Effect of dietary protein on bone loss in elderly men and women: the Framingham Osteoporosis Study

Dietary Approaches for Bone Health: Lessons from the Framingham Osteoporosis Study

Osteoporosis is characterized by systemic impairment of bone mass, strength, and microarchitecture, resulting in increased risk for fragility fracture, disability, loss of independence, and even death. Adequate nutrition is important in achieving and maintaining optimal bone mass, as well as preventing this debilitating disease. It is widely accepted that adequate calcium and vitamin D intake are necessary for good bone health; however, nutritional benefits to bone go beyond these two nutrients. This review article will provide updated information on all nutrients and foods now understood to alter bone health. Specifically, this paper will focus on related research from the Framingham Osteoporosis Study, an ancillary study of the Framingham Heart Study, with data on more than 5000 adult men and women.

The effects of dietary protein and amino acids on skeletal metabolism

Dietary protein is required for optimal skeletal growth and maturation. Although Recommended Dietary Allowances (RDAs) exist for global dietary protein intake, the level and sources of dietary protein that are optimal for skeletal health over the life continuum have not been established. This is partly due to the difficulty in quantifying the effects of variable levels of a nutrient's intake over a lifetime as well as the complex nature of the relationships between dietary protein and calcium economy. Areas of current uncertainty include the precise source and amount of dietary protein required for optimal skeletal accretion and maintenance of skeletal mass, as well as the site-specific effects of dietary protein. The cellular and molecular mechanisms that underpin the actions of dietary protein on mineral metabolism and skeletal homeostasis remain unclear. This review attempts to summarize recent data bearing on these questions.

The Effect of a Whey Protein Supplement on Bone Mass in Older Caucasian Adults

CONTEXT

It has been assumed that the increase in urine calcium (Ca) that accompanies an increase in dietary protein was due to increased bone resorption. However, studies using stable Ca isotopes have found that dietary protein increases Ca absorption without increasing bone resorption.

OBJECTIVE

The objective of the study was to investigate the impact of a moderately high protein diet on bone mineral density (BMD).

DESIGN

This was a randomized, double-blind, placebo-controlled trial of protein supplementation daily for 18 months.

SETTING

The study was conducted at two institutional research centers.

PARTICIPANTS

Two hundred eight older women and men with a body mass index between 19 and 32 kg/m(2) and a self-reported protein intake between 0.6 and 1.0 g/kg participated in the study.

INTERVENTION

Subjects were asked to incorporate either a 45-g whey protein or isocaloric maltodextrin supplement into their usual diet for 18 months.

MAIN OUTCOME MEASURE

BMD by dual-energy x-ray absorptiometry, body composition, and markers of skeletal and mineral metabolism were measured at baseline and at 9 and 18 months.

RESULTS

There were no significant differences between groups for changes in L-spine BMD (primary outcome) or the other skeletal sites of interest. Truncal lean mass was significantly higher in the protein group at 18 months (P = .048). C-terminal telopeptide (P = .0414), IGF-1 (P = .0054), and urinary urea (P < .001) were also higher in the protein group at the end of the study period. There was no difference in estimated glomerular filtration rate at 18 months.

CONCLUSION

Our data suggest that protein supplementation above the recommended dietary allowance (0.8 g/kg) may preserve fat-free mass without adversely affecting skeletal health or renal function in healthy older adults.

Defining meal requirements for protein to optimize metabolic roles of amino acids

Dietary protein provides essential amino acids (EAAs) for the synthesis of new proteins plus an array of other metabolic functions; many of these functions are sensitive to postprandial plasma and intracellular amino acid concentrations. Recent research has focused on amino acids as metabolic signals that influence the rate of protein synthesis, inflammation responses, mitochondrial activity, and satiety, exerting their influence through signaling systems including mammalian/mechanistic target of rapamycin complex 1 (mTORC1), general control nonrepressed 2 (GCN2), glucagon-like peptide 1 (GLP-1), peptide YY (PYY), serotonin, and insulin. These signals represent meal-based responses to dietary protein. The best characterized of these signals is the leucine-induced activation of mTORC1, which leads to the stimulation of skeletal muscle protein synthesis after ingestion of a meal that contains protein. The response of this metabolic pathway to dietary protein (i.e., meal threshold) declines with advancing age or reduced physical activity. Current dietary recommendations for protein are focused on total daily intake of 0.8 g/kg body weight, but new research suggests daily needs for older adults of ≥1.0 g/kg and identifies anabolic and metabolic benefits to consuming at least 20-30 g protein at a given meal. Resistance exercise appears to increase the efficiency of EAA use for muscle anabolism and to lower the meal threshold for stimulation of protein synthesis. Applying this information to a typical 3-meal-a-day dietary plan results in protein intakes that are well within the guidelines of the Dietary Reference Intakes for acceptable macronutrient intakes. The meal threshold concept for dietary protein emphasizes a need for redistribution of dietary protein for optimum metabolic health.

Bone Mineral Density and Protein-Derived Food Clusters from the Framingham Offspring Study

BACKGROUND

Dietary protein is beneficial to bone health; however, dietary patterns of protein intake and their relationship with bone mineral density (BMD) have not been evaluated.

OBJECTIVE

To examine the relationship of dietary protein food clusters with BMD at the femoral neck, trochanter, total femur, and lumbar spine among middle-aged and older men and women.

DESIGN

Cross-sectional study.

PARTICIPANTS AND SETTING

Two thousand seven hundred fifty-eight community-dwelling individuals from the Framingham Offspring Study.

METHODS

BMD was measured by Lunar DPX-L (Lunar Radiation Corporation) in 1996-2001. Dietary intakes were estimated using the Willett food frequency questionnaire in either 1995-1998 or 1998-2001, and the exam closest to a participant's BMD measurement was used. Cluster analysis (FASTCLUS procedure, k-means method) was used to classify participants into groups, determined by major sources of protein. Generalized linear regression was used to compare adjusted least-squares mean BMD across protein food clusters for all pairwise comparisons.

RESULTS

From 2,758 participants (44% men; mean age 61±9 years, range=29 to 86 years), five protein food clusters were identified (chicken, fish, processed foods, red meat, and low-fat milk). Three of these food clusters showed associations with BMD. The red meat protein food cluster presented with significantly lower femoral neck BMD compared with the low-fat milk cluster (red meat 0.898±0.005 g/cm(2) vs low-fat milk 0.919±0.007 g/cm(2); P=0.04). Further, the processed foods protein cluster presented with significantly lower femoral neck BMD compared with the low-fat milk cluster (processed foods 0.897±0.004 g/cm(2) vs low-fat milk 0.919±0.007 g/cm(2); P=0.02). A similar, yet nonsignificant, trend was observed for other BMD sites examined.

CONCLUSIONS

Diets with the greatest proportion of protein intake from red meat and processed foods may not be as beneficial to the skeleton compared with dietary patterns where the highest proportion of protein is derived from low-fat milk.

Dietary Protein Requirement of Men >65 Years Old Determined by the Indicator Amino Acid Oxidation Technique Is Higher than the Current Estimated Average Requirement

BACKGROUND

The current estimated average requirement (EAR) and RDA for protein of 0.66 and 0.8 g ⋅ kg-1 ⋅ d-1, respectively, for adults, including older men, are based on nitrogen balance data analyzed by monolinear regression. Recent studies in young men and older women that used the indicator amino acid oxidation (IAAO) technique suggest that those values may be too low. This observation is supported by 2-phase linear crossover analysis of the nitrogen balance data.

OBJECTIVE

The main objective of this study was to determine the protein requirement for older men by using the IAAO technique.

