Aging, protein requirements, and protein turnover

Post-prandial tracer studies of protein and amino acid utilisation: what can they tell us about human amino acid and protein requirements?

Nitrogen balance (NB), the principal methodology used to derive recommendations for human protein and amino acid requirements, has been widely criticised, and calls for increased protein and amino acid requirement recommendations have been made, often on the basis of post-prandial amino acid tracer kinetic studies of muscle protein synthesis, or of amino acid oxidation. This narrative review considers our knowledge of the homeostatic regulation of the FFM throughout the diurnal cycle of feeding and fasting and what can and has been learnt from post-prandial amino acid tracer studies, about amino acid and protein requirements. Within the FFM, muscle mass in well fed weight-stable adults with healthy lifestyles appears fixed at a phenotypic level within a wide range of habitual protein intakes. However homoeostatic regulation occurs in response to variation in habitual protein intake, with adaptive changes in amino acid oxidation which influence the magnitude of diurnal losses and gains of body protein. Post-prandial indicator amino acid oxidation (IAAO) studies have been introduced as an alternative to NB and to the logistically complex 24 h [13C-1] amino acid balance studies, for assessment of protein and amino acid requirements. However, a detailed examination of IAAO studies shows both a lack of concern for homeostatic regulation of amino acid oxidation and  major flaws in their design and analytical interpretation, which seriously constrain their ability to provide reliable values. New ideas and a much more critical approach to existing work is needed if real progress is to be made in the area.

Protein-enriched and anti-inflammatory dietary patterns, healthy lifestyle index and depressive symptoms: A cross-sectional study of 287,945 adults in China

OBJECTIVES

Depressive symptoms have a considerable negative impact on mental health. This study aimed to understand the relationship between the protein-enriched and anti-inflammatory dietary index scores, modified healthy lifestyle index scores (Modified HLIS), and depressive symptoms.

METHODS

This study used convenience sampling to conduct a single-center cross-sectional survey. From January 1, 2015 to December 31, 2020, a total of 287,945 Chinese adults from a health management center of a general hospital completed an online self-reported health questionnaire, which included demographic characteristics, the Dietary Diversity Scale, the Modified Healthy Lifestyle Index Scores and the Patient Health Questionnaire-9.

RESULTS

The higher anti-inflammatory dietary index scores (POR = 0.87; 95 % CI: 0.86-0.87; p < 0.001), moderate modified healthy lifestyle index scores (POR = 0.76; 95 % CI: 0.75-0.78; p < 0.001) and sufficient modified healthy lifestyle index scores (POR = 0.53; 95 % CI: 0.52-0.54; p < 0.001) were negatively associated with depressive symptoms, while the higher protein-enriched dietary index scores (POR = 1.01; 95 % CI: 1.01-1.02; p < 0.001) was positively correlated with depressive symptoms.

CONCLUSIONS

This study demonstrated that protein-enriched and anti-inflammatory dietary index scores, and multiple healthy lifestyles are associated depressive symptoms in adults.

Dietary protein requirements and recommendations for healthy older adults: a critical narrative review of the scientific evidence

Adequate protein intake is essential for the maintenance of whole-body protein mass. Different methodological approaches are used to substantiate the evidence for the current protein recommendations, and it is continuously debated whether older adults require more protein to counteract the age-dependent loss of muscle mass, sarcopenia. Thus, the purpose of this critical narrative review is to outline and discuss differences in the approaches and methodologies assessing the protein requirements and, hence, resulting in controversies in current protein recommendations for healthy older adults. Through a literature search, this narrative review first summarises the historical development of the Food and Agriculture Organization/World Health Organization/United Nations University setting of protein requirements and recommendations for healthy older adults. Hereafter, we describe the various types of studies (epidemiological studies and protein turnover kinetic measurements) and applied methodological approaches founding the basis and the different recommendations with focus on healthy older adults. Finally, we discuss important factors to be considered in future studies to obtain evidence for international agreement on protein requirements and recommendations for healthy older adults. We conclude by proposing future directions to determine 'true' protein requirements and recommendations for healthy older adults.

New Therapeutic Approaches and Biomarkers for Increased Healthspan

Healthcare costs have increased in developing countries over the last few decades, mostly due to the escalation in average life expectancy and the concomitant increase in age-related disorders. To address this issue, widespread research is now being undertaken across the globe with the aim of finding a way of increasing healthy aging. A number of potential interventions have already shown promise, including lifestyle changes and the use of natural products or pharmaceuticals that may delay the onset of diseases associated with the aging process. In parallel, a number of potential biomarkers have already been identified that can be used for assessing risk of developing age-associated disorders and for monitoring response to therapeutic interventions. This review describes the most recent advances towards the goal of achieving healthier aging with fewer disabilities that may lead to enhanced quality of life and reduced healthcare costs around the world.

The Role of Nutrition in Attenuating Age-Related Skeletal Muscle Atrophy

The elderly population is increasing rapidly worldwide, and we are faced with the significant challenge for maintaining or improving physical activity, independence, and quality of life. Sarcopenia, the age-related decline of skeletal muscle mass, is characterized by loss of muscle quantity and quality resulting to a gradual slowing of movement, a decrease in strength and power, elevated risk of fall-related injury, and often frailty. Supplemental, hormonal, and pharmacological approaches have been attempted to attenuate sarcopenia but these have not achieved outstanding results. In this review, we summarize the current knowledge of nutrition-based therapies for counteracting sarcopenia.

The application of stable-isotope tracers to study human musculoskeletal protein turnover: a tale of bag filling and bag enlargement

The nutritional regulation of protein and amino acid balance in human skeletal muscle carried out by the authors with Mike Rennie is reviewed in the context of a simple physiological model for the regulation of the maintenance and growth of skeletal muscle, the "Bag Theory". Beginning in London in the late 1970s the work has involved the use of stable isotopes to probe muscle protein synthesis and breakdown with two basic experimental models, primed-dose continuous tracer infusions combined with muscle biopsies and arterio-venous (A-V) studies across a limb, most often the leg, allowing both protein synthesis and breakdown as well as net balance to be measured. In this way, over a 30 year period, the way in which amino acids and insulin mediate the anabolic effect of a meal has been elaborated in great detail confirming the original concepts of bag filling within the muscle endomysial "bag", which is limited by the "bag" size unless bag enlargement occurs requiring new collagen synthesis. Finally we briefly review some new developments involving ² H₂ O labelling of muscle proteins.

Low Dietary Protein Intakes and Associated Dietary Patterns and Functional Limitations in an Aging Population: A NHANES analysis

OBJECTIVE

To investigate protein intakes across demographic characteristics in relation to dietary patterns and functional outcomes in older adults.

DESIGN

Observational and cross-sectional study.

SETTING

Non-institutionalized participants from the 2005-2014 National Health and Nutrition Examination Survey.

