The effect of soy protein and soy isoflavones on calcium metabolism in postmenopausal women: a randomized crossover study

Calcium kinetic rates in Caucasian males and females from birth to adulthood

Calcium plays an important role in bone physiology and its kinetics change over lifetime. The analysis of calcium deposition and release through stable isotope techniques has guided recommendations on nutritional uptake for overall health. In addition, calcium kinetics have great relevance for toxicokinetic studies of bone-seeking elements (e.g, aluminium and lead) since these elements use common uptake and release pathways. While the impact of many factors on calcium kinetics have been investigated individually, a consolidated age- and sex-dependent kinetic description amenable for toxicokinetic modeling, however, is still lacking. Motivated by this need, we systematically reviewed the existing literature on calcium kinetics and assembled a large and consistent dataset. Then, building on the work of O'Flaherty in the 1990s, we formulated age- and sex-dependent functions describing calcium deposition, release, net retention, and mass. This description represents the current knowledge on calcium kinetics in a reference individual of Caucasians as most data was from this population.

Effects of Isoflavonoid and Vitamin D Synergism on Bone Mineral Density-A Systematic and Critical Review

Phytoestrogens are non-steroidal plant compounds, which bind to α and β estrogen receptors, thereby causing specific effects. The best-known group of phytoestrogens are flavonoids, including isoflavonoids-genistein and daidzein. They play a role in the metabolism of bone tissue, improving its density and preventing bone loss, which contributes to reducing the risk of fractures. Vitamin D is found in the form of cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2) and is traditionally recognized as a regulator of bone metabolism. The aim of this review was to evaluate the synergistic effect of isoflavonoids and vitamin D on bone mineral density (BMD). The MEDLINE (PubMed), Scopus and Cochrane databases were searched independently by two authors. The search strategy included controlled vocabulary and keywords. Reference publications did not provide consistent data regarding the synergistic effect of isoflavonoids on BMD. Some studies demonstrated a positive synergistic effect of these compounds, whereas in others, the authors did not observe any significant differences. Therefore, further research on the synergism of isoflavonoids and vitamin D may contribute to a significant progress in the prevention and treatment of osteoporosis.

The skeletal safety of milk-derived proteins: A meta-analysis of randomized controlled trials

PURPOSE

There has been a persistent claim that dairy products contain calcium-leaching proteins, although the soundness of such a claim has been challenged. A meta-analysis of randomized controlled trials (RCTs) on the effects of milk-derived protein supplementation on bone health indices in adults was performed to reconcile the controversy surrounding the potential skeletal safety concerns of proteins of dairy origin.

METHODS

The PubMed and Web of Science databases were searched for relevant RCTs. A random-effects model was used to generate pooled effect sizes and 95% confidence intervals.

RESULTS

Milk-derived protein supplementation did not significantly affect whole-body BMD (n = 7 RCTs) and BMD at the lumbar spine (n = 10), hip (n = 8), femoral neck (n = 9), trochanter (n = 5), intertrochanter (n = 2), and ultradistal radius (n = 2). The concentrations of bone formation markers (bone-specific alkaline phosphatase [n = 11], osteocalcin [n = 6], procollagen type 1 amino-terminal propeptide [n = 5]), bone resorption markers (N-terminal telopeptide of type 1 collagen [n = 7], C-terminal telopeptide of type 1 collagen [n = 7], deoxypyridinoline [n = 4]), and parathyroid hormone (n = 7) were not significantly affected. However, increased insulin-like growth factor-1 (IGF-1) concentrations (n = 13) were observed. Reduced IGF-1 concentrations were observed when soy protein was used as a comparator, and increased IGF-1 concentrations were observed when carbohydrate was used.

CONCLUSION

Our findings do not support the claim that proteins of dairy origin are detrimental to bone health.

The health effects of soy: A reference guide for health professionals

Soy is a hotly debated and widely discussed topic in the field of nutrition. However, health practitioners may be ill-equipped to counsel clients and patients about the use of soyfoods because of the enormous, and often contradictory, amount of research that has been published over the past 30 years. As interest in plant-based diets increases, there will be increased pressure for practitioners to gain a working knowledge of this area. The purpose of this review is to provide concise literature summaries (400-500 words) along with a short perspective on the current state of knowledge of a wide range of topics related to soy, from the cholesterol-lowering effects of soy protein to the impact of isoflavones on breast cancer risk. In addition to the literature summaries, general background information on soyfoods, soy protein, and isoflavones is provided. This analysis can serve as a tool for health professionals to be used when discussing soyfoods with their clients and patients.

Effects of physical exercise in sarcopenia. A systematic review

From the third decade of life and due to multiple causes, muscle mass and strength are gradually lost, which affects the function of the musculoskeletal system. This combined loss of muscle mass and strength with aging is called sarcopenia, and is associated with greater morbidity and mortality in the elderly. Early treatment is therefore essential, and physical exercise is the therapeutic approach that has given the best results. This literature review intended to analyze the effect of physical exercise, excluding the role that other treatments proposed, including the nutritional approach, could play in the treatment of sarcopenia, refers to 12 articles. In studies including high intensity strength exercises in isolation, either alone or combined with aerobic exercise, improvements were seen in muscle mass, muscle strength, and functional test times. There is also a significant increase in fat-free mass in individuals who exercised more frequently (more than two sessions per week). Current evidence shows that strength-resistance training and its combination in multimodal programs with aerobic exercise show significantly beneficial effects on anthropometric and muscle function parameters. Programs of prescribed exercises including strength exercises adequate to the characteristics should therefore be adapted to the characteristics of each individual and replace the usual practice of prescribing aerobic exercises (walking) only.

Short-Term RCT of Increased Dietary Potassium from Potato or Potassium Gluconate: Effect on Blood Pressure, Microcirculation, and Potassium and Sodium Retention in Pre-Hypertensive-to-Hypertensive Adults

Increased potassium intake has been linked to improvements in cardiovascular and other health outcomes. We assessed increasing potassium intake through food or supplements as part of a controlled diet on blood pressure (BP), microcirculation (endothelial function), and potassium and sodium retention in thirty pre-hypertensive-to-hypertensive men and women. Participants were randomly assigned to a sequence of four 17 day dietary potassium treatments: a basal diet (control) of 60 mmol/d and three phases of 85 mmol/d added as potatoes, French fries, or a potassium gluconate supplement. Blood pressure was measured by manual auscultation, cutaneous microvascular and endothelial function by thermal hyperemia, utilizing laser Doppler flowmetry, and mineral retention by metabolic balance. There were no significant differences among treatments for end-of-treatment BP, change in BP over time, or endothelial function using a mixed-model ANOVA. However, there was a greater change in systolic blood pressure (SBP) over time by feeding baked/boiled potatoes compared with control (-6.0 mmHg vs. -2.6 mmHg; p = 0.011) using contrast analysis. Potassium retention was highest with supplements. Individuals with a higher cardiometabolic risk may benefit by increasing potassium intake. This trial was registered at ClinicalTrials.gov as NCT02697708.

Effects of Dietary Phytoestrogens on Hormones throughout a Human Lifespan: A Review

Dietary phytoestrogens are bioactive compounds with estrogenic activity. With the growing popularity of plant-based diets, the intake of phytoestrogen-rich legumes (especially soy) and legume-derived foods has increased. Evidence from preclinical studies suggests these compounds may have an effect on hormones and health, although the results of human trials are unclear. The effects of dietary phytoestrogens depend on the exposure (phytoestrogen type, matrix, concentration, and bioavailability), ethnicity, hormone levels (related to age, sex, and physiological condition), and health status of the consumer. In this review, we have summarized the results of human studies on dietary phytoestrogens with the aim of assessing the possible hormone-dependent outcomes and health effects of their consumption throughout a lifespan, focusing on pregnancy, childhood, adulthood, and the premenopausal and postmenopausal stages. In pregnant women, an improvement of insulin metabolism has been reported in only one study. Sex hormone alterations have been found in the late stages of childhood, and goitrogenic effects in children with hypothyroidism. In premenopausal and postmenopausal women, the reported impacts on hormones are inconsistent, although beneficial goitrogenic effects and improved glycemic control and cardiovascular risk markers have been described in postmenopausal individuals. In adult men, different authors report goitrogenic effects and a reduction of insulin in non-alcoholic fatty liver patients. Further carefully designed studies are warranted to better elucidate the impact of phytoestrogen consumption on the endocrine system at different life stages.

