Reduced bone mineral density is not associated with significantly reduced bone quality in men and women practicing long-term calorie restriction with adequate nutrition

The Effects of Different Dietary Patterns on Bone Health

Bone metabolism is a process in which osteoclasts continuously clear old bone and osteoblasts form osteoid and mineralization within basic multicellular units, which are in a dynamic balance. The process of bone metabolism is affected by many factors, including diet. Reasonable dietary patterns play a vital role in the prevention and treatment of bone-related diseases. In recent years, dietary patterns have changed dramatically. With the continuous improvement in the quality of life, high amounts of sugar, fat and protein have become a part of people's daily diets. However, people have gradually realized the importance of a healthy diet, intermittent fasting, calorie restriction, a vegetarian diet, and moderate exercise. Although these dietary patterns have traditionally been considered healthy, their true impact on bone health are still unclear. Studies have found that caloric restriction and a vegetarian diet can reduce bone mass, the negative impact of a high-sugar and high-fat dietary (HSFD) pattern on bone health is far greater than the positive impact of the mechanical load, and the relationship between a high-protein diet (HPD) and bone health remains controversial. Calcium, vitamin D, and dairy products play an important role in preventing bone loss. In this article, we further explore the relationship between different dietary patterns and bone health, and provide a reference for how to choose the appropriate dietary pattern in the future and for how to prevent bone loss caused by long-term poor dietary patterns in children, adolescents, and the elderly. In addition, this review provides dietary references for the clinical treatment of bone-related diseases and suggests that health policy makers should consider dietary measures to prevent and treat bone loss.

Caloric restriction reduces trabecular bone loss during aging and improves bone marrow adipocyte endocrine function in male mice

Introduction

Caloric restriction (CR) is a nutritional intervention that increases life expectancy while lowering the risk for cardio-metabolic disease. Its effects on bone health, however, remain controversial. For instance, CR has been linked to increased accumulation of bone marrow adipose tissue (BMAT) in long bones, a process thought to elicit detrimental effects on bone. Qualitative differences have been reported in BMAT in relation to its specific anatomical localization, subdividing it into physiological and potentially pathological BMAT. We here examine the local impact of CR on bone composition, microstructure and its endocrine profile in the context of aging.

Methods

Young and aged male C57Bl6J mice were subjected to CR for 8 weeks and were compared to age-matched littermates with free food access. We assessed bone microstructure and BMAT by micro-CT, bone fatty acid and transcriptomic profiles, and bone healing.

Results

CR increased tibial BMAT accumulation and adipogenic gene expression. CR also resulted in elevated fatty acid desaturation in the proximal and mid-shaft regions of the tibia, thus more closely resembling the biochemical lipid profile of the distally located, physiological BMAT. In aged mice, CR attenuated trabecular bone loss, suggesting that CR may revert some aspects of age-related bone dysfunction. Cortical bone, however, was decreased in young mice on CR and remained reduced in aged mice, irrespective of dietary intervention. No negative effects of CR on bone regeneration were evident in either young or aged mice.

Discussion

Our findings indicate that the timing of CR is critical and may exert detrimental effects on bone biology if administered during a phase of active skeletal growth. Conversely, CR exerts positive effects on trabecular bone structure in the context of aging, which occurs despite substantial accumulation of BMAT. These data suggest that the endocrine profile of BMAT, rather than its fatty acid composition, contributes to healthy bone maintenance in aged mice.

Adaptive metabolic response to short-term intensive fasting

BACKGROUND & AIMS

Short-term intensive fasting (STIF), known as beego in Chinese phonetic articulation, has been practiced for more than two thousand years. However, the potential risk of STIF and the body's response to the risk have not been adequately evaluated. This study aims to address this issue, focusing on the STIF-triggered metabolic response of the liver and kidney.

METHODS

The STIF procedure in the clinical trial includes a 7-day water-only intensive fasting phase and a 7-day gradual refeeding phase followed by a regular diet. The intensive fasting in humans was assisted with psychological induction. To gain insights not available in the clinical trial, we designed a STIF program for mice that resulted in similar phenotypes seen in humans. Plasma metabolic profiling and examination of gene expression as well as liver and kidney function were performed by omics, molecular, biochemical and flow cytometric analyses. A human cell line model was also used for mechanistic study.

RESULTS

Clinically significant metabolites of fat and protein were found to accumulate during the fasting phase, but they were relieved after gradual refeeding. Metabolomics profiling revealed a universal pattern in the consumption of metabolic intermediates, in which pyruvate and succinate are the two key metabolites during STIF. In the STIF mouse model, the accumulation of metabolites was mostly counteracted by the upregulation of catabolic enzymes in the liver, which was validated in a human cell model. Kidney filtration function was partially affected by STIF but could be recovered by refeeding. STIF also reduced oxidative and inflammatory levels in the liver and kidney. Moreover, STIF improved lipid metabolism in mice with fatty liver without causing accumulation of metabolites after STIF.