PARTICIPANTS

Data from 11,680 adults were categorized into 51-60 years (n= 4,016), 61-70 years (n=3,854), and 71 years and older (n=3,810) for analysis.

MEASUREMENTS

Adults were stratified by meeting or not meeting the protein recommendation (0.8 g/kg/d) to compare demographics, diet quality with Healthy Eating Index-2015, functional limitations, and other dietary intakes. Dietary recalls were collected using the multiple pass method. Data analyses were weighted to create a nationally-representative sample.

RESULTS

Dietary protein intakes were significantly lower in older age groups, with up to 46% of the oldest adults not meeting the protein intake recommendation. Participants consuming protein below the recommended intake level had significantly poorer diet quality across all age groups (P<0.01), however, overall diet quality was better in older adults. Those not meeting the protein recommendation were more likely to have intakes of other nutrients below recommended levels. Those below the protein recommendation had significantly more functional limitations across all age groups, while grip strength was significantly lower in those over 70 years old.

CONCLUSION

Lower protein intakes, and lower diet quality and physical functioning are related in an aging population. Meeting the protein recommendation was linked to better overall diet quality and may be protective of lean mass; therefore, evaluation of individual characteristics which may affect protein intakes is crucial in supporting older adults to meet their protein needs.

Effect of nutritional supplement combined with exercise intervention on sarcopenia in the elderly: A meta-analysis

OBJECTIVES

This systematic review was conducted to explore whether nutritional supplement can improve the benefits of exercise intervention on sarcopenia in the elderly.

METHODS

Databases, including PubMed, Embase, Cochrane Library, Web of Science, CINAHL, CBM, CNKI, WANFANG, and VIP, were searched. All related papers with randomized controlled trials (RCT) methodology that were included in the databases from inception to 19 July 2016 were selected for the study. The tool "assessing risk of bias" from Cochrane Handbook 5.10 was used to evaluate the quality of included papers. A meta-analysis of eligible studies was performed using Stata12.0. Data that we were unable to convene or merge were subjected to descriptive analysis.

RESULTS

Six trials were included in our study, which included 429 elderly patients with sarcopenia. The overall methodological quality of the trials was moderate. Compared with the exercise group, patients who were given nutritional supplements gained a bigger boost in fat-free mass (standard mean difference (SMD) = 5.78, 95% CI: 5.17 to 6.40, P = 0.000) and muscle mass (SMD = 2.048, 95% CI: 0.907 to 3.189, P = 0.000), as well as showed enhancement of keen extension strength (SMD = 1.08, 95% CI: 0.71 to 1.45, P = 0.000) and usual walk speed (SMD = 0.570, 95% CI: 0.19 to 0.95, P = 0.003).

CONCLUSION

Nutritional supplementation may magnify the effect of exercise intervention on sarcopenia elderly in terms of muscle mass, muscle strength, and physical performance. Inconsistencies were present among research studies. More robust studies are needed to determine the most suitable type of nutrient and target population and to explore the actual role of combined intervention in managing sarcopenia in the elderly.

Design of a randomized trial to determine the optimum protein intake to preserve lean body mass and to optimize response to a promyogenic anabolic agent in older men with physical functional limitation

The dietary protein allowance for older men to maintain lean body mass and muscle strength and to accrue optimal anabolic responses to promyogenic stimuli is poorly characterized. The OPTIMEN trial was designed to assess in older men with moderate physical dysfunction and insufficient habitual protein intake (<recommended dietary allowance, RDA, 0.8g·kg^-1·d^-1) the efficacy of consuming diets containing 163% RDA (1.3g·kg^-1·d^-1) for protein, compared to RDA, to increase lean mass, muscle performance, and physical function. A second aim was to determine whether increasing protein intake to 1.3 versus 0.8g·kg^-1·d^-1 would augment anabolic responses to a promyogenic agent, testosterone. For this randomized, double-blind, placebo-controlled six-month intervention trial, 92 men, 65years or older, with Short Physical Performance Battery scores 3-10, and habitual protein intakes <RDA, were assigned to one of four groups: 100% RDA plus placebo intramuscular injections weekly; 100% RDA plus weekly intramuscular injections of 100mg testosterone enanthate; 163% RDA plus placebo injections; or 163% RDA plus testosterone injections. All participants received portion-controlled packaged meals and group-specific dietary supplements containing either mixtures of casein and whey or carbohydrate, with identical appearance. The primary outcome was change in lean body mass assessed using dual energy X-ray absorptiometry. Secondary outcomes included maximal voluntary strength and power in leg press and chest press exercises, 6-minute walking distance, stair climbing power, and self-reported physical function. Results of the OPTIMEN trial have important implications for dietary protein guidance and policy, and efficacy of promyogenic drugs.

Approved health claims for amino acids in/as food supplements

Food supplements in the European Union (EU) were initially regulated by Directive 2002/46/EC, whereas in 2006, EU adopted the new Regulation on nutrition and health claims made on food – Regulation 1924/2006. Meanwhile, in the United States of America (USA), dietary supplement is defined by the congress of Dietary Supplement Health and Education Act (DSHEA, 1994). Food supplements can be beneficial to the health of consumers, but scientific reviews of the existing data should be made by competent authorities. In Europe, a scientific review is made by European Food and Safety Authority (EFSA), the Panel of Dietetic Products, Nutrition and Allergies (NDA Panel). Amino-acids have been the object of many scientific studies, with many of them showing their implication in health. Amino-acids carry out a big role in many body functions, cells structure, transport and storage of nutrition, leading us to the main aim of this article that is providing data related to amino-acids implication in health benefits, specifically health claims of Arginine (Erection, vascular system, muscle integrity and hematopoesis immune system function, spermatogenesis), Glutamine (intestinal health, supporting glycogen replenishment, increasing cell swelling, immune health, abundance in the body, muscle function), Lysine (cardiovascular system, increase metabolism, bones, body tissue, immune system function). Nevertheless, they don`t take their credit yet and are not properly recognized in medical sciences in Europe, since the health claims of food containing amino-acids are still considered to be not established in terms of cause and effect relationship.

Digestion and Postprandial Metabolism in the Elderly

The elderly are an increasing segment of the population. Despite the rapid gains in medical knowledge and treatments, older adults are more likely to experience chronic illnesses that decrease quality of life and accelerate mortality. Nutrition is a key modifiable lifestyle factor which greatly impacts chronic disease risk. Yet despite the importance of nutrition, relatively little is known of the impact of advancing age on the gastrointestinal function, the digestive responses, and the post-meal metabolic adaptations that occur in response to ingested food. Knowledge of the age-related differences in digestion and metabolism in the elderly is essential to the development of appropriate nutritional recommendations for the maintenance of optimal health and prevention of disease.

