The effect of a high-protein, high-sodium diet on calcium and bone metabolism in postmenopausal women and its interaction with vitamin D receptor genotype

Higher frequency of adding salt to foods increases the risk of low bone mineral density in individuals over 60 - A Mendelian randomization study

BACKGROUND

Adding salt to foods is associated with an increased osteoporosis risk, but the causality of this relationship remains unknown.

METHODS

in this study, we conducted a two-sample Mendelian randomization (MR) study to investigate the potential causal effect of adding salt to foods on bone mineral density (BMD). Utilizing data from the UK Biobank to estimate adding salt to foods based on self-reported consumption and genetic association data for BMD from the Genetic Factors for Osteoporosis (GEFOS) consortium, we examined various BMD sites: forearm (distal 1/3 radius), lumbar spine (L1-4), femoral neck, total body BMD (TB-BMD), and age-specific TB-BMD (0-15, 15-30, 30-45, 45-60, and over 60 years). The primary analysis used the inverse variance weighted method, supplemented by sensitivity analyses employing multiple MR methods, MR-PRESSO, and leave-one-out approach. Pleiotropy and heterogeneity were assessed using MR-Egger intercept, funnel plots, Cochran's Q, and Rucker's Q.

RESULTS

we found a suggestive association between higher frequency of adding salt to foods and decreased TB-BMD in Europeans over 60 (OR = 0.84, 95 % CI = 0.721-0.979, p = 0.026). This association remained robust across different methods and sensitivity analyses, showing no apparent heterogeneity or pleiotropy. However, no causal effect was detected on BMD in other age groups or skeletal sites.

CONCLUSION

this MR study suggests a higher frequency of adding salt to foods significantly increases low BMD risk in individuals over 60, underscoring the importance of reducing salt consumption in this demographic for osteoporosis prevention.

Vitamin D supplementation and body composition changes in collegiate basketball players: a 12-week randomized control trial

Background

Vitamin D promotes bone and muscle growth in non-athletes, suggesting supplementation may be ergogenic in athletes. Our primary aim was to determine if modest Vitamin D supplementation augments favorable body composition changes (increased bone and lean mass and decreased fat mass) and performance in collegiate basketball players following 12 weeks of standardized training.

Methods

Members of a men’s and women’s NCAA D1 Basketball team were recruited. Volunteers were randomized to receive either a weekly 4000 IU Vitamin D₃ supplement (D3) or placebo (P) over 12 weeks of standardized pre-season strength training. Pre- and post-measurements included 1) serum 25-hydroxy vitamin D (25(OH)D); 2) body composition variables (total body lean, fat, and bone mass) using dual-energy X-ray absorptiometry (DXA) scans and 3) vertical jump test to assess peak power output. Dietary intake was assessed using Food Frequency questionnaires. Main outcome measures included changes (∆: post-intervention minus pre-intervention) in 25(OH)D, body composition, and performance.

Results

Eighteen of the 23 players completed the trial (8 females/10 males). Eight received the placebo (20 ± 1 years; 3 females) while ten received Vitamin D₃ (20 ± 2 years; 5 females). Weekly Vitamin D₃ supplementation induced non-significant increases (∆) in 25(OH)D (2.6 ± 7.2 vs. −3.5 ± 5.3 ng/mL; p = 0.06), total body bone mineral content (BMC) (73.1 ± 62.5 vs. 84.1 ± 46.5 g; p = 0.68), and total body lean mass (2803.9 ± 1655.4 vs. 4474.5 ± 11,389.8 g; p = 0.03), plus a non-significant change in body fat (−0.5 ± 0.8 vs. −1.1 ± 1.2%; p = 0.19) (Vitamin D₃ vs. placebo supplementation groups, respectively). Pre 25(OH)D correlated with both Δ total fat mass (g) (r = 0.65; p = 0.003) and Δ total body fat% (r = 0.56; p = 0.02). No differences were noted in peak power output ∆ between the D3 vs. P group (−127.4 ± 335.4 vs. 50.9 ± 9 W; NS). Participants in the D3 group ingested significantly fewer total calories (−526.2 ± 583.9 vs. −10.0 ± 400 kcals; p = 0.02) than participants in the P group.