METHODS

Six men aged >65 y were studied; each individual was tested 7 times with protein intakes ranging from 0.2 to 2.0 g ⋅ kg-1 ⋅ d-1 in random order for a total of 42 studies. The diets provided energy at 1.5 times the resting energy expenditure and were isocaloric. Protein was consumed hourly for 8 h as an amino acid mixture with the composition of egg protein with L-[1-13C]phenylalanine as the indicator amino acid. The group mean protein requirement was determined by applying a mixed-effects change-point regression analysis to F13CO2 (label tracer oxidation in breath 13CO2), which identified a breakpoint in F13CO2 in response to graded intakes of protein.

RESULTS

The estimated protein requirement and RDA for older men were 0.94 and 1.24 g ⋅ kg-1 ⋅ d-1, respectively, which are not different from values we published using the same method in young men and older women.

CONCLUSIONS

The current intake recommendations for older adults for dietary protein of 0.66 g ⋅ kg-1 ⋅ d-1 for the EAR and 0.8 g ⋅ kg-1 ⋅ d-1 for the RDA appear to be underestimated by ∼30%. Future longer-term studies should be conducted to validate these results. This trial was registered at clinicaltrials.gov as NCT01948492.

The relationship between dietary protein consumption and risk of fracture: a subgroup and dose-response meta-analysis of prospective cohort studies

It is still debate of the relationship between the dietary protein consumption and risk of fracture. We searched Medline and Embase to assess the effects of dietary protein consumption on risk of fracture. Twelve prospective cohort studies with 407,104 participants were included, higher total protein consumption may be decrease 11% risk of hip fractures, with adj. RR of 0.89 (0.82, 0.97), no significant difference was found for total protein and risk of all fractures and limb fracture; for animal protein consumption and risk of all fractures and hip fracture, with adj.RR of 0.79 (032, 1.96) and 1.04 (0.70, 1.54); for vegetable protein consumption and risk of all fractures, hip fracture and limb fractures with adj.RR of 0.77 (0.52, 1.12), 1.00 (0.53, 1.91), and 0.94 (0.40, 2.22), the subgroup of vegetable protein consumption and risk of all fractures of postmenopausal women with adj.RR of 0.78(0.52,1.16). Dose-response meta-analysis the relationship of total/animal/vegetable protein and hip fracture was consistent to the results of forest plot, the line of total protein and hip fracture was below the Y = 1.0 line. This meta-analysis showed that total dietary protein consumption may be decrease the risk of hip fracture, but not for animal or vegetable protein.

Lifestyle and osteoporosis

Osteoporosis is associated with a number of lifestyle factors, including nutritional factors such as intake of calcium, protein, dairy food, fruits and vegetables and vitamin D status, and behavioural factors such as physical activity, smoking and alcohol consumption. Ensuring adequate calcium intake and vitamin D status and having regular weight-bearing physical activity throughout life are important for bone health and the prevention of osteoporosis and related fractures. Studies have shown that smoking and excessive alcohol intake have adverse effects on bone health and increase the risk of fracture. There is evidence suggesting that adequate protein intake and higher intake of fruits and vegetables are beneficial to bone health.

Protein malnutrition attenuates bone anabolic response to PTH in female rats

PTH is indicated for the treatment of severe osteoporosis. Elderly osteoporotic patients frequently suffer from protein malnutrition, which may contribute to bone loss. It is unknown whether this malnutrition may affect the response to PTH. Therefore, the aim of the present study was to assess whether an isocaloric low-protein (LP) diet may influence the bone anabolic response to intermittent PTH in 6-month-old female rats. Six-month-old female rats were either pair fed an isocaloric LP diet (2.5% casein) or a normal-protein (NP) diet (15% casein) for 2 weeks. The rats continued on their respective diet while being treated with 5- or 40-μg/kg recombinant human PTH amino-terminal fragment 1-34 (PTH-[1-34]) daily, or with vehicle for 4 weeks. At the end of this period, areal bone mineral density, bone mineral content, microstructure, and bone strength in axial compression of proximal tibia or 3-point bending for midshaft tibia tests were measured. Blood was collected for the determination of IGF-I and osteocalcin. After 4 weeks of PTH-(1-34), the dose-dependent increase of proximal tibia bone mineral density, trabecular microstructure variables, and bone strength was attenuated in rats fed a LP diet as compared with rats on a NP intake. At the level of midshaft tibia cortical bone, PTH-(1-34) exerted an anabolic effect only in the NP but not in the LP diet group. Protein malnutrition was associated with lower IGF-I levels. Protein malnutrition attenuates the bone anabolic effects of PTH-(1-34) in rats. These results suggest that a sufficient protein intake should be recommended for osteoporotic patients undergoing PTH therapy.

Building healthy bones throughout life: an evidence-informed strategy to prevent osteoporosis in Australia

Osteoporosis imposes a tremendous burden on Australia: 1.2 million Australians have osteoporosis and 6.3 million have osteopenia. In the 2007–08 financial year, 82 000 Australians suffered fragility fractures, of which > 17 000 were hip fractures. In the 2000–01 financial year, direct costs were estimated at $1.9 billion per year and an additional $5.6 billion on indirect costs. Osteoporosis was designated a National Health Priority Area in 2002; however, implementation of national plans has not yet matched the rhetoric in terms of urgency. Building healthy bones throughout life, the Osteoporosis Australia strategy to prevent osteoporosis throughout the life cycle, presents an evidence-informed set of recommendations for consumers, health care professionals and policymakers. The strategy was adopted by consensus at the Osteoporosis Australia Summit in Sydney, 20 October 2011. Primary objectives throughout the life cycle are: to maximise peak bone mass during childhood and adolescence to prevent premature bone loss and improve or maintain muscle mass, strength and functional capacity in healthy adults to prevent and treat osteoporosis in order to minimise the risk of suffering fragility fractures, and reduce falls risk, in older people. The recommendations focus on three affordable and important interventions — to ensure people have adequate calcium intake, vitamin D levels and appropriate physical activity throughout their lives. Recommendations relevant to all stages of life include: daily dietary calcium intakes should be consistent with Australian and New Zealand guidelines serum levels of vitamin D in the general population should be above 50nmol/L in winter or early spring for optimal bone health regular weight-bearing physical activity, muscle strengthening exercises and challenging balance/mobility activities should be conducted in a safe environment.

Nutritional aspects of bone health

Bone mass, geometry and microstructure, and bony tissue material level properties determine bone strength, hence the resistance to fracture. At a given age, all these variables are the consequence of the amount accumulated and of the structure developed during growth, up to the so-called peak bone mass, and of the bone loss and microstructure degradation occurring later in life. Genetic factors primarily contribute to the variance of the determinants of bone strength. Nutritional intakes are environmental factors that influence both processes, either directly by modifying modelling and remodelling, or indirectly through changes in calcitropic hormone secretion and action. Some effects of nutrition on the offspring bone could take place during foetal life. There are interplays between genetic factors, nutritional intakes and physical exercise. Among the nutrients, sufficient dietary intakes of calcium and protein are necessary for bone health in childhood and adolescence as well as later in life.

A fruit, milk and whole grain dietary pattern is positively associated with bone mineral density in Korean healthy adults

BACKGROUND/OBJECTIVES

Osteoporosis is a major health problem that will grow in burden with ageing of the global population. Modifiable risk factors for osteoporosis, including diet, have significant implications for disease prevention. We examined associations between dietary patterns and bone mineral density (BMD) in a Korean adult population.

SUBJECTS/METHODS

In total, 1828 individuals from the Healthy Twin Cohort were included as subjects. Information on general characteristics, lifestyles and health status was obtained through a health examination, and BMD was assessed using DEXA. Dietary intake was assessed using a 3-day food record, and dietary patterns were examined by factor analysis. Associations between dietary patterns and BMD were examined using mixed linear regression, adjusting for family and twin structure as well as other potential risk factors for bone health.