Nutritional balance of essential amino acids and carbohydrates of the adult worker honeybee depends on age

Dietary sources of essential amino acids (EAAs) are used for growth, somatic maintenance and reproduction. Eusocial insect workers such as honeybees are sterile, and unlike other animals, their nutritional needs should be largely dictated by somatic demands that arise from their role within the colony. Here, we investigated the extent to which the dietary requirements of adult worker honeybees for EAAs and carbohydrates are affected by behavioural caste using the Geometric Framework for nutrition. The nutritional optimum, or intake target (IT), was determined by confining cohorts of 20 young bees or foragers to liquid diets composed of specific proportions of EAAs and sucrose. The IT of young, queenless bees shifted from a proportion of EAAs-to-carbohydrates (EAA:C) of 1:50 towards 1:75 over a 2-week period, accompanied by a reduced lifespan on diets high in EAAs. Foragers required a diet high in carbohydrates (1:250) and also had low survival on diets high in EAA. Workers exposed to queen mandibular pheromone lived longer on diets high in EAA, even when those diets contained 5× their dietary requirements. Our data show that worker honeybees prioritize their intake of carbohydrates over dietary EAAs, even when overeating EAAs to obtain sufficient carbohydrates results in a shorter lifespan. Thus, our data demonstrate that even when young bees are not nursing brood and foragers are not flying, their nutritional needs shift towards a diet largely composed of carbohydrates when they make the transition from within-hive duties to foraging.

Animal protein intake is associated with higher-level functional capacity in elderly adults: the Ohasama study

OBJECTIVES

To determine the association between protein intake and risk of higher-level functional decline in older community-dwelling adults.

DESIGN

Prospective.

SETTING

Ohasama Town, Japan.

PARTICIPANTS

Residents (N = 1,007; mean age 67.4 ± 5.5) free of functional decline at baseline; follow-up was conducted for 7 years.

MEASUREMENTS

Nutrient and food intakes were determined using a validated 141-item food frequency questionnaire. Participants were divided into quartiles according to intake levels of total, animal, and plant protein. Subscales of the Tokyo Metropolitan Institute of Gerontology Index of Competence subscales were used to assess higher-level functional decline. Logistic regression analysis was used to examine the future risk of higher-level functional decline in relation to protein intake, with lowest protein intake as reference.

RESULTS

During the study period, 24.4% of eligible participants reported declines in higher-level functional capacity. After adjustment for putative confounding factors, men in the highest quartile of animal protein intake had significantly lower risk of higher-level functional decline than those in the lowest quartile (odds ratio (OR) = 0.41, 95% confidence interval (CI) = 0.20-0.83; P for trend .01). These associations were not seen in women (OR = 0.76, 95% CI = 0.41-1.34; P for trend .37). No consistent association was observed between plant protein intake and future higher-level functional decline in either sex.

CONCLUSION

Higher protein, particularly animal protein, was associated with lower risk of decline in higher-level functional capacity in older men. Animal protein intake may be a modifiable indicator for early detection and prevention of higher-level functional decline in elderly adults.

Molecular alterations in proteasomes of rat liver during aging result in altered proteolytic activities

Aging induces alterations of tissue protein homoeostasis. To investigate one of the major systems catalysing intracellular protein degradation we have purified 20S proteasomes from rat liver of young (2 months) and aged (23 months) animals and separated them into three subpopulations containing different types of intermediate proteasomes with standard- and immuno-subunits. The smallest subpopulation ΙΙΙ and the major subpopulation Ι comprised proteasomes containing immuno-subunits β1i and β5i beside small amounts of standard-subunits, whereas proteasomes of subpopulation ΙΙ contained only β5i beside standard-subunits. In favour of a relative increase of the major subpopulation Ι, subpopulation ΙΙ and ΙΙΙ were reduced for about 55 % and 80 %, respectively, in aged rats. Furthermore, in all three 20S proteasome subpopulations from aged animals standard-active site subunits were replaced by immuno-subunits. Overall, this transformation resulted in a relative increase of immuno-subunit-containing proteasomes, paralleled by reduced activity towards short fluorogenic peptide substrates. However, depending on the substrate their hydrolysing activity of long polypeptide substrates was significantly higher or unchanged. Furthermore, our data revealed an altered MHC class I antigen-processing efficiency of 20S proteasomes from liver of aged rats. We therefore suggest that the age-related intramolecular alteration of hepatic proteasomes modifies its cleavage preferences without a general decrease of its activity. Such modifications could have implications on protein homeostasis as well as on MHC class I antigen presentation as part of the immunosenescence process.

Percutaneous endoscopic gastrostomy (PEG) tube feeding of nursing home residents is not associated with improved body composition parameters

OBJECTIVES

To study differences in nutritional status and body composition, by feeding modality, among disabled nursing home residents.

DESIGN

A retrospective chart-review study.

SETTING

A nursing wing of a public urban geriatric center.

PARTICIPANTS

Three groups of patients: non-dysphagic, orally-fed dysphagic and percutaneous endoscopic gastrostomy -fed dysphagic patients.

INTERVENTION

Standard nursing care.

MEASUREMENTS

Basal metabolic rate, total energy expenditure and nitrogen balance under oral or percutaneous endoscopic gastrostomy feeding. Dietary intake was assessed during a 3-days period by daily-food intake protocols and a 24-hours urinary creatinine excretion to detect nitrogen balance and calculate body composition parameters.

RESULTS

Data of 117 patients (55.5% females), mean age 84.6±7.5 (range 66-98 years) was analyzed. Dysphagic patients (60) differed from non-dysphagic patients (57) by lower body mass index (p=0.020), fat mass index (p=0.017), daily protein intake (p<0.0001), daily energy intake (p<0.001), protein related energy intake (p<0.001) and a negative nitrogen balance (p<0.001). In regression analyses, dysphagia was associated with increased risk of having a body mass index lower than 22.0kg/m2 (OR=2.60, 95% CI 1.135-5.943), a negative nitrogen balance (OR=2.33, 95% CI 1.063-4.669), a low fat mass index (OR=2.53, 95% CI 1.066-6.007), and low daily protein and energy intakes per body weight (OR=2.87, 95% CI 1.316-6.268 and OR=2.99, 95% CI 1.297-6.880). Compared with orally-fed dysphagic patients (21pts.), percutaneous endoscopic gastrostomy -fed patients (39pts.) received an additional mean energy intake of 30.5% kcal per day and mean protein intake of 26.0%. This additional intake was not associated with improved body composition parameters (such as fat free mass, skeletal mass or body mass index).

CONCLUSION

Dysphagic nursing home residents are characterized by worse nutritional, metabolic and body composition parameters, compared with non-dysphagic residents. Body composition parameters did not differ between orally-fed and percutaneous endoscopic gastrostomy-fed dysphagic patients, despite significantly better nutritional and metabolic parameters in PEG-fed patients. Other approaches (perhaps physical training, pharmacological etc.) should be sought to improve body composition of such patients.

