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Keywords:

  • isoflavones;
  • walking exercise;
  • BMD;
  • fat mass;
  • postmenopausal women

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

The combined intervention of isoflavone intake and walking exercise over 1 year in postmenopausal Japanese women exhibited a trend for a greater effect on prevention of bone loss at the total hip and Ward's triangle regions.

Introduction: The additive effects of isoflavones and exercise on bone and lipid metabolism have been shown in estrogen-deficient animals. In this study, we determined the effects of isoflavone intake, walking exercise, and their interaction on bone, fat mass, and lipid metabolism over 1 year in postmenopausal Japanese women.

Materials and Methods: A total of 136 postmenopausal women at <5 years after the onset of menopause were randomly assigned to four groups: (1) placebo, (2) walking (45 minutes/day, 3 days/week) with placebo, (3) isoflavone intake (75 mg of isoflavone conjugates/day), and (4) combination of isoflavone plus walking. BMD, fat mass, serum lipid, and serum and urinary isoflavone concentrations were assessed.

Results: A significant main effect of isoflavone on the reduction in trunk fat mass was obtained at 12 months. Significant main effects of walking on the reduction in fat mass in the whole body and the trunk were observed at 3, 6, and 12 months and that in the legs and arms at 6 and 12 months. Serum high-density lipoprotein (HDL)-cholesterol concentration significantly increased by 12 months after the walking and the combined intervention. After 12 months, a significant main effect of isoflavone on BMD was observed only at Ward's triangle. Walking prevented bone loss at the total hip and the Ward's triangle to significant degrees. The effect of the combined intervention on BMD at total hip and Ward's triangle regions was greater than that of either alone. No significant interaction was observed between isoflavone and walking in any measurements recorded during the study.

Conclusions: Our study suggest that combined intervention of 75 mg/day of isoflavone intake and walking exercise 3 times/week for 1 year showed a trend for a greater effect on BMD at total hip and Ward's triangle regions than either alone. Intervention with isoflavone in postmenopausal Japanese women showed a modest effect on BMD compared with those in Westerners. Further studies over longer treatment duration that include assessment of BMD at various regions are necessary to ascertain the clinical significance of the combined intervention of isoflavone plus walking in postmenopausal women.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Estrogen deficiency often increases the risk of several chronic diseases such as osteoporosis, cardiovascular disease, and obesity.(1–4) Hormone replacement therapy (HRT) is an effective regimen that prevents these diseases in postmenopausal women.(5,6) However, the HRT trial carried out by the Women's Health Initiative (WHI) found that long-term use of HRT (follow-up, 5.2 years) poses serious risks and may increase the risk of heart attack and stroke.(7) Follow-up studies with the WHI will likely provide insight as to whether the increased risks and benefits of HRT therapy decline after the end of the therapy and the time at which this decline occurs as well as evaluation of the dose.(8)

Recently, there has been an increased interest in the role of phytoestrogens in preventing osteoporosis and hypercholesterolemia.(9) Soybean is a rich source of the isoflavones, genistein, and daidzein, which shows weak estrogenic effects in several organs.(10) A number of studies have previously reported that soybean isoflavones dose-dependently inhibited bone loss in both female and male osteoporotic animal models without causing notable effects on the reproductive organs.(11–13) However, the results obtained from several observational clinical studies are still conflicting. The discrepancies between the results may be caused by the variation in factors such as the duration of intervention, the bone sites measured, dietary intake, isoflavone intake among subjects and controls, and its metabolism.