CONCLUSIONS

The accumulation of metabolites induced by STIF can be relieved by spontaneous upregulation of catabolic enzymes, suggesting an adaptive and protective metabolic response to STIF stress in the mammalian body.

New Insights into Calorie Restriction Induced Bone Loss

Caloric restriction (CR) is now a popular lifestyle choice due to its ability in experimental animals to improve lifespan, reduce body weight, and lessen oxidative stress. However, more and more emerging evidence suggests this treatment requires careful consideration because of its detrimental effects on the skeletal system. Experimental and clinical studies show that CR can suppress bone growth and raise the risk of fracture, but the specific mechanisms are poorly understood. Reduced mechanical loading has long been thought to be the primary cause of weight loss-induced bone loss from calorie restriction. Despite fat loss in peripheral depots with calorie restriction, bone marrow adipose tissue (BMAT) increases, and this may play a significant role in this pathological process. Here, we update recent advances in our understanding of the effects of CR on the skeleton, the possible pathogenic role of BMAT in CR-induced bone loss, and some strategies to mitigate any potential side effects on the skeletal system.

Dietary interventions and molecular mechanisms for healthy musculoskeletal aging

Over the past decade, extensive efforts have focused on understanding age-associated diseases and how to prolong a healthy lifespan. The induction of dietary protocols such as caloric restriction (CR) and protein restriction (PR) has positively affected a healthy lifespan. These intervention ideas (nutritional protocols) have been the subject of human cohort studies and clinical trials to evaluate their effectiveness in alleviating age-related diseases (such as type II diabetes, cardiovascular disease, obesity, and musculoskeletal fragility) and promoting human longevity. This study summarizes the literature on the nutritional protocols, emphasizing their impacts on bone and muscle biology. In addition, we analyzed several CR studies using Gene Expression Omnibus (GEO) database and identified common transcriptome changes to understand the signaling pathway involved in musculoskeletal tissue. We identified nine novel common genes, out of which five were upregulated (Emc3, Fam134b, Fbxo30, Pip5k1a, and Retsat), and four were downregulated (Gstm2, Per2, Fam78a, and Sel1l3) with CR in muscles. Gene Ontology enrichment analysis revealed that CR regulates several signaling pathways (e.g., circadian gene regulation and rhythm, energy reserve metabolic process, thermogenesis) involved in energy metabolism. In conclusion, this study summarizes the beneficiary role of CR and identifies novel genes and signaling pathways involved in musculoskeletal biology.

Effects of caloric restriction on human physiological, psychological, and behavioral outcomes: highlights from CALERIE phase 2

Caloric restriction (CR) is a strategy that attenuates aging in multiple nonhuman species. The Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) trials are part of a research program aiming to test the effects of CR on aging and longevity biomarkers in humans. Building on CALERIE phase 1, CALERIE phase 2 (CALERIE 2) was the largest study to date to assess sustained CR in healthy humans without obesity. In a 24-month randomized controlled trial comprising 218 participants at baseline, CALERIE 2 showed that moderate CR, 11.9% on average, induced improvements in aging-related biomarkers without adversely affecting psychological or behavioral outcomes. The objectives of this report are to summarize and review the highlights of CALERIE 2 and report previously unpublished results on eating disorder symptoms and cognitive function. This article specifically summarizes the physiological, psychological, aging, behavioral, and safety results of the trial. Also provided are research directions beyond CALERIE 2 that highlight important opportunities to investigate the role of CR in aging, longevity, and health span in humans.

Caloric Intake in Renal Patients: Repercussions on Mineral Metabolism

The aim of this paper is to review current knowledge about how calorie intake influences mineral metabolism focussing on four aspects of major interest for the renal patient: (a) phosphate (P) handling, (b) fibroblast growth factor 23 (FGF23) and calcitriol synthesis and secretion, (c) metabolic bone disease, and (d) vascular calcification (VC). Caloric intake has been shown to modulate P balance in experimental models: high caloric intake promotes P retention, while caloric restriction decreases plasma P concentrations. Synthesis and secretion of the phosphaturic hormone FGF23 is directly influenced by energy intake; a direct correlation between caloric intake and FGF23 plasma concentrations has been shown in animals and humans. Moreover, in vitro, energy availability has been demonstrated to regulate FGF23 synthesis through mechanisms in which the molecular target of rapamycin (mTOR) signalling pathway is involved. Plasma calcitriol concentrations are inversely proportional to caloric intake due to modulation by FGF23 of the enzymes implicated in vitamin D metabolism. The effect of caloric intake on bone is controversial. High caloric intake has been reported to increase bone mass, but the associated changes in adipokines and cytokines may as well be deleterious for bone. Low caloric intake tends to reduce bone mass but also may provide indirect (through modulation of inflammation and insulin regulation) beneficial effects on bone. Finally, while VC has been shown to be exacerbated by diets with high caloric content, the opposite has not been demonstrated with low calorie intake. In conclusion, although prospective studies in humans are needed, when planning caloric intake for a renal patient, it is important to take into consideration the associated changes in mineral metabolism.