Age and sex affect protein metabolism at protein intakes that span the range of adequacy: comparison of leucine kinetics and nitrogen balance data

Research suggests that changes in leucine oxidation (leuox) with feeding may reflect adult protein requirements. We evaluated this possibility by assessing the effects of age, sex, and different protein intakes on whole-body leucine kinetics and nitrogen balance. Thirty-four young (n=18, 22-46 years) and old (n=16, 63-81 years) men and women completed three 18-day trials with protein intakes of 0.50, 0.75 and 1.00 g protein·kg body weight(-1)·d(-1). Fasting and fed-state leucine kinetics were quantified on day 12 of each trial using a primed, constant infusion of L-[1-13C]leucine. Protein requirement was estimated using classical nitrogen balance measurements and calculations. Leucine kinetics parameters were influenced by age and sex across all protein intakes. With feeding, leuox increased more in old vs. young adults. Independent of age, fasting and fed-state leuox were lower, and net leucine balance (fasting+fed-state) was higher in women vs. men. Among all subjects and protein intakes, nitrogen balance was correlated with fed-state leuox (r=0.39), fed-state leucine balance (r=0.60), net leucine balance (r=0.49) and the change in leuox from the fasting to fed state (r=0.49) (P<.05 for all results). At the highest protein intake, the change in leuox with feeding was inversely correlated with protein requirement (r=-0.39). These findings indicate that leucine kinetics, especially leuox, reflect nitrogen balance-based estimates of the need for dietary protein and generally support the view that protein requirement is comparable between young and old adults.

Glutathione redox control of asthma: from molecular mechanisms to therapeutic opportunities

Asthma is a chronic inflammatory disorder of the airways associated with airway hyper-responsiveness and airflow limitation in response to specific triggers. Whereas inflammation is important for tissue regeneration and wound healing, the profound and sustained inflammatory response associated with asthma may result in airway remodeling that involves smooth muscle hypertrophy, epithelial goblet-cell hyperplasia, and permanent deposition of airway extracellular matrix proteins. Although the specific mechanisms responsible for asthma are still being unraveled, free radicals such as reactive oxygen species and reactive nitrogen species are important mediators of airway tissue damage that are increased in subjects with asthma. There is also a growing body of literature implicating disturbances in oxidation/reduction (redox) reactions and impaired antioxidant defenses as a risk factor for asthma development and asthma severity. Ultimately, these redox-related perturbations result in a vicious cycle of airway inflammation and injury that is not always amenable to current asthma therapy, particularly in cases of severe asthma. This review will discuss disruptions of redox signaling and control in asthma with a focus on the thiol, glutathione, and reduced (thiol) form (GSH). First, GSH synthesis, GSH distribution, and GSH function and homeostasis are discussed. We then review the literature related to GSH redox balance in health and asthma, with an emphasis on human studies. Finally, therapeutic opportunities to restore the GSH redox balance in subjects with asthma are discussed.

Nutrition and sarcopenia: evidence for an interaction

Nutritional interventions that might influence sarcopenia, as indicated by literature reporting on sarcopenia per se as well as dynapenia and frailty, are reviewed in relation to potential physiological aetiological factors, i.e. inactivity, anabolic resistance, inflammation, acidosis and vitamin D deficiency. As sarcopenia occurs in physically active and presumably well-nourished populations, it is argued that a simple nutritional aetiology is unlikely and unequivocal evidence for any nutritional influence is extremely limited. Dietary protein is probably the most widely researched nutrient but only for frailty is there one study showing evidence of an aetiological influence and most intervention studies with protein or amino acids have proved ineffective with only a very few exceptions. Fish oil has been shown to attenuate anabolic resistance of muscle protein synthesis in one study. There is limited evidence for a protective influence of antioxidants and inducers of phase 2 proteins on sarcopenia, dynapenia and anabolic resistance in human and animal studies. Also fruit and vegetables may protect against acidosis-induced sarcopenia through their provision of dietary potassium. While severe vitamin D deficiency is associated with dynapenia and sarcopenia, the evidence for a beneficial influence of increasing vitamin D status above the severe deficiency level is limited and controversial, especially in men. On this basis there is insufficient evidence for any more specific nutritional advice than that contained in the general healthy lifestyle–healthy diet message: i.e. avoiding inactivity and low intakes of food energy and nutrients and maintain an active lifestyle with a diet providing a rich supply of fruit and vegetables and frequent oily fish.

Evidence-based dietary guidance and the role of dairy products for appropriate nutrition in the elderly

Food consumption surveys in the elderly come to the general conclusions that most elderly people outside institutions eat reasonably well. There is, however, tremendous variation in health status between older adults. The aging process is complex and influenced not only by factors intrinsic to the individual but also by extrinsic factors. The latter includes nutrition. In the various phases in the aging process, nutritional status and thus appropriate nutrition differ. Undernutrition is a great concern. In community-dwelling people older than 70 years, 5%-10% are undernourished, and for institutionalized elderly, this is up to 30%-65%. The cause is often inappropriate food consumption, and treatment is not always evidence based. National evidence-based dietary guidelines are mainly for healthy elderly people and vary between regions and even between institutes within the same region. To understand these differences, insight is required into the paradigm applied for nutritional science and the designs, selection of the older population, methodology, and endpoints of studies supplying the science behind the guidelines. A European project (Eurecca) compiles and harmonizes dietary guidelines. These activities underpin the need for sound evidence to improve the nutrition of older adults in different health phases. For frail elderly, there is also a plea to take into account results of studies on food satisfaction. First studies in this field show the effectiveness of an adapted social context for meals, appropriate nutritional care, and availability of tasty drinks and foods for selected groups of older adults. Because of the nutrient richness of dairy products and their good taste, these foods are helpful in the diet of healthy as well as frail elderly people. Key teaching points: Most elderly people eat reasonably well. There are, however, large differences in health status between elderly people and therefore also in nutrient requirements. Undernutrition is a main concern. In community-dwelling people older than 70 years, 5%-10% are undernourished, and for institutionalized elderly, this is up to 30%-65%. Evidence-based dietary guidelines are developed mainly for healthy elderly people and vary between regions. Harmonization will improve public health as well as clinical nutritional strategies. Given the nutrient density of dairy products, these products are included in balanced dietary advice for older adults.

Dietary protein and beef consumption predict for markers of muscle mass and nutrition status in older adults

OBJECTIVE

To determine the relationship of beef and protein intake to nutrition status, body composition, strength, and biochemical measures of vitamin and mineral status, inflammation and blood lipids in older adults.

DESIGN

Cross-sectional observational study.