Conclusions

Modest (~517 IU/day) Vitamin D₃ supplementation did not enhance favorable changes in total body composition or performance, over 3 months of training, in collegiate basketball players. Weight training provides a robust training stimulus for bone and lean mass accrual, which likely predominates over isolated supplement use with adequate caloric intakes.

Whole-diet interventions and cardiovascular risk factors in postmenopausal women: A systematic review of controlled clinical trials

OBJECTIVES

Menopause is accompanied by many metabolic changes, increasing the risk of cardiometabolic diseases. The impact of diet, as a modifiable lifestyle factor, on cardiovascular health in general populations has been well established. The purpose of this systematic review is to summarize the evidence on the effects of whole diet on lipid profile, glycemic indices, and blood pressure in postmenopausal women.

METHODS

Embase, Medline, Cochrane Central Register of Controlled Trials, and Google Scholar were searched from inception to February 2021. We included controlled clinical trials in postmenopausal women that assessed the effect of a whole-diet intervention on lipid profile, glycemic indices, and/or blood pressure. The risk of bias in individual studies was assessed using RoB 2 and ROBINS-I tools.

SUMMARY OF EVIDENCE

Among 2,134 references, 21 trials met all eligibility criteria. Overall, results were heterogenuous and inconsistent. Compared to control diets, some studies showed that participants experienced improvements in total cholesterol (TC), low-density lipoprotein cholesterol (LDL), systolic blood pressure (SBP), fasting blood sugar (FBS), and apolipoprotein A (Apo-A) after following fat-modified diets, but some adverse effects on triglycerides (TG), very low-density lipoprotein cholesterol (VLDL), lipoprotein(a) (Lp(a)), and high-density lipoprotein cholesterol (HDL) concentrations were also observed. A limited number of trials found some effects of the Paleolithic, weight-loss, plant-based, or energy-restricted diets, or of following American Heart Association recommendations on TG, TC, HDL, insulin, FBS, or insulin resistance.

CONCLUSION

Current evidence suggests that diet may affect levels of some lipid profile markers, glycemic indices, and blood pressure among postmenopausal women. However, due to the large heterogeneity in intervention diets, comparison groups, intervention durations, and population characteristics, findings are inconclusive. Further well-designed clinical trials are needed on dietary interventions to reduce cardiovascular risk in postmenopausal women.

Dietary Protein Intake above the Current RDA and Bone Health: A Systematic Review and Meta-Analysis

Dietary intake of protein is fundamental for optimal acquisition and maintenance of bone across all life stages; however, it has been hypothesized that intakes above the current recommended dietary allowance (RDA) might be beneficial for bone health. We utilized the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines when preparing and reporting this systematic review and meta-analysis. A literature search strategy through April 11, 2017, was developed for the following 3 databases: PubMed, Ovid Medline, and Agricola. Included studies were those randomized controlled trials and prospective cohort studies among healthy adults ages 18 and older that examined the relationships between varying doses of protein intake at or above the current U.S. RDA (0.8 g/kg/d or 10%-15% of total caloric intake) from any source on fracture, bone mineral density (BMD)/bone mineral content (BMC), and/or markers of bone turnover. Twenty-nine articles were included for data extraction (16 randomized controlled trials [RCTs] and 13 prospective cohort studies). Meta-analysis of the prospective cohort studies showed high vs low protein intakes resulted in a statistically significant 16% decrease in hip fractures (standardized mean difference [SMD] = 0.84, 95% confidence interval [CI], 0.73, 0.95; I² = 36.8%). Data from studies included in these analyses collectively lean toward the hypothesis that protein intake above the current RDA is beneficial to BMD at several sites. This systematic review supports that protein intakes above the current RDA may have some beneficial role in preventing hip fractures and BMD loss. There were no differences between animal or plant proteins, although data in this area were scarce. Larger, long-term, and more well-controlled clinical trials measuring fracture outcomes and BMD are needed to adequately assess whether protein intake above the current RDA is beneficial as a preventative measure and/or intervention strategy for osteoporosis. Key teaching points: • • Bone health is a multifactorial musculoskeletal issue, and optimal protein intakes are key in developing and maintaining bone throughout the life span. • • Dietary protein at levels above the current RDA may be beneficial in preventing hip fractures and BMD loss. • • Plant vs animal proteins do not seem to differ in their ability to prevent bone loss; however, data in this area are scarce. • • Larger, long-term RCTs using women not using hormone replacement therapy (HRT) are needed to adequately assess the magnitude of impact that protein intakes above the RDA have on preventing bone loss.

