The effect of dose, frequency, and timing of protein supplementation on muscle mass in older adults: A systematic review and meta-analysis

Protein supplementation has shown to improve muscle mass in older adults. However, its effect may be influenced by supplementation dose, frequency and timing. This systematic review aimed to assess the effect of dose, frequency and timing of protein supplementation on muscle mass in older adults. Five databases were systematically searched from inception to 14 March 2023, for randomised controlled trials investigating the effect of protein supplementation on muscle mass in adults aged ≥ 65 years. Random effects meta-analyses were performed, stratified by population. Subgroups were created for dose ( ≥ 30 g, < 30 g/day), frequency (once, twice, three times/day) and timing of supplementation (at breakfast, breakfast and lunch, breakfast and dinner, all meals, between meals). Heterogeneity within and between subgroups was assessed using I 2 and Cochran Q statistics respectively. Thirty-eight articles were included describing community-dwelling (28 articles, n = 3204, 74.6 ± 3.4 years, 62.8 % female), hospitalised (8 articles, n = 590, 77.0 ± 3.7 years, 50.3 % female) and institutionalised populations (2 articles, n = 156, 85.7 ± 1.2 years, 71.2 % female). Protein supplementation showed a positive effect on muscle mass in community-dwelling older adults (standardised mean difference 0.116; 95 % confidence interval 0.032 – 0.200 kg, p = 0.007, I 2 = 15.3 %) but the effect did not differ between subgroups of dose, frequency and timing (Q = 0.056, 0.569 and 3.084 respectively, p > 0.05). Data including hospitalised and institutionalised populations were limited. Protein supplementation improves muscle mass in community-dwelling older adults, but its dose, frequency or timing does not significantly influence the effect.


Introduction
Low muscle mass is a diagnostic measure of sarcopenia (Cruz-Jentoft et al., 2019), which is associated with a high risk of falls and fractures (Yeung et al., 2019), dependency in activities of daily living (Wang et al., 2020) and mortality (Xu et al., 2021) in older adults.Muscle mass declines when muscle protein breakdown exceeds muscle protein synthesis (Olaniyan et al., 2020).The decline in muscle mass in older adults, is exacerbated by inadequate protein intake and reduced responsiveness to muscle protein synthesis (Deer and Volpi, 2015).
To maintain and regain muscle mass, older adults require a higher protein intake relative to body weight compared to young adults (Bauer et al., 2013).In older adults, muscle protein synthesis is maximally stimulated by 0.4 ± 0.19 g high-quality protein per kg body weight per meal (Moore et al., 2015).This has led to the hypothesis that an even distribution of protein intake across three main meals is effective in improving muscle mass in older adults (Paddon-Jones and Leidy, 2014).Accordingly, the expert guidelines recommend older adults should have an adequate daily protein intake with at least 25-30 g of high-quality protein per meal to preserve or to improve muscle mass.This recommendation is based on the findings from observational studies and short-term experimental studies with muscle protein synthesis as the outcome measure, (Farsijani et al., 2016;Loenneke et al., 2016;Mamerow et al., 2014), but lacks support from a comprehensive review of literature.Dietary protein intake per meal is often sub-optimal, especially at breakfast and lunch in community-dwelling older adults and at breakfast and dinner in institutionalised older adults (Tieland et al., 2012a).Protein supplementation is frequently recommended for older adults with inadequate protein intake.However, it is unknown if a particular dose, frequency, or timing offer superior benefits on muscle mass gain and therewith support the above recommendation.A systematic review and meta-analysis consolidating the evidence until 2019, showed that protein supplementation significantly improved lean body mass in community-dwelling older adults with some included articles providing simultaneous exercise interventions (Wirth et al., 2020).In a latest systematic review including a mixed population of older adults, protein supplementation was shown to improve appendicular lean mass when coupled with resistant exercises and the effect was not associated with per-meal protein dose (Kirwan et al., 2021).However, the exclusive effect of different doses, frequencies and specific timing of protein supplementation as a strategy to improve muscle mass in different population of older adults is unknown.
This systematic review aimed to assess the effect of dose, frequency, and timing of protein supplementation on muscle mass in older adults, stratified by population.