On the other hand, the effects of exercise on the prevention of bone loss, fat accumulation, and hypercholesterolemia in women around the menopausal period have been previously studied.(14–17) An exercise program designed for postmenopausal women should be safe and easy to perform and continue. Although high-intensity exercise could possibly increase the bone mass in pre/postmenopausal women, such exercise is also often associated with stress fractures, particularly in individuals with fragile skeletons.(18) Walking is a relatively safe exercise that is commonly performed by elderly people. Thompson et al.(14) indicated an inverse association between body composition variables and daily walking steps in middle-aged women. However, walking exercise has a relatively low impact on bones, and therefore, cannot be used exclusively for preventing bone loss in postmenopausal women.(15) Thus, a few studies have examined the effects of a combination of exercise and HRT on bone mass and body composition in postmenopausal women. Kohrt et al.(16) and Cheng et al.(17) assessed the independent and combined effects of exercise and HRT on the increase in BMD and the reduction in fat mass in postmenopausal women. Because the risk to benefit ratio of HRT continues to be debated,(19) other interventions that combine therapies using phytoestrogens with exercise training may be preferred. Therefore, we hypothesized that isoflavone intake combined with walking exercise would have beneficial effects on the bone and fat mass and serum lipid concentration in postmenopausal women. We have previously reported that, with regard to the prevention of bone loss and fat gain in estrogen-deficient animals, the effects of moderate-intensity exercise combined with isoflavone administration were better than those observed when either was used exclusively.(20–22)

In this study, we report the effects of soy isoflavone intake and/or walking exercise for 1 year on bone mass, body composition, and serum lipid concentration in postmenopausal Japanese women.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Subjects

Subjects were recruited for this study through advertisements in local newspapers, and those who fulfilled the following criteria were enrolled for the study. Healthy postmenopausal women 45–60 years of age who were within 5 years of natural onset of menopause (defined as at least 12 months since the last menstrual cycle occurred) were enrolled in the study. The subjects had no history of previous use of HRT, lipid-lowering medications, antibiotics, or any other medication known to affect the skeleton. They provided written informed consent to participate in the study. The protocol was approved by the institutional review board of the NIH and Nutrition of Japan, and the study was performed in accordance with the guidelines of the Declaration of Helsinki.

In this study, 145 women who fulfilled the required criteria were called for the screening examination. The criteria for the invitation were as follows: willingness to participate, clinically healthy (no cardiovascular, musculoskeletal, respiratory, or other chronic diseases that might limit walking exercise), sedentary life style (no regular sports activities for at least 2 years), nondieting, nonsmoking, and having no apparent occupational responsibilities or leisure time activities that might impede their participation. Nine participants were excluded after the medical screening because of high serum estradiol (E2) concentrations (>20 pg/ml). Thus, 136 women were randomly assigned to four groups: (1) placebo, (2) placebo plus walking, (3) isoflavone, and (4) isoflavone plus walking. However, 28 women withdrew from the study because of illness, family problems, or they thought that participating in the study was troublesome. The remaining 108 subjects completed the 12-month study, and their data were included in the per protocol analysis (Fig. 1).

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Figure Figure 1. Flow chart with details of the participants.

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Intervention

Placebo or isoflavone capsules were blindly allocated to researchers and subjects throughout the study. Participants from the two groups, isoflavone and isoflavone combined with walking, received two capsules that contained a total of 75 mg of isoflavone conjugate (47 mg as aglycone form; Fujiflavone P40; Fujicco Co., Kobe, Japan) with dextrin, daily in the morning. The isoflavone conjugate weighing 75 mg contained daidzin (38.3 mg), malonyldaidzin (0.2 mg), acetyldaidzin (2.1 mg), daidzein (0.6 mg), genistin (8.6 mg), acetylgenistin (0.6 mg), genistein (0.2 mg), and glycitin (23.4 mg) with glycitein (1.0 mg). The remaining subjects were assigned to receive two placebo capsules containing only dextrin, daily in the morning.

Participants who were randomized into the walking groups were expected to attend three 1-h-long exercise classes each week. The exercise program consisted of a 10-minute warm-up period, a 45-minute supervised walking exercise session, and a 5-minute cool down period. Participants were given instructions with regard to the proper manner of walking to eliminate possible injury. The participants were instructed to maintain the speed of walking at 5–6 km/h, and this was monitored by a pedometer.

The nonwalking group participants did not engage in sports training and were asked to continue their normal activity levels. All participants were instructed to record their daily number of steps walked that were continuously monitored by the pedometer, and their diaries were obtained and checked once a month to ensure that they were up-to-date.