RESULTS

Four dietary patterns were identified (Rice and kimchi; eggs, meat and flour; Fruit, milk and whole grains; and Fast food and soda). The 'Fruit, milk and whole grains' pattern was associated with a reduced risk of having low BMD in men (odds ratio (OR)=0.38; 95% confidence interval (CI)=0.22-0.67) and women (OR=0.45; 95% CI=0.28-0.72) and was positively associated with BMD at multiple sites. The 'rice and kimchi' pattern had a positive association with only whole-arm BMD in men and women.

CONCLUSIONS

Our results suggest that a dietary pattern with high intake of dairy products, fruits and whole grains may contribute positively to bone health in a Korean adult population, and dietary pattern-based strategies could have potential in promoting bone health.

Protein intake and lumbar bone density: the Multi-Ethnic Study of Atherosclerosis (MESA)

Dietary protein has been shown to increase urinary Ca excretion in randomised controlled trials, and diets high in protein may have detrimental effects on bone health; however, studies examining the relationship between dietary protein and bone health have conflicting results. In the present study, we examined the relationship between dietary protein (total, animal and vegetable protein) and lumbar spine trabecular volumetric bone mineral density (vBMD) among participants enrolled in the Multi-Ethnic Study of Atherosclerosis (n 1658). Protein intake was assessed using a FFQ obtained at baseline examination (2000-2). Lumbar spine vBMD was measured using quantitative computed tomography (2002-5), on average 3 years later. Multivariable linear and robust regression techniques were used to examine the associations between dietary protein and vBMD. Sex and race/ethnicity jointly modified the association of dietary protein with vBMD (P for interaction = 0·03). Among white women, higher vegetable protein intake was associated with higher vBMD (P for trend = 0·03), after adjustment for age, BMI, physical activity, alcohol consumption, current smoking, educational level, hormone therapy use, menopause and additional dietary factors. There were no consistently significant associations for total and animal protein intakes among white women or other sex and racial/ethnic groups. In conclusion, data from the present large, multi-ethnic, population-based study suggest that a higher level of protein intake, when substituted for fat, is not associated with poor bone health. Differences in the relationship between protein source and race/ethnicity of study populations may in part explain the inconsistent findings reported previously.

Dietary protein intake in elderly women: association with muscle and bone mass

BACKGROUND

An inadequate food intake, mainly with regard to protein intake, seems to contribute to a reduction of skeletal muscle and bone mass in the elderly. This study was undertaken to evaluate differences in protein intake in women with or without sarcopenia and verify the intake level that is related to a better bone and muscle mass.

METHODS

Elderly women older than 65 years with sarcopenia (n = 35) and without sarcopenia (n = 165) participated in the study. Assessment of bone mineral density of the lumbar spine and femur was taken, body composition was evaluated by dual-energy x-ray absorptiometry, and an evaluation of protein intake was performed through 3-day dietary records.

RESULTS

Muscle, bone, and fat mass was significantly higher in women who had protein intake >1.2 g/kg/d. A lower intake of essential amino acids in women with sarcopenia was also observed. Protein and energy intake were significant predictors of muscle mass. The presence of osteoporosis was a predictor of muscle strength. In conclusion, the present study demonstrated that in elderly women, an adequate protein intake in terms of quality and quantity, without need of supplementation, could have a positive impact on bone mineral density, lean mass, and skeletal muscle mass.

Protective association of milk intake on the risk of hip fracture: results from the Framingham Original Cohort

Dairy foods are rich in bone-beneficial nutrients, yet the role of dairy foods in hip fracture prevention remains controversial. Our objective was to evaluate the association of milk, yogurt, cheese, cream, and milk + yogurt intakes with incident hip fracture in the Framingham Original Cohort. A total of 830 men and women from the Framingham Original Cohort, a prospective cohort study, completed a food-frequency questionnaire (1988 to 1989) and were followed for hip fracture until 2008. In this population-based study, Cox-proportional hazards regression was used to estimate hazard ratios (HR) by categories of energy-adjusted dairy intake (servings/wk), adjusting for standard confounders and covariates. The exposure was energy-adjusted intakes of milk, yogurt, cheese, cream, and milk + yogurt (servings/wk). Risk of hip fracture over the follow-up was the primary outcome; the hypothesis being tested was formulated after data collection. The mean age at baseline was 77 years (SD 4.9, range 68 to 96). Ninety-seven hip fractures occurred over the mean follow-up time of 11.6 years (range 0.04 to 21.9 years). The mean ± SD (servings/wk) of dairy intakes at baseline were: milk = 6.0 ± 6.4; yogurt = 0.4 ± 1.3; cheese = 2.6 ± 3.1; and cream = 3.4 ± 5.5. Participants with medium (>1 and <7 servings/wk) or higher (≥7 servings/wk) milk intake tended to have lower hip fracture risk than those with low (≤1 serving/wk) intake (high versus low intake HR 0.58, 95% confidence interval [CI] 0.31-1.06, p = 0.078; medium versus low intake HR 0.61, 95% CI 0.36-1.08, p = 0.071; p trend = 0.178]. There appeared to be a threshold for milk, with 40% lower risk of hip fracture among those with medium/high milk intake compared with those with low intake (p = 0.061). A similar threshold was observed for milk + yogurt intake (p = 0.104). These associations were further attenuated after adjustment for femoral neck bone mineral density. No significant associations were seen for other dairy foods (p range = 0.117 to 0.746). These results suggest that greater intakes of milk and milk + yogurt may lower risk for hip fracture in older adults through mechanisms that are partially, but not entirely, attributable to effects on bone mineral density.

The role of dietary protein and vitamin D in maintaining musculoskeletal health in postmenopausal women: a consensus statement from the European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis (ESCEO)

From 50 years of age, postmenopausal women are at an increased risk of developing sarcopenia and osteoporosis as a result of deterioration of musculoskeletal health. Both disorders increase the risk of falls and fractures. The risk of developing sarcopenia and osteoporosis may be attenuated through healthy lifestyle changes, which include adequate dietary protein, calcium and vitamin D intakes, and regular physical activity/exercise, besides hormone replacement therapy when appropriate. Protein intake and physical activity are the main anabolic stimuli for muscle protein synthesis. Exercise training leads to increased muscle mass and strength, and the combination of optimal protein intake and exercise produces a greater degree of muscle protein accretion than either intervention alone. Similarly, adequate dietary protein intake and resistance exercise are important contributors to the maintenance of bone strength. Vitamin D helps to maintain muscle mass and strength as well as bone health. These findings suggest that healthy lifestyle measures in women aged >50 years are essential to allow healthy ageing. The European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis (ESCEO) recommends optimal dietary protein intake of 1.0-1.2g/kgbodyweight/d with at least 20-25g of high-quality protein at each main meal, with adequate vitamin D intake at 800IU/d to maintain serum 25-hydroxyvitamin D levels >50nmol/L as well as calcium intake of 1000mg/d, alongside regular physical activity/exercise 3-5 times/week combined with protein intake in close proximity to exercise, in postmenopausal women for prevention of age-related deterioration of musculoskeletal health.

Additive effects of nutritional supplementation, together with bisphosphonates, on bone mineral density after hip fracture: a 12-month randomized controlled study

Background

After a hip fracture, a catabolic state develops, with increased bone loss during the first year. The aim of this study was to evaluate the effects of postoperative treatment with calcium, vitamin D, and bisphosphonates (alone or together) with nutritional supplementation on total hip and total body bone mineral density (BMD).

Methods

Seventy-nine patients (56 women), with a mean age of 79 years (range, 61–96 years) and with a recent hip fracture, who were ambulatory before fracture and without severe cognitive impairment, were included. Patients were randomized to treatment with bisphosphonates (risedronate 35 mg weekly) for 12 months (B; n=28), treatment with bisphosphonates along with nutritional supplementation (40 g protein, 600 kcal daily) for the first 6 months (BN; n=26), or to controls (C; n=25). All participants received calcium (1,000 mg) and vitamin D3 (800 IU) daily. Total hip and total body BMD were assessed with dual-energy X-ray absorptiometry at baseline, 6, and 12 months. Marker of bone resorption C-terminal telopeptide of collagen I and 25-hydroxy vitamin D were analyzed in serum.