SETTING

State of Ohio, U.S.A.

PARTICIPANTS

142 adults ages 60-88.

MEASUREMENTS

Subjects completed a Diet History Questionnaire, and questionnaires related to nutrition status and activity. Subjects also underwent measurements of body composition and strength, and a subset took part in a blood draw for biochemical measurements.

RESULTS

Beef intake (g/d) was positively correlated to muscle mass measured by mid-arm muscle area (R=0.128, p=0.030). From multiple linear regression analysis, a 1oz/d (~28g/d) increase in beef consumption predicts for a 2.3cm(2) increase in mid-arm muscle area. Beef intake was negatively correlated to total (R=-0.179, p=0.035) and HDL (R=-0.247, p=0.004) cholesterol, and there was no association between beef and LDL-cholesterol, triglycerides, liver enzymes, or inflammatory markers. Protein intake (% of total energy) was positively correlated to nutrition status measured by the Mini Nutrition Assessment (R=0.196, p=0.020), and calf circumference (R=0.190, p=0.024), and these correlations remained when potential confounders were accounted for in multiple linear regression models. Protein intake was also positively correlated with BMI when analyzed with multiple linear regression.

CONCLUSIONS

Beef intake was positively associated with mid-arm muscle area, and protein intake was positively associated with nutrition status, calf circumference, and BMI in older adults. Consuming lean cuts of beef in moderation may be a healthy way in which older adults can increase protein intake, preserve muscle mass and improve nutrition status.

Physiopathological mechanism of sarcopenia

The etiology of sarcopenia is multifactorial but still poorly understood, and the sequelae of this phenomenon represent a major public health issue. Age-related loss of muscle mass can be counteracted by adequate metabolic interventions including nutritional intake and exercise training. Other strategies including changes in daily protein pattern, the speed of protein digestion, or specific amino acid supplementation may be beneficial to improve short-term muscle anabolic response in elderly people. A multimodal approach combining nutrition, exercise, hormones, and specific anabolic drugs may be an innovative treatment for limiting the development of sarcopenia with aging.

Metabotyping of Caenorhabditis elegans and their culture media revealed unique metabolic phenotypes associated to amino acid deficiency and insulin-like signaling

Insulin/IGF-like signaling (IIS) and nutrient sensing are among the most potent regulators of health status and aging. Here, a global view of the metabolic changes in C. elegans with impaired function of IIS represented by daf-2 and daf-16 and the intestinal di- and tripeptide transport pept-1 was generated using (1)H nuclear magnetic resonance spectroscopic analysis of worm extracts and spent culture media. We showed that specific metabolic profiles were significantly associated with each type of mutant. On the basis of the metabonomics data, selected underlying processes were further investigated using proteomic and transcriptomic approaches. The observed changes suggest a decreased activity of the one carbon metabolism in pept-1(lg601) mutants. Higher concentration of branched-chain amino acids (BCAA) and altered transcript levels of genes involved in BCAA metabolism were observed in long-living strains daf-2(e1370) and daf-2(e1370);pept-1(lg601) when compared to wild types and daf-16(m26);daf-2(e1370);pept-1(lg601) C. elegans, suggesting a DAF-16-dependent mechanism.

Middle age is not associated with altered fibrinogen concentration and production in males

Whether ageing is associated with increased fibrinogen concentration and production remains unclear. We measured fibrinogen fractional (FSR) and absolute synthesis (ASR) rates in male volunteers, of either young (mean age: 28 years, range: 22-34) or middle age (mean age: 57 years, range: 38-72), using a leucine-tracer isotope dilution technique. In the middle-age group, neither fibrinogen FSR (20.8 +/- 1.6%/day) nor ASR (1.8 +/- 0.1 g/day), or concentration (274 +/- 15 mg/dl), were different from those of the younger group (FSR: 20.2 +/- 1.4; ASR: 1.7 +/- 0.2; concentration: 265 +/- 8, respectively). Leucine Ra, an index of endogenous proteolysis, was approximately 20% lower in the older than in the younger group (P < 0.02). Thus, middle age in males is not associated with increased fibrinogen concentration and turnover, whereas endogenous protein breakdown in decreased. Factor(s) different from age per se are likely to be involved in the dysfibrinogenemia possibly occurring with ageing. Protein turnover is already reduced in middle-age males.

Energy expenditure and aging

The study of energy expenditure (EE) has deep roots in understanding aging and lifespan in all species. In humans, total EE decreases substantially in advanced age resulting from parallel changes in resting metabolic rate (RMR) and activity EE. For RMR, this reduction appears to be due to a reduction in organ mass and specific metabolic rates of individual tissues. However, these anatomical changes explain very little regarding the decline in activity EE, which is governed by both genetic and environmental sources. The biological control centers for activity EE are closely coupled with body mass fluctuations and seem to originate in the brain. Several candidate neuromodulators may be involved in the age-related reduction of activity EE that include: orexin, agouti-related proteins and dopaminergic pathways. Unfortunately, the existing body of research has primarily focused on how neuromodulators influence weight gain and only a few studies have been performed in aging models. Recent evidence suggests that activity EE has an important role in dictating lifespan and thus places emphasis on future research to uncover the underlying biological mechanisms. The study of EE continues to unlock clues to aging.

Estimation of protein loss from wound fluid in older patients with severe pressure ulcers

OBJECTIVE

Protein loss from wound fluid is usually recognized as one of the factors contributing to the deterioration of the nutritional status in older patients with severe pressure ulcers. We quantified the protein loss owing to pressure ulcers and investigated associations with wound-related factors and nutritional status.

METHODS

This cross-sectional study included 25 patients (>or=60 y) from 10 institutions, with full-thickness pressure ulcers. Wound fluid was collected once after accumulating beneath a film dressing. The amount of protein loss per day was estimated by the volume of wound fluid per hour and the total protein concentration in the wound fluid. Wound evaluations and nutritional assessments were performed. Correlations between variables were obtained using Spearman's rank correlation.

RESULTS

The median age of the patients was 79 y (range 61-100), and median body mass index was 19.6 kg/m(2) (12.2-24.9). The median amount of protein loss was 0.2g/d (0.04-2.1), which corresponded to 0.01 g x kg(-1) x d(-1) (<0.01-0.04) and 0.6% (0.1-13.8) of protein intake. Four wounds characterized as infected or surgically debrided lost 1.5-2.1g of protein per day, which was substantially higher than other wounds lost. Protein loss was correlated with wound severity including area, depth, the wound severity score, and infectious markers (all Ps<0.05), but not with body mass index or arm muscle circumference (P>0.05).

CONCLUSION

The amount of protein loss could be small and thus may not be related directly to nutritional status, although it increased as the wound became more severe.

Leucine: a key amino acid in ageing-associated sarcopenia?

