The goal of this randomized clinical trial is to learn about the effect of consuming a probiotic on the microbiota associated with immune health and inflammation in healthy women and men after 6 weeks of intervention.

The main questions to answer are:

1. To study changes in the intestinal microbiota associated with immune health and inflammation related to probiotic intake.
2. To evaluate changes in salivary cortisol after ingestion of the probiotic.
3. To compile the number and intensity of catarrhal episodes suffered by the participants along the study.

For this purpose, a randomized, double blind parallel study has been designed.

Target sample size is 60 subjects.

Participants will be allocated in two groups for 6 weeks:

• Experimental group (n=30): daily consumption of one probiotic capsule.
• Placebo group (n=30): daily consumption of one placebo capsule.

Volunteers who wish to participate in the study will be interviewed by phone to verify that they meet the main inclusion criteria. Volunteers who meet the main inclusion criteria will be invited to an information and screening visit to resolve any doubts. Volunteers who agree to participate in the study will sign the informed consent and will be randomly allocated to one of the two arms of the study and will be provided with any required material.

During the intervention, volunteers will attend two Clinical investigation visits. The first one will be carried out on the first day of the study and the last one will take place at the end of the 6 weeks. In both visits anthropometric and body composition measurements, stool and saliva samples, as well as data about dietary, physical activity and catarrhal episodes will be taken.

Inclusion Criteria:

• Volunteers of both sexes.
• Age between 40 and 65 years old.
• Volunteers with a body mass index between 18.5 and 30 kg/m2.
• Subjects have to present a stable weight (+/- 3 kg) in the last three months prior to the start of the study.
• Subjects must be able to understand and be willing to sign the informed consent, and comply with all study procedures and requirements.

Exclusion Criteria:

• Subjects with relevant functional or structural anomalies of the digestive system, such as malformations, angiodysplasias, active peptic ulcers, chronic inflammatory or malabsorption diseases, hiatal hernia, reflux, etc.
• Subjects with surgical interventions with permanent consequences in the digestive system (for example, gastroduodenostomy).
• Subjects following treatments that alter gastrointestinal function, either chronically or occasionally.
• Subjects who are being treated with antibiotics (in order to participate, they do not have to have taken antibiotics during the two months prior to the baseline visit).
• Subjects with any type of cancer or undergoing treatment for it, or less than 5 years since its eradication.
• Subjects with any liver disease (may participate with non-alcoholic fatty liver disease).
• Subjects with allergy to any component of the product under study.
• Subjects with a high alcohol intake, more than 14 units (women)/day and 20 units (men)/day.
• Women who are breastfeeding or pregnant.
• Subjects who present some type of cognitive and/or psychological impairment.
• Subjects with poor collaboration or with difficulties for following the study procedures.
• Subjects who work with shift changes that include nights.
• Subjects who follow any type of supplementation that interferes with the study (example: consumption of probiotics).
• Subjects who are immersed in diet/exercise changes.

The products (experimental and placebo), will be produced by an external producer, who will save the codes. None of the researchers involved in the study development or analyses will know the association until the end of the study.