Calorie Restriction and Aging in Humans

Calorie restriction (CR), the reduction of dietary intake below energy requirements while maintaining optimal nutrition, is the only known nutritional intervention with the potential to attenuate aging. Evidence from observational, preclinical, and clinical trials suggests the ability to increase life span by 1-5 years with an improvement in health span and quality of life. CR moderates intrinsic processes of aging through cellular and metabolic adaptations and reducing risk for the development of many cardiometabolic diseases. Yet, implementation of CR may require unique considerations for the elderly and other specific populations. The objectives of this review are to summarize the evidence for CR to modify primary and secondary aging; present caveats for implementation in special populations; describe newer, alternative approaches that have comparative effectiveness and fewer deleterious effects; and provide thoughts on the future of this important field of study.

N,N-Dimethlyacetamide Prevents the High-Fat Diet-Induced Increase in Body Weight

Increased body weight caused by visceral fat accumulation is on the rise and is reaching epidemic proportions worldwide. Hence, means and ways to tackle the problem of increased adiposity is of utmost importance. In this work, we report the effect of a water-soluble small molecule N,N-Dimethlyacetamide (DMA) on weight gain and adiposity in vitro and in vivo. To monitor the in vitro effect of DMA on adipogenesis, 3T3-L1 preadipocytes and pluripotent C2C12 cells were differentiated to adipocytes in the presence of DMA (5 mM and 10 mM). Oil red O staining and reverse transcriptase polymerase chain reaction (RT-PCR) were performed to evaluate the differentiation to adipocytes. To study the in vivo effect of DMA on body weight, experiments were done with C57BL/6J male mice (6 weeks old). The mice were randomly assigned to receive either high-fat diet (HFD; 45% fat) or a normal diet (7% fat) and were either intraperitoneally injected with DMA or phosphate-buffered saline (PBS) once a week for 20 weeks. Glucose tolerance test was performed on living mice. Post-experiment, the epididymal and subcutaneous adipose tissue were excised from the sacrificed animal, and histology, RT-PCR and plasma triglyceride assay were performed. DMA had no inhibitory effect on adipocyte differentiation when applied only once. However, sustained treatment with DMA inhibited the adipocyte differentiation in both 3T3-L1 and C2C12 cells, and significantly lowered the expression of adipocyte markers, in particular, fatty acid-binding protein 4 (fabp4). Under HFD, C57BL/6J mice treated with DMA had lower body weight compared with PBS treatment. Moreover, the HFD-induced higher body weight was controlled when the mice were switched from PBS to DMA treatment. Further, the HFD-mediated adipocyte hypertrophy from epididymal and subcutaneous adipose tissue was significantly reduced with DMA treatment. Interestingly, the glucose clearance and triglyceride levels in the plasma were improved in mice when DMA treatment was initiated early. Taken together, our results show that DMA exhibits a clear potential to prevent weight gain and restricts adiposity in response to high-fat feeding.

Genetic background, epigenetic factors and dietary interventions which influence human longevity

Longevity is mainly conditioned by genetic, epigenetic and environmental factors. Different genetic modifications seem to be positively associated to longevity, including SNPs in SIRT1, APOE, FOXO3A, ACE, ATM, NOS1 and NOS2 gene. Epigenetic changes as DNA hyper- and hypo-methylation influence significantly human longevity by activating/deactivating different genes involved in physiological mechanisms. Several studies have confirmed that centenarians have a lower DNA methylation content compared to young subjects, which showed more homogeneously methylated DNA region. Also the up-regulation of miR-21 seems to be more associated with longevity in different populations of long-lived subjects, suggesting its role as potential epigenetic biomarkers. A non-pharmacological treatment that seems to contrast age-related diseases and promote longevity is represented by dietary intervention. It has been evaluated the effects of dietary restriction of both single nutrients or total calories to extend lifespan. However, in daily practice it is very difficult to guarantee adherence/compliance of the subjects to dietary restriction and at the same time avoid dangerous nutritional deficiencies. As consequence, the attention has focused on a variety of substances both drugs and natural compounds able to mime the beneficial effects of caloric restriction, including resveratrol, quercetin, rapamycin, metformin and 2-deoxy-D-glucose.

The effects of calorie restriction, intermittent fasting and vegetarian diets on bone health

Uncountable health care organizations, clinicians, and individuals are striving to prevent obesity and the many chronic medical conditions linked to it by advocating a healthy lifestyle that includes measures such as reducing dietary calorie intake (i.e., calorie restriction = CR and intermittent fasting = IF) or limiting/abolishing animal source foods (i.e., practices termed vegetarianism and veganism). Although these regimens are traditionally considered healthy, their real impact on bone health has yet to be established, and some studies have reported that they have negative effects on bone outcomes. The current work provides an overview of the studies carried out to examine the effect/s of CR, IF and vegetarian/vegan diets on bone health, and, in particular, on bone mineral density (BMD) and fracture risk. Although data on this subject are limited to small studies and there is no information specifically referring to fractures, CR, but not IF, seems to reduce BMD but does not seem to affect bone quality. Vegetarian diets (particularly vegan ones) are associated with significantly lower BMD values with respect to omnivorous ones and could, potentially, increase the risk of fractures. Given these considerations, individuals who decide to follow these diets should be aware of the risk of osteoporosis and of bone fractures and should introduce dietary sources of calcium and Vitamin D and/or supplementation. Future studies examining fracture/osteoporosis incidence in selected populations will be able expand our knowledge about the safety of these diets and the risks linked to them.