During ageing, a progressive loss of muscle mass has been well described in both man and rodents. This loss of proteins results from an imbalance between protein synthesis and degradation rates. Although some authors have shown a decrease of myofibrillar protein synthesis rates in human volunteers, this imbalance is not clearly apparent when basal rates of protein turnover are measured. A decrease in muscle protein synthesis stimulation was detected nevertheless in ageing rats during the postprandial period, suggesting that the 'meal signal' was altered during ageing. Many results now suggest that aged muscle is less sensitive to the stimulatory effect of amino acids at physiological concentrations but is still able to respond if the increase in aminoacidaemia is sufficiently large. Indeed amino acids play an important role in regulating muscle protein turnover both in vitro and in vivo. At the molecular level, amino acids modulate gene expression. Amino acid response elements have been characterised in the promoter of transcriptional factor CCAAT-enhancer binding protein homologous protein and asparagine synthetase genes. Among amino acids, leucine seems to play the major role in regulating the metabolic function. It inhibits proteolysis and stimulates muscle protein synthesis independently of insulin. Leucine has been shown to act as a real mediator by modulating specifically the activities of intracellular kinases linked to the translation of proteins such as phosphatidylinosinol 3' kinase and mammalian target of rapamycin-70 kDa ribosomal protein S6 (p70S6K) kinases. We recently demonstrated in vitro that protein synthesis of ageing rat muscles becomes resistant to the stimulatory effect of leucine in its physiological concentration range. However, when leucine concentration was increased greatly above its postprandial level, protein synthesis was stimulated normally. Moreover, we studied the effect of meal leucine supplementation on in vivo protein synthesis in adult and ageing rats. Leucine supplementation had no additional effect on muscle protein synthesis in adults but totally restored its stimulation in ageing rats. Whether chronic oral leucine supplementation would be beneficial for maintaining muscle protein mass in elderly men and women remains to be studied.

Physiopathological mechanism of sarcopenia

The aetiology of sarcopenia is multifactorial but still poorly understood while the sequelae of this phenomenon, i.e. loss of independence and metabolic complications, represent a major public health. The most evident metabolic explanation for muscle decline in elderly people is an imbalance between protein synthesis abd breakdown rates but other causes like neurodegenerative processes, reduction in anabolic hormone productions or sensitivity such as insulin, growth and sex hormones, dysregulation of cytokine secretions, modification in the response to inflammatory events, inadequate nutritional intakes and sedentary lifestyle are involved. Consequently, the age-related loss of muscle mass could be counteracted by adequate metabolic interventions including nutritional intakes or exercise training. Recent observations clearly show that changes in quantitative as well as qualitative intakes of dietary protein are able to counteract some pathophysiological processes related to muscle loss progression. Other strategies including changes in daily protein pattern, the speed of protein digestion or specific amino acids supplementation may be beneficial to improve short term muscle anabolic response in elderly people. The beneficial impact of resistance or endurance training on muscle mass and function is highlighted in many studies suggesting that the potential anabolic response to exercise still remains despite a lesser metabolic response to nutrients. Thus a multimodal approach combining nutrition, exercise, hormones, specific anabolic drugs may an innovative treatment for limiting the development of sarcopenia with aging.

Metabolic shifts due to long-term caloric restriction revealed in nonhuman primates

The long-term health benefits of caloric restriction (CR) are well known but the associated molecular mechanisms are poorly understood despite increasing knowledge of transcriptional and related metabolic changes. We report new metabolic insights into long-term CR in nonhuman primates revealed by the holistic inspection of plasma (1)H NMR spectroscopic metabolic and lipoprotein profiles. The results revealed attenuation of aging-dependant alterations of lipoprotein and energy metabolism by CR, noted by relative increase in HDL and reduction in VLDL levels. Metabonomic analysis also revealed animals exhibiting distinct metabolic trajectories from aging that correlated with higher insulin sensitivity. The plasma profiles of insulin-sensitive animals were marked by higher levels of gluconate and acetate suggesting a CR-modulated increase in metabolic flux through the pentose-phosphate pathway. The metabonomic findings, particularly those that parallel improved insulin sensitivity, are consistent with diminished adiposity in CR monkeys despite aging. The metabolic profile and the associated pathways are compatible with our previous findings that CR-induced gene transcriptional changes in tissue suggest the critical regulation of peroxisome proliferator-activated receptors as a key mechanism. The metabolic phenotyping provided in this study can be used to define a reference molecular profile of CR-associated health benefits and longevity in symbiotic superorganisms and man.

Dietary protein requirements of younger and older adults

BACKGROUND

For older men and women, the Estimated Average Requirement (EAR) and Recommended Dietary Allowance (RDA) for protein are not known with confidence. Data from the limited research studies available suggest that the EAR and RDA might be greater than the assumed 0.66 and 0.80 g protein x kg body wt(-1) x d(-1), respectively.

OBJECTIVE

This study assessed the effect of age on the EAR and RDA for protein.

DESIGN

Twenty-three younger (age: 21-46 y; 11 men, 12 women) and 19 older (age: 63-81 y; 8 men, 11 women) persons completed three 18-d trials with protein intakes of 0.50, 0.75, and 1.00 g protein x kg body wt(-1) x d(-1). Nitrogen balance was determined by using data from total nitrogen analyses of duplicate food composites and complete urine and feces collections from days 14 to 17 of each trial. Each subject's protein requirement was estimated by using linear regression of protein intake and nitrogen balance data from all 3 trials and inverse prediction.

RESULTS

The mean (+/- SD) protein requirement was not different between the younger and older subjects: 0.61 +/- 0.14 compared with 0.58 +/- 0.12 g protein x kg body wt(-1) . d(-1). On the basis of individual requirement estimates from the younger and older subjects combined (2.5% trimming from each tail and variation estimated by the bootstrap), an adequate protein allowance for these subjects was calculated to be 0.85 +/- 0.21 g protein x kg body wt(-1) x d(-1).

CONCLUSIONS

These short-term nitrogen balance results suggest that the requirement for total dietary protein is not different for healthy older adults than for younger adults and that the allowance estimate does not differ statistically from the RDA.

Role of dietary protein in the sarcopenia of aging

Sarcopenia is a complex, multifactorial process facilitated by a combination of factors including the adoption of a more sedentary lifestyle and a less than optimal diet. Increasing evidence points to a blunted anabolic response after a mixed nutrient meal as a likely explanation for chronic age-related muscle loss. There is currently insufficient longer-term research with defined health outcomes to specify an optimal value for protein ingestion in elderly individuals. However, there is general agreement that moderately increasing daily protein intake beyond 0.8 g x kg(-1) x d(-1) may enhance muscle protein anabolism and provide a means of reducing the progressive loss of muscle mass with age. The beneficial effects of resistance exercise in aging populations are unequivocal. However, research has not identified a synergistic effect of protein supplementation and resistance exercise in aging populations. There is little evidence that links high protein intakes to increased risk for impaired kidney function in healthy individuals. However, renal function decreases with age, and high protein intake is contraindicated in individuals with renal disease. Assessment of renal function is recommended for older individuals before they adopt a higher-protein diet.