Results

Analysis of complete cases (70/79 at 6 months and 67/79 at 12 months) showed an increase in total hip BMD of 0.7% in the BN group, whereas the B and C groups lost 1.1% and 2.4% of BMD, respectively, between baseline and 6 months (P=0.071, between groups). There was no change in total body BMD between baseline and 12 months in the BN group, whereas the B group and C group both lost BMD, with C losing more than B (P=0.009). Intention-to-treat analysis was in concordance with the complete cases analyses.

Conclusion

Protein-and energy-rich supplementation in addition to calcium, vitamin D, and bisphosphonate therapy had additive effects on total body BMD and total hip BMD among elderly hip fracture patients.

Vegetarian diets and bone status

Osteoporosis is a common chronic condition associated with progressive loss of bone mineral density (BMD) and compromised bone strength, with increasing risk of fracture over time. Vegetarian diets have been shown to contain lower amounts of calcium, vitamin D, vitamin B-12, protein, and n-3 (ω-3) fatty acids, all of which have important roles in maintaining bone health. Although zinc intakes are not necessarily lower quantitatively, they are considerably less bioavailable in vegetarian diets, which suggests the need for even higher intakes to maintain adequate status. At the same time, healthy vegetarian diets tend to contain more of several protective nutrients, including magnesium, potassium, vitamin K, and antioxidant and anti-inflammatory phytonutrients. On balance, there is evidence that vegetarians, and particularly vegans, may be at greater risk of lower BMD and fracture. Attention to potential shortfall nutrients through the careful selection of foods or fortified foods or the use of supplements can help ensure healthy bone status to reduce fracture risk in individuals who adhere to vegetarian diets.

Clinical and histological evaluation of postextraction platelet-rich fibrin socket filling: a prospective randomized controlled study

OBJECTIVES

The aims were to investigate whether the use of platelet-rich fibrin membranes (PRF) for socket filling could improve microarchitecture and intrinsic bone tissue quality of the alveolar bone after premolar extraction and to assess the influence of the surgical procedure before implant placement.

MATERIAL AND METHODS

Twenty-three patients requiring premolar extraction followed by implant placement were randomized to three groups: (1) simple extraction and socket filling with PRF, (2) extraction with mucosal flap and socket filling with PRF, and (3) controls with simple extraction without socket filling. Implant placement was performed at week 8, and a bone biopsy was obtained for histomorphometric analysis.

RESULTS

Analysis by microcomputed tomography showed better bone healing with improvement of the microarchitecture (P < 0.05) in group 1. This treatment had also a significant effect (P < 0.05) on intrinsic bone tissue quality and preservation of the alveolar width. An invasive surgical procedure with a mucosal flap appeared to completely neutralize the advantages of the PRF.

CONCLUSIONS

These results support the use of a minimally traumatic procedure for tooth extraction and socket filling with PRF to achieve preservation of hard tissue.

Biomarker-calibrated protein intake and bone health in the Women's Health Initiative clinical trials and observational study

BACKGROUND

The effects of dietary protein on bone health are controversial.

OBJECTIVE

We examined the relation between protein intake with fracture and bone mineral density (BMD) within the Women's Health Initiative (WHI).

DESIGN

This prospective analysis included 144,580 women aged 50-79 y at baseline in the WHI clinical trials (CTs) and observational study (OS) that recruited participants in 1993-1998 with follow-up through 2011. Self-reported clinical fractures were collected semiannually through the original end of the trials (WHI CTs) and annually (WHI OS) by questionnaires. Hip fracture was adjudicated by a central review of radiology reports. BMDs for total body, hip, and spine were measured at baseline and 3 and 6 y in 9062 women at 3 WHI clinics by using dual-energy X-ray absorptiometry. Protein intake was assessed via food-frequency questionnaire and calibrated by using biomarkers of energy and protein intakes. Associations between protein intake and fracture were estimated by using Cox proportional hazards regression, and the relation between protein intake and BMD was estimated by using linear regression.

RESULTS

Median biomarker-calibrated protein intake was 15% of energy intake. Per 20% increase in calibrated protein intake (percentage of energy), there was no significant association with total fracture (HR: 0.99; 95% CI: 0.97, 1.02) or hip fracture (HR: 0.91; 95% CI: 0.84, 1.00), but there was an inverse association with forearm fracture (HR: 0.93; 95% CI: 0.88, 0.98). Each 20% increase in calibrated protein intake was associated with a significantly higher BMD for total body (mean 3-y change: 0.003 g/cm²; 95% CI: 0.001, 0.005 g/cm²) and hip (mean 3-y change: 0.002 g/cm²; 95% CI: 0.001, 0.004 g/cm²).

CONCLUSIONS

Higher biomarker-calibrated protein intake within the range of usual intake was inversely associated with forearm fracture and was associated with better maintenance of total and hip BMDs. These data suggest higher protein intake is not detrimental to bone health in postmenopausal women.

Dietary pattern classifications with nutrient intake and body composition changes in Korean elderly

BACKGROUND/OBJECTIVES

The body composition changes in aging increased the risk of metabolic disorder. Recent dietary studies have increasingly focused on the correlations between dietary patterns and chronic diseases to overcome the limitations of traditional single-nutrient studies because nutrients in food have complex relations that interact.

SUBJECTS/METHODS

This study was conducted to classify a dietary pattern among Korean elderly using cluster analysis and to explore the relationships between dietary patterns and body composition changes in Korean elderly aged 65 years or older. The study subjects (n = 1,435) were individuals who participated in the Korean National Health Examination and Nutrition Survey (KNHANES) in 2011.

RESULTS

There were three dietary patterns derived by cluster analysis in this study: 'Traditional Korean' (37.49% of total population), 'Meat and Alcohol' (19.65%) and 'Westernized Korean' (42.86%). The (1) 'Traditional Korean' pattern was characterized by high consumptions of white rice and low protein, low fat, and low milk products, while (2) 'Westernized Korean' pattern ate a Korean-style diet base with various foods such as noodles, bread, eggs and milk, (3) 'Meat and Alcohol' pattern had high consumptions of meat and alcohol. In body composition changes, compared with the 'Traditional Korean' pattern, the 'Meat & alcohol' pattern was associated with a 50% increased risk of having elevated BMI (kg/m²), 'Westernized Korean' pattern was associated with a 74% increased abnormality of ASM/Wt (kg) by logistics analysis. Most of the Korean adult population continues to follow ether a traditional Korean having beneficial effects for successful aging. However, the 'Traditional Korean' pattern showed low protein intake (0.7 g/kg), calcium intake, and vitamin D intake as well as low of appendicular skeletal muscle mass (ASM (kg)) among 3 groups.

CONCLUSIONS

Considering the low ASM, consumption of protein, calcium and vitamin D should be increased for Korean elderly health body composition.

[Utility of bone turnover markers in metabolic bone disease detection in patients with phenylketonuria]

BACKGROUND AND OBJECTIVE

Mineral bone disease is more common in phenylketonuric patients. The objectives of this study were to determine the usefulness of biochemical bone markers to identify phenylketonuric patients with mineral bone disease (MBD) and know the underlying bone remodeling alterations.

PATIENTS AND METHOD

Cross-sectional study of 43 phenylketonuric patients>7 years (range: 7.1-41 years). A nutritional survey was performed and bone alkaline phosphatase (BAP), procollagen type 1 N-terminal propeptide (PNP-1), beta-crosslaps and ratio calcium/creatinine in urine were determined.