Search strategy
This review was conducted according to the Preferred Reporting Item for Systematic Reviews and meta-Analyses guidelines (Moher et al., 2009).The search was constructed in consultation with a senior liaison librarian (research and expert searching) from a biomedical university library (Brownless Biomedical Library, Faculty of Medicine, Dentistry & Health Sciences, The University of Melbourne, Victoria, Australia) to address a broad research question and registered with the PROSPERO International Prospective Register of Systematic Reviews (CRD42018111306).The search was updated from a previous systematic review (Martin-Cantero et al., 2020) and adopted to match the PICOS (Participants, Intervention, Comparisons, Outcomes, and Study design) criteria of the present research question (Table 1).A combination of MeSH terms and keywords, such as muscle mass, fat-free mass, lean mass, nutrition, diet and elderly were used.The complete search strategy is shown in Table S1 (Supporting Information).Five electronic databases (MEDLINE, EMBASE, CINAHL, Cochrane Central Register of Controlled Trials and SPORTDiscus) were systematically searched for articles from inception to the 14th of March 2023.

Article selection
After removing duplicates, the articles obtained from the search were independently screened and assessed for eligibility by two assessors (JH, NK or SYT).Disagreements were resolved by a third assessor (EMR).
The inclusion criteria consisted of randomised controlled trials (RCT) published in English language, assessing the effect of protein supplementation on muscle mass with no additional exercise interventions in humans with a mean or median age of 65 years or older.Protein supplementation was defined as the provision of protein additional to the habitual diet (World Health Organization, 2024).The control group was required to have no supplementation or have a placebo product, without additional protein.Articles were included if at least one muscle mass measurement (i.e.appendicular lean mass, lean mass, fat free mass, skeletal muscle mass, muscle cross sectional area) at both baseline and post-intervention or its change in response to the intervention was reported.Articles including exercise interventions other than habitual physical activity/usual care were included only if they had a control group and a separate intervention arm receiving protein supplementation without the exercise intervention.
Exclusion criteria consisted of animal or in vitro studies, populations with genetically inherited muscular diseases (muscular dystrophies or inflammatory myopathies) or with diseases significantly affecting muscle mass (i.e.cancer, Human Immunodeficiency Virus [HIV]/acquired immunodeficiency syndrome [AIDS], chronic kidney diseases) and interventions involving anabolic drug, hormone therapies or neuromuscular electrical stimulation.

Data extraction
Data were extracted independently by two assessors (NK, JH) and conflicts were resolved by a third assessor (EMR).Study characteristics extracted included: first author, year of publication, study population, the sample size of the intervention and control groups (number of participants recruited and included in the analysis), mean, standard deviation (SD) or median, interquartile range (IQR) age of participants, and the number of females in each group.The intervention characteristics extracted included the type of protein intervention and control, dose of protein supplemented (grams) per serving and per day, frequency (times per day), the timing of supplementation relative to mealtimes (between mealtimes, breakfast, lunch, dinner), duration of the intervention, adherence (%) and the baseline protein intake of intervention and control groups.Data extracted on muscle mass measures and the effect of the intervention compared to the control included: instrument [e.g.dualenergy X-ray absorptiometry (DXA)], the measure of muscle mass (e.g.appendicular lean mass), units to express muscle mass (e.g.kg), pre-and post-intervention values with variance (e.g.SD) of the muscle mass measure or their change, mean difference in muscle mass measure from pre-to post-intervention and the statistical significance (p-value).When multiple measures of muscle mass were reported, the measure which best reflects the change in appendicular lean mass were chosen as the majority of the net increase in lean tissue mass often occur in the extremities (Norton et al., 2016).Accordingly, a hierarchy for each instrument was followed.If measured by DXA, appendicular lean mass was extracted over leg lean mass, over total lean mass, over arm lean mass over trunk lean mass.If measured by bioelectrical impedence analysis (BIA), appendicular lean mass was extracted over skeletal muscle mass over total lean mass, over fat free mass.Within a muscle mass measure, absolute measures were chosen over relative measures (i.e. appendicular lean mass in kg, over appendicular lean mass index).

Quality assessment
The quality assessment of articles was performed independently by two assessors (JH, NK), following the Cochrane Risk of Bias Tool (Higgins et al., 2011).Disagreements between authors were discussed with a third assessor (EMR).Articles were graded as low risk, high risk or unclear risk in accordance to seven domains of bias: random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting and other sources of bias.