Sarcopenic obesity in older adults: aetiology, epidemiology and treatment strategies

The prevalence of obesity in combination with sarcopenia (the age-related loss of muscle mass and strength or physical function) is increasing in adults aged 65 years and older. A major subset of adults over the age of 65 is now classified as having sarcopenic obesity, a high-risk geriatric syndrome predominantly observed in an ageing population that is at risk of synergistic complications from both sarcopenia and obesity. This Review discusses pathways and mechanisms leading to muscle impairment in older adults with obesity. We explore sex-specific hormonal changes, inflammatory pathways and myocellular mechanisms leading to the development of sarcopenic obesity. We discuss the evolution, controversies and challenges in defining sarcopenic obesity and present current body composition modalities used to assess this condition. Epidemiological surveys form the basis of defining its prevalence and consequences beyond comorbidity and mortality. Current treatment strategies, and the evidence supporting them, are outlined, with a focus on calorie restriction, protein supplementation and aerobic and resistance exercises. We also describe weight loss-induced complications in patients with sarcopenic obesity that are relevant to clinical management. Finally, we review novel and potential future therapies including testosterone, selective androgen receptor modulators, myostatin inhibitors, ghrelin analogues, vitamin K and mesenchymal stem cell therapy.

Obesity Interventions for Older Adults: Diet as a Determinant of Physical Function

Throughout the world, a high prevalence of obesity in older populations has created a new phenotype of frailty: the obese, functionally frail older adult. The convergence of the obesity epidemic with global graying will undoubtedly increase the prevalence of this concern. Barriers to treatment include ambiguities about the appropriate level of obesity that should trigger an intervention, due to age-related physiologic changes and a lack of consensus on specific criteria and cutoffs. Moreover, obesity interventions for this population have been limited by concerns about negative effects on lean mass, bone mineral density, and even mortality. However, newly reported approaches for restoring physical function by obesity reduction have shown good short-term efficacy. Because the majority of these interventions have used exercise as part of the treatment, this review focuses specifically on current understanding of the discrete effects of dietary interventions for geriatric obesity with regards to functional outcomes on tests including the Short Physical Performance Battery, the Physical Performance Test, and the Western Ontario and McMaster Universities Osteoarthritis Index. The literature showed roughly equal benefits to function from a weight reduction diet or exercise regimen, although neither modality was as efficacious alone as the 2 combined. Only 1 of 3 studies of protein intake during weight loss showed a positive effect of protein on function, but findings to date are too limited to prove or disprove a protein benefit. We conclude that although diet and exercise should be combined whenever possible, it remains important to further investigate the beneficial and likely unique effects that calorie restriction and/or nutrient modification can provide, particularly for obese and functionally frail older populations.

Effect of alternate day fasting on markers of bone metabolism: An exploratory analysis of a 6-month randomized controlled trial

BACKGROUND

Alternate day fasting (ADF) is a novel diet therapy that reduces body weight, but its effect on bone health remains unknown.

OBJECTIVE

This study examined the impact of ADF versus traditional daily calorie restriction (CR) on markers of bone metabolism in a 6-month randomized controlled trial.

METHODS

Overweight and obese subjects (n = 100) were randomized to 1 of 3 groups for 6 months: 1) ADF (25% energy intake fast day, alternated with 125% intake feast day; 2) CR (75% intake every day); or 3) control (usual intake every day).

RESULTS

Body weight decreased similarly (P < 0.001) by ADF (-7.8±1.2%) and CR (-8.8±1.5%), relative to controls by month 6. Lean mass, total body bone mineral content and total body bone mineral density remained unchanged in all groups. Circulating osteocalcin, bone alkaline phosphatase, and C-terminal telopeptide type I collagen (CTX) did not change in any group. IGF-1 increased (P < 0.01) in the CR group, with no change in the ADF or control group. When the data were sub-analyzed according to menopausal status, there were no differences between premenopausal or postmenopausal women for any marker of bone metabolism.

CONCLUSION

These findings suggest that 6 months of ADF does not have any deleterious impact on markers of bone metabolism in obese adults with moderate weight loss.