RESULTS

A percentage of 20.9 of patients had pathological biochemical bone markers, 90% of them being adults. BAP was decreased in 70% of them and beta-crosslaps in 42.8%. BAP values were more often pathological in phenylketonuric patients with a late diagnosis (41.7 vs. 10.7%; P<.05) and in patients with MBD (60 vs. 14.3%; P<.05). PNP-1 values and calcium/creatinine were similar among all phenylketonuric patients regardless of presenting MBD, late diagnosis or tetrahydrobipterin treatment (enzyme cofactor). Patients with decreased BAP and beta-crosslaps had lower natural protein intake: BAP (0.21 ± 0.13 vs. 0.65 ± 0.65 g/kg; P<.05); beta-crosslaps (0.29 ± 0.23 vs. 0.65 ± 0.66 g/kg; P<.05). None of the tetrahydrobiopterin treated patients showed altered values of BAP, PNP-1 or calcium/creatinine.

CONCLUSIONS

Adult phenylketonuric patients with lower natural protein intake tend to have lower values of BAP, which is a marker that may be useful to identify patients at risk for MBD.

Effects of the amount and source of dietary protein on bone status in rats

This study examined the effects of the dietary amount and source of protein on bone status in rats. 140 male Wistar rats aged 8 weeks were randomly allocated to 4 groups (n = 35) fed normal-protein (NP, 10% richness) or high-protein (HP, 45% richness) diets based on whey protein (WP) or soy protein (SP) sources for 12 weeks. Plasma urea was 46% higher for the HP compared to the NP diet (p < 0.001). Urinary calcium was 65% higher for the HP compared to the NP and 60% higher for the WP compared to the SP diets (all, p < 0.001). Urinary pH was 8% more acidic in the HP compared to the NP diet (p < 0.001) and 4% in the WP compared to the SP diet (p < 0.01). The plasma osteocalcin concentration was 19% higher for the NP compared to the HP (p < 0.05) and 25% for the SP compared to the WP diets (p < 0.01). Femur ash, metaphyseal and diaphyseal cross-sectional, trabecular and cortical areas were 3% higher in the HP compared to the NP diet (all, p < 0.05). Femur diaphyseal periosteal and endocortical perimeters were also 3% higher in the HP compared to the NP diet (both, p < 0.01). Groups fed the SP diet showed 2% higher femur ash percentage, 7% higher calcium content (both, p < 0.001), and 3% higher diaphyseal cortical area and thickness (both, p < 0.05) than those fed the WP diet. Some interactions were found, such as the greater effects of the SP diet on decreasing the higher plasma urea concentration promoted by the intake of the HP diet (p < 0.001). Under adequate Ca intake, HP diets could better maintain bone properties than NP diets, even with increasing some acidity markers, which could be reduced by the intake of SP sources.

Health effects of protein intake in healthy elderly populations: 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 elderly persons in order to evaluate the evidence for an optimal protein intake. The literature search covered year 2000–2011. Prospective cohort, case–control, and intervention studies of a general healthy population in settings similar to the Nordic countries with protein intake from food-based sources were included. Out of a total of 301 abstracts, 152 full papers were identified as potentially relevant. After careful scrutiny, 23 papers were quality graded as A (highest, n=1), B (n=18), or C (n=4). The grade of evidence was classified as convincing, probable, suggestive, or inconclusive. The evidence is assessed as: probable for an estimated average requirement (EAR) of 0.66 g good-quality protein/kg body weight (BW)/day based on nitrogen balance (N-balance) studies and the subsequent recommended dietary allowance (RDA) of 0.83 g good-quality protein/kg BW/day representing the minimum dietary protein needs of virtually all healthy elderly persons. Regarding the optimal level of protein related to functional outcomes like maintenance of bone mass, muscle mass, and strength, as well as for morbidity and mortality, the evidence is ranging from suggestive to inconclusive. Results from particularly prospective cohort studies suggest a safe intake of up to at least 1.2–1.5 g protein/kg BW/day or approximately 15–20 E%. Overall, many of the included prospective cohort studies were difficult to fully evaluate since results mainly were obtained by food frequency questionnaires that were flawed by underreported intakes, although some studies were ‘calibrated’ to correct for under- or over-reporting. In conclusion, the evidence is assessed as probable regarding the EAR based on N-balance studies and suggestive to inconclusive regarding an optimal protein intake higher than the estimated RDA assessed from N-balance studies, but an exact level cannot be determined. Potentially adverse effects of a protein intake exceeding 20–23 E% remain to be investigated.

Calcium homeostasis and bone metabolic responses to high-protein diets during energy deficit in healthy young adults: a randomized controlled trial

BACKGROUND

Although consuming dietary protein above current recommendations during energy deficit (ED) preserves lean body mass, concerns have been raised regarding the effects of high-protein diets on bone health.

OBJECTIVE

The objective was to determine whether calcium homeostasis and bone turnover are affected by high-protein diets during weight maintenance (WM) and ED.

DESIGN

In a randomized, parallel-design, controlled trial of 32 men and 7 women, volunteers were assigned diets providing protein at 0.8 [Recommended Dietary Allowance (RDA)], 1.6 (2 × RDA), or 2.4 (3 × RDA) g · kg(-1) · d(-1) for 31 d. Ten days of WM preceded 21 d of ED, during which total daily ED was 40%, achieved by reduced dietary energy intake (∼30%) and increased physical activity (∼10%). The macronutrient composition (protein g · kg(-1) · d(-1) and % fat) was held constant from WM to ED. Calcium absorption (ratio of (44)Ca to (42)Ca) and circulating indexes of bone turnover were determined at day 8 (WM) and day 29 (ED).

RESULTS

Regardless of energy state, mean (±SEM) urinary pH was lower (P < 0.05) at 2 × RDA (6.28 ± 0.05) and 3 × RDA (6.23 ± 0.06) than at the RDA (6.54 ± 0.06). However, protein had no effect on either urinary calcium excretion (P > 0.05) or the amount of calcium retained (P > 0.05). ED decreased serum insulin-like growth factor I concentrations and increased serum tartrate-resistant acid phosphatase and 25-hydroxyvitamin D concentrations (P < 0.01). Remaining markers of bone turnover and whole-body bone mineral density and content were not affected by either the protein level or ED (P > 0.05).

CONCLUSION

These data demonstrate that short-term consumption of high-protein diets does not disrupt calcium homeostasis and is not detrimental to skeletal integrity. This trial was registered at www.clinicaltrials.gov as NCT01292395.

Dietary protein is beneficial to bone health under conditions of adequate calcium intake: an update on clinical research

PURPOSE OF REVIEW

To underscore recent clinical studies, which evaluate the association between dietary protein and bone health.

RECENT FINDINGS

Epidemiologic studies show greater protein intake to be beneficial to bone health in adults. In addition, randomized controlled trials show that protein's positive effect on bone health is augmented by increased calcium intake. The relation between dietary protein and fracture risk is unclear. Dietary protein may positively impact bone health by increasing muscle mass, increasing calcium absorption, suppressing parathyroid hormone, and augmenting insulin-like growth factor 1 production; but the effects of other factors that contribute to this association, such as dietary protein dose and timing response, require further research.

SUMMARY

The positive effects of protein intake on bone health may only be beneficial under conditions of adequate calcium intake. Dietary protein's relation with fracture risk requires further investigation.

Milk and yogurt consumption are linked with higher bone mineral density but not with hip fracture: the Framingham Offspring Study

Dairy foods are a complex source of essential nutrients. In this study, fluid dairy intake, specifically milk, and yogurt intakes were associated with hip but not spine bone mineral density (BMD), while cream may adversely influence BMD, suggesting that not all dairy products are equally beneficial for the skeleton.

