Precision Medicine and Physical Function

Inclusion Criteria: * English-speaking older adults aged 65 to 85 years (of all genders and sexes, race or ethnicity) * A University of North Carolina at Chapel Hill (UNC) Geriatrics Medicine clinic patient; * Chronic medical conditions -these are based on the 21 Medicare multiple chronic conditions (e.g., alcohol abuse, arthritis (osteoarthritis, rheumatoid), asthma, atrial fibrillation, autism spectrum disorders, cancer (breast, colorectal, lung, prostate), chronic kidney disease, chronic obstructive pulmonary disease, depression, diabetes, drug/substance abuse, heart failure, hepatitis, HIV/AIDS, hyperlipidemia, hypertension, ischemic heart disease, osteoporosis, schizophrenia/other psychotic disorders, stroke); Exclusion Criteria: * Age \<65 years and \>85 years old * A medical diagnosis of dementia * Those without a negative subjective weakness screener (\<1) * Individuals with life-threatening or untreated psychiatric diagnosis that would interfere with study participation and require significant modification to meet their needs such as untreated major depressive disorder, substance abuse, suicidal ideation or untreated severe mental illness (schizophrenia, bipolar disorder) * Life-threatening illness including those receiving palliative care or hospice services * Individuals unwilling/unable to provide consent * Inability to complete the protocol procedures * Elective surgery in the next four months * Medications - antiobesity (weight loss agents) medications that lead to weight loss * Hospitalization for heart failure in past 6 months, advanced non-skin cancer (Stage III or IV) on treatment; Advanced liver failure; Chronic renal insufficiency on hemodialysis; advanced Chronic obstructive pulmonary disease (COPD) that would prevent engagement \*\*\*Vitamin D \>80 ng/dL: * At baseline, the investigators will check Vit D levels - recognize that processing is highly dependent on the McLendon lab and may take up to 7+ days to come back. * Concurrently, the investigators will consider continuing consent, enrollment, study procedures. * Provide at Visit 2 the beta-hydroxymethyl butyrate/Vitamin D supplement * Once the results have been received and reviewed - if the levels exceed 80 ng/dL, then the participant will be informed. * At that point, the investigators will either exclude the participant or, if available, see whether the company is willing to provide formulations of just beta-hydroxymethyl butyrate (HMB)and provide this to the participant * These guidelines account for the fact that Vit D is not recommended by American Geriatrics Society to check routinely, and that levels \<80 (or even 120 ng/mL) rarely lead to toxicity.