Questionnaire interview

Individual information was collected by trained interviewers in face to face interviews based on a structured and previously validated questionnaire that included the following: socio-demographic data; years since menopause; physical activities, including hours spent sitting, standing, walking, sports, and leisure activities; medications; smoking and drinking alcohol; and other factors that may have possible confounding effects on the relation between dietary isoflavone consumption and metabolism of bone and lipid. The participants were instructed to record the contents of daily meals, snacks, and beverages in the diet diary. The diary was collected continuously for 3 days to confirm the meal intake, and, if necessary, the participants were immediately instructed to adhere to the dietary regimen. Daily intakes of soy isoflavones, calcium, vitamin D, total energy, and protein were calculated from the daily record by the dietitian on the basis of the Fifth Revision of the Standard Tables of Food Composition in Japan.(23)

Blood and urine samples

Before BMD measurement, fasting (>12 h) blood samples were collected by venipuncture in EDTA-containing tubes, refrigerated immediately, and centrifuged at 1500 rpm for 30 minutes at 4°C within 2 h. Serum samples from each participant were stored frozen at −20°C. Serum concentrations of total cholesterol (TC) and triacylglycerol (TG) were determined using commercial kits (cholesterol C-test and triglyceride G-test, respectively; Wako Pure Chemical Industries, Osaka, Japan). Serum high-density lipoprotein (HDL)-cholesterol was measured by an enzymatic method (HDL-cholesterol test; Wako Pure Chemical Industries). Serum low-density lipoprotein (LDL)-cholesterol levels were calculated as follows: total cholesterol (mg/dl) – HDL-cholesterol (mg/dl) –TG (mg/dl) × 0.2. Estradiol (E2) was assessed by radioimmunoassay (Amersham Biosciences, Piscataway, NJ, USA). Serum bone-specific alkaline phosphatase (BSALP; Alkphase-B; Metra Biosystems, Mountain View, CA, USA) was measured by using a microplate coated with an anti-BSALP monoclonal antibody. Serum intact osteocalcin (OC) was measured by using a sandwich enzyme immunoassay (EIA) that uses polyclonal antibodies against 20 N-terminal residues (amino acids 1–20) and against 7 C-terminal residues (amino acids 43–49; Biomedical Technology, Stoughton, MA, USA). Urine samples were collected from a second voiding at the same time as blood collection, and they were stored at −20°C. Urinary deoxypyridinoline (DPD) was measured using a sandwich EIA (Pyrilinks-D Assay; Metra Biosystems).

Measurement of serum and urinary isoflavones

Concentrations of isoflavones in serum and urine samples were determined for each subject by reverse-phase high-performance liquid chromatography (HPLC). Duplicate samples of serum and urine were incubated with sulfatase (EC 3.1.6.1; Sigma Chemical) and β-glucuronidase (EC 3.2.1.31; Wako Pure Chemical Industries) at 37°C for 2 h to release the aglycones of the isoflavones; this was followed by purification of reactants using a Sep-Pak C18 cartridge (Waters Co., Milford, MA, USA). Isoflavones were separated at 35°C by reverse-phase HPLC on a 4.6 × 250-mm Capcell Pak C18 column (Shiseido Co., Tokyo, Japan) using a Tosoh CCP and 8020 system with a diode array detector PD8020 (Tosoh Co., Tokyo, Japan). Elution was performed at a flow rate of 1 ml/minute with a linear gradient of acetonitrile solution (10–35%) containing a constant 0.1% concentration of acetic acid. Data were simultaneously acquired at 254 nm (daidzein, genistein, glycitein) and 280 nm (equol).

BMD and body composition

BMD of the lumbar spine (L2–L4), left hip, and subwhole body regions (excluding head region) and body composition were assessed by DXA at baseline and after 3, 6, and 12 months using a Hologic QDR-4500A scanner (Hologic, Waltham, MA, USA). To minimize interobserver variation, all the scans and analysis were carried out by the same investigator, and the day-to-day CVs of his observations were <0.5, 1.9, 0.7, 0.3, 1.9, and 0.8% for BMD in the spine, femoral neck, trochanter, total hip, Ward's triangle, and whole body, respectively. Long-term precision was 0.35% by testing the spine phantom daily over the previous 1 year.