Calorie restriction in humans: An update

Calorie restriction (CR), a nutritional intervention of reduced energy intake but with adequate nutrition, has been shown to extend healthspan and lifespan in rodent and primate models. Accumulating data from observational and randomized clinical trials indicate that CR in humans results in some of the same metabolic and molecular adaptations that have been shown to improve health and retard the accumulation of molecular damage in animal models of longevity. In particular, moderate CR in humans ameliorates multiple metabolic and hormonal factors that are implicated in the pathogenesis of type 2 diabetes, cardiovascular diseases, and cancer, the leading causes of morbidity, disability and mortality. In this paper, we will discuss the effects of CR in non-obese humans on these physiological parameters. Special emphasis is committed to recent clinical intervention trials that have investigated the feasibility and effects of CR in young and middle-aged men and women on parameters of energy metabolism and metabolic risk factors of age-associated disease in great detail. Additionally, data from individuals who are either naturally exposed to CR or those who are self-practicing this dietary intervention allows us to speculate on longer-term effects of more severe CR in humans.

Circulating markers of ageing and allostatic load: A slow train coming

Dealing with the growing burden of age-related morbidities is one of the greatest challenges facing modern society. How we age across the lifecourse and how psychosocial and lifestyle factors interplay with the biology of ageing remains to be fully elucidated. Sensitive and specific biomarkers with which to interrogate the biology of the ageing process are sparse. Recent evidence suggests that non-coding RNAs are key determinants of such processes and that these can be used as potential circulatory bio-markers of ageing. They may also provide a mechanism which mediates the spread of allostatic load across the body over time, ultimately reflecting the immunological health and physiological status of tissues and organs. The interplay between exosomal microRNAs and ageing processes is still relatively unexplored, although circulating microRNAs have been linked to the regulation of a range of physiological and pathological processes and offer insight into mechanistic determinants of healthspan.

Effects of obesity treatments on bone mineral density, bone turnover and fracture risk in adults with overweight or obesity

BACKGROUND

New evidence suggests that obesity is deleterious for bone health, and obesity treatments could potentially exacerbate this.

MATERIALS AND METHODS

This narrative review, largely based on recent systematic reviews and meta-analyses, synthesizes the effects on bone of bariatric surgery, weight loss pharmaceuticals and dietary restriction.

RESULTS AND CONCLUSIONS

All three obesity treatments result in statistically significant reductions in hip bone mineral density (BMD) and increases in bone turnover relative to pre-treatment values, with the reductions in hip BMD being strongest for bariatric surgery, notably Roux-en Y gastric bypass (RYGB, 8%-11% of pre-surgical values) and weakest for dietary restriction (1%-1.5% of pre-treatment values). Weight loss pharmaceuticals (orlistat or the glucagon-like peptide-1 receptor agonist, liraglutide) induced no greater changes from pre-treatment values than control, despite greater weight loss. There is suggestive evidence that liraglutide may increase bone mineral content (BMC) - but not BMD - and reduce fracture risk, but more research is required to clarify this. All three obesity treatments have variable effects on spine BMD, probably due to greater measurement error at this site in obesity, suggesting that future research in this field could focus on hip rather than spine BMD. Various mechanisms have been proposed for BMD loss with obesity treatments, notably reduced nutritional intake/absorption and insufficient exercise, and these are potential avenues for protection against bone loss. However, a pressing outstanding question is whether this BMD reduction contributes to increased fracture risk, as has been observed after RYGB, and whether any such increase in fracture risk outweighs the risks of staying obese (unlikely).

Dietary restrictions, bone density, and bone quality

Caloric restriction (CR), protein restriction (PR), and specific amino acid restriction (e.g., methionine restriction (MR)) are different dietary interventions that have been confirmed with regard to their comprehensive benefits to metabolism and health. Based on bone densitometric measurements, weight loss induced by dietary restriction is known to be accompanied by reduced areal bone mineral density, bone mass, and/or bone size, and it is considered harmful to bone health. However, because of technological advancements in bone densitometric instruments (e.g., high-resolution X-ray tomography), dietary restrictions have been found to cause a reduction in bone mass/size rather than volumetric bone mineral density. Furthermore, when considering bone quality, bone health consists of diverse indices that cannot be fully represented by densitometric measurements alone. Indeed, there is evidence that moderate dietary restrictions do not impair intrinsic bone material properties, despite the reduction in whole-bone strength because of a smaller bone size. In the present review, we integrate research evidence from traditional densitometric measurements, metabolic status assays (e.g., energy metabolism, oxidative stresses, and inflammatory responses), and biomaterial analyses to provide revised conclusions regarding the effects of CR, PR, and MR on the skeleton.