Incidence of osteoporosis in patients with urolithiasis

Introduction.

Clinical researches have shown an increased bone disintegration and lower bone mass in patients with calcium urolithiasis.

Goal.

The goal of our research was to establish the incidence of osteoporosis in adult patients with calcium urolithiasis, on the basis of measuring mineral bone density, using DEXA method, with a special reflection on age subgroups.

Material and methods.

Clinical research was prospective and it was implemented at the University Clinical Center of Banja Luka, at the Clinic for Endocrinology, Diabetes and Metabolic Diseases and at the Urology Clinic. Material in this research consisted of patients divided in two groups, a working and a control group. One hundred and twenty (120) patients were included in both these groups, divided in three age subgroups: 20-40, 40-60 and over 60. The working group consisted of the patients with calcium urolithiasis and the control group consisted of patients without calcium urolithiasis. Establishing of mineral bone density at L2-L4 of lumbal spine vertebrae and hip was done for the patients in both these groups, using DEXA method.

Results.

Analysis of mineral bone density using DEXA method in patients in age groups of working and control groups, as well as in the total sample of working and control groups, have shown that the patients of the working group, over 60, had a decreased mineral bone density (30% of osteopenia and 15% osteoporosis) significantly more expressed when compared to the other two age groups (12.5% in the subgroup 20-40 and 17.5% in the subgroup 40-60), which presents a statistically significant difference (p<0.05). In the control group, when taking into account age groups, osteopenia and osteoporosis were marked in 37.5% and 2.5% in the group of patients over 60, whereas in the youngest population, 5% of osteopenia was found, which presents a statistically significant difference (p<0.05). When observing the total sample of working and control group, there was a statistically significant difference in the working and control group (p<0.01); incidence of osteoporosis in the working group amounted to 7.5% and in the control group it was 0.8%.

Conclusion.

Urolithiasis and osteoporosis are two multifactorial diseases which are evidently reciprocal. This is why we suggest that educating the population about the risk factors for occurrence of these diseases as well as preventive measures that may contribute to their decrease should begin as early as possible.

Health effects of protein intake in healthy adults: a systematic literature review

The purpose of this systematic review is to assess the evidence behind the dietary requirement of protein and to assess the health effects of varying protein intake in healthy adults. The literature search covered the years 2000-2011. Prospective cohort, case-control, and intervention studies were included. Out of a total of 5,718 abstracts, 412 full papers were identified as potentially relevant, and after careful scrutiny, 64 papers were quality graded as A (highest), B, or C. The grade of evidence was classified as convincing, probable, suggestive or inconclusive. The evidence is assessed as: probable for an estimated average requirement of 0.66 g good-quality protein/kg body weight (BW)/day based on nitrogen balance studies, suggestive for a relationship between increased all-cause mortality risk and long-term low-carbohydrate-high-protein (LCHP) diets; but inconclusive for a relationship between all-cause mortality risk and protein intake per se; suggestive for an inverse relationship between cardiovascular mortality and vegetable protein intake; inconclusive for relationships between cancer mortality and cancer diseases, respectively, and protein intake; inconclusive for a relationship between cardiovascular diseases and total protein intake; suggestive for an inverse relationship between blood pressure (BP) and vegetable protein; probable to convincing for an inverse relationship between soya protein intake and LDL cholesterol; inconclusive for a relationship between protein intake and bone health, energy intake, BW control, body composition, renal function, and risk of kidney stones, respectively; suggestive for a relationship between increased risk of type 2 diabetes (T2D) and long-term LCHP-high-fat diets; inconclusive for impact of physical training on protein requirement; and suggestive for effect of physical training on whole-body protein retention. In conclusion, the evidence is assessed as probable regarding the estimated requirement based on nitrogen balance studies, and suggestive to inconclusive for protein intake and mortality and morbidity. Vegetable protein intake was associated with decreased risk in many studies. Potentially adverse effects of a protein intake exceeding 20-23 E% remain to be investigated.