PURPOSE

This study seeks to examine associations of milk, yogurt, cheese, cream, most dairy (total dairy without cream), and fluid dairy (milk + yogurt) with BMD at femoral neck (FN), trochanter (TR), and spine, and with incident hip fracture over 12-year follow-up in the Framingham Offspring Study.

METHODS

Three thousand two hundred twelve participants completed a food frequency questionnaire (1991–1995 or 1995–1998) and were followed for hip fracture until 2007 [corrected]. Two thousand five hundred and six participants had DXA BMD (1996-2001). Linear regression was used to estimate adjusted mean BMD while Cox-proportional hazards regression was used to estimate adjusted hazard ratios (HR) for hip fracture risk. Final models simultaneously included dairy foods adjusting for each other.

RESULTS

Mean baseline age was 55 (±1.6) years, range 26-85. Most dairy intake was positively associated with hip and spine BMD. Intake of fluid dairy and milk was related with hip but not spine BMD. Yogurt intake was associated with TR-BMD alone. Cheese and cream intakes were not associated with BMD. In final models, yogurt intake remained positively associated with TR-BMD, while cream tended to be negatively associated with FN-BMD. Yogurt intake showed a weak protective trend for hip fracture [HR(95%CI), ≤4 serv/week, 0.46 (0.21-1.03) vs. >4 serv/week, 0.43 (0.06-3.27)]. No other dairy groups showed a significant association (HRs range, 0.53-1.47) with limited power (n, fractures = 43).

CONCLUSION

Milk and yogurt intakes were associated with hip but not spine BMD, while cream may adversely influence BMD. Thus, not all dairy products are equally beneficial for the skeleton. Suggestive fracture results for milk and yogurt intakes need further confirmation.

Comparison of 2 weight-loss diets of different protein content on bone health: a randomized trial

BACKGROUND

It has been hypothesized that hip-fracture rates are higher in developed than in developing countries because high-protein (HP) Western diets induce metabolic acidosis and hypercalciuria. Confounders include interactions between dietary protein and calcium, sodium, and potassium.

OBJECTIVE

We determined whether an HP or a high-normal-protein (HNP) weight-loss diet caused greater loss in bone mineral density (BMD) over 24 mo.

DESIGN

The Weight Loss, Protein and Bone Density Study was conducted from 2008 to 2011 in 323 overweight [body mass index (BMI; in kg/m(2)) >27] postmenopausal women, with a total hip BMD t score less than -2.0. Subjects were randomly assigned to receive an isocaloric calcium-replete HP (≥90 g protein/d) or HNP (<80 g protein/d) weight-loss diet, with the aim of a difference of 20 g protein/d. A total of 186 subjects (90 subjects in the HP group, 96 subjects in the HNP group) completed 12 mo, and 137 subjects (69 subjects in the HP group, 68 subjects in the HNP group) completed 24 mo.

RESULTS

Biomarkers confirmed a difference in protein intake of 16 and 13.1 g at 12 and 24 mo, respectively. Mean (±SE) weight loss was equal; HP subjects lost 7.9 ± 0.9 kg and HNP subjects lost 8.9 ± 0.9 kg at 24 mo. Subjects lost 1-2% BMD annually at lumbar spine vertebrae 2-4, the forearm, the femoral neck, and hip. ANCOVA showed no effect of the HP or HNP diet (P > 0.05 for diet and diet-time interactions). A diet-by-time analysis showed that the HNP diet increased C-terminal telopeptide and osteocalcin (P ≤ 0.001 for each) despite hypercalciuria (P = 0.029).

CONCLUSION

High dietary protein intake during weight loss has no clinically significant effect on bone density but slows bone turnover. This trial was registered at the Australian and New Zealand Clinical Trials Registry (http://www.anzctr.org.au) as ACTRN12608000229370.

Diet-induced weight loss: the effect of dietary protein on bone

High-protein (>30% of energy from protein or >1.2 g/kg/day) and moderately high-protein (22% to 29% of energy from protein or 1.0 to 1.2 g/kg/day) diets are popular for weight loss, but the effect of dietary protein on bone during weight loss is not well understood. Protein may help preserve bone mass during weight loss by stimulating insulin-like growth factor 1, a potent bone anabolism stimulator, and increasing intestinal calcium absorption. Protein-induced acidity is considered to have minimal effect on bone resorption in adults with normal kidney function. Both the quantity and predominant source of protein influence changes in bone with diet-induced weight loss. Higher-protein, high-dairy diets may help attenuate bone loss during weight loss.

Association of total protein intake with bone mineral density and bone loss in men and women from the Framingham Offspring Study

OBJECTIVE

To examine (i) the association of percentage of total energy intake from protein (protein intake %) with bone mineral density (BMD, g/cm2) and bone loss at the femoral neck, trochanter and lumbar spine (L2-L4) and (ii) Ca as an effect modifier.

SETTING

The Framingham Offspring Study.

SUBJECTS

Men (n 1280) and women (n 1639) completed an FFQ in 1992-1995 or 1995-1998 and underwent baseline BMD measurement by dual-energy X-ray absorptiometry in 1996-2000. Men (n 495) and women (n 680) had follow-up BMD measured in 2002-2005.

DESIGN

Cohort study using multivariable regression to examine the association of protein intake % with each BMD, adjusting for covariates. Statistical interaction between protein intake % and Ca (total, dietary, supplemental) intake was examined.

RESULTS

The mean age at baseline was 61 (sd 9) years. In the cross-sectional analyses, protein intake % was positively associated with all BMD sites (P range: 0·02-0·04) in women but not in men. Significant interactions were observed with total Ca intake (<800 mg/d v. ≥800 mg/d) in women at all bone sites (P range: 0·002-0·02). Upon stratification, protein intake % was positively associated with all BMD sites (P range: 0·04-0·10) in women with low Ca intakes but not in those with high Ca intakes. In the longitudinal analyses, in men, higher protein intake % was associated with more bone loss at the trochanter (P = 0·01) while no associations were seen in women, regardless of Ca intake.

CONCLUSIONS

This suggests that greater protein intake benefits women especially those with lower Ca intakes. However, protein effects are not significant for short-term changes in bone density. Contrastingly, in men, higher protein intakes lead to greater bone loss at the trochanter. Longer follow-up is required to examine the impact of protein on bone loss.

The association of red meat, poultry, and egg consumption with risk of hip fractures in elderly Chinese: a case-control study

BACKGROUND/PURPOSE

The epidemiological evidence that the consumption of red meat, poultry or eggs may be associated with the risk of hip fractures is inconsistent and no studies have differentiated between types of red meat or poultry. We evaluated the association between the consumption of red meat, poultry or eggs and the risk of hip fracture.

METHODS

A 1:1 age- (±3years) and gender-matched case-control study of 646 pairs (female/male: 484/162) of elderly Chinese was conducted between June 2009 and January 2013 in Guangdong, China. Information on meat and egg consumption was collected using a 79-item food frequency questionnaire administered in face-to-face interviews. Conditional logistic regression was used to test the relationship between intake of red meat, poultry, and eggs and the risk of hip fracture. Multivariate ORs and their 95% CIs were estimated.

RESULTS

After adjusting for potential confounders, risk of hip fracture was found to be positively associated with total red meat consumption (P for trend <0.001), but not with total poultry or egg consumption. The adjusted ORs (95% CIs) for hip fractures, comparing extreme quartiles, were 2.94 (1.82, 4.76) for total red meat, 1.11 (0.74, 1.66) for total poultry, and 0.99 (0.63, 1.56) for eggs. Subtype analyses indicated that the unfavorable effect of total red meat was primarily associated with the consumption of fatty pork and organ meat, whereas fatty and lean poultry had opposite effects. Men with higher fatty pork intake tended to have greater risk than women (P interaction=0.019).