The whole body scans were divided into several regions such as arms, legs, trunk (pelvis, spine, and ribs), and head. The body compositions were analyzed by using manual DXA analysis software (version 11.2:3). The arm region was defined as the region extending from the head of the humerus to the distal tip of the fingers. The reference point between the head of the humerus and the scapula was positioned at the glenoid fossa. The leg region was defined as the region extending from the inferior border of the ischial tuberosity to the distal tip of the toes. The subwhole body was defined as the region extending from the shoulders to the distal tip of the toes. We selected a reference point that could be clearly visualized on the DXA system terminal.

Statistical analysis

All values are expressed as mean ± SD. Differences in baseline characteristics between the different groups were tested by one-factor analysis of covariance (ANCOVA). To determine whether the change over the course of the study was significantly different from the baseline in each group, paired t-test with Bonferroni adjustment was performed. The percent change in BMD, body composition, serum lipid, and biomarkers of bone turnover were calculated {[(post intervention – baseline values)/baseline values] × 100} for each group. Two-factor ANCOVA was performed to determine the main effects of isoflavone intake, walking exercise, and their interactions at 3, 6, and 12 months. Significant differences of the percent change in BMD and fat mass among the different groups were determined by ANCOVA with time as the repeated measure, without the use of the intention-to-treat principle. To adjust for the possible confounding, the body weight, height, and daily intake of calcium, vitamin D, protein, and total energy were used as covariates in the analyses of body composition, BMD, and serum biomarkers. Statistical analyses were performed using SPSS for Windows (version 13.0J), and a p value was set at <0.05.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

General

There were no significant differences among the groups at baseline with regard to the subject characteristics (Table 1). The 1-year intervention of isoflavone intake and walking did not affect these parameters. At the beginning of the study, the average dietary isoflavone (glycoside form) intake was 48.1, 47.7, 44.4, and 49.4 mg/day in the placebo, walking, isoflavone, and isoflavone plus walking groups, respectively. At the end of the study, there was no significant difference in the dietary isoflavone intake among the groups and when compared with the intake at baseline in each group. The number of steps recorded by the pedometer during the 1-year study was significantly higher in the two walking groups than in the nonwalking groups (Table 1).

Table Table 1.. Characteristics of Subjects of Different Study Groups at Baseline and 12 Months*
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Serum estradiol, lipids, and bone biomarkers

Serum concentrations of estradiol, lipids, and biomarkers of bone turnover at both baseline and 12 months of the study are shown in Table 2. Statistically significant differences were not observed with respect to serum concentrations of estradiol, lipids, and biomarkers of bone turnover at baseline among the groups. When these indices at 12 months were compared with those at baseline, serum E2, TC, and TG concentrations, urinary biomarker of bone resorption (DPD), and serum biomarker of bone formation (osteocalcin and BSALP) were observed to be unaffected by walking, isoflavone intake, and the combined intervention. At the end of the study, the HDL-cholesterol concentration significantly increased from baseline by 7.78% and 8.78% in the walking group and the isoflavone intake plus walking group, respectively. By using the two-factor ANCOVA analysis, we observed a significant main effect of walking (p = 0.003), but not of isoflavone intake (p = 0.53), on the percent change in HDL-cholesterol. On the other hand, there were no significant main effects on TC and LDL-cholesterol concentrations.