Diet and bone mineral density study in postmenopausal women from the TwinsUK registry shows a negative association with a traditional English dietary pattern and a positive association with wine

BACKGROUND

The effect of diet on bone mineral density (BMD) remains controversial, mainly because of difficulties in isolating dietary factors from the confounding influences of age, lifestyle, and genetic factors.

OBJECTIVE

The aim of this study was to use a novel method to examine the relation between BMD and diet.

DESIGN

A co-twin control study design with linear regression modeling was used to test for associations between BMD and habitual intakes of calcium, vitamin D, protein, and alcohol plus 5 previously identified dietary patterns in postmenopausal women from the TwinsUK registry. This approach exploited the unique matching of twins to provide an estimate of an association that was not confounded by age, genetic background, or shared lifestyle.

RESULTS

In >2000 postmenopausal women (BMD data on 1019, 1218, and 1232 twin pairs at the hip neck, hip, and spine, respectively), we observed a positive association between alcohol intake (from wine but not from beer or spirits) and spine BMD (P = 0.01) and a negative association with a traditional 20th-century English diet at the hip neck (P = 0.01). Both associations remained borderline significant after adjustment for mean twin-pair intakes (P = 0.04 and P = 0.055, respectively). Other dietary patterns and intakes of calcium, vitamin D, and protein were unrelated to BMD.

CONCLUSION

Our results showed that diet has an independent but subtle effect on BMD; wine intake was positively associated with spine BMD, whereas a traditional (20th-century) English diet had a negative association with hip BMD.

A calcitonin receptor (CALCR) single nucleotide polymorphism is associated with growth performance and bone integrity in response to dietary phosphorus deficiency

Although concerns over the environmental impact of excess P in the excreta from pig production and governmental regulations have driven research toward reducing dietary supplementation of P to swine diets for over a decade, recent dramatic increases in feed costs have further motivated researchers to identify means to further reduce dietary P supplementation. We have demonstrated that genetic background impacts P utilization in young pigs and have identified genetic polymorphisms in several target genes related to mineral utilization. In this study, we examined the impact of a SNP in the calcitonin receptor gene (CALCR) on P utilization in growing pigs. In Exp. 1, 36 gilts representing the 3 genotypes identified by this CALCR SNP (11, 12, and 22) were fed a P-adequate (PA) or a marginally P-deficient (approximately 20% less available P; PD) diet for 14 wk. As expected, P deficiency reduced plasma P concentration, bone strength, and mineral content (P < 0.05). However, the dietary P deficiency was mild enough to not affect the growth performance of these pigs. A genotype x dietary P interaction (P < 0.05) was observed in measures of bone integrity and mineral content, with the greatest reduction in bone strength and mineral content due to dietary P deficiency being associated with the allele 1. In Exp. 2, 168 pigs from a control line and low residual feed intake (RFI) line were genotyped for the CALCR SNP and fed a PA diet. As expected, pigs from the low RFI line consumed less feed but also gained less BW when compared with the control line (P < 0.05). Although ADFI did not differ between genotypes, pigs having the 11 genotype gained less BW (P < 0.05) than pigs having the 12 or 22 genotypes. Pigs of the 11 and 12 genotypes had bones that tolerated greater load when compared with animals having the 22 genotype (P < 0.05). A similar trend was observed in bone modulus and ash % (P < 0.10). These data are supportive of the association of this CALCR SNP with bone integrity and its response to dietary P restriction. Although the allele 1 is associated with greater bone integrity and mineral content during adequate P nutrition, it is also associated with the greatest loss in bone integrity and mineral content in response to dietary P restriction. Understanding the underlying genetic mechanisms that regulate P utilization may lead to novel strategies to produce more environmentally friendly pigs.

Vitamin D repletion does not alter urinary calcium excretion in healthy postmenopausal women

OBJECTIVE

To evaluate, in a posthoc analysis of a previous study, whether vitamin D repletion in postmenopausal women with insufficient vitamin D increases urinary calcium excretion, as vitamin D therapy might contribute to hypercalciuria and calcium stones in susceptible individuals, and the effect of vitamin D on the risk of urolithiasis warrants attention.

