In 2018, for the first time, the number of people aged 65 and over exceeded the number of children under the age of 5. A rise in ageing societies is coming, and new efforts are needed to ensure that this increase in life expectancy is accompanied by years of health and a good quality of life. The new focus for our ageing society will be an extended healthspan, the period of life spent in good health. This is an important shift, as population ageing is a defining global trend of our time. By 2030, 1 in 6 people in the world will be 60 years and older, according to the World Health Organization. In this sense, the imperative to maintain the health and activity levels of the senior demographic has never been more critical. Advances in healthcare, science, and technology have contributed to increased longevity, yet this does not always equate to improved health.

The prevalence of malnutrition or the risk thereof among the elderly living independently in Europe ranges from 13.5% to 29.7%, highlighting a pressing need for nutritional intervention. Addressing this, the pursuit of innovative nutritional sources and the creation of new food products enriched with these sources are essential to bridging the nutritional gap, ensuring healthier aging prospects for this population. The formulation of food products tailored to the elderly must consider their unique nutritional requirements, particularly concerning protein and micronutrient intake. Recent advances in food technology facilitate the development of plant-based beverages that are palatable, nutritionally adequate, and accessible. Moreover, the growing market share of plant-based non-dairy beverages provides a promising alternative, offering opportunities to deliver bioactive compounds with health-promoting properties, appealing to health-conscious and lactose-intolerant consumers.

Given the nutritional challenges and health risks faced by the aging population, particularly in relation to protein intake and malnutrition, another critical aspect that warrants attention is the immune system's health through diet. The immune system, which naturally weakens with age, plays a crucial role in the elderly's ability to resist infections and recover from illnesses. Research highlights the impact of not only macronutrients but micronutrients such as vitamins D, C, E, and zinc on enhancing immune responses, suggesting that diets rich in these nutrients can significantly benefit immune health in older adults. Strengthening the immune system through diet becomes even more pertinent considering the increased vulnerability of the elderly to infectious diseases, including respiratory infections like influenza and pneumonia, which are leading causes of morbidity and mortality in this population. Developing food products that are not only nutritionally adequate but also tailored to support immune function could provide a dual benefit: improving general health and enhancing the body's defence mechanisms.

The present research project is structured into three coordinated phases and is enabled by the multidisciplinary nature of the IMMUGOLD consortium. In the first phase, AZTI conducted an extensive literature and technical review to identify functional ingredients capable of supporting immune function while remaining compatible with the technological, sensory, and stability requirements of a plant-based beverage. This process identified vitamin D, zinc, FOS, and L-leucine as the most suitable bioactive components, considering bioavailability, processing stability, and expected physiological effects. In the second phase, COSTA carried out the development and reformulation of the oat-based beverage to ensure nutritional adequacy, ingredient stability under thermal treatment, and organoleptic acceptability for older consumers. Finally, the third phase involves a clinical study, to be executed by Universitat Rovira i Virgili (URV), which aims to evaluate the effects of the newly developed fortified beverage on markers of immune function and systemic inflammation in community-dwelling older adults, with secondary outcomes including nutritional status and other health-related parameters relevant to ageing.

The multidisciplinary expertise of the consortium, including computational modelling, ingredient research, nutrition, food product development, and clinical epidemiology, ensures the feasibility of the project and the successful achievement of its objectives: AZTI provides evidence-based solutions for functional ingredients; COSTA develops innovative plant-based beverages; and URV contributes extensive experience in designing and implementing nutritional programs and clinical studies.

Randomised, placebo-controlled, parallel, and double-blind intervention study.

There will be 4 visits in total, attended in the Centre MQ Reus:

• Screening visit (V0, week -1):

  • Information to the volunteer and signature of the informed consent.

  • Revision of the eligibility criteria.

  • Elaboration of study clinical history.

  • Vital signs (blood pressure/resting heart rate).

  • Checking the concomitant medication.

  • Capillary blood sampling (Finger-prick blood sampling).

  • Anthropometry: waist circumference; hip; body weight and composition; height.

  • Delivery of the 3-day dietary record and the material for urine, saliva, and faeces recollection for V1.

  • Schedule the first visit and instructions (fasting).

    - Basal visit (V1, week 0):

  • Isokinetic assessment (±5 days V1) *

  • Revision of the study clinical history.

  • Vital signs (blood pressure/resting heart rate).

  • Checking the concomitant medication.

  • Anthropometry: waist circumference; hip; body weight and composition; height.

  • Checking the physical activity (IPAQ-E).

  • Checking the quality of life (SF-36 Health survey questionnaire)

  • Checking the Fraility

  • Checking the Sleep quality

  • Checking the Depressive symptoms

  • Checking the Cognitive function (MMSE and Fototest)

  • Checking the Reported illness (adapted version of the FLU-PRO plus)

  • Ultrasound (muscle mass and abdominal fat).

  • Checking the Sarcopenic parameters (muscle strength based on grip dynamometry; skeletal muscle mass index (SMI) based on bioimpedance analysis (BIA), kg/m2 and appendicular skeletal muscle mass index (ASMI) based on bioimpedance analysis (BIA), low physical performance or physical function based on 4 m gait speed, m/s.