Effects of physical exercise in sarcopenia. A systematic review

From the third decade of life and due to multiple causes, muscle mass and strength are gradually lost, which affects the function of the musculoskeletal system. This combined loss of muscle mass and strength with aging is called sarcopenia, and is associated with greater morbidity and mortality in the elderly. Early treatment is therefore essential, and physical exercise is the therapeutic approach that has given the best results. This literature review intended to analyze the effect of physical exercise, excluding the role that other treatments proposed, including the nutritional approach, could play in the treatment of sarcopenia, refers to 12 articles. In studies including high intensity strength exercises in isolation, either alone or combined with aerobic exercise, improvements were seen in muscle mass, muscle strength, and functional test times. There is also a significant increase in fat-free mass in individuals who exercised more frequently (more than two sessions per week). Current evidence shows that strength-resistance training and its combination in multimodal programs with aerobic exercise show significantly beneficial effects on anthropometric and muscle function parameters. Programs of prescribed exercises including strength exercises adequate to the characteristics should therefore be adapted to the characteristics of each individual and replace the usual practice of prescribing aerobic exercises (walking) only.

Effects of an 8-Week Protein Supplementation Regimen with Hyperimmunized Cow Milk on Exercise-Induced Organ Damage and Inflammation in Male Runners: A Randomized, Placebo Controlled, Cross-Over Study

Prolonged strenuous exercise may induce inflammation, cause changes in gastrointestinal permeability, and lead to other unfavorable biological changes and diseases. Nutritional approaches have been used to prevent exercise-induced inflammatory responses and gastrointestinal disorders. Hyperimmunized milk, obtained by immunizing cows against specific antigens, promotes the development of immunity against pathogens, promotes anti-inflammatory effects, and protects intestinal function. Immune protein (IMP) is a concentrated product of hyperimmunized milk and is a more promising means of supplementation to protect against acute infections and inflammation. To determine whether IMP has protective properties against exercise-induced gastrointestinal dysfunction and inflammation, we examined biochemical markers, intestinal damage markers, and pro-/anti-inflammatory profiles of young male runners using a randomized, placebo controlled, cross-over design. Urine samples were collected and used for measurements of creatinine, N-acetyl-β-d-glucosaminidase, osmotic pressure, and specific gravity. Titin was measured as a muscle damage marker. Further, urine concentrations of complement 5a, calprotectin, fractalkine, myeloperoxidase, macrophage colony-stimulating factor, monocyte chemotactic protein-1, intestinal fatty acid binding protein (I-FABP), interferon (IFN)-γ, interleukin (IL)-1β, IL-1 receptor antagonist, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p40, and tumor necrosis factor (TNF)-α were measured by enzyme-linked immunosorbent assays. We demonstrated that urine osmotic pressure, urine specific gravity, I-FABP, IFN-γ, IL-1β, and TNF-α were reduced by 8 weeks of IMP supplementation, indicating that IMP may have potential in preventing strenuous exercise-induced renal dysfunction, increased intestinal permeability, and inflammation. Thus, IMP supplementation may be a feasible nutritional approach for the prevention of unfavorable exercise-induced symptoms.

Soy isoflavones prevent bone resorption and loss, a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Osteoporosis is a common bone disease characterized by reduced bone mass resulting from continuous bone resorption.

METHODS

PubMed, Scopus, and Embase were searched to find published trials on the effect of soy isoflavones on bone mineral density (BMD) and bone turnover markers (bone-specific alkaline phosphatase, osteocalcin, osteoprotegerin, pyridinoline, deoxypyridinoline, C-telopeptide, and N-telopeptide). Random-effects inverse-variance model was used to calculate the pooled effects.

RESULTS

A total of 5313 articles were found, screened, and assessed for eligibility, and finally 52 trials were included in the meta-analysis. Consumption of soy isoflavones caused significant improvement in BMD of lumbar spine (mean difference (MD) = 0.76%; 95% CI: 0.09, 1.42%; p = 0.03), hip (MD = 0.22%; 95% CI: 0.02, 0.42%; p = 0.04), and femoral neck (MD = 2.27%; 95% CI: 1.22, 3.31%; p < 0.001). Subgroup analysis showed that in all 3 sites, the improvement was significant in normal weight subjects and interventions longer than a year, although trial location and dosage were also factors influencing isoflavones' impact on BMD. Among markers of bone turnover, osteoprotegerin (MD = 5.79; 95% CI: 3.08, 8.51 pg/ml; p < 0.001), pyridinoline (MD = -5.13; 95% CI: -7.76, -2.50 nmol/mmol; p < 0.001), and C-telopeptides (MD = -0.08; 95% CI: -0.16, -0.00 ng/ml; p = 0.04) were favorably affected by isoflavones while osteocalcin and bone alkaline phosphatase did not change. Subgroup analysis of bone markers showed that in overweight/obese individuals and dosages <90 mg/day, isoflavones are more effective.

CONCLUSIONS

Soy isoflavones prevent osteoporosis-related bone loss in any weight status or treatment duration. They increase BMD in normal weight subjects and diminish bone resorption in overweight/obese individuals. Although bone resorption may be decelerated over short-term isoflavone consumption, periods longer than a year are probably needed to affect BMD. Isoflavones also appear benefits on bone in any dose or subjects' ethnicity.

Dietary protein and bone health across the life-course: an updated systematic review and meta-analysis over 40 years

We undertook a systematic review and meta-analysis of published papers assessing dietary protein and bone health. We found little benefit of increasing protein intake for bone health in healthy adults but no indication of any detrimental effect, at least within the protein intakes of the populations studied. This systematic review and meta-analysis analysed the relationship between dietary protein and bone health across the life-course. The PubMed database was searched for all relevant human studies from the 1st January 1976 to 22nd January 2016, including all bone outcomes except calcium metabolism. The searches identified 127 papers for inclusion, including 74 correlational studies, 23 fracture or osteoporosis risk studies and 30 supplementation trials. Protein intake accounted for 0-4% of areal BMC and areal BMD variance in adults and 0-14% of areal BMC variance in children and adolescents. However, when confounder adjusted (5 studies) adult lumbar spine and femoral neck BMD associations were not statistically significant. There was no association between protein intake and relative risk (RR) of osteoporotic fractures for total (RR_(random) = 0.94; 0.72 to 1.23, I² = 32%), animal (RR _(random) = 0.98; 0.76 to 1.27, I² = 46%) or vegetable protein (RR _(fixed) = 0.97 (0.89 to 1.09, I² = 15%). In total protein supplementation studies, pooled effect sizes were not statistically significant for LSBMD (total n = 255, MD_(fixed) = 0.04 g/cm² (0.00 to 0.08, P = 0.07), I² = 0%) or FNBMD (total n = 435, MD_(random) = 0.01 g/cm² (-0.03 to 0.05, P = 0.59), I² = 68%). There appears to be little benefit of increasing protein intake for bone health in healthy adults but there is also clearly no indication of any detrimental effect, at least within the protein intakes of the populations studied (around 0.8-1.3 g/Kg/day). More studies are urgently required on the association between protein intake and bone health in children and adolescents.

Soy Protein Isolate Suppresses Bone Resorption and Improves Trabecular Microarchitecture in Spontaneously Hyperphagic, Rapidly Growing Male OLETF Rats

BACKGROUND

Traditionally, milk proteins have been recommended for skeletal health; recently, soy proteins have emerged as popular alternatives. Excess adiposity appears detrimental to skeletal health, as obese adolescents have increased fracture rates compared with healthy controls. However, soy protein effects on skeletal health during excess adiposity remain unknown.