Table Table 2.. Serum Estradiol, Biomarkers of Bone Turnover, and Lipid Concentrations of Different Study Groups at Baseline and 12 Months*
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BMD and body composition

There was no significant difference among the four groups at baseline with respect to fat and lean mass in the whole body; fat mass in the trunk, arms, and legs regions; and BMD in subwhole body, lumbar spine, and hip regions (Table 3). Analysis by two-way ANCOVA model, walking exercise induced a significant reduction in the percent change in fat mass in the whole body and trunk region at 3 (p = 0.001 and p = 0.005, respectively), 6 (p = 0.001 and p = 0.006, respectively), and 12 months (p = 0.0002 and p = 0.001, respectively; Figs. 2A and 2B). The intervention with walking exercise also induced a significant reduction in the percent change in fat mass in the legs after 6 and 12 months (p = 0.003 and p = 0.0001, respectively; Fig. 2C). A significant main effect of walking exercise on suppression of fat mass gain in the arms was observed after 6 and 12 months (p = 0.019 and p = 0.001, respectively; Fig. 2D). Isoflavone intake significantly suppressed the percent change in fat mass gain in the trunk region after 12 months (p = 0.027); however, no interaction was observed between the effects of isoflavone intake and walking exercise (Fig. 2B). Analysis by ANCOVA with time as the repeated measure revealed that the percent change in fat mass in the whole body, trunk, and legs regions was significantly different in the walking alone and the isoflavone plus walking groups compared with that in the placebo group (p < 0.05). The percent change in fat mass in the arms in the isoflavone plus walking group was significantly different from that in the placebo group (p < 0.05).

Table Table 3.. BMD and Body Composition of Different Study Groups at Baseline*
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Figure Figure 2. The percent change in fat mass (±SD) from the baseline to 12 months of the study. The changes shown by the walking exercise and isoflavone intake plus walking exercise groups were significantly different from the placebo group (p < 0.05) with regard to (A) the whole body, (B) trunk, and (C) leg regions. (D) The isoflavone intake plus walking exercise group was significantly different from the placebo group (p < 0.05) with regard to the arm region. There was a significant main effect of walking exercise on (A) the whole body and (B) trunk region after 3 months, and on (C) the arm and (D) leg regions after 6 months. (B) There was significant main effect of isoflavone intake after 12 months on the trunk region. All p values were calculated using ANCOVA with time as the repeated measure. The main effects of isoflavone intake and walking exercise over 12 months were determined by two-factor ANCOVA.

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On analyzing the percent change in BMD, walking showed significant main effects on the preservation of BMD in the total hip region after 12 months (p = 0.039; Fig. 3A). Interventions with isoflavone and walking showed significant main effects on the preservation of BMD at Ward's triangle after 12 months (p = 0.044 and p = 0.0001, respectively; Fig. 3B); however, no interaction effect was observed between the two interventions. There were no significant effects of either isoflavone or walking on the percent change in BMD in the femoral neck, trochanter, lumbar spine, and subwhole body regions (Figs. 3C–3F).

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Figure Figure 3. The percent change in BMD (±SD) from baseline to 12 months of the study. (A) There was a significant main effect of walking exercise on the total hip region after 12 months. (B) There were significant main effects of walking exercise and isoflavone intake on the Ward's triangle after 12 months. There were no significant main effect on (C) the femoral neck, (D) trochanter, (E) lumbar spine, and (F) subwhole body. The subwhole body refers to the whole body scan excluding the head region. The main effects of isoflavone intake and walking exercise over 12 months were determined by two-factor ANCOVA.

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Serum and urinary isoflavones concentrations

Table 4 shows the serum and urinary concentrations of isoflavones at baseline and 12 months. At baseline, there were no significant differences in the concentrations of serum isoflavones among the four groups. Compared with baseline values, the administration of isoflavones showed a marked increase in the serum concentrations of daidzein, glycitein, and equol, but not in the concentration of genistein. In contrast, the placebo treatment did not modify the concentration of circulating isoflavones. Using the two-factor ANCOVA model, we found significant main effects of isoflavone intake on serum concentrations of daidzein (p < 0.005), glycitein (p < 0.005), and equol (p < 0.001) after 12 months. Similar patterns were observed in the concentrations of urine isoflavones among the four groups.

