The Effect of Dietary Protein Quality, in Particular the Distribution of Animal and Vegetable Proteins, on the Frequency of Sarcopenia Among Lebanese Older Adults

1. Introduction

Sarcopenia is characterized by an uncontrolled loss of skeletal muscle mass and muscle strength with aging. It may start as early as the 4th decade of life, and the decline can reach up to 50% by the 8th decade of an individual’s life [1]. The consequences of this pathological change are numerous, and are often associated with an increased risk of fractures and frailty, which can in turn contribute to functional impairment and disability and many other profound health outcomes [2,3,4]. Ultimately, sarcopenia increases the risk of mortality among older people. Numerous factors have been linked to the development of sarcopenia, including unfavourable genetics and heredity, lack of physical activity, low dietary intake of protein [5], and subclinical inflammation inducing insulin and anabolic resistance [6].

Since skeletal muscle mass declines in older adults, higher protein intake is proposed to preserve protein balance [7], i.e., the balance between protein synthesis rate and protein degradation rate, to maintain muscle mass and consequently to prevent the development of sarcopenia [7]. It is acknowledged that dietary animal protein contains higher levels of essential amino acids than dietary vegetable protein sources, which may support muscle protein synthesis [8]. Furthermore, the profile of essential amino acid content in animal proteins meets human requirements, whereas plant proteins are deficient in one or more essential amino acids. For example, cereals are low in lysine relative to human requirements, and legumes are deficient in sulphur-containing amino acids. It should be noted however that deficiencies in essential amino acids found in plant proteins can be overcome by using blends of plant proteins, with one protein compensating for the deficiencies in essential amino acids found in the other, and vice versa.

Nevertheless, there is no clear evidence to propose that protein or amino acid supplementation increase muscle mass and muscle strength in healthy older adults [9,10]. Besides, the association between protein intake and muscle mass in older adults yields inconsistent results. Although it has been shown that consuming animal and mix plant proteins increases muscle mass [11], other studies have reached conflicting conclusions particularly when these proteins were combined with resistance training [12,13].

Animal protein was shown to be more effective in preserving skeletal muscle mass than plant proteins. Previous studies have revealed that subjects with a high intake of animal proteins have a higher muscle mass, lower risks of functional impairment and greater maintenance of grip strength in adults over the age of 50 years [14,15]. Daly et al. have shown that a diet enriched with lean red meat is capable of considerably improving total body and leg lean tissue mass and leg muscle strength in older women [16]. Furthermore, Korat et al. findings pointed out that plant protein intake was associated to higher possibility of healthy aging [17]. A recent systematic review and dose-response meta- analysis of prospective cohort studies indicated that a better consumption of total and plant protein was correlated with decrease risk of frailty in older individuals [18]. However, a recent study has shown that a lacto-ovo-vegetarian diet, consisting mainly of vegetables, dairy products and eggs, had no effect on muscle mass and strength in older men, nor in those following a diet that included beef, during a 12-week program of strength training [19].

To avoid the controversy, it is important to observe the association between dietary protein, particularly the effect of animal protein and plant protein, and muscle mass among the Lebanese older population, since to our knowledge, such studies have not been examined or published before. Compared with populations in which animal-derived protein constitutes a larger proportion of dietary protein, Lebanese older adults may obtain a considerable proportion of their protein from plant-based sources, including legumes and cereals. Although plant proteins contribute considerably to overall protein intake, differences in essential amino acid composition, leucine content and digestibility may influence their capacity to stimulate muscle protein synthesis. Thus, the aim of this study was to evaluate the relationship between dietary protein intake, in particular the distribution of animal and vegetable proteins, and skeletal muscle mass and thus on the development of sarcopenia in Lebanese older adults.

