Anabolic Response to Beef vs Plant Protein in (Pre)Frail Older Adults Using a Novel Stable Isotope Pulse Method

Inclusion criteria: * Age 65-95 years old * Ability to walk, sit down, and stand up (independently or with walking assistance device) * No recent use (\< 4 weeks prior to start of the study) of dietary supplements and medication influencing protein and amino acid metabolism (e.g., antibiotics, oral corticosteroids) * Willingness to lay supine in bed for up to 6 hours * Willingness and ability to comply with the protocol Exclusion criteria * Presence of malnutrition (BMI \< 17 kg/m2), 2). BMI \>35 kg/m2 to avoid weight-related metabolic disturbances, * Established diagnosis and active treatment of chronic disease: Insulin-dependent diabetes mellitus, active malignancy, heart disease, kidney disease, liver disease, HIV/AIDS, Asthma (moderate to severe), Hep (A, B, or C) * History of untreated metabolic disease including hepatic or renal disorder * Presence of fever within the last 3 days * Cirrhosis of liver * Diagnosis of dementia, neurodegenerative disease (e.g., Alzheimer's disease, Parkinson's disease, Huntington's chorea, frontotemporal dementia). * (Possible) pregnancy * Presence of acute illness or metabolically unstable chronic illness * Active dependence on alcohol or drugs * Newly prescribed long-term oral corticosteroids * Planned elective surgery requiring 2 or more days of hospitalization during the entire study * Failure to give informed consent or Investigator's uncertainty about the willingness or ability of the subject * Already enrolled in another clinical trial * Any condition according to the PI or nurse that was found during the screening visit, that would interfere with the study or safety of the patient * Known allergy to any of the components of the feeding (soy, beef) * Established daily diet of vegetarian/vegan composition