Despite the fact that dairy products are greatly consumed, it remains today very difficult to determine with a classical blood biochemical test whether a person has ingested a fresh fermented dairy product or just milk, while their biological, metabolic and health impacts may be different.

The metabolic footprint left by the consumption of these products could be modified by the age of the consumer. Indeed, in the elderly, the processes of digestion, assimilation and metabolism are known to be altered /different compared to healthy adults. Thus, different metabolic signatures in the elderly could appear as the result of a less effective use and metabolism of the nutrients ingested. This could further also result in different or altered biological effects on dairy products.

The two main objectives of this project are to:

• Determine precisely the plasma and urine metabolic signatures resulting from acute (postprandial) ingestion of yogurt or milk.
• Characterize the metabolic signature following the consumption of these dairy products in the elderly and compared with the signature of reference (adult).
• Understand the mechanisms and metabolic pathways involved if discriminating metabolites between age are detected..

The clinical study is open, monocentric, controlled and randomized, in a cross experimental design.

The study is not performed in a double blind way. However, the measure bias will be limited because of the standardized and objective characteristic of the main criteria. Moreover, biological samples will be analyzed by the same partners of the project. Each subject will be its own control, so that confusion factors related to individual variability will be eliminated.

A total of 28 volunteers (men) will participate in the study: 14 adults and 14 old people (>65 yrs-old). After 3 weeks of controlled diet (without consumption of dairy products) the volunteers will ingest 600g of milk or yogurt. After 1 week of wash-out, the other product will be consumed. Blood and urine will be collected during the postprandial period.

The monocentric characteristic of the study, the low number of subjects and the expertise of the involved staff will enable to limit the number of missing data.

The randomization (latin square) has been established by a bio-statistician of the project before the study started. A document describing the randomization proceeding is confidentially kept.

Inclusion Criteria:

• no pathology and no medical treatment
• BMI >=21 and <=30 kg/m²
• normal biological status
• no dislike for diary intake

Exclusion Criteria:

• smoking
• no pathology and no medical treatment (no antibiotics in the last 3 months)
• consumption of nutritional supplements several times at week

The identified individual participant data for all outcome measures will be made available, only after joined consent of promotor and investigator. Data use and transfer to a third party will be performed according to the agreement signed as part of the grant funded by CNIEL.