Continuous glucose monitors (CGMs) measure plasma glucose concentration continually and thus they are a key tool in the management of diabetes, including type 2 diabetes (T2D). A key factor in diabetes management is a reduction of dietary carbohydrates (CHO) and/or exchanging high glycemic index (GI) CHO with low GI CHO. However, the protein and fat content of the meal can have a significant impact on the glucose readings obtained from a CGM as there is no enough data available on their sensitivity during meals.

The study involves 1 screening visit of approximately 1 hour and 9 study days of approximately 8 hours. Subjects will be asked to arrive in the fasted state on all study days. Fasting prior to screening is not required. On the screening day, body weight, height, and body composition by Dual-energy X-ray absorptiometry (DXA) will be measured. In addition, habitual dietary intake, physical activity level (PASE), and quality of life (SGRQ-C) will be assessed.

To test the relation between plasma amino acid, triglycerides, and glucose concentration measured by standard methods (such as finger stick) and continuous wearable devices, a premarket FDA-approved continuous glucose monitor (CGM) from Abbott (FreeStyle Libre Pro) that monitors glucose concentrations every 15 min is used. The single-use sensors are placed on the upper arm and contain a very tiny 5 mm filament (<0.4 mm diameter) that is introduced into the skin when the sensor is placed. On the first study day, the CGM will be placed to monitor glucose concentrations until the last study day. At least every 14 days, sensors will be replaced by new ones. On each study day, body weight and height will be measured and the glucose concentration data will be downloaded from the sensor onto the reader device. A catheter will be inserted in a peripheral vein of the lower arm or hand to enable blood sampling. The arm will be put in a hot box to allow collecting arterialized venous blood samples. After taking a baseline blood sample, the predefined meal will be consumed within 10 min. Small arterialized venous blood samples (5 ml) will subsequently be drawn at times: 15, 30, 45, 60, 90, 120, 180, 240, 300, 360, 420, and 480 minutes (13 blood samples, total blood approx 65 ml). Samples will be collected in predefined tubes, plasma/serum separated, aliquoted, and stored at -80 deg. Celsius for later assays and/or send to a local accredited laboratory for the concentrations of amino acids and other parameters (including fatty acids, glucose, insulin).

Inclusion Criteria:

• Ability to walk, sit down and stand up independently
• Ability to lie in a supine or slightly elevated position for 8.5 hours
• BMI between 25 and 35 kg/m2
• Willingness and ability to comply with the protocol

Exclusion Criteria:

• Established diagnosis of malignancy
• Established diagnosis of Insulin-Dependent Diabetes Mellitus
• History of untreated metabolic diseases including hepatic or renal disorder
• Presence of acute illness or metabolically unstable chronic illness
• Recent myocardial infarction (less than 1 year)
• Any other 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
• Failure to give informed consent or Investigator's uncertainty about the willingness or ability of the subject to comply with the protocol requirements

Healthy older adults (60-85y; equal gender) with a BMI between 25 and 35 will be recruited from an existing database of CTRAL. In addition, we will recruit older adults that respond to distributed flyers and advertisements in the newspaper and to radio announcements in the community of the College Station/Bryan area. Informed consent will be obtained on the screening day before any study-related procedures will be performed. If inclusion/exclusion criteria are met, subjects are invited to take part in the study.