OBJECTIVE

The study objective was to examine the effects of isocaloric diets containing milk protein isolate (MPI), soy protein isolate (SPI), or a 50/50 combination (MIX) as the sole protein source on metabolic health indicators and bone outcomes in rapidly growing, hyperphagic, male Otsuka Long Evans Tokushima Fatty (OLETF) rats.

METHODS

OLETF rats, aged 4 wk, were randomly assigned to 3 treatment groups (MPI, SPI, or MIX, n = 20 per group) and provided with access to experimental diets ad libitum for 16 wk.

RESULTS

Body mass did not differ between the groups, but SPI had lower percentage body fat than MPI (P = 0.026). Insulin was lower in MPI than in MIX (P = 0.033) or SPI (P = 0.044), but fasting blood glucose was not different between the groups. SPI significantly reduced serum cholesterol compared with MPI (P = 0.001) and MIX (P = 0.002). N-terminal propeptide of type I collagen (P1NP) was higher in MIX than MPI (P = 0.05); C-terminal telopeptide of type 1 collagen (CTx) was higher in MPI than SPI (P < 0.001) and MIX (P < 0.001); the P1NP to CTx ratio was significantly higher in SPI and MIX than in MPI (P < 0.001). Trabecular separation was reduced in SPI compared with MPI (P = 0.030) and MIX (P = 0.008); trabecular number was increased in SPI compared with MIX (P = 0.038). No differences were seen in cortical geometry and biomechanical properties.

CONCLUSIONS

In the context of excess adiposity, soy- and milk-based proteins have comparable effects on cortical bone geometry and biomechanical properties, whereas soy-based proteins favorably affect the trabecular microarchitecture, and the combination of both proteins may offer additional benefits to bone remodeling in rapidly growing male OLETF rats.

Soy, Soy Foods and Their Role in Vegetarian Diets

Soy is a basic food ingredient of traditional Asian cuisine used for thousands of years. In Western countries, soybeans have been introduced about a hundred years ago and recently they are mainly used for surrogate foods production. Soy and soy foods are common nutritional solutions for vegetarians, due to their high protein content and versatility in the production of meat analogues and milk substitutes. However, there are some doubts about the potential effects on health, such as the effectiveness on cardiovascular risk reduction or, conversely, on the possible disruption of thyroid function and sexual hormones. The soy components that have stimulated the most research interest are isoflavones, which are polyphenols with estrogenic properties highly contained in soybeans. In this review, we discuss the characteristics of soy and soy foods, focusing on their nutrient content, including phytoestrogens and other bioactive substances that are noteworthy for vegetarians, the largest soy consumers in the Western countries. The safety of use will also be discussed, given the growing trend in adoption of vegetarian styles and the new soy-based foods availability.

The Effect of Soy Isoflavones on the Menopause Rating Scale Scoring in Perimenopausal and Postmenopausal Women: A Pilot Study

INTRODUCTION

Menopause is associated with many unpleasant symptoms which vary in different phases of menopausal transition. Although, Hormone Replacement Therapy (HRT) is considered the most effective mode of treatment for these symptoms, its use is associated with increased risk of breast cancer, endometrial cancer and thromboembolic events. Soy isoflavones are being widely used as a safer alternative to HRT, even though scientific evidence of their efficacy is poor or lacking.

AIM

To study the effect of soy isoflavone supplementation on the menopausal symptoms in perimenopausal and postmenopausal women.

MATERIALS AND METHODS

An observational pilot study was done involving 29 perimenopausal and 21 postmenopausal women prescribed 100 mg soy isoflavones for 12 weeks. Menopause Rating Scale (MRS) questionnaire was administered to the patients before starting soy isoflavone therapy and at the end of treatment. Responses were analysed using Statistical Package for Social Sciences (SPSS) software 23.0.

RESULTS

Total score of both the groups were comparable at baseline. Among perimenopausal women highest score was given to symptoms of psychological domain. Urogenital symptoms were the worst among postmenopausal women. After 12 weeks of treatment, total scores improved significantly by 19.55% and 12.62% in the perimenopausal and postmenopausal women respectively. The greatest improvement was seen in scores of hot flashes for both the groups and the least improvement was shown by symptoms of urogenital subscale.

CONCLUSION

Soy isoflavone improves the MRS score among both the perimenopausal and postmenopausal women. As they are most effective for somatic and psychological symptoms, their use could be beneficial during perimenopause.

Calcium Balance in Chronic Kidney Disease

PURPOSE OF REVIEW

The kidneys play a critical role in the balance between the internal milieu and external environment. Kidney failure is known to disrupt a number of homeostatic mechanisms that control serum calcium and normal bone metabolism. However, our understanding of calcium balance throughout the stages of chronic kidney disease is limited and the concept of balance itself, especially with a cation as complex as calcium, is often misunderstood. Both negative and positive calcium balance have important implications in patients with chronic kidney disease, where negative balance may increase risk of osteoporosis and fracture and positive balance may increase risk of vascular calcification and cardiovascular events. Here, we examine the state of current knowledge about calcium balance in adults throughout the stages of chronic kidney disease and discuss recommendations for clinical strategies to maintain balance as well as future research needs in this area.

RECENT FINDINGS

Recent calcium balance studies in adult patients with chronic kidney disease show that neutral calcium balance is achieved with calcium intake near the recommended daily allowance. Increases in calcium through diet or supplements cause high positive calcium balance, which may put patients at risk for vascular calcification. However, heterogeneity in calcium balance exists among these patients. Given the available calcium balance data in this population, it appears clinically prudent to aim for recommended calcium intakes around 1000 mg/day to achieve neutral calcium balance and avoid adverse effects of either negative or positive calcium balance. Assessment of patients' dietary calcium intake could further equip clinicians to make individualized recommendations for meeting recommended intakes.

Calcium-41: a technology for monitoring changes in bone mineral

The rare, long-lived radiotracer, ⁴¹Ca, measured by accelerator mass spectrometry in the urine or serum following incorporation into the bone provides an ultra-sensitive tool to assess changes in bone calcium balance in response to an intervention. Changes in bone balance can be followed for years with one small dose that is both radiologically and biologically non-invasive. Sequential interventions can be compared, with greater precision than they can with biochemical markers of bone turnover and with greater power than with bone densitometry. This method is especially useful to screen interventions over a period of weeks. The development and validation of this tool and its applications are reviewed. Mini abstract: Use of ⁴¹Ca measured in the urine or blood by accelerator mass spectrometry to assess bone balance provides a tool to compare the relative efficacy of multiple interventions. This perspective provides insights in the use of this novel method and comparisons with more traditional methods for evaluating the efficacy of interventions.

Calcium Homeostasis in Health and in Kidney Disease

Calcium is an important ion in cell signaling, hormone regulation, and bone health. Its regulation is complex and intimately connected to that of phosphate homeostasis. Both ions are maintained at appropriate levels to maintain the extracellular to intracellular gradients, allow for mineralization of bone, and to prevent extra skeletal and urinary calcification. The homeostasis involves the target organs intestine, parathyroid glands, kidney, and bone. Multiple hormones converge to regulate the extracellular calcium level: parathyroid hormone, vitamin D (principally 25(OH)D or 1,25(OH)2D), fibroblast growth factor 23, and α-klotho. Fine regulation of calcium homeostasis occurs in the thick ascending limb and collecting tubule segments via actions of the calcium sensing receptor and several channels/transporters. The kidney participates in homeostatic loops with bone, intestine, and parathyroid glands. Initially in the course of progressive kidney disease, the homeostatic response maintains serum levels of calcium and phosphorus in the desired range, and maintains neutral balance. However, once the kidneys are no longer able to appropriately respond to hormones and excrete calcium and phosphate, positive balance ensues leading to adverse cardiac and skeletal abnormalities. © 2016 American Physiological Society. Compr Physiol 6:1781-1800, 2016.