Dietary protein intake is associated with lean mass change in older, community-dwelling adults: the Health, Aging, and Body Composition (Health ABC) Study

BACKGROUND

Dietary surveys suggest that many older, community-dwelling adults consume insufficient dietary protein, which may contribute to the age-related loss of lean mass (LM).

OBJECTIVE

The objective of the study was to determine the association between dietary protein and changes in total LM and nonbone appendicular LM (aLM) in older, community-dwelling men and women.

DESIGN

Dietary protein intake was assessed by using an interviewer-administered 108-item food-frequency questionnaire in men and women aged 70-79 y who were participating in the Health, Aging, and Body Composition study (n=2066). Changes in LM and aLM over 3 y were measured by using dual-energy X-ray absorptiometry. The association between protein intake and 3-y changes in LM and aLM was examined by using multiple linear regression analysis adjusted for potential confounders.

RESULTS

After adjustment for potential confounders, energy-adjusted protein intake was associated with 3-y changes in LM [beta (SE): 8.76 (3.00), P=0.004] and aLM [beta (SE): 5.31 (1.64), P=0.001]. Participants in the highest quintile of protein intake lost approximately 40% less LM and aLM than did those in the lowest quintile of protein intake (x+/-SE: -0.501+/-0.106 kg compared with -0.883+/-0.104 kg for LM; -0.400+/-0.058 kg compared with -0.661+/-0.057 kg for aLM; P for trend<0.01). The associations were attenuated slightly after adjustment for change in fat mass, but the results remained significant.

CONCLUSION

Dietary protein may be a modifiable risk factor for sarcopenia in older adults and should be studied further to determine its effects on preserving LM in this population.

Adequate range for sulfur-containing amino acids and biomarkers for their excess: lessons from enteral and parenteral nutrition

The adequacy range of dietary requirements of specific amino acids in disease states is difficult to determine. In health, several techniques are available allowing rather precise quantification of requirements based on growth of the organism, rises in plasma concentration, or increases in the oxidation of marker amino acids during incremental administration of the amino acid under study. Requirements may not be similar in disease with regard to protein synthesis or with regard to specific functions such as scavenging of reactive oxygen species by compounds including glutathione. Requirements for this purpose can be assessed only when such a function can be measured and related to clinical outcome. There is apparent consensus concerning normal sulfur amino acid (SAA) requirements. WHO recommendations amount to 13 mg/kg per 24 h in healthy adults. This amount is roughly doubled in artificial nutrition regimens. In disease or after trauma, requirements may be altered for methionine, cysteine, and taurine. Although in specific cases of congenital enzyme deficiency, prematurity, or diminished liver function, hypermethionemia or hyperhomocysteinemia may occur, SAA supplementation can be considered safe in amounts exceeding 2-3 times the minimal recommended daily intake. Apart from some very specific indications (e.g., acetaminophen poisoning), the usefulness of SAA supplementation is not yet established. There is a growing body of data pointing out the potential importance of oxidative stress and resulting changes in redox state in numerous diseases including sepsis, chronic inflammation, cancer, AIDS/HIV, and aging. These observations warrant continued attention for the potential role of SAA supplementation. In particular, N-acetylcysteine remains promising for these conditions.

Protein quantity and quality at levels above the RDA improves adult weight loss

Evidence is accumulating that diets with reduced carbohydrates and increased levels of high quality protein are effective for weight loss. These diets appear to provide a metabolic advantage during restricted energy intake that targets increased loss of body fat while reducing loss of lean tissue and stabilizing regulations of blood glucose. We have proposed that the branched-chain amino acid leucine is a key to the metabolic advantage of a higher protein diet because of its unique roles in regulation of muscle protein synthesis, insulin signaling and glucose re-cycling via alanine. These metabolic actions of leucine require plasma and intracellular concentrations to increase above minimum levels maintained by current dietary guidelines and dietary practices in the U.S. Initial findings support use of dietary at levels above 1.5 g/kg . d during weight loss. Further, our research suggests that increased use of high quality protein at breakfast maybe important for the metabolic advantage of a higher protein diet.

Micronutrient requirements in older women

The nutritional requirements of older women is an area of great interest because the extended life expectancy leads to an increase in women living into their 80s, 90s, and longer. The recommended dietary allowances (RDAs) and dietary reference intakes (DRIs) are not specific for women living to advanced ages, and little research has been conducted specifically on the micronutrient needs of elderly women. Older adults are at greater risk for nutritional deficiencies than are younger adults due to physiologic changes associated with aging, acute and chronic illnesses, prescription and over-the-counter medications, financial and social status, and functional decline. Among the significant age-associated changes in nutrient requirements, the need for energy decreases and the requirements for protein increase with age. Among the micronutrients, the significant ones that may be associated with deficiencies in elderly women include vitamin B-12, vitamin A, vitamin C, vitamin D, calcium, iron, zinc, and other trace minerals. In old and very old women, these are micronutrients of interest but there is a great need for research to determine appropriate recommendations. The importance of these selected nutrients and the reasons for the likelihood of deficiency are discussed briefly. However, there is little specific information regarding micronutrient requirements for elderly women. One reason for this is the difficulty in conducting reliable and valid studies due to the heterogeneity of older adults and their unique rate of aging associated with their health status, limited income, disability, and living situation.

Protein Needs of Older Adults Engaged in Resistance Training: A Review

Protein recommendations by some professional organizations for young adults engaged in resistance training (RT) are higher than the recommended dietary allowance (RDA), but recommendations for resistance-training older adults (>50 years old) are not well characterized. Some argue that the current RDA is adequate, but others indicate increased protein needs. Although concerns have been raised about the consequences of high protein intake, protein intake above the RDA in older adults is associated with increased bone-mineral density when calcium intake is adequate and does not appear to compromise renal health in older individuals with normal renal function. Individual protein needs for older adults in RT are likely highly variable according to health and training regimen, but an intake of 1.0–1.3 g · kg−1· day−1should adequately and safely meet the needs of older adults engaged in RT, provided that their energy needs are met.