2. Methods

2.1. Design and Participants

This study was a cross-sectional study among sarcopenic and non-sarcopenic older adults. A total of 162 older adults aged >60 years recruited from Saint Charles Hospital and its affiliated geriatric center between June and October 2025 were encouraged to take part in the research. Skeletal muscle mass was estimated by bioelectrical impedance analysis (BIA) (Tanita MC-780 MA). Skeletal muscle mass index was calculated as skeletal muscle mass/ height ², and the sarcopenia cut-off thresholds taken were 7.26 kg/m² for males and 5.45 kg/m² for females [20]. Subjects were included if they are more than 60 years old and, sarcopenic (for the sarcopenic group) and could carry out the required tests, anthropometric measurements as well as the Food Frequency Questionnaire (FFQ). Potential participants were excluded if they present severe cognitive impairment and/or severe dysfunction of heart, liver, and kidney [14]. Informed consent was obtained from all subjects involved in the study. Study procedures were completed in agreement with the Declaration of Helsinki ethical principles for medical research involving human subjects. All protocols were approved by the Ethics Committee of Saint Charles Hospital, Lebanon.

2.2. Minimum Sample Size

Sample size calculation was considered to achieve the main objective of the study. The minimum sample size required to detect an effect size of 0.5 between the sarcopenic and non-sarcopenic older adults, a power of 80%, and a significance level of 0.05 is 75 subjects per group. Thus, the minimum sample size needed is 128 subjects. The calculation was done using G*Power version 3.0.10.

2.3. Nutritional and Dietary Assessment

Participants were asked to take a food-frequency questionnaire (FFQ) in Arabic language for dietary assessment [21]. Consequently, data of food consumption frequency and estimated quantities were converted into grams per day. The estimation of energy and nutrient intakes were completed using Nutrilog^® 2.3 software. The database of the American University of Beirut was used for the Lebanese food recipes [21]. As for the international food items, the United States Department of Agriculture (USDA) database and the French food composition table CIQUAL were acquired to grant the necessary nutrient values [22,23]. Vegetable proteins included legumes such as beans, lentils, chickpeas, and green peas as well as nuts, cereals and seeds. Animal proteins included meat, poultry, fish, eggs and dairy. Personal interviews were performed to collect data on demographic characteristics, lifestyles, previous medical history as well as medication use for all the subjects. Participants were also asked about their use of nutritional supplements and their type, i.e.: vitamin D, calcium, omega-3 polyunsaturated fatty acids, multivitamin, etc.

2.4. Strength Assessment

Hand grip strength and Short Physical Performance Battery (SPPB) were used to assess physical function and muscle performance for all the participants. Hand grip strength was measured in the dominant hand with a Martin vigorimeter (Martin; Elmed, Addison, IL, USA), and the force was stated in kilograms [24]. The thresholds taken for low muscle strength were less than 27 kg for men and less than 16 kg for women. Physical performance was assessed using the gait speed (time to walk a distance of 6 meters) and the chair stand test (time to stand up from a chair 5 times without suing arms). Low physical performance was identified as a 5-time sit-to-stand-test time ≥ 20 seconds or a 6-meter gait speed < 0.8 m/s.

2.5. Statistical Analysis

The SPSS software version 27 was used for the statistical analysis. The Chi-2 test was used to compare two categorical variables, with the effect size estimated using Cramer’s V. The independent samples t test was used to compare two means, with the effect size estimated using Cohen’s d. A logistic regression was conducted afterwards to assess factors associated with the presence/absence of sarcopenia; variables entered in the model were those that showed a p < 0.25 in the bivariate analysis [25]. P < 0.05 was deemed statistically significant.

3. Results

Participants with sarcopenia had significantly lower mean skeletal muscle mass percentage, hand grip strength, SPPB scores, and animal and vegetable protein intakes than those without sarcopenia (Table 1).

The correlation matrix assessing factors associated with the total, animal and vegetable protein intake showed that higher handgrip strength was significantly associated with more animal protein intake, whereas higher SPPB scores were significantly but weakly associated with the total, animal and vegetable protein intake (Table 2).

Multivariable Analysis

The results of the logistic regression showed that a higher skeletal muscle mass percentage (aOR = 0.77), a higher SPPB (aOR = 0.51), and a higher animal (aOR = 0.84) and vegetable (aOR = 0.86) protein intake were significantly associated with lower odds of having sarcopenia (Table 3).

To account for potential confounding factors, all multivariate analyses were adjusted for gender, smoking status, physical activity level, diabetes mellitus, cardiovascular disease (CVD), and hypertension. After adjustment for these covariates, the observed associations remained statistically significant, indicating that the relationship between the exposure and the outcome was independent of differences in these demographic, lifestyle and clinical characteristics.