Potassium citrate supplementation results in sustained improvement in calcium balance in older men and women

The dietary acid load created by the typical Western diet may adversely impact the skeleton by disrupting calcium metabolism. Whether neutralizing dietary acid with alkaline potassium salts results in sustained improvements in calcium balance remains controversial. In this randomized, double-blind, placebo-controlled study, 52 men and women (mean age 65.2 ± 6.2 years) were randomly assigned to potassium citrate 60 mmol/d, 90 mmol/d, or placebo daily with measurements of bone turnover markers, net acid excretion, and calcium metabolism, including intestinal fractional calcium absorption and calcium balance, obtained at baseline and at 6 months. At 6 months, net acid excretion was significantly lower in both treatment groups compared to placebo and it was negative, meaning subjects' dietary acid was completely neutralized (-11.3 mmol/d on 60 mmol/d; -29.5 mmol/d on 90 mmol/d, p < 0.001 compared to placebo). At 6 months, 24-hour urine calcium was significantly reduced in persons taking potassium citrate 60 mmol/d (-46 ± 15.9 mg/d) and 90 mmol/d (-59 ± 31.6 mg/d) compared with placebo (p < 0.01). Fractional calcium absorption was not changed by potassium citrate supplementation. Net calcium balance was significantly improved in participants taking potassium citrate 90 mmol/d compared to placebo (142 ± 80 mg/d on 90 mmol/d versus -80 ± 54 mg/d on placebo; p = 0.02). Calcium balance was also improved on potassium citrate 60 mmol/d, but this did not reach statistical significance (p = 0.18). Serum C-telopeptide decreased significantly in both potassium citrate groups compared to placebo (-34.6 ± 39.1 ng/L on 90 mmol/d, p = 0.05; -71.6 ± 40.7 ng/L on 60 mmol/d, p = 0.02) whereas bone-specific alkaline phosphatase did not change. Intact parathyroid hormone was significantly decreased in the 90 mmol/d group (p = 0.01). Readily available, safe, and easily administered in an oral form, potassium citrate has the potential to improve skeletal health. Longer-term trials with definitive outcomes such as bone density and fracture are needed.

Oral calcium carbonate affects calcium but not phosphorus balance in stage 3-4 chronic kidney disease

Patients with chronic kidney disease (CKD) are given calcium carbonate to bind dietary phosphorus, reduce phosphorus retention, and prevent negative calcium balance; however, data are limited on calcium and phosphorus balance during CKD to support this. Here, we studied eight patients with stage 3 or 4 CKD (mean estimated glomerular filtration rate 36 ml/min) who received a controlled diet with or without a calcium carbonate supplement (1500 mg/day calcium) during two 3-week balance periods in a randomized placebo-controlled cross-over design. All feces and urine were collected during weeks 2 and 3 of each balance period and fasting blood, and urine was collected at baseline and at the end of each week. Calcium kinetics were determined using oral and intravenous (45)calcium. Patients were found to be in neutral calcium and phosphorus balance while on the placebo. Calcium carbonate supplementation produced positive calcium balance, did not affect phosphorus balance, and produced only a modest reduction in urine phosphorus excretion compared with placebo. Calcium kinetics demonstrated positive net bone balance but less than overall calcium balance, suggesting soft-tissue deposition. Fasting blood and urine biochemistries of calcium and phosphate homeostasis were unaffected by calcium carbonate. Thus, the positive calcium balance produced by calcium carbonate treatment within 3 weeks cautions against its use as a phosphate binder in patients with stage 3 or 4 CKD, if these findings can be extrapolated to long-term therapy.

Milk and acid-base balance: proposed hypothesis versus scientific evidence

Recently the lay press has claimed a hypothetical association among dairy product consumption, generation of dietary acid, and harm to human health. This theoretical association is based on the idea that the protein and phosphate in milk and dairy products make them acid-producing foods, which cause our bodies to become acidified, promoting diseases of modern civilization. Some authors have suggested that dairy products are not helpful and perhaps detrimental to bone health because higher osteoporotic fracture incidence is observed in countries with higher dairy product consumption. However, scientific evidence does not support any of these claims. Milk and dairy products neither produce acid upon metabolism nor cause metabolic acidosis, and systemic pH is not influenced by diet. Observations of higher dairy product intake in countries with prevalent osteoporosis do not hold when urban environments are compared, likely due to physical labor in rural locations. Milk and other dairy products continue to be a good source of dietary protein and other nutrients. Key teaching points: Measurement of an acidic pH urine does not reflect metabolic acidosis or an adverse health condition. The modern diet, and dairy product consumption, does not make the body acidic. Alkaline diets alter urine pH but do not change systemic pH. Net acid excretion is not an important influence of calcium metabolism. Milk is not acid producing. Dietary phosphate does not have a negative impact on calcium metabolism, which is contrary to the acid-ash hypothesis.

Simple isotopic method using oral stable or radioactive tracers for estimating fractional calcium absorption in adult women

We extended a simple oral method for estimating fractional calcium absorption determined by double isotopic methods using radioactive or stable isotope across wide age of adult women. Fractional calcium absorption can be estimated by using either a radioactive or stable oral isotope across the entire age spectrum of adult women.

INTRODUCTION

A method for estimating fractional calcium absorption using a single serum collection following a single oral radioactive isotopic tracer has been validated against a classical double isotopic tracer ratio method in adults. Our goal was to extend this simplified method to include use of stable isotopes and a broad age range.

METHODS

We used our database of 56 observations from 26 white adult women aged 19-67 years receiving either radioactive or stable isotopes. Reference values for fractional calcium absorption were determined from 24-h double isotopic ratios in serum and urine and from full kinetic modeling.

RESULTS

Equations for estimating fractional calcium absorption were developed from isotopic enrichment in serum and urine from an oral tracer and measures of body size using the multiple linear regression analysis. Equations using a 4- to 6-h sample following an oral dose of either a stable or radioactive isotope corrected for body size were highly correlated with the reference values for fractional calcium absorption across different aged populations (r > 0.8, p < 0.001).

CONCLUSION

Fractional calcium absorption can be estimated by a single oral tracer method using either radioactive or stable calcium isotopes across the entire age spectrum in healthy white adult women.

Causal assessment of dietary acid load and bone disease: a systematic review & meta-analysis applying Hill's epidemiologic criteria for causality

Background

Modern diets have been suggested to increase systemic acid load and net acid excretion. In response, alkaline diets and products are marketed to avoid or counteract this acid, help the body regulate its pH to prevent and cure disease. The objective of this systematic review was to evaluate causal relationships between dietary acid load and osteoporosis using Hill's criteria.

Methods

Systematic review and meta-analysis. We systematically searched published literature for randomized intervention trials, prospective cohort studies, and meta-analyses of the acid-ash or acid-base diet hypothesis with bone-related outcomes, in which the diet acid load was altered, or an alkaline diet or alkaline salts were provided, to healthy human adults. Cellular mechanism studies were also systematically examined.

Results

Fifty-five of 238 studies met the inclusion criteria: 22 randomized interventions, 2 meta-analyses, and 11 prospective observational studies of bone health outcomes including: urine calcium excretion, calcium balance or retention, changes of bone mineral density, or fractures, among healthy adults in which acid and/or alkaline intakes were manipulated or observed through foods or supplements; and 19 in vitro cell studies which examined the hypothesized mechanism. Urine calcium excretion rates were consistent with osteoporosis development; however calcium balance studies did not demonstrate loss of whole body calcium with higher net acid excretion. Several weaknesses regarding the acid-ash hypothesis were uncovered: No intervention studies provided direct evidence of osteoporosis progression (fragility fractures, or bone strength as measured using biopsy). The supporting prospective cohort studies were not controlled regarding important osteoporosis risk factors including: weight loss during follow-up, family history of osteoporosis, baseline bone mineral density, and estrogen status. No study revealed a biologic mechanism functioning at physiological pH. Finally, randomized studies did not provide evidence for an adverse role of phosphate, milk, and grain foods in osteoporosis.