Data synthesis and meta-analysis
Articles were stratified according to the study population: community-dwelling, hospitalised or institutionalised older adults.Changes in muscle mass (kg) pre-and post-intervention between the intervention and control group were expressed as standardised mean differences (SMD) with 95 % confidence intervals (CI).SMDs were calculated using the mean and SD of the muscle mass pre-and postintervention or mean change in muscle mass and SD for each group or mean difference in change between groups, and the sample size of both the intervention and control groups.When 95 % CIs or standard errors (SE) of the mean were reported, these were converted to SD (Higgins JPT, 2021).Meta-analyses using a random-effects model were performed to determine the effect of protein supplementation on muscle mass and were stratified by population.If a study had multiple intervention arms, such as different protein supplementation (e.g.whey protein and soy protein) or different doses (e.g. to meet an intake of 1.2 g/kg/day and 1.5 g/kg/day), the number of participants in the control arm was equally divided by the number of intervention arms tested (Higgins and Deeks, 2021).with protein supplementation at breakfast.e group with protein supplementation at evening.f whey protein supplementation.g group with soy protein supplementation.h group with whey and soy protein supplementation.i group with protein intake 1.2 g/kg body weight.j group with protein intake 1.5 g/kg body weight.k sample size included in the analysis is not given stratified for intervention and control group.NR: Not reported.NR* Not reported stratified for intervention and control groups, total sample age 65.6 ± 3.2 years.If protein supplementation showed a significant positive effect on muscle mass in a specific population, further analysis was conducted to investigate the effect of dose (< or ≥ median dose of protein supplementation/day), frequency (times/day) and timing of protein supplementation relative to mealtimes.Meta-analyses were performed when more than two studies could be pooled.Articles were excluded if the data on the dose, frequency or timing of supplementation was not reported.
Statistical heterogeneity between articles was evaluated using the Isquared (I 2 ) test and was defined as low (I 2 ≤25 %), moderate (I 2 >25 % and <75 %), or high (I 2 ≥75 %) heterogeneity.The Cochran Q value was used to assess between-group heterogeneity (Higgins et al., 2003).The Z value of the SMD was used to determine which dose, frequency and timing subgroup showed the highest effect size for muscle mass gain by protein supplementation.Sensitivity analysis was performed to determine if the effect of protein supplementation on muscle mass gain was modified by the different types of protein and other ingredients in protein supplementation found to improve muscle mass in older adults namely amino acids and b-hydroxy-b-methylbutyrate (Martin-Cantero et al., 2020).Additional sensitivity analysis was performed to determine if the effect of protein supplementation on muscle mass gain was different in those reported to be healthy, frail or pre-frail and those with sarcopenia.Further sensitivity analysis was performed by including only the articles with low risk of bias to assess if the inclusion of articles with unclear and high risk of bias lead to different findings.Publication bias was visually evaluated by funnel plots showing the SE against the SMD and quantified using the Egger's regression test (Egger et al., 1997).All meta-analyses and publication bias were performed using Comprehensive Meta-Analysis (version 3.3; Biostat Inc., Englewood, NK).All tests were two-tailed and p<0.05 was set as the level of significance.

Results
Fig. 1 shows the PRISMA flow diagram for the selected articles.A total of 17247 articles were identified through the database search.Following the removal of duplicates, 15373 articles were screened for title and abstract and 971 articles were identified for full-text assessment.Thirty-eight articles (38 studies) were included in the systematic review and meta-analysis.
Among institutionalised older adults, one article provided a dose of 20 g/day whey based supplementation, three times/day for 24 weeks (Bjorkman et al., 2012) whereas in the other article a dose of 15.3 g/day soy based supplementation was provided once/ day at the evening for 10 weeks (Fiatarone et al., 1994).Neither of the articles reported baseline protein intake of the participants.

Effect of dose, frequency, and timing of protein supplementation on muscle mass
The meta-analysis on the effect of protein supplementation on muscle mass stratified by population included 38 articles with 3514 participants.Protein supplementation showed a significant positive effect on muscle mass in community-dwelling participants (SMD 0.116; 95 % CI 0.032-0.200kg, p = 0.007, Z-value 3.715, I 2 = 15.3 %).No statistically significant effect was found in hospitalised (SMD 0.063; Muscle mass measures presented as mean ± SD unless otherwise stated.a Change reported as the muscle mass post-intervention minus pre-intervention.b Mean difference defined as the mean change of muscle mass measure in the intervention group minus the mean change of muscle mass measure in the control group.c mean (SE), d median [interquartile range], e mean (95 % CI).f Results for the male and female subgroups were pooled.g % change in FFM.h Calculated according to Janssen et al., 2001(Janssen et al., 2000).i Calculated according to (Studenski et al., 2014).j Calculated as D 2 /Ric (cm 2 /Ω); D -distance between the sensor electrodes, Ric -raw intracellular resistance of calf.k Study has multiple intervention groups.l Results reported for two groups stratified by the level of sarcopenia.m Results reported for two groups stratified by low and normal appendicular skeletal muscle index.
ALM: appendicular lean mass; ASMM: Appendicular skeletal muscle mass; BIA: bioelectrical impedance analysis; BIS: bioimpedance spectroscopy; BMI: Body mass index; CT: computerised tomography; DXA: Dual-energy X-ray absorptiometry; FFM: fat free mass; legMM: leg muscle mass; SMI: skeletal mass index; SMM: skeletal muscle mass; TMA: Thigh-muscle area; TLM: Total lean mass.For consistency in reporting, the terms "muscle mass" and "skeletal muscle" were replaced with the term "lean mass" when agreed with the corresponding body composition instrument used and methods described.

