The VOILA Intervention Study

Inclusion Criteria: * Age ≥70 years * A body mass index of 18.5-35.0 kg/m2 * Able to give written informed consent * Community-dwelling * Mentally competent with a Mini-Mental State Examination (MMSE) score of ≥24 points * Able to follow the study protocol Additional group-specific criteria: Metabolically compromised group \- Framingham Risk Score ≥14 and Metabolomic Mortality Score of ≥0.173 Reduced mobility group - People able to walk but needing walking aids to walk anywhere outside their house Total knee replacement intervention and control group \- Discharged from MUMC+ after undergoing elective knee replacement surgery (intervention starts \~4 weeks after surgery) Active reference group * People who meet the "Nederlandse Norm Gezond Bewegen". This means they partake in at least moderate exercise for at least 30 minutes on 5 days of the week, as determined by the SQUASH questionnaire (40). * Framingham Risk Score of \<14 and Metabolic Mortality Score of \<0.173 Exclusion Criteria: * Already using prebiotic fibres\* * Use of laxatives\* * Not willing to stop using dietary supplements in high doses (high doses: 0.10\*Upper Level or more)\* * Following a structured, intense exercise programme (currently or in the last year)\* * Allergic, intolerant or hypersensitive to milk/lactose (self-reported)\* * Dietary restrictions on milk/lactose/prebiotics/vitamin D/calcium consumption\* * Abnormal hepatic or renal laboratory parameters (estimated glomerular filtration rate (eGFR) \<30 ml/min/1.73 m2 (screening) or contra-indication by treating medical practitioner (data from hospital) * Diagnosis of disorders/diseases in which a high protein intake can be harmful, such as renal impairment or failure, liver disease, or diabetes associated with nephropathy (treating medical practitioner has the decisive voice). * Diseases, conditions or disorders which may affect the ability to follow the study protocol and which cannot be overcome with help of a caregiver Any other medical condition that may interfere with the safety of the participants during training or assessment of the outcome parameters, in the investigators' judgement * Current participation in other scientific research that conflicts with this study (e.g. intervention studies or weight management studies) * Not signed up to a general practitioner * No permission to request information from the general practitioner/ treating specialist(s) about medical history, medication use. Specific for TKR group: * Referral to rehabilitation facility after hospital discharge * Osteoarthritis of the knee secondary to septic arthritis, osteonecrosis, fracture, osteochondritis dissecans, or malignant processes * Collagen disorders, e.g. Marfan and Ehler-Danlos * Total hip prosthesis or TKR in both legs