recently the INTERHEART case controlled study identified that more than 35% of heart attacks were due to abnormal blood lipids; those with abnormal blood lipids have a threefold risk of heart attack compared to those with normal levels (Yusuf et al., 2004). Consistent with our result, in a recent meta-analysis (Taku et al., 2007) of 11 randomized controlled trials published from 1990 to 2006 described no significant changes in HDL cholesterol and triacyglycerol were found after consumption of soy protein. In several studies, similar to the result of this study, soy protein did not show any significant increase in blood HDL (Ma et al., 2005; Hoie et al., 2005; Sacks et al., 2006; Thorp et al., 2008; Xiao, 2008). Also in a rat model Reza et al. (2008) indicated that at the end of 7th week feeding dietary soybean, unchanged level of HDL was seen. However, Anderson et al. (1995) and Weggemans and Trautwein (2003) found increasing in HDL cholesterol after intake of soy protein.
| Table 3: | Characteristics of 52 hyperlipidemic patients before and after intervention |
| Values are Mean±SD, LDL: Low-density lipoprotein, HDL: High-density lipoprotein, SD: WHR: waist to hip ratio, BMI: Body mass index, * Significantly at p<0.05 | |
Zhan and Ho (2005) reported improvements in HDL cholesterol after soy protein consumption were only observed in studies of >12 week duration. It seems that 4 week treatment period of current study was brief for increasing the HDL level. In the present study, LDL cholesterol was reduced 7.3% in the group that consumed soy protein. However, Dent et al. (2001) and Ma et al. (2005) found no effect of soy protein treatment on circulating LDL cholesterol may be due to more valuable baseline LDL values. Over a period of 5 years, each 1% decline in LDL cholesterol is associated with a reduction of ~1% CVD event risk and if maintained during a longer period of time, CVD event risk reduction may be as much as 3% for each 1% reduction in LDL cholesterol (Brown et al., 2006). Harland and Haffner (2008) observed that the modest amounts of soy protein (25 g) in to the diet of adult with normal or mild hypercholesterolaemic resulted in significant (6%) reduction in LDL cholesterol. Furthermore, Jenkins et al. (2010), Bruckert and Rosenbaum (2011) and Hansel et al. (2011) also reported a 3-10% reduction in blood LDL using soy protein, which support the results of the current study. The effect of LDL reduction by soy protein consumption has benefit for CHD prevention. A decrease of 1 mg dL-1 in LDL cholesterol results in about a 1 to 2% decrease in the factor for CHD (Lichtenstein et al., 2006). Soybeans contain 2 types of storage protein, the globulins 11 S and 7 S. Cell culture studies suggest that these globulins stimulate LDL receptor activity (Lovati et al., 1992). The result of more recent study on rats also showed that the oral daily administration of soybean 7 S globulin in the diet to hypercholesterolemic rats promotes the reduction of LDL cholesterol (Ferreira et al., 2011). The results of this study showed an insignificant reduction in total cholesterol. In 29 controlled studies (Anderson et al., 1995), a trend emerged that soy protein selectively reduced blood cholesterol in direct proportion to the degree of hypercholesterolemia. In hyperlipidemic patients with initial blood cholesterol was <255 mg dL-1, similar to the present study, there was no significant reduction in blood cholesterol by soy protein (Sacks et al., 2006). Thus the response to soy protein was determined by the initial blood cholesterol level.
The range of soy protein that was used in previous studies was 25 to 135 g d-1; the range for isoflavones was 40 to 318 mg (Sacks et al., 2006). In the present study, the soy protein was used contained 1.5 mg isoflavones/g protein. The isoflavone content of soy products has been hypothesized to contribute to their LDL lowering effects. (Zhan and Ho, 2005; Xiao, 2008; Messina, 2008; Blachier et al., 2010) similar to the result of the present study.
However, other well-controlled studies did not find significant effects of soy isoflavones on LDL cholesterol (Weggemans and Trautwein, 2003; Kreijkamp-Kaspers et al., 2004; Zittermann et al., 2004; McVeigh et al., 2006; Taku et al., 2007, 2008; Thorp et al., 2008; Campbell et al., 2010; Maki et al., 2010). The mechanisms responsible for the effect of soy isoflavones on the lipid are still being explored.
In some intervention studies, 3 days food record has been used (Hermansen et al., 2005) to reach a more accurate energy estimation and macronutrients intake; the subjects of this study were asked to record their food for one week.
In conclusion, the results of the present study showed that short-term consumption of soy protein with a low calorie diet as a part of healthy diet lowered the serum LDL cholesterol level. This effect is beneficial and may reduce the cardiovascular risk factor in hyperlepidemic patients and postponement of the requirement for drug therapy for these patients.
ACKNOLEDGEMENT
This work was supported by a grant (Grant No. 28.3311) from Deputy of Research, Qazvin University of Medical Sciences, Qazvin, Iran and thanks are due to Mr. Hamid Joratty (Chemical Engineer) (Shaddasht Soy Protein Company, Qazvin, Iran) for soy protein dedication. We would also like to thank Dr. Saeed Assefzadeh, Department of Social Medicine for consultation and Mrs. Mohtaram Adineh, laboratory of Human Nutrition, Qazvin University of Medical Sciences for analyzing the data on the diet composition. None of the authors had any conflicts of interest with regard to the organization sponsoring the research.