Sensitivity analysis
Sensitivity analysis only including the articles on communitydwelling older adults, showed no effect size differences between the subgroups for the type of protein and other ingredients in protein supplementation found to improve muscle mass in older adults (heterogeneity Q b = 4.053, p = 0.669) (Appendices: Figure B).Additional sensitivity analysis showed no differences in the effect sizes between the subgroups for the health status (Healthy, Frail/ Pre-frail, Sarcopenia) (heterogeneity Q b = 3.90, p = 0.142) (Appendices: Figure C).The metaanalysis including only the articles with low risk of bias showed a positive trend on improving muscle mass by protein supplementation in community-dwelling older adults (SMD 0.162; 95 % CI − 0.001-0.326kg, p = 0.052, Z-value 1.946,I 2 = 38.5 %) and this positive trend was not influenced by the dose, frequency, or timing of protein supplementation.

Publication bias
Visual evaluation of funnel plots revealed non-asymmetry and the Egger regression test indicated no statistically significant publication bias among articles included in all meta-analysis.

Discussion
In community-dwelling older adults, the positive effect of protein supplementation on muscle mass was not found to be significantly influenced by dose, frequency or timing of supplementation.Data was limited in hospitalised and institutionalised older adults.
By including protein supplementations with no restrictions for additional amino acids and other muscle stimulating nutrients, and therewith including nearly three times more articles and participants, our findings showed an improved muscle mass gain by protein supplementation without exercise interventions, which contradicts to the results of a recent meta-analysis.However, findings from both reviews suggest dose and the frequency of protein intervention are not associated with an increase in lean mass in older adults (Kirwan et al., 2021).Similar to our findings, a positive effect of protein supplementation on improving lean body mass independent of the timing of supplementation in community-dwelling older adults was reported in another recent review.However, the majority of the RCTs included in this review had simultaneous exercise interventions and therefore the effect may be modified by exercises (Wirth et al., 2020).Our data have provided evidence that protein supplementation alone has a positive effect on improving muscle mass in community-dwelling older adults  and the effect is not be influenced by dose, frequency or timing of supplementation.
In hospitalised and institutionalised older adults, protein supplementation showed no effect on improving muscle mass, likely due to the limited number of participants included in the meta-analysis.The known effects of acute and chronic disease, high catabolic stress and low physical activity on protein metabolism may also contribute to this negative finding (Degens, 2010;Drummond et al., 2012;Wall et al., 2016;Williams et al., 2012).The recommendation for daily protein intake to maintain muscle mass, vary from 1.0 g/kg in healthy older adults to 2.0 g/kg in older adults with severe illness and injury (Deutz et al., 2014).However, observational data has shown that the average daily dietary protein intakes in community-dwelling, hospitalised and institutionalised older adults are 1.1, 0.65 and 0.8 g/kg of body weight respectively (Tieland et al., 2012a;Weijzen et al., 2020).In this review, the baseline protein intake was reported in only three out of the nine articles in hospitalised and institutionalised participants, which was > 0.8 g/kg body weight.Consequently, with only the absolute dose of protein supplementation reported in majority of the articles, it is unclear if the participants achieved recommended daily protein intake.Additionally, there was high variability in dose (14.7-40 g/day) and duration of supplementation (1.4-54 weeks) between the studies.Therefore, large, well designed RCTs are required to assess the impact of protein supplementation on muscle mass in hospitalised and institutionalised older adults with an emphasis on baseline protein intake, protein supplementation and total protein intake.
A higher daily dose (≥30 g) of protein supplementation was not associated with improvements in muscle mass in community-dwelling older adults, which is in contrast to our hypothesis.Higher doses of protein is needed to stimulate muscle protein synthesis in older adults due to age associated anabolic resistance (Katsanos et al., 2005;Wall et al., 2015) and diminished muscle protein accretion particularly in response to smaller doses of protein (Katsanos et al., 2005).Despite higher doses of protein supplementation, its utilisation in muscle protein synthesis is influenced by multiple factors.Therefore, finding on dose of protein supplementation in this review may be impacted by the high variability in the type of protein interventions, duration of supplementation (6-104 weeks), participants' diverse health status (healthy, sarcopenic, frail) and baseline protein intake exceeding the recommended daily allowance.These factors have previously been associated with difficulty to identify consistent positive effect by additional protein supplementation (Daly and Nowson, 2018), (Martin-Cantero et al., 2020).
No evidence was found in this review that frequency or the timing of protein supplementation influenced greater muscle mass gain in community-dwelling older adults.The current recommendations suggest that an even distribution of protein across three main meals with at least 25-30 g of high-quality protein per meal help improve muscle protein synthesis in older adults (Murphy et al., 2016;Paddon-Jones et al., 2015).Additionally in an RCT designed to supplement breakfast and lunch and thereby achieve ~30 g protein intake at all three meals in community-dwelling older adults, a greater improvement in lean mass in the intervention group was observed compared to the control group (Norton et al., 2016).Furthermore, in large cohorts of community-dwelling older adults, consuming ≥30 g protein, ≥ 2 times/day and an even distribution of protein intake across meals have shown greater positive associations with lean mass (Farsijani et al., 2016;Loenneke et al., 2016).