Effect of Two-Year Caloric Restriction on Bone Metabolism and Bone Mineral Density in Non-Obese Younger Adults: A Randomized Clinical Trial

Although caloric restriction (CR) could delay biologic aging in humans, it is unclear if this would occur at the cost of significant bone loss. We evaluated the effect of prolonged CR on bone metabolism and bone mineral density (BMD) in healthy younger adults. Two-hundred eighteen non-obese (body mass index [BMI] 25.1 ± 1.7 kg/m(2) ), younger (age 37.9 ± 7.2 years) adults were randomly assigned to 25% CR (CR group, n = 143) or ad libitum (AL group, n = 75) for 2 years. Main outcomes were BMD and markers of bone turnover. Other outcomes included body composition, bone-active hormones, nutrient intake, and physical activity. Body weight (-7.5 ± 0.4 versus 0.1 ± 0.5 kg), fat mass (-5.3 ± 0.3 versus 0.4 ± 0.4 kg), and fat-free mass (-2.2 ± 0.2 versus -0.2 ± 0.2 kg) decreased in the CR group compared with AL (all between group p < 0.001). Compared with AL, the CR group had greater changes in BMD at 24 months: lumbar spine (-0.013 ± 0.003 versus 0.007 ± 0.004 g/cm(2) ; p < 0.001), total hip (-0.017 ± 0.002 versus 0.001 ± 0.003 g/cm(2) ; p < 0.001), and femoral neck (-0.015 ± 0.003 versus -0.005 ± 0.004 g/cm(2) ; p = 0.03). Changes in bone markers were greater at 12 months for C-telopeptide (0.098 ± 0.012 versus 0.025 ± 0.015 μg/L; p < 0.001), tartrate-resistant acid phosphatase (0.4 ± 0.1 versus 0.2 ± 0.1 U/L; p = 0.004), and bone-specific alkaline phosphatase (BSAP) (-1.4 ± 0.4 versus -0.3 ± 0.5 U/L; p = 0.047) but not procollagen type 1 N-propeptide; at 24 months, only BSAP differed between groups (-1.5 ± 0.4 versus 0.9 ± 0.6 U/L; p = 0.001). The CR group had larger increases in 25-hydroxyvitamin D, cortisol, and adiponectin and decreases in leptin and insulin compared with AL. However, parathyroid hormone and IGF-1 levels did not differ between groups. The CR group also had lower levels of physical activity. Multiple regression analyses revealed that body composition, hormones, nutrients, and physical activity changes explained ∼31% of the variance in BMD and bone marker changes in the CR group. Therefore, bone loss at clinically important sites of osteoporotic fractures represents a potential limitation of prolonged CR for extending life span. Further long-term studies are needed to determine if CR-induced bone loss in healthy adults contributes to fracture risk and if bone loss can be prevented with exercise.

Energy restriction and potential energy restriction mimetics

Energy restriction (ER; also known as caloric restriction) is the only nutritional intervention that has repeatedly been shown to increase lifespan in model organisms and may delay ageing in humans. In the present review we discuss current scientific literature on ER and its molecular, metabolic and hormonal effects. Moreover, criteria for the classification of substances that might induce positive ER-like changes without having to reduce energy intake are summarised. Additionally, the putative ER mimetics (ERM) 2-deoxy-d-glucose, metformin, rapamycin, resveratrol, spermidine and lipoic acid and their suggested molecular targets are discussed. While there are reports on these ERM candidates that describe lifespan extension in model organisms, data on longevity-inducing effects in higher organisms such as mice remain controversial or are missing. Furthermore, some of these candidates produce detrimental side effects such as immunosuppression or lactic acidosis, or have not been tested for safety in long-term studies. Up to now, there are no known ERM that could be recommended without limitations for use in humans.

Loss of bone strength in response to exercise-induced weight loss in obese postmenopausal women: results from a pilot study

OBJECTIVE

Exercise-induced weight loss (WL) can lead to decreased areal bone mineral density (aBMD). It is unknown whether this translates into decreased volumetric BMD (vBMD) or bone strength. The purpose of this pilot study was to determine whether exercise-induced WL results in decreased vBMD and bone strength in postmenopausal women.

METHODS

Fourteen subjects participated in a 4-month endurance exercise WL intervention. A weight stable (WS) control group (n=10) was followed for 4 months. Proximal femur aBMD was measured by DXA. Femoral neck vBMD and estimates of bone strength (cross-sectional moment of inertia (CSMI) and section modulus (SM)) were measured by quantitative CT.

RESULTS

Women were 54.6±2.4 years, BMI 32.1±5.9 kg/m(2) and 54.4±2.9 years, BMI 27.9±3.6 kg/m(2) in the WL and WS groups, respectively. The WL group lost 3.0±2.6 kg which was predominately fat mass. There was a significant decrease in SMmax. Changes in CSMImax and total hip aBMD were not significant. Total hip vBMD did not decrease significantly in response to WL. There were no significant changes in the WS group.

CONCLUSIONS

WL may lead to decreased bone strength before changes in BMD are detected. Further studies are needed to determine whether bone-targeted exercise can preserve bone strength during WL.