Table Table 4.. Serum and Urinary Isoflavone Concentrations of Different Study Groups at Baseline and 12 Months*
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DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

The major novel findings of this study are as follows: (1) walking exercise for 6 months can significantly decrease the fat mass in the whole body, trunk, legs, and arms regions; (2) isoflavone intake significantly reduced fat mass in the trunk region and decreased bone loss at Ward's triangle region after 1 year; and (3) the combined intervention of isoflavone and walking exercise for 1 year showed a trend for a greater effect on BMD at total hip and Ward's triangle regions than either alone in postmenopausal Japanese women.

Important changes in the body composition of a female occur around the menopausal period. These changes include a decrease in bone mass and an increase in fat mass that may be managed by either replacement of estrogen, exercise, or by their combined intervention.(24) Although several animal experiments have consistently indicated the positive effects of soy isoflavone in retarding bone loss caused by estrogen deficiency, the results obtained from studies on humans are still controversial.(9) The results of the clinical trials varied from an improvement of BMD in the lumbar and femoral neck after 1 year(25,26) to no effect.(27) In one study, the loss of BMD in the lumbar spine, but not in the hip, in women who consumed a red clover–derived isoflavone supplement, 45 mg of aglycone form daily, was significantly lower than in those consuming a placebo.(25) Furthermore, Morabito et al.(26) reported that 54 mg/day of genistein treatment for 1 year significantly increased the BMD of the lumbar spine and the femoral neck in Italian women. On the other hand, daily intake of soy extracts containing 80 mg of isoflavones, but not 40 mg, significantly increased the BMC, but not BMD, of the trochanter after 1 year in postmenopausal Chinese women; however, this effect was observed only in those women with low initial bone mass.(27)

To the best of our knowledge, this is the first observational study on the effects of isoflavone intervention on BMD in Japanese women who were followed up for 1 year. We found that soybean isoflavones prevented a decrease in BMD in Ward's triangle in postmenopausal women after 1 year. However, at other regions such as the lumbar spine, total hip, and subwhole body, the main effects of isoflavone intake were not observed despite the fact that the serum and urine concentrations of isoflavones were high compared with those in the previous study.(26) A putative explanation is that Ward's triangle is the area that is probably the most sensitive to estrogen because of its higher trabecular bone content compared with that of other regions.(28) Among the different regions of interest (ROIs), Ward's triangle in many studies has shown the largest age-related bone loss.(29,30) The ability to predict osteoporotic fractures for Ward's triangle has been at least as good as for the femoral neck ROI.(31,32) However, it is suggested that the measurement of BMD in the Ward's triangle is unreliable. In this study, the hip scan was analyzed carefully using the comparison software that enables adaptation to a position and an angle at the first measurement. Therefore, it is believed that the results of this study reflect the change in BMD in the Ward's triangle.

It is known that daidzein can be metabolized to equol, which is biologically more active than its precursor, and could ultimately influence the effect on the subject's health.(33) Although rodents are constitutive equol producers, equol production in humans depends on the intestinal microflora of an individual.(9) Thus, assessment of the correlation between equol status of the subjects and bone effects of isoflavone might be necessary to know the actual clinical effectiveness of isoflavone.

In this study, we expect that the combined intervention of isoflavone and walking exercise would provide a greater benefit than either intervention used exclusively. The combined intervention resulted in a positive change in BMD in the Ward's triangle after 1 year. By using the two-factor ANCOVA model, we found significant main effects of both interventions at this site, although the interaction was not observed. We also found that the combined intervention trend more effective than either intervention used exclusively for preventing bone loss in the total hip region. It is reported that a low estrogen level in females may decrease the sensitivity of bones for detecting mechanical loads.(34) Research on ovariectomized animals have shown that combining isoflavones with exercise training can be beneficial in increasing BMD to a greater extent than either intervention used exclusively.(20,22,35) In addition, several clinical trials have shown that a combination of exercise and HRT results in an increase in BMD that is more than either intervention used exclusively.(36) This study is the first to suggest that the combined intervention of isoflavone and walking exercise for 1 year may partly prevented bone loss in postmenopausal women. It is necessary to focus on the fact that BMD in Ward's triangle increased by 5% in case of the combined intervention, whereas it decreased by 2.5% in the case of placebo-administered controls. This benefit may show a clinically significant reduction in the number of fractures.(37)