Conclusions

A causal association between dietary acid load and osteoporotic bone disease is not supported by evidence and there is no evidence that an alkaline diet is protective of bone health.

Interpretation of 41Ca data using compartmental modeling in post-menopausal women

Calcium-41 (t(1/2) = 10(5) years) can be used after a single dose to follow calcium metabolism over a subject's lifetime. The aims of this study were to expand a (41)Ca kinetic model and estimate bone resorption in women with stable bone loss, compare the rates with those calculated with classical isotope studies, and to use the model to simulate dynamic changes in urinary (41)Ca:Ca ratios and bone balance for the design and interpretation of (41)Ca studies. Forty-two women >5 years post-menopause were given (41)Ca intravenously. Bone mineral content and bone mineral density of total body were measured by dual-energy X-ray absorptiometry at the beginning of the study. Urine collections were made periodically for up to ~5 years while subjects were free living. Urinary (41)Ca:Ca ratios were measured using accelerator mass spectrometry. The isotope data were analyzed by compartmental modeling. Four compartments were necessary to fit the urinary tracer data and total bone calcium. The final model included pathways for absorption, distribution, urinary excretion, and endogenous excretion and was used to calculate rates of bone turnover. Estimates of bone resorption in a subset of the women (n = 13), studied previously in a 3-week balance and full kinetic study with (45)Ca, agreed with those using (41)Ca methodology. Thus, rates of bone resorption can be estimated from (41)Ca urinary data in stable post-menopausal women. The model was used to simulate dynamic changes in urinary (41)Ca:Ca ratios and bone balance, as a result of interventions that perturb calcium metabolism to aid in study design and interpretation.

Soy components vs. whole soy: are we betting our bones on a long shot?

Soybeans are a good source of bone-healthy nutrients. Epidemiological studies in Asia evaluating diets containing traditional whole soy foods show a positive association with bone mineral density and fracture protection. Smaller scale intervention studies in Western nations mainly feature isolated soy protein (SP) and purified or concentrated soy isoflavones (SI) rather than whole soy foods and they have produced inconsistent results. Consumption of SP does not alter calcium (Ca) retention even though urinary Ca excretion is less in diets with SP compared with proteins higher in sulfur-containing amino acids. SI, often consumed at higher concentrations than would be available in traditional Asian diets, are not yielding the type of incontrovertible evidence that might be expected in support of their benefit to bone health. This forces one to ask whether whole soy might provide a superior effect on bone.

Effect of protein intake on bone and muscle mass in the elderly

The aging process is frequently characterized by an involuntary loss of muscle (sarcopenia) and bone (osteoporosis) mass. Both chronic diseases are associated with decreased metabolic rate, increased risk of falls/fracture, and, as a result, increased morbidity and loss of independence in the elderly. The quality and quantity of protein intake affects bone and muscle mass in several ways and there is evidence that increased essential amino acid or protein availability can enhance muscle protein synthesis and anabolism, as well as improve bone homeostasis in older subjects. A thorough evaluation of renal function is important, since renal function decreases with age. Finally, protein and calcium intake should be considered in the prevention or treatment of the chronic diseases osteoporosis and sarcopenia.

The role of soy in vegetarian diets

Soyfoods have long been prized among vegetarians for both their high protein content and versatility. Soybeans differ markedly in macronutrient content from other legumes, being much higher in fat and protein, and lower in carbohydrate. In recent years however, soyfoods and specific soybean constituents, especially isoflavones, have been the subject of an impressive amount of research. Nearly 2,000 soy-related papers are published annually. This research has focused primarily on the benefits that soyfoods may provide independent of their nutrient content. There is particular interest in the role that soyfoods have in reducing risk of heart disease, osteoporosis and certain forms of cancer. However, the estrogen-like effects of isoflavones observed in animal studies have also raised concerns about potential harmful effects of soyfood consumption. This review addresses questions related to soy and chronic disease risk, provides recommendations for optimal intakes, and discusses potential contraindications. As reviewed, the evidence indicates that, with the exception of those individuals allergic to soy protein, soyfoods can play a beneficial role in the diets of vegetarians. Concerns about adverse effects are not supported by the clinical or epidemiologic literature. Based on the soy intake associated with health benefits in the epidemiologic studies and the benefits noted in clinical trials, optimal adult soy intake would appear to be between two and four servings per day.

Effects of soy isoflavone supplements on bone turnover markers in menopausal women: systematic review and meta-analysis of randomized controlled trials

INTRODUCTION

Effects of soy isoflavone supplements on bone turnover markers remain unclear. This up-to-date systematic review and meta-analysis of randomized controlled trials (RCTs) was performed primarily to more completely and precisely clarify the effects on urinary deoxypyridinoline (DPD) and serum bone alkaline phosphatase (BAP) and secondarily to evaluate the effects on other bone turnover markers, compared with placebo in menopausal women.

METHODS

PubMed, CENTRAL, ICHUSHI, and CNKI were searched in June 2009 for relevant studies of RCTs. Data on study design, participants, interventions, and outcomes were extracted and methodological quality of each included trial was assessed.

RESULTS

From 3740 identified relevant articles, 10 (887 participants), 10 (1210 participants), and 8 (380 participants) RCTs were selected for meta-analysis of effects on DPD, BAP, and serum osteocalcin (OC), respectively, using Review Manager 5.0.22. Daily ingestion of an average 56 mg soy isoflavones (aglycone equivalents) for 10 weeks to 12 months significantly decreased DPD by 14.1% (95% CI: -26.8% to -1.5%; P=0.03) compared to baseline (heterogeneity: P<0.00001; I(2)=93%; random effects model). The overall effect of soy isoflavones on DPD compared with placebo was a significant decrease of -18.0% (95% CI: -28.4% to -7.7%, P=0.0007; heterogeneity: P=0.0001; I(2)=73%; random effects model). Subgroup analyses and meta-regressions revealed that isoflavone dose and intervention duration did not significantly relate to the variable effects on DPD. Daily supplementation of about 84 mg and 73 mg of soy isoflavones for up to 12 months insignificantly increased BAP by 8.0% (95% CI: -4.2% to 20.2%, P=0.20; heterogeneity: P<0.00001; I(2)=98%) and OC by 10.3% (95% CI: -3.1% to 23.7%, P=0.13; heterogeneity: P=0.002; I(2)=69%) compared with placebo (random effects model), respectively.

CONCLUSIONS

Soy isoflavone supplements moderately decreased the bone resorption marker DPD, but did not affect bone formation markers BAP and OC in menopausal women. The effects varied between studies, and further studies are needed to address factors relating to the observed effects of soy isoflavones on DPD and to verify effects on other bone turnover markers.

Absorption of calcium from milk and tempeh consumed by postmenopausal Malay women using the dual stable isotope technique

Assessment of calcium bioavailability from non-dairy foods containing moderate amounts of calcium is especially important in populations that have habitually low dairy consumption. Absorption of calcium from milk and tempeh (a traditional fermented soy product) was compared in a sample of Malay subjects. A randomized, crossover design was utilized to assess calcium absorption in 20 postmenopausal women from either a glass of milk (114 g) or from a meal of tempeh (206 g); each containing 130 mg calcium. At each study of Phase 1 (mid-July) and Phase 2 (mid-August), intravenous (42)Ca and oral (44)Ca were administered and calcium absorption was measured in 24-h urine collections post-dosing; with a 1-month washout period between phases. Absorption of calcium from tempeh did not differ significantly from milk (36.9 +/- 10.6% vs. 34.3 +/- 8.6%, respectively). Due to differences in the calcium content of tempeh, four servings of this product would be needed to get the same amount of absorbed calcium as that obtained from a 4-ounce glass of milk. Tempeh may provide readily available calcium for this population of women at risk for low bone mass.

