High-Protein Diet and Sarcopenic Obesity Indices in Older Adults Undergoing Resistance Training: A Randomized Controlled Trial

Novotny M¹, Angelov G², Fabbri E³

Introduction

Sarcopenic obesity describes the simultaneous loss of skeletal muscle mass and function alongside an increase in adiposity, a phenotype increasingly recognised as a distinct geriatric syndrome rather than a simple additive combination of sarcopenia and obesity [1,2]. The 2022 ESPEN and EASO consensus statement formalised diagnostic criteria requiring evidence of both impaired muscle function and abnormal body composition, moving the field toward standardised case identification [1]. Global prevalence estimates vary widely by definition and population but converge on a substantial burden among community-dwelling and hospitalised older adults, with figures commonly exceeding 10-15% in adults over 65 years [3]. The clinical relevance of sarcopenic obesity extends beyond cosmetic or metabolic concern: it independently predicts disability, falls, cardiometabolic disease, and mortality, and its two components interact synergistically, with excess fat mass promoting inflammatory infiltration of skeletal muscle and accelerating anabolic resistance [2,4].

Two intervention strategies dominate the management literature: dietary protein augmentation and resistance exercise training. Each independently influences body composition, yet neither alone reliably reverses the sarcopenic obesity phenotype: caloric restriction for weight loss without adequate protein or exercise accelerates lean mass loss, while resistance training without sufficient dietary substrate blunts hypertrophic adaptation [5,6]. This tension is particularly acute in older adults, for whom intentional weight loss is often clinically indicated to reduce cardiometabolic risk yet simultaneously threatens the already reduced muscle reserve that underlies frailty and functional dependence. This has motivated combined-intervention research pairing high-protein diets with structured resistance training as a rational, complementary strategy that targets both arms of the sarcopenic obesity phenotype simultaneously rather than sequentially. This narrative review synthesises the published clinical trial, systematic review, and mechanistic literature addressing this combination in older adults, with attention to muscle mass, muscle strength, fat mass, and physical function as the principal sarcopenic obesity indices.

Methods

This is a narrative review of published randomised controlled trials, systematic reviews and meta-analyses, and mechanistic physiology studies addressing dietary protein intake, resistance exercise, and sarcopenic obesity outcomes in adults aged approximately 60 years and older. Relevant literature was identified through structured searches of PubMed, Europe PMC, and Crossref using combinations of terms including "sarcopenic obesity," "high-protein diet," "resistance training," "muscle protein synthesis," and "older adults." Priority was given to randomised trials directly testing combined diet-exercise interventions, meta-analyses pooling protein supplementation with resistance training, and consensus statements defining diagnostic criteria. Reference lists of identified reviews were hand-searched for additional primary trials. Findings are synthesised thematically rather than through formal quantitative pooling, consistent with a narrative review format.

Epidemiology and Diagnostic Framework

Diagnostic ambiguity has historically hampered sarcopenic obesity research, as trials have used inconsistent thresholds for low muscle mass, low muscle strength, and excess adiposity. The revised European consensus on sarcopenia (EWGSOP2) established muscle strength as the primary case-finding criterion, with muscle quantity or quality confirming diagnosis and physical performance indicating severity [7]. Building on this, the ESPEN-EASO consensus statement proposed a two-step algorithm: screening with body mass index or waist circumference plus a muscle-function or muscle-mass indicator, followed by confirmatory dual-energy X-ray absorptiometry or bioelectrical impedance assessment of fat and lean mass, with staging based on presence of complications (Table 1) [1]. Applying harmonised criteria, pooled prevalence in community-dwelling older adults has been estimated at roughly 11%, rising substantially in populations with obesity or chronic disease, and prevalence differs markedly between Asian and Western cohorts owing to differing body composition thresholds [3,4]. Gait speed, a simple and reproducible physical performance measure, independently predicts survival across large aging cohorts and is widely incorporated into sarcopenic obesity severity staging [8].

Mechanistic Rationale for Combined Intervention

Aging skeletal muscle exhibits "anabolic resistance," a blunted muscle protein synthetic response to a given dose of dietary amino acids or resistance exercise stimulus compared with younger muscle [9]. This phenomenon reflects impaired amino acid transport, reduced mTORC1 signalling sensitivity, and altered splanchnic amino acid extraction, and is exacerbated by physical inactivity and by the low-grade inflammation associated with visceral adiposity [9,2]. Leucine, a branched-chain amino acid, acts as a key trigger of muscle protein synthesis via mTORC1 activation, and older muscle appears to require a higher leucine "threshold" per meal to achieve maximal stimulation [10]. Correspondingly, a moderate serving of high-quality protein (approximately 30 g) maximally stimulates muscle protein synthesis in older adults, whereas smaller doses produce a blunted response relative to younger individuals receiving the same amount [10]. Because typical Western dietary patterns skew protein intake toward the evening meal, redistributing protein more evenly across breakfast, lunch, and dinner appears to enhance 24-hour muscle protein synthesis independent of total daily intake [11,12]. Resistance exercise independently sensitises muscle to the anabolic effect of subsequent protein ingestion for up to 24-48 hours, providing the physiological basis for combining structured resistance training with strategically timed, distributed high-protein feeding [9]. Excess visceral and intramuscular adiposity compounds anabolic resistance through additional pathways, including elevated circulating pro-inflammatory cytokines, ectopic lipid deposition within myofibres, and reduced insulin-mediated amino acid delivery to skeletal muscle, all of which further dampen the muscle protein synthetic response to feeding and exercise in adults with sarcopenic obesity relative to lean older adults [2,4]. This mechanistic interplay explains why weight-loss interventions in older adults with obesity carry a disproportionate risk of accelerating sarcopenia unless muscle-protective strategies, namely adequate protein provision and resistance loading, are deliberately incorporated into the intervention design [5].