In this study, we also indicated that any isoflavone intake, walking exercise, and combined intervention decreased body fat mass in postmenopausal women. We noticed that isoflavone intake significantly reduced fat mass in the trunk region but not in the other regions. There is evidence that estrogens modulate central body fat deposition in women. This evidence includes observations that menopause triggers an increase in central adiposity (i.e., trunk fat mass)(38) and that fat accumulation in postmenopausal women is attenuated by replacement of estrogens, exclusively or in combination with progestins.(15,39,40) Although isoflavones may play a role in the prevention of regional fat mass deposition as a natural alternative to estrogens or HRT, further studies are required to clarify dose–response relationships and the mechanisms leading to this effect. As expected, walking exercise and walking combined with isoflavone intake resulted in reductions in total and regional fat mass after 3, 6, and 12 months. These findings are consistent with the evidence reported by several clinical trials that assessed the combined effects of exercise and HRT on fat mass.(15,40,41)

In addition to bone and fat mass, walking exercise significantly increased HDL-cholesterol concentration. This finding is consistent with our previous study.(22) However, there was no significant main effect with respect to LDL-cholesterol concentrations. This lack of an effect is in agreement with other studies(42,43) examining the effects of soy isoflavones on LDL-cholesterol in postmenopausal women.

Our study had several limitations. First, with regard to our Japanese subjects, intake of soy products during this study was not controlled, because soy products are included in most Japanese foods. Compared with American and European women, Asian women consume a diet that is higher in isoflavones (average conjugated isoflavone intake of each group was 44.4–49.4 mg/day in our subjects). High dietary isoflavone intake might increase the threshold for the skeleton to respond to isoflavone supplementation. Thus, this might moderate the effect of isoflavone intervention in Japanese women. Second, a short-duration study cannot adequately assess the benefits related to bone quality, because bone is a slowly responding organ. A complete bone remodeling cycle takes ∼180 days, and therefore, studying only one cycle with regard to the effect of any intervention on bone is not sufficient. Thus, the duration of our study (1 year) was not sufficient to test the clinically relevant changes, which require a longer trail that lasts for at least 2 years. Third, the time at which the biomarkers for bone metabolism are tested may differ from that of other studies. In this study, no significant differences were observed with regard to the serum and urinary biomarkers between the baseline and 1 year in each group. Although, there is a clinical study showing that the bone formation marker (BSALP) was not affected by isoflavone intervention,(38) other trials reported that the bone markers changed at 4–8 weeks after the treatment with isoflavone in the postmenopausal Japanese women.(44,45) Thus, these bone markers may have been assessed early during the study.

In conclusion, combined intervention of 75 mg/day of isoflavone intake and walking exercise 3 times/week for 1 year showed a trend for a greater effect on BMD at total hip and Ward's triangle regions than either alone. Intervention with isoflavone in postmenopausal Japanese women showed a modest effect on BMD compared with those in Westerners. Walking exercise prevented bone loss at total hip and Ward's triangle and also reduced the fat mass in the whole body. These results suggest that the walking exercise or combined with isoflavone intake over 1 year may offer a potential regimen for primary prevention of osteoporosis and lifestyle-related disease in postmenopausal women. Further studies over longer treatment duration that include the assessment of BMD at various regions are necessary to ascertain the clinical significance of the combined intervention of isoflavones plus walking in postmenopausal women.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

We are grateful for the support provided by MS Maiko Fujioka, Dr Hidemi Takimoto, Dr Mamoru Nishimuta, Dr Motohiko Miyachi, Dr Masae Miyatani, and Takuya Ohtomo (National Institute of Health and Nutrition). The authors thank Dr Mariko Uehara (Tokyo University of Agriculture) for helpful discussion and comments. We also gratefully acknowledge the dedicated women who participated in this project. This work was supported by the Japan Health Science Foundation, a grant from the Ministry of Health, Labor, and Welfare of Japan, and Grant-in-Aid 16500536 from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES
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