CONCLUSIONS

Our findings suggest that greater consumption of fatty, but not lean, red meat and poultry may increase the risk of hip fracture. These results provide preliminary evidence for the feasibility of a dietary program for the prevention of hip fractures, which should be confirmed by further studies.

Dietary protein in relation to bone stiffness index and fat-free mass in a population consuming relatively low protein diets

Dietary protein has a mixed effect on skeletal health and the effect may differ by amount or source of protein. The purpose of this study was to investigate dietary protein in relation to bone density and fat-free mass in rural Korean residents consuming relatively low protein diets. Between 2008 and 2010, 3,330 participants were recruited for a baseline examination of a community-based study in Kangwha. Of those, 1,182 men and 1,393 postmenopausal women were eligible for the present study. Diet was assessed using a food-frequency questionnaire developed for Korean adults. Calcaneal bone density measured by ultrasound was expressed as the stiffness index (SI). Fat-free mass index (FFMI) was defined as fat-free mass in kilograms divided by the height in meters squared. The mean ages of men and women were 59.5 and 60.0 years, respectively. The median daily intakes of total and meat protein were 52.3 and 6.7 g in men and 45.0 and 3.0 g in women, respectively. After controlling for potential confounders, SI and FFMI showed an increasing trend with a higher meat protein intake in men (P for trend = 0.017 and 0.033, respectively), but not in women. No positive association was observed for other food sources of protein. In conclusion, our findings suggest that meat protein contributes to skeletal health in men consuming relatively low protein diets.

Consumption of yogurts fortified in vitamin D and calcium reduces serum parathyroid hormone and markers of bone resorption: a double-blind randomized controlled trial in institutionalized elderly women

CONTEXT

Nutritional prevention of bone deterioration with fortified foods seems particularly suitable in institutionalized elderly women at risk of vitamin D deficiency, secondary hyperparathyroidism, increased bone resorption, and osteoporotic fracture.

OBJECTIVE

The objective was to evaluate whether fortification of yogurts with vitamin D and calcium exerts an additional lowering effect on serum PTH and bone resorption markers as compared with isocaloric and isoprotein dairy products in elderly women.

DESIGN

A randomized double-blind controlled-trial, 56-day intervention was conducted in institutionalized women (mean age 85.5 years) consuming 2 125-g servings of either vitamin D- and calcium-fortified yogurt (FY) at supplemental levels of 10 μg/d vitamin D₃ and 800 mg/d calcium or nonfortified control yogurt (CY) providing 280 mg/d calcium.

MAIN OUTCOMES

The endpoints were serum changes from baseline (day 0) to day 28 and day 56 in 25-hydroxyvitamin-D (25OHD), PTH, and bone resorption markers tartrate-resistant acid phosphatase isoform-5b (TRAP5b), the primary outcome, and carboxyl-terminal cross-linked telopeptide of type I collagen (CTX).

RESULTS

At day 56, serum 25OHD increased (mean ± SEM) by 25.3 ± 1.8 vs 5.2 ± 2.5 nmol/L in FY (n = 29) and CY (n = 27), respectively (P < .0001). The corresponding changes in PTH were -28.6% ± 7.2% vs -8.0% ± 4.3% (P = .0003); in TRAP5b, -21.9% ± 4.3% vs 3.0% ± 3.2% (P < .0001); and in CTX, -11.0% ± 9.7% vs -3.0% ± 4.1% (P = .0146), in FY and CY, respectively. At day 28, these differences were less pronounced but already significant for 25OHD, PTH, and TRAP5b.

CONCLUSIONS

This study in institutionalized elderly at high risk for osteoporotic fracture suggests that fortification of dairy products with vitamin D₃ and calcium provides a greater prevention of accelerated bone resorption as compared with nonfortified equivalent foods.

Nutritional disturbance in acid-base balance and osteoporosis: a hypothesis that disregards the essential homeostatic role of the kidney

The nutritional acid load hypothesis of osteoporosis is reviewed from its historical origin to most recent studies with particular attention to the essential but overlooked role of the kidney in acid–base homeostasis. This hypothesis posits that foods associated with an increased urinary acid excretion are deleterious for the skeleton, leading to osteoporosis and enhanced fragility fracture risk. Conversely, foods generating neutral or alkaline urine would favour bone growth and Ca balance, prevent bone loss and reduce osteoporotic fracture risk. This theory currently influences nutrition research, dietary recommendations and the marketing of alkaline salt products or medications meant to optimise bone health and prevent osteoporosis. It stemmed from classic investigations in patients suffering from chronic kidney diseases (CKD) conducted in the 1960s. Accordingly, in CKD, bone mineral mobilisation would serve as a buffer system to acid accumulation. This interpretation was later questioned on both theoretical and experimental grounds. Notwithstanding this questionable role of bone mineral in systemic acid–base equilibrium, not only in CKD but even more in the absence of renal impairment, it is postulated that, in healthy individuals, foods, particularly those containing animal protein, would induce ‘latent’ acidosis and result, in the long run, in osteoporosis. Thus, a questionable interpretation of data from patients with CKD and the subsequent extrapolation to healthy subjects converted a hypothesis into nutritional recommendations for the prevention of osteoporosis. In a historical perspective, the present review dissects out speculation from experimental facts and emphasises the essential role of the renal tubule in systemic acid–base and Ca homeostasis.

Dietary acid load: a novel nutritional target in chronic kidney disease?

Nonvolatile acid is produced from the metabolism of organic sulfur in dietary protein and the production of organic anions during the combustion of neutral foods. Organic anion salts that are found primarily in plant foods are directly absorbed in the gastrointestinal tract and yield bicarbonate. The difference between endogenously produced nonvolatile acid and absorbed alkali precursors yields the dietary acid load, technically known as the net endogenous acid production, and must be excreted by the kidney to maintain acid-base balance. Although typically 1 mEq/kg/day, dietary acid load is lower with greater intake of fruits and vegetables. In the setting of CKD, a high dietary acid load invokes adaptive mechanisms to increase acid excretion despite reduced nephron number, such as increased per nephron ammoniagenesis and augmented distal acid excretion mediated by the renin-angiotensin system and endothelin-1. These adaptations may promote kidney injury. Additionally, high dietary acid loads produce low-grade, subclinical acidosis that may result in bone and muscle loss. Early studies suggest that lowering the dietary acid load can improve subclinical acidosis, preserve bone and muscle, and slow the decline of glomerular filtration rate in animal models and humans. Studies focusing on hard clinical outcomes are needed.

Risk factors for developing mineral bone disease in phenylketonuric patients

There is a compromised bone mass in phenylketonuria patients compared with normal population, but the mechanisms responsible are still a matter of investigation. In addition, tetrahydrobiopterin therapy is a new option for a significant proportion of these patients and the prevalence of mineral bone disease (MBD) in these patients is unknown. We conducted a cross-sectional observational study including 43 phenylketonuric patients. Bone densitometry, nutritional assessment, physical activity questionnaire, biochemical parameters, and molecular study were performed in all patients. Patients were stratified by phenotype, age and type of treatment. The MBD prevalence in phenylketonuria was 14%. Osteopenic and osteoporotic (n=6 patients) had an average daily natural protein intake significantly lower than the remaining (n=37) patients with PKU (14.33 ± 8.95 g vs 21.25 ± 20.85 g). Besides, a lower body mass index was found. There were no statistical differences in physical activity level, calcium, phosphorus and fat intake, and in phenylalanine, vitamin D, paratohormone, docosahexaenoic and eicosapentaenoic acid blood levels. Mutational spectrum was found in up to 30 different PAH genotypes and no relationship was established among genotype and development of MBD. None of the twelve phenylketonuric patients treated with tetrahydrobiopterin (27.9%), for an average of 7.1 years, developed MBD. Natural protein intake and blood levels of eicosapentaenoic acid were significantly higher while calcium intake was lower in these patients. This study shows that the decrease in natural protein intake can play an important role in MBD development in phenylketonuric patients. Therapy with tetrahydrobiopterin allows a more relaxed protein diet, which is associated with better bone mass.