SUBJECTS AND METHODS

We recruited 18 women at > or =5 years after menopause who had vitamin D insufficiency (serum 25(OH)-vitamin D, 16-24 mg/dL). We excluded women with a history of urolithiasis and kidney disease. Women had one calcium absorption study when vitamin D-insufficient, received vitamin D therapy, and completed a second calcium absorption study when vitamin D-replete. We fed subjects meals that mirrored the nutrient composition from self-reported 7-day diet diaries. To measure calcium absorption, we collected urine for 24 h during both visits.

RESULTS

We achieved vitamin D repletion in all women (25(OH)-vitamin D before and after treatment, 22 and 63 mg/dL, respectively; P < 0.001). The mean calcium intake was 832 mg/day. Residual urine specimens were available for 16 women, allowing a measurement of 24-h urinary calcium. Calcium excretion did not change after vitamin D therapy (212 before vs 195 mg/day after; P = 0.60). Of four women with hypercalciuria (>247 mg/day), calcium excretion decreased in three (377-312 mg/day, not significant).

CONCLUSION

Vitamin D supplementation did not increase the urinary calcium excretion in healthy postmenopausal women. Many stone formers are at risk of premature bone loss, vitamin D insufficiency, or both. Based on the present results we suggest a study of patients with hypercalciuria and nephrolithiasis to determine the risks of vitamin D therapy.

Protein and energy supplementation in elderly people at risk from malnutrition

BACKGROUND

Evidence for the effectiveness of nutritional supplements containing protein and energy, often prescribed for older people, is limited. Malnutrition is more common in this age group and deterioration of nutritional status can occur during illness. It is important to establish whether supplementing the diet is an effective way of improving outcomes for older people at risk from malnutrition.

OBJECTIVES

This review examined trials for improvement in nutritional status and clinical outcomes when extra protein and energy were provided, usually as commercial 'sip-feeds'.

SEARCH STRATEGY

We searched The Cochrane Library, MEDLINE, EMBASE, Healthstar, CINAHL, BIOSIS, CAB abstracts. We also hand searched nutrition journals and reference lists and contacted 'sip-feed' manufacturers.

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials of oral protein and energy supplementation in older people, with the exception of groups recovering from cancer treatment or in critical care.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trials prior to inclusion and independently extracted data and assessed trial quality. Authors of trials were contacted for further information as necessary.

MAIN RESULTS

Sixty-two trials with 10,187 randomised participants have been included in the review. Maximum duration of intervention was 18 months. Most included trials had poor study quality. The pooled weighted mean difference (WMD) for percentage weight change showed a benefit of supplementation of 2.2% (95% confidence interval (CI) 1.8 to 2.5) from 42 trials. There was no significant reduction in mortality in the supplemented compared with control groups (relative risk (RR) 0.92, CI 0.81 to 1.04) from 42 trials. Mortality results were statistically significant when limited to trials in which participants (N = 2461) were defined as undernourished (RR 0.79, 95% CI 0.64 to 0.97).The risk of complications was reduced in 24 trials (RR 0.86, 95% CI 0.75 to 0.99). Few trials were able to suggest any functional benefit from supplementation. The WMD for length of stay from 12 trials also showed no statistically significant effect (-0.8 days, 95% CI -2.8 to 1.3). Adverse effects included nausea or diarrhoea.

AUTHORS' CONCLUSIONS

Supplementation produces a small but consistent weight gain in older people. Mortality may be reduced in older people who are undernourished. There may also be a beneficial effect on complications which needs to be confirmed. However, this updated review found no evidence of improvement in functional benefit or reduction in length of hospital stay with supplements. Additional data from large-scale multi-centre trials are still required.