Phosphate decreases urine calcium and increases calcium balance: a meta-analysis of the osteoporosis acid-ash diet hypothesis

Background

The acid-ash hypothesis posits that increased excretion of "acidic" ions derived from the diet, such as phosphate, contributes to net acidic ion excretion, urine calcium excretion, demineralization of bone, and osteoporosis. The public is advised by various media to follow an alkaline diet to lower their acidic ion intakes. The objectives of this meta-analysis were to quantify the contribution of phosphate to bone loss in healthy adult subjects; specifically, a) to assess the effect of supplemental dietary phosphate on urine calcium, calcium balance, and markers of bone metabolism; and to assess whether these affects are altered by the b) level of calcium intake, c) the degree of protonation of the phosphate.

Methods

Literature was identified through computerized searches regarding phosphate with surrogate and/or direct markers of bone health, and was assessed for methodological quality. Multiple linear regression analyses, weighted for sample size, were used to combine the study results. Tests of interaction included stratification by calcium intake and degree of protonation of the phosphate supplement.

Results

Twelve studies including 30 intervention arms manipulated 269 subjects' phosphate intakes. Three studies reported net acid excretion. All of the meta-analyses demonstrated significant decreases in urine calcium excretion in response to phosphate supplements whether the calcium intake was high or low, regardless of the degree of protonation of the phosphate supplement. None of the meta-analyses revealed lower calcium balance in response to increased phosphate intakes, whether the calcium intake was high or low, or the composition of the phosphate supplement.

Conclusion

All of the findings from this meta-analysis were contrary to the acid ash hypothesis. Higher phosphate intakes were associated with decreased urine calcium and increased calcium retention. This meta-analysis did not find evidence that phosphate intake contributes to demineralization of bone or to bone calcium excretion in the urine. Dietary advice that dairy products, meats, and grains are detrimental to bone health due to "acidic" phosphate content needs reassessment. There is no evidence that higher phosphate intakes are detrimental to bone health.

Soy proteins and isoflavones affect bone mineral density in older women: a randomized controlled trial

BACKGROUND

Soy foods contain several components (isoflavones and amino acids) that potentially affect bone. Few long-term, large clinical trials of soy as a means of improving bone mineral density (BMD) in late postmenopausal women have been conducted.

OBJECTIVE

Our goal was to evaluate the long-term effect of dietary soy protein and/or soy isoflavone consumption on skeletal health in late postmenopausal women.

DESIGN

We conducted a randomized, double-blind, placebo-controlled clinical trial in 131 healthy ambulatory women aged >60 y. Ninety-seven women completed the trial. After a 1-mo baseline period, subjects were randomly assigned into 1 of 4 intervention groups: soy protein (18 g) + isoflavone tablets (105 mg isoflavone aglycone equivalents), soy protein + placebo tablets, control protein + isoflavone tablets, and control protein + placebo tablets.

RESULTS

Consumption of protein powder and isoflavone pills did not differ between groups, and compliance with the study powder and pills was 80-90%. No significant differences in BMD were observed between groups from baseline to 1 y after the intervention or in BMD change between equol and non-equol producers. However, there were significant negative correlations between total dietary protein (per kg) and markers of bone turnover (P < 0.05).

CONCLUSIONS

Because soy protein and isoflavones (either alone or together) did not affect BMD, they should not be considered as effective interventions for preserving skeletal health in older women. The negative correlation between dietary protein and bone turnover suggests that increasing protein intakes may suppress skeletal turnover. This trial was registered at ClinicalTrials.gov as NCT00668447.

Should dairy be recommended as part of a healthy vegetarian diet? Point

A benefit-risk evaluation of the evidence for including dairy foods in the diet is presented. For many persons dairy products provide a substantial portion of essential nutrients, but especially calcium, potassium, and magnesium. Dietary supplements and fortified foods can be alternative sources of these nutrients, although other components of dairy foods such as amino acid composition and conjugated linoleic acid may be instrumental in the benefits associated with dairy product consumption for bone health and reduced risk of stroke, metabolic syndrome, and some cancers. Newer evidence shows that protein-induced calciuria does not have a detrimental effect on net calcium retention, and the concentrations of hormones in milk are not outside of the range of endogenous concentrations. Increased dietary protein, including from milk, can elevate serum concentrations of insulin-like growth factor I, which has an unknown relation to cancer. The concern over consumption of milk leading to increased risk of prostate cancer through reduction of serum 1,25-dihydroxyvitamin D, a potent anti-prostate cancer hormone, has been resolved with new evidence that local production of this hormone is independent of diet. Overall, evidence suggests that being a lactovegetarian has greater health benefits and reduced health risks than being a vegan.

Effects of soy protein and isoflavones on circulating hormone concentrations in pre- and post-menopausal women: a systematic review and meta-analysis

BACKGROUND

Hormonal effects of soy and isoflavones have been investigated in numerous trials with equivocal findings. We aimed to systematically assess the effects of soy and isoflavones on circulating estrogen and other hormones in pre- and post-menopausal women.

METHODS

The Cochrane Library, MEDLINE and EMBASE (plus reviews and experts) were searched to December 2007. Inclusion of randomized or residential crossover trials of soy or isoflavones for 4 or more weeks on estrogens, SHBG, FSH, LH, progesterone and thyroid hormones in women was assessed independently in duplicate. Six percent of papers assessed were included. Data concerning participants, interventions, outcomes, potential effect modifiers and trial quality characteristics were extracted independently in duplicate.

RESULTS

Forty-seven studies (11 of pre-, 35 of post- and 1 of perimenopausal women) were included. In premenopausal women, meta-analysis suggested that soy or isoflavone consumption did not affect primary outcomes estradiol, estrone or SHBG concentrations, but significantly reduced secondary outcomes FSH and LH [by ∼20% using standardized mean difference (SMD), P = 0.01 and 0.05, respectively]. Menstrual cycle length was increased by 1.05 days (95% CI 0.13, 1.97, 10 studies). In post-menopausal women, there were no statistically significant effects on estradiol, estrone, SHBG, FSH or LH, although there was a small statistically non-significant increase in total estradiol with soy or isoflavones (∼14%, SMD, P = 0.07, 21 studies).

CONCLUSIONS

Isoflavone-rich soy products decrease FSH and LH in premenopausal women and may increase estradiol in post-menopausal women. The clinical implications of these modest hormonal changes remain to be determined.

Meta-analysis of the quantity of calcium excretion associated with the net acid excretion of the modern diet under the acid-ash diet hypothesis

BACKGROUND

The acid-ash diet hypothesis of osteoporosis suggests that acid from the modern diet causes a demineralization of the skeleton, and mobilized bone calcium is excreted. A systematic approach has not been used to summarize the findings of the numerous studies about the hypothesis.

OBJECTIVES

The purpose of this meta-analysis was to estimate the quantity of net acid excretion and calciuria associated with the modern diet, to assess the association between acid excretion and calcium excretion, and to assess the influence of urine preservatives on calcium measurement.

DESIGN

We systematically searched for trials of the acid-ash hypothesis and conducted a meta-analysis.

RESULTS

Twenty-five of 105 studies met the inclusion criteria. The estimated quantity of net acid excretion from the weighted average of the control diets from 11 studies was 47 mEq/d. The increase in urinary calcium with a change in renal net acid excretion depended on whether the urine was acidic or alkaline (P < 0.001). A significant linear relation was observed between net acid excretion and calcium excretion for both acidic and alkaline urine (P < 0.001). The estimated change in urine calcium associated with a change of 47 mEq of net acid excretion in acidic urine was 1.6 mmol/d (66 mg/d) of calcium.

CONCLUSION

Evidence suggests a linear association between changes in calcium excretion in response to experimental changes in net acid excretion. However, this finding is not evidence that the source of the excreted calcium is bone or that this calciuria contributes to the development of osteoporosis.