Dairy in adulthood: from foods to nutrient interactions on bone and skeletal muscle health

The risk of fragility fractures exponentially increases with aging. Reduced mass and strength of both bone in osteoporosis and skeletal muscle in sarcopenia play a key role in the age-related incidence of fragility fractures. Undernutrition is often observed in the elderly, particularly in those subjects experiencing osteoporotic fractures, more likely as a cause than a consequence. Calcium (Ca), inorganic phosphate (Pi), vitamin D, and protein are nutrients that impact bone and skeletal muscle integrity. Deficiency in the supply of these nutrients increases with aging. Dairy foods are rich in Ca, Pi, and proteins and in many countries are fortified with vitamin D. Dairy foods are important souces of these nutrients and go a long way to meeting the recommendations, which increase with aging. This review emphaszes the interactions between these 4 nutrients, which, along with physical activity, act through cellular and physiological pathways favoring the maintenance of both bone and skeletal muscle structure and function.

Serum uric acid plays a protective role for bone loss in peri- and postmenopausal women: a longitudinal study

OBJECTIVE

Oxidative stress has been linked to osteoporosis. Serum uric acid (UA), a strong endogenous antioxidant, has been associated with higher bone mineral density (BMD), lower bone turnover and lower prevalence of fractures in a large cross-sectional study of men. Whether this relationship is present in women and how UA relates to changes in BMD longitudinally has not been examined.

METHODS

A sample of 356 peri- and postmenopausal women, mean age 60.5 years was studied. Each individual had baseline BMD and body composition measurements by dual energy x-ray absorptiometry (DXA) and at least one repeat measure, on average 9.7 years later. Annual rate of change in BMD (A%ΔBMD) was calculated. UA was measured at each DXA visit. Calciotropic hormones and bone turnover markers were measured at the final visit only.

RESULTS

Cross-sectional data analyses revealed that women with higher UA levels had significantly higher absolute BMD measures at all skeletal sites. These women also had higher measures of body weight and its components such as lean mass (LM) and fat mass (FM). Results of multiple regression analyses showed a positive association between UA and BMD that remained significant even after accounting for possible confounders including LM and FM. Regression analyses of the longitudinal BMD data demonstrated significant associations between serum UA levels and annual rates of change in BMD at all skeletal sites. After adjustment associations remained significant for lumbar spine, forearm and whole body BMD but not for hip BMD.

CONCLUSION

Higher serum UA levels appear to be protective for bone loss in peri- and postmenopausal women and this relationship is not affected by changes in body composition measures.

Dietary habits, nutrients and bone mass in Spanish premenopausal women: the contribution of fish to better bone health

The moderate consumption of fish is recommended for a healthy diet and is also a feature of the Mediterranean diet. Fish is a major food group in diets throughout the world, and studies show that fish consumption is associated with a lower risk of a number of conditions. Spain has one of the highest annual per capita consumptions of fish worldwide. As fish is a source of high quality protein; n-3 polyunsaturated fatty acids; vitamins, such as A and D; and minerals, such as selenium, calcium, iodine, magnesium, copper and zinc, nutrients that have positive effects on bone characteristics, it has been proposed that its consumption could improve bone health. In this cross-sectional study, we have investigated the relationship between dietary habits and nutrient intake of 151 Spanish premenopausal women and analyzed the association of fish consumption on bone mass measured by quantitative ultrasound of the phalanges. A higher (P < 0.05) bone mass and vitamin D intake (P < 0.05) was observed in the group with a fish intake of 5-7 servings/week. We conclude that increased fish consumption is helpful in maintaining an adequate bone mass in Spanish premenopausal women.

Effects of low-carbohydrate diets versus low-fat diets on metabolic risk factors: a meta-analysis of randomized controlled clinical trials

The effects of low-carbohydrate diets (≤45% of energy from carbohydrates) versus low-fat diets (≤30% of energy from fat) on metabolic risk factors were compared in a meta-analysis of randomized controlled trials. Twenty-three trials from multiple countries with a total of 2,788 participants met the predetermined eligibility criteria (from January 1, 1966 to June 20, 2011) and were included in the analyses. Data abstraction was conducted in duplicate by independent investigators. Both low-carbohydrate and low-fat diets lowered weight and improved metabolic risk factors. Compared with participants on low-fat diets, persons on low-carbohydrate diets experienced a slightly but statistically significantly lower reduction in total cholesterol (2.7 mg/dL; 95% confidence interval: 0.8, 4.6), and low density lipoprotein cholesterol (3.7 mg/dL; 95% confidence interval: 1.0, 6.4), but a greater increase in high density lipoprotein cholesterol (3.3 mg/dL; 95% confidence interval: 1.9, 4.7) and a greater decrease in triglycerides (-14.0 mg/dL; 95% confidence interval: -19.4, -8.7). Reductions in body weight, waist circumference and other metabolic risk factors were not significantly different between the 2 diets. These findings suggest that low-carbohydrate diets are at least as effective as low-fat diets at reducing weight and improving metabolic risk factors. Low-carbohydrate diets could be recommended to obese persons with abnormal metabolic risk factors for the purpose of weight loss. Studies demonstrating long-term effects of low-carbohydrate diets on cardiovascular events were warranted.

Bone health: part 1, nutrition

Nutrition, in sufficient amount and substance, is crucial for healthy growth and development of the skeleton and surrounding tissues, especially in physically active populations. Inadequate nutrition has been linked to maladies such as the female athlete triad, as well as poor training or competitive performance and increased risk of injury. Dietary choices favoring items high in quality protein of animal or plant origin, polyunsaturated fatty acids, fruits and vegetables high in potassium and fiber, and dairy products or other beverages fortified with calcium and vitamin D are essential to athletes to ensure adequate vitamin and mineral availability to the skeleton, which in turn can affect peak physical performance.

Bone Mineral Density and Food-frequency in Korean Adults: The 2008 and 2009 Korea National Health and Nutrition Examination Survey

Background

Diet and Nutrition are important modulators of bone health in men and women. We investigated the associations between frequency of food intake among certain food groups and bone mineral density (BMD) in a large population of Korean adults.

Methods

We used the data from Korea National Health and Nutrition Examination Survey during 2008 to 2009. Participants were aged 20 years and over. BMDs were measured at lumbar spine and femoral neck with dual-energy X-ray absorptiometry. Dietary and supplement intakes were assessed by food-frequency questionnaire. We used multiple linear regression analysis to evaluate the relationships between annual food-frequency of each food group and BMD.

Results

After adjustment of multiple covariates, femoral neck and lumbar BMD significantly increased as the frequency of fruit consumption increased in both men and women. Frequency of other carbohydrates consumption was significantly associated with greater femoral neck and lumbar BMD for women. Frequency of milk and dairy product consumption was significantly associated with greater femoral neck BMD in men. Other food groups, however, had no significant associations with BMDs.

Conclusion

Frequent consumption of fruit has a positive association with BMDs in men and women. Milk and dairy products and other carbohydrates also had positive effects on BMD for men and women, respectively.

Calcium metabolism and correcting calcium deficiencies

Calcium is the most abundant cation in the human body, of which approximately 99% occurs in bone, contributing to its rigidity and strength. Bone also functions as a reservoir of Ca for its role in multiple physiologic and biochemical processes. This article aims to provide a thorough understanding of the absorptive mechanisms and factors affecting these processes to enable one to better appreciate an individual's Ca needs, and to provide a rationale for correcting Ca deficiencies. An overview of Ca requirements and suggested dosing regimens is presented, with discussion of various Ca preparations and potential toxicities of Ca treatment.