Sodium and bone health: impact of moderately high and low salt intakes on calcium metabolism in postmenopausal women

High salt intake is a well-recognized risk factor for osteoporosis because it induces calciuria, but the effects of salt on calcium metabolism and the potential impact on bone health in postmenopausal women have not been fully characterized. This study investigated adaptive mechanisms in response to changes in salt and calcium intake in postmenopausal women. Eleven women completed a randomized cross-over trial consisting of four successive 5-wk periods of controlled dietary intervention, each separated by a minimum 4-wk washout. Moderately low and high calcium (518 versus 1284 mg) and salt (3.9 versus 11.2 g) diets, reflecting lower and upper intakes in postmenopausal women consuming a Western-style diet, were provided. Stable isotope labeling techniques were used to measure calcium absorption and excretion, compartmental modeling was undertaken to estimate bone calcium balance, and biomarkers of bone formation and resorption were measured in blood and urine. Moderately high salt intake (11.2 g/d) elicited a significant increase in urinary calcium excretion (p = 0.0008) and significantly affected bone calcium balance with the high calcium diet (p = 0.024). Efficiency of calcium absorption was higher after a period of moderately low calcium intake (p < 0.05) but was unaffected by salt intake. Salt was responsible for a significant change in bone calcium balance, from positive to negative, when consumed as part of a high calcium diet, but with a low calcium intake, the bone calcium balance was negative on both high and low salt diets.

Low-grade metabolic acidosis may be the cause of sodium chloride-induced exaggerated bone resorption

Stepwise increase in NaCl intake in healthy male test subjects led to a low-grade metabolic acidosis. This was most likely the cause for increased bone resorption during high sodium chloride intake, as determined by analyzing bone resorption markers.

INTRODUCTION

We examined the effect of increased dietary sodium chloride (NaCl) on bone metabolism and acid-base balance.

MATERIALS AND METHODS

Subjects were nine healthy men (mean age, 25.7 +/- 3.1 yr; mean body weight [BW], 71.5 +/- 4.0 kg). During the first period (6 days), subjects received 0.7 mEq NaCl/kg BW per day (phase 1), during the second period (6 days) 2.8 mEq NaCl/kg BW per day (phase 2), during the third period (10 days) 7.7 mEq NaCl/kg BW per day (phase 3), and during the fourth period (6 days) 0.7 mEq NaCl/kg BW per day (phase 4).

RESULTS

Twenty-four-hour urinary excretion of calcium and sodium rose significantly with increasing NaCl intake (p < 0.001 for both). Urinary excretion of bone resorption markers C- and N-terminal telopeptide of type I collagen (CTX, NTX) increased from phase 2 to phase 3 (CTX, p = 0.013; NTX, p < 0.001) and decreased from phase 3 to phase 4 (CTX, p < 0.001; NTX, p = 0.002). Bone formation markers N-terminal propeptide of type I procollagen, bone-specific alkaline phosphatase, and osteocalcin remained unchanged from low to high NaCl intake. Blood pH levels decreased (p = 0.04) between phases 1 and 3. Blood bicarbonate (HCO(3)(-)) and base excess (BE) decreased from phases 1 to 3 (p < 0.001 for both) and from phases 2-3 (HCO(3)(-), p = 0.003; BE, p = 0.015). Nearly all bone resorption markers and acid-base variables reached their baseline levels in phase 4.

CONCLUSIONS

We conclude that low-grade metabolic acidosis may be the cause of NaCl-induced exaggerated bone resorption.

An increase in dietary n-3 fatty acids decreases a marker of bone resorption in humans

Human, animal, and in vitro research indicates a beneficial effect of appropriate amounts of omega-3 (n-3) polyunsaturated fatty acids (PUFA) on bone health. This is the first controlled feeding study in humans to evaluate the effect of dietary plant-derived n-3 PUFA on bone turnover, assessed by serum concentrations of N-telopeptides (NTx) and bone-specific alkaline phosphatase (BSAP). Subjects (n = 23) consumed each diet for 6 weeks in a randomized, 3-period crossover design: 1) Average American Diet (AAD; [34% total fat, 13% saturated fatty acids (SFA), 13% monounsaturated fatty acids (MUFA), 9% PUFA (7.7% LA, 0.8% ALA)]), 2) Linoleic Acid Diet (LA; [37% total fat, 9% SFA, 12% MUFA, 16% PUFA (12.6% LA, 3.6% ALA)]), and 3) alpha-Linolenic Acid Diet (ALA; [38% total fat, 8% SFA, 12% MUFA, 17% PUFA (10.5% LA, 6.5% ALA)]). Walnuts and flaxseed oil were the predominant sources of ALA. NTx levels were significantly lower following the ALA diet (13.20 +/- 1.21 nM BCE), relative to the AAD (15.59 +/- 1.21 nM BCE) (p < 0.05). Mean NTx level following the LA diet was 13.80 +/- 1.21 nM BCE. There was no change in levels of BSAP across the three diets. Concentrations of NTx were positively correlated with the pro-inflammatory cytokine TNFalpha for all three diets. The results indicate that plant sources of dietary n-3 PUFA may have a protective effect on bone metabolism via a decrease in bone resorption in the presence of consistent levels of bone formation.