Short term effects on bone quality associated with consumption of soy protein isolate and other dietary protein sources in rapidly growing female rats

Beneficial effects of soy protein consumption on bone quality have been reported. The effects of other dietary protein sources such as whey protein hydrolysate (WPH) and rice protein isolate (RPI) on bone growth have been less well examined. The current study compared effects of feeding soy protein isolate (SPI), WPH and RPI for 14 d on tibial bone mineral density (BMD) and bone mineral content (BMC) in intact and ovariectomized (OVX) rapidly growing female rats relative to animals fed casein (CAS). The effects of estrogenic status on responses to SPI were also explored. Tibial peripheral quantitative computerized tomography (pQCT) showed all three protein sources had positive effects on either BMD or BMC relative to CAS (P < 0.05), but SPI had greater effects in both intact and OVX female rats. SPI and E2 had positive effects on BMD and BMC in OVX rats (P < 0.05). However, trabecular BMD was lower in a SPI + E2 group compared to a CAS + E2 group. In OVX rats, SPI increased serum bone formation markers, and serum from SPI-fed rats stimulated osteoblastogenesis in ex vivo. SPI also suppressed the bone resorption marker RatLaps (P < 0.05). Both SPI and E2 increased alkaline phosphatase gene expression in bone, but only SPI decreased receptor activator of nuclear factor-kappaB ligand (RANKL) and estrogen receptor gene expression (P < 0.05). These data suggest beneficial bone effects of a soy diet in rapidly growing animals and the potential for early soy consumption to increase peak bone mass.

Soy phytoestrogens: impact on postmenopausal bone loss and mechanisms of action

Due to their ability to mimic the actions of mammalian estrogens, soy phytoestrogens have been proposed as potential therapeutic agents to aid in preventing postmenopausal bone loss. In vitro, phytoestrogens promote osteoblastogenesis and inhibit osteoclastogenesis. Although a relatively large number of intervention studies have been undertaken in animals and humans, the efficacy of phytoestrogens as bone-protective agents in vivo remains unclear. Differences in the bioactivities of individual phytoestrogens, differences in phytoestrogen metabolism and bioavailability within different study populations, and imprecise reporting of the dose of phytoestrogens administered in intervention studies may have contributed to the disparity in study findings.

Soy isoflavones in the management of postmenopausal osteoporosis

This is a review article designed to address the effects of soy isoflavones on bone metabolism in postmenopausal women and their place in the prevention and treatment of postmenopausal osteoporosis. Soy isoflavones are natural products that could be used as an alternative to menopausal hormone therapy because they are structurally and functionally related to 17beta-estradiol. In vitro and animal studies have shown that they act in multiple ways to exert their bone-supporting effects. They act on both osteoblasts and osteoclasts through genomic and nongenomic pathways. Epidemiological studies and clinical trials suggest that soy isoflavones have beneficial effects on bone mineral density, bone turnover markers, and bone mechanical strength in postmenopausal women. However, there are conflicting results related to differences in study design, estrogen status of the body, metabolism of isoflavones among individuals, and other dietary factors. The long-term safety of soy isoflavone supplements remains to be demonstrated.

Phyto-oestrogens and bone health

As oestrogen deficiency is the main cause in the pathogenesis of osteoporosis hormone-replacement therapy remains the mainstay for prevention. However, prophylaxis by hormone-replacement therapy is limited. Phyto-oestrogens, which are weakly-oestrogenic compounds present in plants, deserve particular mention because emerging data support the suggestion that they may prevent bone loss associated with the menopause. In the past few years extensive research using animal models has provided convincing data to indicate a significant improvement in bone mass or other end points following feeding with soyabean. Moreover, observational studies relate the lower incidence of osteoporosis among women in the Eastern world to a diet rich in phyto-oestrogens. However, it is not valid to extrapolate to the Western situation. The varied clinical trials that have been published suggest that isoflavones reduce bone loss in women in the early period post menopause, but a definitive result requires more investigations of the effect of phyto-oestrogens on bone health that have substantial sample size and are of long duration. In addition, the clinical efficacy of soya foods in preventing osteopenia depends on their intestinal metabolism. Thus, phyto-oestrogens are a source for putative innovative dietary health intervention for post-menopausal women. However, more data are necessary, particularly in relation to their effect on the risk of fracture.

A positive association of lumbar spine bone mineral density with dietary protein is suppressed by a negative association with protein sulfur

Dietary protein is theorized to hold both anabolic effects on bone and demineralizing effects mediated by the diet acid load of sulfate derived from methionine and cysteine. The relative importance of these effects is unknown but relevant to osteoporosis prevention. Postmenopausal women (n = 161, 67.9 +/- 6.0 y) were assessed for areal bone mineral density (aBMD) of lumbar spine (LS) and total hip (TH) using dual X-ray absorptiometry, and dietary intakes of protein, sulfur-containing amino acids, and minerals using a USDA multiple-pass 24-h recall. The acidifying influence of the diet was estimated using the ratio of protein:potassium intake, the potential renal acid load (PRAL), and intake of sulfate equivalents from protein. aBMD was regressed onto protein intake then protein was controlled for estimated dietary acid load. A step-down procedure assessed potential confounding influences (weight, age, physical activity, and calcium and vitamin D intakes). Protein alone did not predict LS aBMD (P = 0.81); however, after accounting for a negative effect of sulfate (beta = -0.28; P < 0.01), the direct effect of protein intake was positive (beta = 0.22; P = 0.04). At the TH, protein intake predicted aBMD (beta = 0.18; P = 0.03), but R2 did not improve with adjustment for sulfate (P = 0.83). PRAL and the protein:potassium ratio were not significant predictors of aBMD. Results suggest that protein intake is positively associated with aBMD, but benefit at the LS is offset by a negative impact of the protein sulfur acid load. If validated experimentally, these findings harmonize conflicting theories on the role of dietary protein in bone health.

Soy isoflavones do not affect bone resorption in postmenopausal women: a dose-response study using a novel approach with 41Ca

INTRODUCTION

The purpose of this 3-way crossover study was to identify the effective dose of soy protein isolate enriched with isoflavones for suppressing bone resorption in postmenopausal women using a novel, rapid assessment of antibone resorbing treatments.

METHODS

Thirteen postmenopausal women (>or=6 yr since menopause) were predosed with 41Ca iv. After a 200-d baseline period, subjects were given 43 g soy protein/d that contained 0, 97.5, or 135.5 mg total isoflavones in randomized order. The soy protein isolate powder was incorporated into baked products and beverages. Each 50-d intervention phase was preceded by a 50-d pretreatment phase for comparison. Serum isoflavone levels and biochemical markers were measured at the end of each phase. Twenty-four-hour urine samples were collected approximately every 10 d during each phase for 41Ca/Ca analysis by accelerator mass spectrometry.

RESULTS

Serum isoflavone levels reflected the amount of isoflavones consumed in a dose-dependent manner. None of the isoflavone levels had a significant effect on biochemical markers of bone turnover, urinary cross-linked N teleopeptides of type I collagen and serum osteocalcin, or bone turnover as assessed by urinary 41Ca/Ca ratios.

CONCLUSIONS

Soy protein with isoflavone doses of up to 135.5 mg/d did not suppress bone resorption in postmenopausal women. This is the first efficacy trial using the novel technique of urinary 41Ca excretion from prelabeled bone.

Measuring calcium absorption and utilization in humans

PURPOSE OF REVIEW

Calcium metabolism is comprised primarily of absorption, urinary excretion, endogenous secretion and bone turnover. This review evaluates recent findings relating to the role of genetic and environmental factors, especially diet, on perturbing parameters of calcium metabolism. Calcium dynamics are studied with the use of isotopic tracers. We also cover state-of-the-art methods for stable calcium isotope ratio analysis and offer insights on experimental design.

RECENT FINDINGS

Some progress has been made identifying genetic and hormonal regulators of calcium absorption. Much progress has been made in understanding the role of diet on influencing calcium retention, especially with regard to dietary protein and salt. Long-held views on dietary factors thought to contribute to bone loss through urinary calcium loss have been shown to have no impact on net calcium retention because of compensatory changes in other aspects of calcium metabolism.

