The Effect of a 2-week Preoperative Vegan Diet Versus Omnivorous Diet on the Protein Turnover in the Osteoarthritic Knee

Inclusion Criteria: * Written informed consent; * Patients scheduled for total knee arthroplasty; * BMI between 20-32 kg/m2; * Aged 60 - 80 years; * Mentally competent, as judged by the treating physician; Exclusion Criteria: * Following a vegetarian or vegan diet or a diet that affects protein intake during the six months prior to the study; * Participating in a structured progressive exercise training program in the past three months; * Lost more than 4 kg body weight during three months prior to the study; * Chronic use of medications that affect protein metabolism (i.e. systemic corticosteroids, or prescription strength acne medications); * Being diagnosed with one of the following: diabetes mellitus, rheumatoid arthritis, peripheral artery disease Fontaine III or IV, COPD GOLD III or IV, neoadjuvant chemotherapy or radiotherapy, phenylketonuria, collagen disorders (e.g. Marfan and Ehler-Danlos); * Alcohol abuse; * Surgical intervention to the knee in the past four weeks; * Total parenteral nutrition at day of surgery; * Glomerular filtration rate (GFR) \<20 mL/min/1.73 m2; * Allergic or intolerant to any product included in the diets; * Osteoarthritis of the knee secondary to septic arthritis, osteonecrosis, fracture, osteochondritis dissecans, or malignant processes; * Any other medical condition that may interfere with the safety of the participants or the outcome parameters, in the investigators judgement; * Not willing to stop nutritional supplements, with the exception of vitamin D and supplements on medical advice. * Investigator's uncertainty about the willingness or ability of the participant to comply with the protocol instructions; * Participation in other studies that may have an impact on the outcomes during the three months before the start of the current study.