Nutritional considerations for the older athlete

In this review article, nutritional considerations of the aging athlete are discussed. The focuses of the review include energy, carbohydrate, protein, selected vitamins and minerals, and fluids. Age-associated changes in body composition, resting energy expenditure, and volume and intensity of training, may decrease the need for dietary energy and the intakes of macro- and micronutrients and fluids. The older athlete should monitor nutrient intakes to insure adequacy, especially regarding carbohydrate to promote glucose storage and use as an energy source during exercise, and protein to promote strength-training-induced muscle hypertrophy. Emphasis should also be placed on the dietary intakes of certain micronutrients, as well as the potential need for supplementation of certain vitamins and minerals, including the vitamins B(2), B(6), B(12), D, E, and folate, and the minerals calcium and iron. Age-associated changes in thermoregulation and an increased susceptibility to dehydration underscore the critical importance to the older athlete of adequate fluid intake to sustain health and performance. Nutrition is a tool that the older athlete should use to enhance exercise performance and health.

Optimizing protein intake in aging

PURPOSE OF REVIEW

Our current knowledge on the causes of sarcopenia is still fragmentary. The most evident factors of age-related muscle alterations comprise impairment in protein turnover rate, neurodegenerative processes, reduction in anabolic hormone production and action, dysregulation of cytokine secretions, changes in the response to inflammatory events, sedentary lifestyle and inadequate nutritional intakes. Indeed, nutrition, in particular low protein intakes, may participate in the loss of protein mass during aging. Consequently, numerous studies have focused on the possibility to counteract the age effect on muscle loss by changing the quantity but also the quality of ingested proteins, aiming to optimize protein intake and retention through an improvement in amino acid bioavailability for the muscle tissues.

RECENT FINDINGS

It has long been recognized that numerous dietary parameters, such as the amount of dietary proteins, affect protein metabolism. Recently, new concepts have been developed by testing either different types of protein sources, proteins with various digestion rates, meals with pulse or spread protein-feeding patterns or amino acids with specific anabolic function. This is therefore a new area in which not only quantitative but also qualitative properties of dietary protein are considered as a strategy to limit body protein loss during aging.

SUMMARY

Recent studies have reported sarcopenia to be preventable by using nutritional intervention, but more experimental and clinical evidence is needed to modify the current recommendation in daily protein intake. The new concepts currently developed must be validated using large epidemiological studies in the long term before being applied to the elderly population.

Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle

The nature of the deficit underlying age-related muscle wasting remains controversial. To test whether it could be due to a poor anabolic response to dietary amino acids, we measured the rates of myofibrillar and sarcoplasmic muscle protein synthesis (MPS) in 44 healthy young and old men, of similar body build, after ingesting different amounts of essential amino acids (EAA). Basal rates of MPS were indistinguishable, but the elderly showed less anabolic sensitivity and responsiveness of MPS to EAA, possibly due to decreased intramuscular expression, and activation (phosphorylation) after EAA, of amino acid sensing/signaling proteins (mammalian target of rapamycin, mTOR; p70 S6 kinase, or p70(S6k); eukaryotic initiation factor [eIF]4BP-1; and eIF2B). The effects were independent of insulin signaling since plasma insulin was clamped at basal values. Associated with the anabolic deficits were marked increases in NFkappaB, the inflammation-associated transcription factor. These results demonstrate first, EAA stimulate MPS independently of increased insulin availability; second, in the elderly, a deficit in MPS in the basal state is unlikely; and third, the decreased sensitivity and responsiveness of MPS to EAA, associated with decrements in the expression and activation of components of anabolic signaling pathways, are probably major contributors to the failure of muscle maintenance in the elderly. Countermeasures to maximize muscle maintenance should target these deficits.

Protein and Older Adults

Body composition changes as people get older. One of the noteworthy alterations is the reduction in total body protein. A decrease in skeletal muscle is the most noticeable manifestation of this change but there is also a reduction in other physiologic proteins such as organ tissue, blood components, and immune bodies as well as declines in total body potassium and water. This contributes to impaired wound healing, loss of skin elasticity, and an inability to fight infection. The recommended dietary allowance (RDA) for adults for protein is 0.8 grams of protein per kilogram of body weight. Protein tissue accounts for 30% of whole-body protein turnover but that rate declines to 20% or less by age 70. The result of this phenomenon is that older adults require more protein/kilogram body weight than do younger adults. Recently, it has become clear that the requirement for exogenous protein is at least 1.0 gram/kilogram body weight. Adequate dietary intake of protein may be more difficult for older adults to obtain. Dietary animal protein is the primary source of high biological value protein, iron, vitamin B(12), folic acid, biotin and other essential nutrients. In fact, egg protein is the standard against which all other proteins are compared. Compared to other high-quality protein sources like meat, poultry and seafood, eggs are the least expensive. The importance of dietary protein cannot be underestimated in the diets of older adults; inadequate protein intake contributes to a decrease in reserve capacity, increased skin fragility, decreased immune function, poorer healing, and longer recuperation from illness.

Advancing age and other factors influencing the balance between amino acid requirements and toxicity

As the average human lifespan increases, so does the recognition that advancing age is associated with changes in nutrient intake and requirements as a consequence of biological, social, and pathological factors. Studies show that whereas protein requirements may not differ significantly between younger and older adults, the adaptive mechanisms and responses to nutritional or pathological stressors may differ and alter the balance between requirement and toxicity of specific amino acids (AAs). As an individual gets older, cardiovascular disease and cancer become the leading causes of morbidity and mortality. Advancing age is also associated with changes in appetite, food intake, and physical activity, all of which can influence protein and AA metabolism. The sulfur amino acids (SAAs) methionine and cysteine recently attracted attention because of their pivotal roles in methyl group metabolism and maintenance of the cellular redox state. Methionine, an indispensable AA, is important for methylation reactions and as a precursor for cysteine, which is the rate-limiting AA for glutathione (GSH) synthesis. On one hand, high intake levels or blood concentrations of methionine are associated with adverse consequences such as hyperhomocysteinemia and endothelial dysfunction, which are risk factors for cardiovascular disease. On the other hand, methionine deficiency is reported to lower the threshold of chemical-induced toxicity and play a role in carcinogenesis. Therefore, it is evident that understanding the biological significance of the interrelationship between SAAs, GSH, and methyl group metabolism is key to determining optimal dietary intakes of SAAs in older individuals.

[Preventing dependency in elderly persons: randomized study in the community]

The number of elderly people aged > 85 years will double by the year 2020. Helping the elderly to live independently at home is a major challenge for society. Physical exercise and protein energy intake might both be effective in preventing dependency. This paper describes the organisation of an ongoing study aimed at evaluating the preventive effect of such measures, involving 102 elderly persons randomised into two groups, one receiving preventive measures but not the other. The study organisation was based on representatives and selected workers from associations involved in home assistance for elderly. Their role consisted in recruiting persons for participation in the trial, encouraging them to perform exercises and take dietary supplements, and notifying the research team of all health-related events. This organisation has reached its objectives, even though the supervision of the domestic workers needs to be improved. This network, comprising stable workers (14 years of work experience on average in this study) offers the potential for future research in the community to evaluate preventive measures.