SUMMARY

Much more work needs to be done on understanding genetic regulators of calcium metabolism. Despite recent advances in our knowledge of dietary influences on calcium metabolism, more studies are needed on the role of environmental factors, especially physical activity.

Bioavailability of isoflavones after ingestion of soy beverages in healthy adults

It is unknown whether the bioavailability of isoflavones is affected by the concomitant ingestion of glucosides or aglycones. This study was designed to investigate the effects of soymilk-based beverages containing different types of isoflavones on their absorption, excretion, and metabolism. Twelve healthy volunteers consumed 3 kinds of soymilk: untreated soymilk, beta-glucosidase-treated soymilk, and fermented soymilk. Blood samples were collected after 0, 1, 2, 3, 4, 5, 6, 7, 8, and 24 h. Urine samples were collected from 0 to 48 h. Concentrations of isoflavones and daidzein metabolites in serum and urine were measured by liquid chromatography-mass spectrometry. After the ingestion of soymilk, the total concentration of isoflavones in serum rose slowly and reached a maximum of 0.94 +/- 0.39 micromol/L at 6.0 +/- 1.2 h. However, beta-glucosidase-treated soymilk and fermented soymilk increased the serum isoflavone concentration significantly more quickly with maximum concentrations at 1.0 h of 1.75 +/- 0.33 micromol/L and 2.05 +/- 0.32 micromol/L, respectively. The urinary excretion of isoflavones after ingesting of these aglycone-enriched preparations was significantly greater than after consumption of untreated soymilk up to 8 h after injection, but not thereafter. The total and individual concentrations of isoflavones in serum and urine did not differ when subjects consumed the 2 aglycone-enriched soymilks. However, in equol producers (n = 5), the ingestion of ESM tended to increase urinary excretion of equol compared with the consumption of FSM (P = 0.08). These results demonstrated that the isoflavone aglycones of soymilk were absorbed faster and in greater amounts than their glucosides in healthy adults and that the metabolism of isoflavones might be affected by the type of soymilk consumed.

Meat and soy protein affect calcium homeostasis in healthy women

We showed that increasing dietary protein from omnivorous sources increases intestinal calcium absorption and urinary calcium, whereas a low-protein diet decreases calcium absorption and lowers urinary calcium. To assess the effect of soy protein on this relation, we substituted soy for meat in high- and low-protein diets fed to healthy women. The study consisted of a 2-wk adjustment period followed by a 4-d experimental period in which 20 healthy women consumed, in random order, the following 4 diets: high-protein soy-based, low-protein soy-based, high-protein meat-based, low-protein meat-based. Measures of calcium homeostasis were evaluated at baseline and after 4 d of the experimental period. At 24 h, net acid excretion was higher during the high- compared with the low-protein intervention (P < 0.05), and during the meat compared with the soy intervention (P < 0.05). The high-protein diets increased 24-h urinary calcium (P < 0.001), but urinary calcium did not differ due to the type of protein. Serum concentrations of parathyroid hormone and calcitriol, and urinary nephrogenous cAMP were higher during the low- compared with the high-protein intervention and during the soy compared with the meat protein (P < 0.05). In a subset of subjects, intestinal calcium absorption tended to be lower (P = 0.1) when they consumed the soy diets rather than the meat diets. These data indicate that when soy protein is substituted for meat protein, there is an acute decline in dietary calcium bioavailability.

Effect of soy protein/animal protein ratio on calcium metabolism of the rat

OBJECTIVE

This study examined the effects of a ratio of soy protein to animal protein on bone metabolism of rats.

METHODS

Experimental groups were a high soy protein group (200 g of soy protein and 0 g of casein per kilogram of diet; HSoy), a middle soy protein group (100 g of soy protein and 100 g of casein per kilogram of diet; MSoy), a low soy protein group (50 g of soy protein and 150 g of casein per kilogram of diet; LSoy), and a no soy protein group (0 g of soy protein and 200 g of casein per kilogram of diet; NSoy). Calcium excretion and retention, biochemical parametrically related calcium metabolism, and bone mineral density were measured. Statistical analysis was performed with SAS software.

RESULTS

Urinary excretion of calcium was significantly high in the LSoy and NSoy groups, and there was no difference in absorption of calcium across experimental groups. Calcium retention was significantly higher in the HSoy and MSoy groups than in the LSoy and NSoy groups. Experimental groups showed no differences in the activity of alkaline phosphatase. The casein group (NSoy) showed a remarkably lower degree of serum osteocalcin concentration. The concentration of deoxypyridinoline in urine showed an increasing tendency, i.e., HSoy and MSoy < LSoy < NSoy, indicating that at a higher degree of animal protein/soy proteins, its concentration increases. Wet weight of the femur appeared to be significantly greater in the MSoy and LSoy groups than in the NSoy group. Ash content of the femur and bone density were highest in the MSoy group, with the ratio of 1:1 between soy protein and animal protein.

CONCLUSIONS

This study indicated that deoxypyridinoline concentration was lower and the density of osteocalcin was higher in the MSoy group than in the NSoy group, and that calcium retention was high and bone mineral density was the highest in the MSoy group. The ratio of soy to animal protein that seemed to have the most positively significant effect on calcium metabolism was 1:1.

Calcium bioavailability of calcium carbonate fortified soymilk is equivalent to cow's milk in young women

Calcium (Ca)-fortified soymilk has gained popularity in the United States. Tricalcium phosphate (TCP)-fortified soymilk was shown to have a lower Ca bioavailability than cow's milk in men. However, the most popular soymilk in the U.S. is fortified with Ca carbonate (CC) and has not been evaluated. Ca bioavailability from CC-fortified soymilk (CCSM) and TCP-fortified soymilk (TCPSM) was compared with cow's milk in young healthy women using the dual stable isotope technique. In a 3-way crossover design, 20 volunteers (23 +/- 2 y old) consumed 250 mg Ca in cow's milk, CCSM, or TCPSM along with 10 mg 44Ca after an overnight fast. Cow's milk was extrinsically labeled, whereas each fortified soymilk was intrinsically labeled with each chemical salt of 44Ca at the manufacturing facility. Another stable isotope, 43Ca, was injected i.v. 1 h after the complete consumption of cow's milk or soymilk. Fractional Ca absorption was determined from the ratios of 43Ca:42Ca and 44Ca:42Ca by inductively coupled plasma (ICP)-MS in the 24-h urine samples. A mixed linear model (SAS proc mixed) was used to compare the fractional Ca absorption among groups. Fractional Ca absorption in CCSM (0.211 +/- 0.057) did not differ from that of cow's milk (0.217 +/- 0.040), but both were higher (P < 0.05) than that of TCPSM (0.181 +/- 0.039). Our result suggests that calcium absorption is equivalent for CCSM and cow's milk at similar calcium loads.

Phytoestrogens: end of a tale?

Phytoestrogens are plant-derived hormone-like diphenolic compounds of dietary origin that are present at high levels in plasma of subjects living in areas with low atherosclerosis and cancer incidence. The term phytoestrogen is commonly applied to the soy isoflavones genistein, daidzein and glycitein. As outlined in a previous review article in this journal by Adlercreutz and Mazur 1, these compounds are weakly estrogenic and appear to influence the cardiovascular system, the production, metabolism and biological activity of sex-hormones, as well as malignant cell proliferation, differentiation and angiogenesis. Recently skepticism has developed concerning the true potential of phytoestrogens to beneficially modify these processes. A critical analysis of the early findings from supplementing the diet with soy protein has failed to confirm phytoestrogens as the responsible agent for beneficial cardiovascular effects, be it by way of lipid reduction, vasodilation or lipoprotein oxidation. Furthermore, contrasting data have been reported on the potential of phytoestrogens to prevent hormone-dependent cancers (e.g. breast and prostate) and to successfully treat post-menopausal complaints, an indication for which they are widely used. These potentially negative findings have led health authorities in several countries to suggest maximum daily intake levels for phytoestrogens. There is now growing interest in the use of soy products containing low levels of phytoestrogens and in research on other phytoestrogen free legumes such as lupin.