Effect of dietary supplementation with conjugated linoleic acid on markers of calcium and bone metabolism in healthy adult men

INTRODUCTION

Conjugated linoleic acid (CLA) has been shown to positively influence calcium and bone metabolism in experimental animals and cells in culture, but there are limited human data available.

OBJECTIVE

To investigate the effect of CLA supplementation on biomarkers of calcium and bone metabolism in healthy adult males.

DESIGN

The study consisted of a double-blind, placebo-controlled trial in which 60 healthy adult males (aged 39-64 y) were randomly assigned to receive daily either 3.0 g CLA isomer blend (50:50% cis-9,trans-11:trans-10,cis-12 isomers) or a palm/bean oil blend (placebo) for 8 weeks. Urine and blood samples were collected at weeks 0 and 8 and were analysed for biomarkers of calcium and bone metabolism.

RESULTS

Supplementation with CLA or placebo for 8 weeks had no significant effects on markers of bone formation (serum osteocalcin and bone-specific alkaline phosphatase) or bone resorption (serum C-telopeptide-related fraction of type 1 collagen degradation products, urinary N-telopeptide-related fraction of type 1 collagen degradation products, urinary pyridinoline and deoxypyridinoline), or on serum or urinary calcium levels. Baseline levels of these biochemical parameters were similar in both groups of subjects. While the placebo had no effect, CLA supplementation resulted in a three-fold increase (P<0.00001) in cis-9,trans-11 CLA isomer in total plasma lipids.

CONCLUSION

Under the conditions tested in this double-blind, placebo-controlled trial in adult men, a CLA supplement of mixed isomers did not affect markers of calcium or bone metabolism. Further investigation of the effects of CLA on calcium and bone metabolism in other gender- and age-groups is warranted.

Protein and energy supplementation in elderly people at risk from malnutrition

BACKGROUND

Evidence for the effectiveness of nutritional supplements containing protein and energy, which are often prescribed for older people, is limited. Furthermore malnutrition is more common in this age group and deterioration of nutritional status can occur during illness. It is important to establish whether supplementing the diet is an effective way of improving outcomes for older people at risk from malnutrition.

OBJECTIVES

This review examined the evidence from trials for improvement in nutritional status and clinical outcomes when extra protein and energy were provided, usually in the form of commercial 'sip-feeds'.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, Healthstar, CINAHL, BIOSIS, CAB abstracts. We also hand searched nutrition journals and reference lists and contacted 'sip-feed' manufacturers. Date of most recent search: March 2004.

SELECTION CRITERIA

Randomised controlled trials and quasi-randomised controlled trials of oral protein and energy supplementation in older people with the exception of groups recovering from cancer treatment or in critical care.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trials prior to inclusion and independently extracted data and assessed trial quality. Authors of trials were contacted for further information as necessary.

MAIN RESULTS

Forty-nine trials with 4790 randomised participants have been included in the review. Most included trials had poor study quality. The pooled weighted mean difference [WMD] for percentage weight change showed a benefit of supplementation of 2.3% (95% confidence interval (CI) 1.9 to 2.7) from 34 trials. There was a reduced mortality in the supplemented compared with control groups (relative risk (RR) 0.74, CI 0.59 to 0.92) from 32 trials. The risk of complications from 14 trials showed no significant difference (RR 0.95, 95% CI 0.81 to 1.11). Few trials were able to suggest any functional benefit from supplementation. The pooled weighted mean difference (WMD) for length of stay from 10 trials also showed no statistically significant effect (WMD -1.98 days, 95% CI -5.20 to 1.24).