Benefits of caloric restriction for cardiometabolic health, including type 2 diabetes mellitus risk

In the United States, life expectancy has markedly increased during the past century, and population ageing is expected to double within the next 25 years. The process of ageing in a population is associated with the development of chronic diseases, such as type 2 diabetes mellitus, that can be prevented, and even reversed, with the implementation of healthy lifestyle interventions. The evidence to date, consolidated by the numerous epidemiological studies and clinical trials conducted, suggests that caloric restriction is an effective nutritional intervention for preventing most of these age-related conditions. At a metabolic level, caloric restriction with adequate nutrition has been shown to improve insulin sensitivity, reduce fasting glucose and insulin concentration and prevent obesity, type 2 diabetes, hypertension and chronic inflammation. The purpose of this article is to review current knowledge of the metabolic and clinical implications of caloric restriction with adequate nutrition for the prevention of type 2 diabetes and cardiovascular disease.

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.

Divergent effects of obesity on bone health

Historically, obesity was thought to be advantageous for maintaining healthy bones due to the greater bone mineral density observed in overweight individuals. However, recent observations of increased fracture in some obese individuals have led to concern that common metabolic complications of obesity, such as type 2 diabetes, metabolic syndrome, impaired glucose tolerance, insulin resistance, hyperglycemia, and inflammation may be associated with poor bone health. In support of this hypothesis, greater visceral fat, a hallmark of insulin resistance and metabolic syndrome, is associated with lower bone mineral density. Research is needed to determine if and how visceral fat and/or poor metabolic health are causally associated with bone health. Clinicians should consider adding a marker metabolic health, such as waist circumference or fasting plasma glucose concentration, to other known risk factors for osteoporosis and fracture.

Increased mammalian lifespan and a segmental and tissue-specific slowing of aging after genetic reduction of mTOR expression

We analyzed aging parameters using a mechanistic target of rapamycin (mTOR) hypomorphic mouse model. Mice with two hypomorphic (mTOR(Δ/Δ)) alleles are viable but express mTOR at approximately 25% of wild-type levels. These animals demonstrate reduced mTORC1 and mTORC2 activity and exhibit an approximately 20% increase in median survival. While mTOR(Δ/Δ) mice are smaller than wild-type mice, these animals do not demonstrate any alterations in normalized food intake, glucose homeostasis, or metabolic rate. Consistent with their increased lifespan, mTOR(Δ/Δ) mice exhibited a reduction in a number of aging tissue biomarkers. Functional assessment suggested that, as mTOR(Δ/Δ) mice age, they exhibit a marked functional preservation in many, but not all, organ systems. Thus, in a mammalian model, while reducing mTOR expression markedly increases overall lifespan, it affects the age-dependent decline in tissue and organ function in a segmental fashion.

Forum on bone and skeletal muscle interactions: summary of the proceedings of an ASBMR workshop

Annual costs are enormous for musculoskeletal diseases such as osteoporosis and sarcopenia and for bone and muscle injuries, costing billions annually in health care. Although it is clear that muscle and bone development, growth, and function are connected, and that muscle loads bone, little is known regarding cellular and molecular interactions between these two tissues. A conference supported by the National Institutes of Health (NIH) and the American Society for Bone and Mineral Research (ASBMR) was held in July 2012 to address the enormous burden of musculoskeletal disease. National and international experts in either bone or muscle presented their findings and their novel hypotheses regarding muscle-bone interactions to stimulate the exchange of ideas between these two fields. The immediate goal of the conference was to identify critical research themes that would lead to collaborative research interactions and grant applications focusing on interactions between muscle and bone. The ultimate goal of the meeting was to generate a better understanding of how these two tissues integrate and crosstalk in both health and disease to stimulate new therapeutic strategies to enhance and maintain musculoskeletal health.

Weight loss in obese adults 65years and older: a review of the controversy

Obesity in older adults is ubiquitous in many developed countries and is related to various negative health outcomes, making it an important public health target for intervention. However, treatment approaches for obesity in older adults remain controversial due to concerns surrounding the difficulty of behavior change with advancing age, exacerbating the age-related loss of skeletal muscle and bone, and the feasibility of long-term weight maintenance and related health consequences. This review serves to systematically examine the evidence regarding weight loss interventions with a focus on obese (body mass index 30kg/m(2) and above) older adults (aged 65years and older) and some proposed mechanisms associated with exercise and caloric restriction (lifestyle intervention). Our findings indicate that healthy weight loss in this age group can be achieved through lifestyle interventions of up to a one-year period. Most interventions reviewed reported a loss of lean body mass and bone mineral density with weight loss. Paradoxically muscle quality and physical function improved. Inflammatory molecules and metabolic markers also improved, although the independent and additive effects of exercise and weight loss on these pathways are poorly understood. Using our review inclusion criteria, only one small pilot study investigating long-term weight maintenance and associated health implications was found in the literature. Future research on lifestyle interventions for obese older adults should address the loss of bone and lean body mass, inflammatory mechanisms, and include sufficient follow-up to assess long-term weight maintenance and health outcomes.