  • Checking the 3-day dietary record

  • Checking the Food Frequency Questionnaire (FFQ) adapted to the principal bioactive compounds (vitamin D, L-leucin, Zinc and FOS).

  • Checking the satiety scale (VAS)

  • Checking the Gastrointestinal health by Bristol Scale and Non-validated 5-item questionnaire

  • Blood sample extraction.

  • Collection of feaces samples.

  • Collection of urine samples.

  • Collection of salivary samples.

  • Balanced dietary guidelines for the elderly population explanation.

  • Schedule the next visit and instructions.

  • Administration of plant-based beverage (intervention or control product).

  • Assessment of product acceptance and purchase intention (After the first few home intakes (Week 1) by telephone) *In a subsample of n= 15 subjects, 5 days before or after the visit V10.

    **Isokinetics analysis in order to measure changes in muscle function through variables such as torque, work and power.

    • Mid-study follow-up visit V2 (weeks 6):

  • Revision of study clinical history.

  • Vital signs (blood pressure/resting heart rate).

  • Checking the concomitant medication.

  • Checking the physical activity (IPAQ-E).

  • Checking the Reported illness (adapted version of the FLU-PRO plus)

  • Checking the FFQ

  • Product intake control

  • Record adverse effects

  • Delivery of the 3-day dietary record and the material for urine, saliva and faeces recollection for V3.

  • Schedule the next visit and instructions.

  • Administration of plant-based beverage (intervention or control product). - Final visit (V3 at week 12):

  • Isokinetic assessment (±5 days V1)*

  • Revision of study clinical history.

  • Vital signs (blood pressure/resting heart rate).

  • Checking the concomitant medication.

  • Anthropometry: waist circumference; hip; body weight and composition; height.

  • Checking the physical activity (IPAQ-E).

  • Checking the quality of life (SF-36 Health survey questionnaire)

  • Checking the Fraility

  • Checking the Sleep quality

  • Checking the Depressive symptoms

  • Checking the Cognitive function (MMSE and Fototest)

  • Checking the Reported illness (adapted version of the FLU-PRO plus)

  • Ultrasound (muscle mass and abdominal fat).

  • Checking the Sarcopenic parameters (muscle strength based on grip dynamometry; skeletal muscle mass index (SMI) based on bioimpedance analysis (BIA), kg/m2 and appendicular skeletal muscle mass index (ASMI) based on bioimpedance analysis (BIA), low physical performance or physical function based on 4 m gait speed, m/s.

  • Checking the 3-day dietary record

  • Checking the Food Frequency Questionnaire (FFQ) adapted to the principal bioactive compounds (vitamin D, L-leucin, Zinc and FOS).

  • Checking the satiety scale (VAS)

  • Checking the Gastrointestinal health by Bristol Scale and Non-validated 5-item questionnaire

  • Blood sample extraction.

  • Collection of feaces samples.

  • Collection of urine samples.

  • Collection of salivary samples.

  • Product intake control

  • Record adverse effects

  • Assessment of product acceptance and purchase intention *In a subsample of n= 15 subjects, 5 days before or after the visit V10.

    • Isokinetics analysis in order to measure changes in muscle function through variables such as torque, work and power.

In visits V0, V1 and V3 volunteers must present themselves in fasting conditions of 8 hours to obtain fasting blood samples.

- Assessment of product acceptance and purchase intention Acceptance will be assessed at baseline and at the final visit and purchase intention will be assessed at the final visit. The questionnaire is short, requires only a few minutes to complete, and will be administered verbally in person (V3), or by phone (after V1, during the first week).

The questionnaire includes an evaluation of several attributes of the product. Participants are asked to rate each aspect on a scale from 1 to 5, where 1 indicates that the attribute is "very unpleasant" and 5 indicates that it is "very pleasant," with the option to use intermediate values to better reflect their opinion. The attributes assessed are colour, smell, appearance, flavour, texture, sweetness (in this case, 1 meaning "not sweet" and 5 meaning "very sweet"), and overall acceptance of the product.

Additionally, participants are asked to rate their intention to purchase the product on a scale from 1 to 5, where 1 corresponds to "very unlikely" and 5 to "very likely." Finally, an open section is provided for any additional comments or observations the participant may wish to share.

Inclusion Criteria:

• Men or women ≥60 years old <80 years old.
• Written informed consent provided before the initial screening visit.

Exclusion Criteria:

• Hypoglycaemic treatment or type 1 and type 2 diabetes mellitus diagnosed.
• Anaemia (haemoglobin ≤13 g/dL in men and ≤12 g/dL in women).
• Intestinal malabsorption diseases, such as chron disease, colitis ulcerous, and irritable bowel syndrome.
• Immune pathology or depressed immune system.
• Use of antioxidants or nutritional supplements.
• Known allergy or hypersensitivity to oat, coconut, or any formulation ingredient.
• Renal diseases or history of hypercalcemia, sarcoidosis, or hyperparathyroidism.
• History of inborn errors of metabolism affecting branched-chain amino acid metabolism.
• Chronic alcoholism.
• Current or past participation in a clinical trial or consumption of a research product in the 30 days before inclusion in the study.
• Failure to follow the study guidelines.