Strengths and limitations
The strengths of this systematic review include the stratification of protein supplementation by dose, frequency and timing on muscle mass in older adults without potential effect modifications of exercise interventions.However, the high inter-study variability of intervention characteristics such as type and duration of protein supplementation, baseline protein intake and the health status of the participants and the limited number of articles particularly in hospitalised and institutionalised older adults, represent a limitation of this review.The methods used to assess muscle mass were highly variable.However, we tried to account for this with the use of the SMD as the summary statistic, which is recommended by the Cochrane reviews when studies have used different instruments to measure the same construct.Although the muscle mass gain by protein supplementation in community-dwelling older adults was statistically significant in our meta-analysis, if this level of muscle gain lead to improved functional and metabolic outcomes remain to be understood.More than half of the included RCTs were classified as low quality, implying the risk of bias.The majority of the risk of bias is related to the double blinding which is challenging in nutrition intervention trials due to the lack of a suitable placebo and difficulty to control the dietary behaviours.Moreover, the included RCTs were originally designed to assess the effect of protein supplementation on muscle mass, and not specifically to assess the intervention characteristics, which may contribute to less certainty in the conclusions.

Recommendations for future research
The findings on the effect of dose, frequency and timing of protein supplementation need to be confirmed in large RCTs specifically designed to compare different doses, frequencies and timing of supplementation in community-dwelling older adults.Interventions should clearly report the details of protein supplementation including the dose, frequency, timing relative to mealtimes, composition, adherence, baseline protein intake and the per meal dietary protein intake of participants.Large adequately powered RCTs are needed to assess the effect of protein supplementation on muscle mass in hospitalised and institutionalised older adults.

Conclusions
Protein supplementation improved muscle mass in communitydwelling older adults but data were limited in hospitalised and institutionalised older adults.The positive effect on muscle mass by protein supplementation in community-dwelling older adults was not influenced by the dose, frequency or timing of supplementation.or "whey protein" or "amino acid" or "branched chain" or creatin* or fortif* or nourish* or "meal plan" or supplement* or leucine or "protein synthesis") OR (("vitamin d" or epa or dha or hmb or ala or "beta-hydroxy-beta-methylbutyrate" or "eicosapentaenoic acid" or "docosahexaenoic acid" or "alpha-linolenic acid" or casein)).Limiters: English language, publication type: Academic Journal
Figure A.1).The majority of the risk of bias was related to blinding of participants and personnel (18 out of 38 articles; unclear and high risk in 11 and 7 articles respectively) and blinding of outcome assessment (12 out of 38 articles; unclear and high risk in 11 and 1 article respectively) (Appendices: Figure A.2).

Fig. 2 .
Fig. 2. Forest plot showing the effect of protein supplementation on muscle mass in older adults, stratified by the population.

Fig. 3 .
Fig. 3. Forest plot showing the effect of protein supplementation grouped by dose (<30 g/day vs. ≥30 g/day) on muscle mass in community-dwelling older adults.

