This study will explore differences in energy metabolism and metabolic flexibility under various conditions in older men and women.

Inclusion Criteria:

• Body mass index (BMI) >20.0 and <39.0 kg/m2
• Ambulatory (may use assistance device e.g., cane, walker)
• Not a current smoker (within past 10 years)
• Low or moderate risk based on the responses from the AHA/ACSM Health/Fitness Facility Preparticipation Screening Questionnaire
• Normal muscle mass and strength/performance or sarcopenia included in low muscle mass and low grip strength
• If on thyroid medication or hormone replacement therapy, has been on a constant dosage for at least 2 months prior to Screening Visit
• Willingness to follow protocol as described
• Voluntarily signed and dated an informed consent form (ICF), approved by an Independent Ethics Committee (IEC)/Institutional Review Board (IRB) prior to any participation in the study

Exclusion Criteria:

• Active/treated disease, under the care of a physician, for the following: metabolic/endocrine (diabetes), hepatic, or renal disease, myocardial infarction, peripheral vascular disease, respiratory or neuromuscular disease
• Participates in a resistance exercise program
• Poor appetite with recent unexplained weight loss over the past 6 months
• Current infection (requiring medication or which might be expected to require hospitalization); has had inpatient surgery, or corticosteroid treatment (excluding topical creams) in the last 3 months or antibiotics in the last 3 weeks.
• Active malignancy, excluding carcinoma in-situ of the cervix, cutaneous malignancies (basal cell carcinoma, squamous cell carcinoma, except melanoma)
• Chronic, contagious, infectious disease, such as active tuberculosis, Hepatitis A, B or C, or HIV
• Taking medications/dietary supplements or substances that could profoundly modulate metabolism in the opinion of the principal investigator or study physician, Exceptions for multi-vitamin/mineral supplement, topical or optical steroids and short-term use (less than two weeks) of dexamethasone
• Allergy or intolerance to any foods
• History of gastrointestinal disease, or surgeries, gastroparesis, or taking medications that are known in the opinion of the PI or study physician to interfere with consumption/digestion/absorption of nutrients
• Eating disorder, severe dementia or delirium, history of significant neurological or psychiatric disorder, alcoholism, substance abuse or other conditions that may interfere with compliance with study protocol procedures in the opinion of the principal investigator or study physician
• Participant in a concomitant AN trial or trial of a non-registered drug (or is within the 30 day follow-up period for such a trial) or that otherwise conflicts with this study unless otherwise approved