The ageing population makes it necessary to find effective strategies for the prevention of sarcopenia (the progressive loss of muscle mass and strength and a decline in physical performance) that can be counteracted with foods containing protein and adequate intake of vitamin D. This study will evaluate the effectiveness of consuming a food based on plant proteins and vitamin D supplementation. Intervention studies in humans conducted to date have mostly focused on the effect of animal proteins (mainly from whey) on disease progression. A study on the effect of pea proteins has not yet been conducted and will provide information on the effectiveness of these proteins in modulating markers linked to the disease. The effect on the gut microbiota will also be considered, as the existence of a gut-muscle axis has been suggested, in which microbial genera producing short-chain fatty acids have been linked to a positive effect on muscle mass through anabolic stimulation. Thus, the analysis of the modulation of the intestinal microbiota, through the dietary intervention proposed in this study, may represent a further step in research related to the prevention of this disease. Sarcopenic volunteers aged between 65 and 80 will be recruited to consume either a shortbread biscuit made with wheat flour enriched with hydrolysed pea protein and a vitamin D supplement in extra virgin olive oil, or a control biscuit and a placebo (extra virgin olive oil) for 12 weeks. The study will be randomised, parallel, single-blind. The effect of consuming the experimental biscuit and vitamin D supplementation compared to that of a traditional control biscuit and a placebo oil solution will be evaluated on certain markers related to sarcopenia. In particular, the following will be considered: muscle strength, measuring grip strength and leg strength (chair stand test); muscle mass through the measurement of appendicular muscle mass, and the calculation of the appendicular muscle mass index; physical performance using the Short Physical Performance Battery; the inflammatory response and other blood biomarkers related to sarcopenia. In addition, the following will be assessed: dietary habits through a food diary and quality of life through the SarQoL questionnaire. Finally, the effect of nutritional intervention on the modulation of the gut microbiota will be evaluated through 16S rRNA sequencing and bioinformatic analysis of the data.

Sarcopenia, characterized by the age-related loss of muscle mass, strength, and physical performance, is a growing public health concern given the global aging population. Physical activity-the standard treatment-is often not feasible for frail or bedridden elderly individuals, highlighting the need for alternative strategies. Nutritional interventions, particularly those involving protein and vitamin D supplementation, have shown promise in managing sarcopenia.

This randomized, single-blind, parallel-design clinical trial aims to evaluate the effect of consuming a shortbread biscuit enriched with hydrolyzed pea protein, combined with a daily dose of vitamin D3 (20 μg/day, 800 IU/day), on muscle mass, muscle strength, physical performance, and gut microbiota composition in sarcopenic individuals aged 65-80 years. The study will enroll 74 participants meeting specific inclusion criteria.

Participants will be randomly assigned to one of two groups:

1. Intervention Group: Receives a 50 g daily portion of a functional biscuit enriched with hydrolyzed pea protein, and 2 drops/day of a vitamin D3 supplement (providing 20 μg/day).
2. Control Group: Receives a similar biscuit without added protein and a placebo oil (extra virgin olive oil) in replace of vitamin D3.

The intervention will last for 12 weeks. Measurements will be taken at baseline, mid-point (6 weeks), and study end (12 weeks), including handgrip strength, chair stand test, bioimpedance-based muscle mass, and SPPB. Blood samples will be analyzed for markers related to inflammation (e.g., CRP, IL-6, TNF-α), oxidative stress (oxLDL), anabolic signaling (IGF-1), and vitamin D status (25-hydroxycholecalciferol), among others. Gut microbiota composition and short-chain fatty acid (SCFA) production will be assessed via stool sample analysis and 16S rRNA sequencing.

Participants will also complete quality-of-life (SarQoL) and food frequency questionnaires, along with 3-day dietary diaries at each time point. Compliance will be monitored via dietary diary entries and return of supplement containers. A sample size of 74 participants (32 per group + 15% dropout) was calculated to detect a 25% difference in treatment success (as defined by surpassing the sarcopenia threshold in ASMI).

The study further investigates the potential of plant-based protein sources, particularly hydrolyzed pea protein, to serve as effective dietary interventions in the elderly. It also explores the gut-muscle axis, examining how nutritional modulation of the microbiota may impact sarcopenia-related outcomes.

The trial is conducted at the Internal Medicine Unit 2 of the S. Maria della Misericordia Hospital (Udine, Italy) under the coordination of Prof. Alessandro Cavarape. All procedures follow ethical guidelines and include appropriate monitoring for adverse events.

Inclusion Criteria

Given the multifactorial, heterogeneous nature of sarcopenia, volunteers will be enrolled if they meet at least one of the following three diagnostic criteria :

• Ishii equation values: patients with a score ≥105 for males and ≥120 for females will be included. The Ishii screening test is a widely used method that estimates the probability of sarcopenia using a score derived from an equation based on three variables: age, grip strength, and calf circumference.
• Appendicular skeletal muscle mass index (ASMI): <7.0 kg/m2 for males and <5.5 kg/m2 for females.
• Short physical performance battery score ≤8

In addition, the following inclusion criteria are considered:

• Body mass index ≥19 <30 kg/m2
• Ability to act

Exclusion criteria

• Age <65 or >80 years;
• Body mass index <19 or ≥30 kg/m²;
• Diagnosis of cancer within the previous five years;
• Regular intake of vitamin D supplements;
• Dysphagia and difficulty chewing;
• Allergy or other intolerances to gluten;
• Allergy to eggs;
• Intestinal disorders (Crohn's disease, ulcerative colitis, bacterial overgrowth syndrome, constipation, coeliac disease, irritable bowel syndrome) that could affect the gut microbiota;
• Pacemaker recipients;
• Acute inflammation (CRP >10 mg/L);
• Anaemia (haemoglobin <13 g/dL in men; <12 g/dL in women);
• Renal failure (glomerular filtration rate (GFR) >45 mL/min/1.73 m²);
• Chronic liver disease (transaminases < 40 IU in men, < 35 IU/L in women);
• Inability to act