Skeletal effects of long-term caloric restriction in rhesus monkeys

Age-related bone loss is well established in humans and is known to occur in nonhuman primates. There is little information, however, on the effect of dietary interventions, such as caloric restriction (CR), on age-related bone loss. This study examined the effects of long-term, moderate CR on skeletal parameters in rhesus monkeys. Thirty adult male rhesus monkeys were subjected to either a restricted (R, n = 15) or control (C, n = 15) diet for 20 years and examined throughout for body composition and biochemical markers of bone turnover. Total body, spine, and radius bone mass and density were assessed by dual-energy X-ray absorptiometry. Assessment of biochemical markers of bone turnover included circulating serum levels of osteocalcin, carboxyterminal telopeptide of type I collagen, cross-linked aminoterminal telopeptide of type I collagen, parathyroid hormone, and 25(OH)vitamin D. Overall, we found that bone mass and density declined over time with generally higher levels in C compared to R animals. Circulating serum markers of bone turnover were not different between C and R with nonsignficant diet-by-time interactions. We believe the lower bone mass in R animals reflects the smaller body size and not pathological osteopenia.

Metabolic and neuropsychiatric effects of calorie restriction and sirtuins

Most living organisms, including humans, age. Over time the ability to do physical and intellectual work deteriorates, and susceptibility to infectious, metabolic, and neurodegenerative diseases increases, which leads to general fitness decline and ultimately to death. Work in model organisms has demonstrated that genetic and environmental manipulations can prevent numerous age-associated diseases, improve health at advanced age, and increase life span. Calorie restriction (CR) (consumption of a diet with fewer calories but containing all the essential nutrients) is the most robust manipulation, genetic or environmental, to extend longevity and improve health parameters in laboratory animals. However, outside of the protected laboratory environment, the effects of CR are much less certain. Understanding the molecular mechanisms of CR may lead to the development of novel therapies to combat diseases of aging and to improve the quality of life. Sirtuins, a family of NAD(+)-dependent enzymes, mediate a number of metabolic and behavioral responses to CR and are intriguing targets for pharmaceutical interventions. We review the molecular understanding of CR; the role of sirtuins in CR; and the effects of sirtuins on physiology, mood, and behavior.

Adiponectin and osteocalcin: relation to insulin sensitivity

Obesity and osteoporosis have grave consequences for human health, quality of life, and even the efficiency of the labor force. Interestingly, these diseases share several features including a genetic predisposition and a common progenitor cell. Recent findings show that high adipocyte count in bone marrow is directly related to bone loss, as fat cells replace osteoblasts resulting in reduced bone mineral density and increased propensity towards osteoporosis. This close relationship has a positive aspect, whereby higher osteocalcin levels results in increased adiponectin production while the presence of adiponectin influences osteoblast proliferation and differentiation in a positive way. We focus on how osteoblasts and adipocytes affect each other and ultimately insulin resistance through the hormones they produce. This approach to whole animal physiology is the main stay of Alternative Medicine. It is assumed that the body is linked together intricately, and treating one is equal to treating the whole body. As we go further into bone and adipocytes physiology, it is evident that these organs affect each other. Therefore, elucidation on the actions of fat on bone and vice versa will unravel the complex mechanism of insulin resistance.

Different effects on bone strength and cell differentiation in pre pubertal caloric restriction versus hypothalamic suppression

Hypothalamic amenorrhea and energy restriction during puberty affect peak bone mass accrual. One hypothesis suggests energy restriction alters hypothalamic function resulting in suppressed estradiol levels leading to bone loss. However, both positive and negative results have been reported regarding energy restriction and bone strength. Therefore, the purpose of this study was to investigate energy restriction and hypothalamic suppression during pubertal onset on bone mechanical strength and the osteogenic capacity of bone marrow-derived cells in two models: female rats treated with gonadotropin releasing hormone antagonists (GnRH-a) or 30% energy restriction. At 23 days of age, female Sprague Dawley rats were assigned to three groups: control group (C, n=10), GnRH-a group (n=10), and Energy Restriction (ER, n=12) group. GnRH-a animals received daily injections for 27 days. The animals in the ER group received 70% of the control animals' intake. After sacrifice (50 days of age), body weight, uterine and muscle weights were measured. Bone marrow-derived stromal cells were cultured and assayed for proliferation and differentiation into osteoblasts. Outcome measures included bone strength, bone histomorphometry and architecture, serum IGF-1 and osteocalcin. GnRH-a suppressed uterine weight, decreased osteoblast proliferation, bone strength, trabecular bone volume and architecture compared to control. Elevated serum IGF-1 and osteocalcin levels and body weight were found. The ER model had an increase in osteoblast proliferation compared to the GnRH-a group, similar bone strength relative to body weight and increased trabecular bone volume in the lumbar spine compared to control. The ER animals were smaller but had developed bone strength sufficient for their size. In contrast, suppressed estradiol via hypothalamic suppression resulted in bone strength deficits and trabecular bone volume loss. In summary, our results support the hypothesis that during periods of nutritional stress the increased vertebral bone volume may be an adaptive mechanism to store mineral which differs from suppressed estradiol resulting from hypothalamic suppression.