Direct trial evidence supports combining dietary protein augmentation with resistance training in older adults, though effect sizes vary by population and protocol (Table 2, Figure 1). A randomised controlled trial in overweight and obese older adults found that a high-protein diet combined with resistance exercise better preserved fat-free mass during a hypocaloric weight-loss intervention than diet or exercise-supported weight loss with standard protein intake, though effects on fat mass were comparable across arms [13]. Structured comparisons of aerobic and resistance exercise during intentional weight loss in obese older adults have shown that resistance training, though not maximising weight loss itself, better preserves lean mass, muscle strength, and physical function than aerobic exercise alone [5,6]. A meta-analysis and meta-regression of protein supplementation trials found that protein supplementation augmented resistance-training-induced gains in fat-free mass and one-repetition-maximum strength across the adult lifespan, with the anabolic benefit plateauing above intakes of roughly 1.6 g/kg/day [14]. An earlier meta-analysis restricted to resistance-training studies similarly found that protein supplementation significantly enhanced training-induced increases in muscle mass and strength, an effect that remained significant when analyses were confined to older adults [15]. Systematic reviews and network meta-analyses focused specifically on sarcopenia and sarcopenic obesity populations have reinforced these findings: protein supplementation combined with resistance exercise programs improves lean mass, handgrip strength, and gait speed more than either resistance exercise or supplementation alone among community-dwelling older adults with sarcopenia [16,17]. Network meta-analyses comparing exercise modalities and nutritional supplementation strategies specifically in sarcopenic obesity populations have similarly ranked combined resistance training plus protein or protein-related supplementation among the most effective interventions for body composition and functional outcomes, ahead of aerobic exercise or nutrition alone [18,19,20]. A recent trial comparing protein supplementation strategies alongside resistance training in healthy elderly adults reported improvements in both body composition and physical function measures, supporting the combined approach across a range of supplement formulations [21]. Adjunctive nutrients such as leucine-enriched whey protein with vitamin D, and beta-hydroxy-beta-methylbutyrate, have shown incremental benefit atop standard protein and resistance training regimens in sarcopenic populations, although evidence quality and effect consistency remain more limited than for total protein intake itself [22,23,24]. A comprehensive review of sarcopenic-obesity-specific nutritional and exercise trials around the age of retirement similarly concluded that combined interventions outperform single-modality approaches for improving both muscle and adiposity indices, albeit with substantial between-study heterogeneity in protein dosing, training intensity, and outcome measurement [25].

trials and meta-analyses [13,14,15,21].

Practical Protein Dosing and Exercise Prescription

Synthesising dose-response findings, expert consensus recommends older adults consume approximately 1.0-1.2 g protein/kg body weight/day, rising to 1.2-1.5 g/kg/day for those undertaking resistance training or recovering from acute illness [26]. Distributing protein across three to four meals, each providing at least 25-30 g of high-quality protein, appears to more effectively stimulate 24-hour muscle protein synthesis than the same total intake concentrated at a single meal [10,11,12]. On the exercise side, position statements recommend progressive resistance training targeting all major muscle groups two to three times weekly, using loads of moderate-to-high intensity (60-80% of one-repetition maximum) progressed over time, alongside multicomponent programs incorporating balance and power training for frailty prevention [27,28]. Practical implementation should account for protein timing relative to the resistance training session, with post-exercise protein feeding capitalising on the exercise-induced sensitisation of muscle to amino acids described above (Figure 2) [9].

Conclusion

Converging evidence from randomised trials, meta-analyses, and mechanistic physiology supports combining a high-protein diet with progressive resistance training as an effective, complementary strategy for improving the muscle mass, strength, adiposity, and physical function indices that define sarcopenic obesity in older adults. While optimal protein dose, distribution pattern, and training prescription continue to be refined, the weight of evidence favours protein intakes of at least 1.2 g/kg/day distributed across meals alongside structured, progressive resistance exercise over either strategy in isolation. Future adequately powered trials using harmonised ESPEN-EASO diagnostic criteria and standardised outcome batteries are needed to clarify which subgroups of older adults with sarcopenic obesity benefit most from this combined approach, and to determine whether adjunctive nutrients such as leucine-enriched whey protein or beta-hydroxy-beta-methylbutyrate meaningfully augment outcomes beyond total protein intake and resistance exercise dose alone. In the interim, clinicians managing older adults with sarcopenic obesity can reasonably prioritise the combination of adequate, well-distributed dietary protein and progressive resistance training as a

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