Fig. 4 .
Fig. 4. Forest plot showing the effect of protein supplementation grouped by frequency (once/day vs. twice/day vs. three times/day) on muscle mass in communitydwelling older adults.

Fig. 5 .
Fig. 5. Forest plot showing the effect of protein supplementation grouped by timing of supplementation relative to mealtimes on muscle mass in community-dwelling older adults (BF: breakfast; L: lunch; D: dinner).
Fig. A2.Summary of review authors' judgements on each risk of bias item for each included article using Cochrane risk of bias tool.

Fig. B1 .
Fig. B1.Forest plot showing the effect of protein supplementation on muscle mass in community-dwelling older adults, stratified by the type of protein and other ingredients in protein supplementation found to improve muscle mass in older adults.The term "Protein" alone is used when the type of protein is not specified.(AA: Amino acids; HMB: b-hydroxy-b-methylbutyrate).

Fig. C1 .
Fig. C1.Forest plot showing the effect of protein supplementation on muscle mass in community-dwelling older adults, stratified by the health status of the participants.

Table 1
PICOS criteria for inclusion and exclusion of articles.

Table 2
Study characteristics of included articles, stratified by the population.

author, year Health status Intervention group Control group N/n a Age, years Female b N/n a Age, years Female b (mean ± SD) n (mean ± SD) n Community-dwelling older adults
c Study has multiple intervention groups.d group

Table 3
Intervention characteristics of the included articles, stratified by population.
(continued on next page) J.Hettiarachchi et al.

Table 4
Muscle mass measures and the effect of the intervention group compared to the control group, stratified by population.

Table 4
(continued ) (old or older or aged) adj (person* or patient* or people or male or female or males or females or men or women or individual* or population)) or elder or geriatric*).mp.[mp=title, abstract, heading word, drug trade name, original title, device manufacturer, drug manufacturer, device trade name, keyword, " or epa or dha or hmb or ala or "beta-hydroxy-beta-methylbutyrate" or "eicosapentaenoic acid" or "docosahexaenoic acid" or "alpha-linolenic acid" or casein).mp.[mp=title, original title, abstract, mesh headings, heading words, keyword] Physical Activity" or workout* or "resistance training" or aerobic or flexibility or "physical rehabilitation" or "physical therapy" or fitness or "physical therapy modalities" or "physical and rehabilitation medicine" or "physical conditioning" or deconditioning or physiotherapy or "training program*" or "weight training" or "weight lift*" or weightlift*).mp.[mp=title, original title, abstract, mesh headings, heading words, keyword] Nutrition* or diet*) adj2 (therapy or supplement* or intervention* or support)) or "whey protein" or "amino acid" or "branched chain" or creatin* or fortif* or nourish* or "meal plan" or supplement* or leucine or "protein synthesis").mp.[mp=title, original title, abstract, mesh headings, heading words, keyword] (old or older or aged) adj (person* or patient* or people or male or female or males or females or men or women or individual* or population)) or elder or geriatric*).mp.[mp=title, original title, abstract, mesh headings, heading words, keyword] or muscles or muscular) N1 (mass or weakness or weak or atroph* or hypertroph* or wasting or wasted or sarcopeni*)) OR ("fat free mass" or "lean body mass" or "lean muscle mass") 28951 2 (((Nutrition* or diet*) N2 (therapy or supplement* or intervention* or support)) or "whey protein" or "amino acid" or "branched chain" or creatin* or fortif* or nourish* or "meal plan" or supplement* or leucine or "protein synthesis") OR (("vitamin d" or epa or dha or hmb or ala or "beta-hydroxy-beta-methylbutyrate" or "eicosapentaenoic acid" or "docosahexaenoic acid" or "alpha-linolenic acid" or casein)) 281748 3 (Exercis* or "Physical Activity" or workout* or "resistance training" or aerobic or flexibility or "physical rehabilitation" or "physical therapy" or fitness or "physical therapy modalities" or "physical and rehabilitation medicine" or "physical conditioning" or deconditioning or physiotherapy or "training program*" or "weight training" or "weight lift*" or weightlift*) English language, publication type: Randomised Controlled Trial, Age groups: Aged: 65+ years.Exclude MEDLINE records.33 or muscles or muscular) N1 (mass or weakness or weak or atroph* or hypertroph* or wasting or wasted or sarcopeni*)) OR ("fat free mass" or "lean body mass" or "lean muscle mass") Nutrition* or diet*) N2 (therapy or supplement* or intervention* or support))