AUTHORS' CONCLUSIONS

Supplementation produces a small but consistent weight gain in older people. There may also be a beneficial effect on mortality. However, there was no evidence of improvement in clinical outcome, functional benefit or reduction in length of hospital stay with supplements. Additional data from large-scale multi-centre trials are still required.

Effects of thickened beverages fortified with inulin on beverage acceptance, gastrointestinal function, and bone resorption in institutionalized adults

OBJECTIVES

We wanted to develop thickened beverages that contain soluble fiber (inulin) with acceptable consistency, taste, and texture and to determine the effects of these beverages on bone resorption markers (to determine calcium retention), bowel frequency, and indicators of gastrointestinal function in institutionalized adults bound to wheelchairs.

METHODS

A double-blind, 3-wk, cross-over study testing 13-g/d inulin-fortified versus isocaloric standard modified starch-thickened beverages was conducted in institutionalized adults who were bound to wheelchairs and had dysphagia or did not have dysphagia. Beverage acceptability, as assessed by discriminative and descriptive sensory testing, bowel frequency, fecal output, and laxative use, were determined by direct testing or by nursing charts. Bone resorption was measured by using the urinary excretion of fasting calcium and of cross-linked N-telopeptides of collagen.

RESULTS

Sensory panelists were unable to detect a difference between beverages thickened with modified starch and those fortified with inulin. Few differences were found between the control and inulin-fortified beverages for sensory descriptors. No significant difference was found in frequency of bowel movements between treatments; however, weighted bowel movement frequency increased by 13% with inulin (P < 0.01), whereas enema and laxative administration decreased by 13% (P < 0.05). Bone resorption, as an indicator of calcium retention, remained unchanged.

CONCLUSIONS

Inulin was incorporated into thickened beverages, with no decrease in acceptability; when consumed, perceived stool output increased in residents of long-term care facilities.

Effects of a low sodium diet on bone metabolism

Osteoporosis is a serious public health problem, and dietary interventions may potentially be helpful in preventing this disorder. The purpose of this study was to determine the effects of a low sodium diet on bone metabolism in postmenopausal women. This was a longitudinal study to determine the effects of a low sodium (2-g/day) diet on bone. Forty postmenopausal African-American and Caucasian women were enrolled in a 2-g/day sodium diet for 6 months. Sodium and calcium excretion, bone turnover, and calcitropic hormones (intact parathyroid hormone (PTH) and 1,25 dihydroxyvitamin D) were measured before and 6 months after the intervention. In women who had baseline sodium excretions equal to or greater than the average sodium intake in the United States (> or =3.4 g/day), the low sodium diet resulted in significant decreases in sodium excretion (P = 0.01), in calcium excretion (P = 0.01), and in a biomarker of bone turnover, aminoterminal propeptide of type I collagen (P = 0.04). However, there were no significant changes in calcitropic hormones, including intact PTH (P = 0.97) or 1,25 dihydroxyvitamin D (P = 0.49) with the low sodium diet. These findings suggest that in postmenopausal women with sodium intakes > or =3.4 g/day, a low sodium diet may have benefits for skeletal health.

Effect of a high-protein, high-salt diet on calcium and bone metabolism in postmenopausal women stratified by hormone replacement therapy use

The objective of this study was to investigate the influence of a high-sodium, high-protein diet on bone metabolism in postmenopausal women (aged 49-60 y) stratified by hormone replacement therapy (HRT) use. In a crossover trial, 18 women (n = 8 HRT users (+HRT) and n = 10 nonusers (-HRT)) were randomly assigned to a diet high in protein (90 g/day) and sodium (180 mmol/day) (calciuric diet) or a diet moderate in protein (70 g/day) and low in sodium (65 mmol/day) for 4 weeks followed by crossover to alternative dietary regimen for a further 4 weeks. The calciuric diet significantly (P < 0.05) increased urinary sodium, calcium and nitrogen in both groups. While the calciuric diet increased urinary N-telopeptide crosslinks of collagen (by approximately 25%, P = 0.003) in the -HRT group, it had no effect in the +HRT group. It appears that postmenopausal HRT use attenuates the increase in a marker of bone resorption associated with a calciuric diet.