4. Discussion

The present study investigated the association between dietary protein quality and sarcopenia among Lebanese older adults. Our findings suggest that protein intake from both animal and plant sources were associated with the maintenance of muscle mass, muscle function, and physical performance in older adults. Therefore, protein intake contributes to the prevention and management of sarcopenia through their roles in maintaining skeletal muscle mass and function. However, the evidence indicated that animal protein exerts a slight greater positive effect on muscle mass preservation compared to plant-based protein sources.

McCann et al. [26] in their recent systematic review and meta- analysis of randomized controlled trials reported that animal protein resulted in greater increase in muscle mass than plant protein. The advantage of animal protein was seen when compared with non-soy plant proteins and plant based dietary interventions [26]. In contrast, no significant differences were shown for muscle strength or physical performance outcomes. These findings suggest that protein source may be important for maintaining or increasing muscle mass and thus improving muscle function [26]. Furthermore, the trend observed in this study, i.e., that animal proteins appear to have more beneficial effects on muscle mass, is consistent with recent meta-analyses showing that the consumption of animal proteins leads to greater gains in lean body mass than that of plant proteins [27,28]. This advantage has largely been attributed to higher digestibility and more favorable essential amino acid profile, in particular the leucine content, which plays a central role in stimulating muscle protein synthesis [26,28,29]. Animal-derived protein such as whey, milk, eggs, meat, chicken and fish normally provide complete amino acid profile than most plant protein [26]. In addition, evidence from observational studies and randomized controlled trials support this hypothesis. For example, Houston et al. [30] demonstrated that higher total protein intake was associated with reduced lean mass loss over a three-year period in older adults. Similarly, research by Daly et al. [16] found that combining resistance training with higher consumption of lean red meat significantly increase muscle mass and strength in elderly women.

This study has several implications for clinical practice. Older adults at risk of sarcopenia may benefit from prioritizing high quality protein sources with rich essential amino acid profile. While animal proteins appear to provide a better anabolic stimulus [31,32], plant-based diet have also demonstrated comparable effects to some animal proteins, especially when consumed in sufficient quantities and combined with resistance exercise [28,33]. Plant-based proteins offer several nutritional and health advantages, and may be less effective on a gram-for-gram basis for stimulating muscle protein synthesis [34]. Many plant proteins contain lower concentrations of one or more essential amino acids. For instance, cereals are often limited in lysine, while legumes may contain lower amounts of methionine [34]. These limitations can reduce the anabolic response compared with animal protein sources. However, the strategic combination of complementary plant proteins, such as legumes and grains, can improve amino acid balance and overall protein. Further research should also investigate the effects of emerging plant protein sources with protein combinations, and long-term clinical outcomes should be considered in sarcopenic older adults.

The results of the present study have important clinical implications for the prevention and management of sarcopenia among older adults. Healthcare professionals, including physicians, dietitians, nurses and physiotherapists, should reflect on dietary protein quality in addition to total protein intake when assessing older adults at risk of muscle loss. Evaluating the sources and the allocation of protein between the meals may help classify individuals with suboptimal protein quality and direct them to specific nutritional interventions. Dietitians can encourage the inclusion of high-quality protein sources while promoting complementary plant-protein combinations. Furthermore, combining a high-quality protein intake with resistance exercise could grant greater benefits for preserving muscle mass, muscle strength and physical performance. These strategies may possibly facilitate earlier nutritional intervention and strengthen a comprehensive approach to the prevention and management of sarcopenia in older adults.

The findings of this work should be interpreted considering several limitations. First, dietary intake was assessed using self-reported dietary data, which may be subject to recall and reporting bias. Second, although potential confounding factors such as age, sex, total protein intake, physical activity and comorbidities were considered, residual confounding cannot be completely excluded. Finally, the recruitment of participants from selected Lebanese communities may limit the generalizability of the findings to the broader Lebanese older-adult population.

In conclusion, although both animal and plant proteins contribute to muscle health in older people, current evidence suggests that animal protein has a minor greater positive effect on muscle mass and muscle function, the key components of sarcopenia prevention. This advantage is most likely attributable to its superior amino acid profile and digestibility. Nevertheless, high-quality plant proteins may provide comparable benefits when consumed appropriately, emphasizing the importance of overall protein quality and adequacy rather than protein source alone.