KEs could represent a practical STAK method that does not require any change in diet. However, there is a critical need to elucidate how KE metabolism varies between individuals to inform KE use in the field. This high impact project will contribute important knowledge that aims to develop next-generation KE molecules and formulations that are designed to meet the needs of operators at different points in their career. The long-term goal is to create evidence-based guidelines for deployment of KE compounds based on individual characteristics.This is an open label, one arm study to characterize the effects of age and metabolic health on ketone responsiveness. Enrollment will include a large group representing a range of ages and metabolic health status. N of 300 will be recruited and tested at the Physical Activity and Education services facility at the Ohio State University, Columbus, OH, and an N of 100 will be recruited and tested at the Buck Institute in Novato, California. Data/sample collection will include blood (capillary and whole venous blood) and study product tolerability.This study aims to recruit equal numbers of male and female participants between the ages of 20 to 70yr. Thus, recruitment will employ a balanced sample of men and women with a range of ages (equal representation in each of the 5 included decades; 20-29yr, 30-39yr, 40-49yr, 50-59yr, 60-70yr) and metabolic health via HbA1c clinical ranges (normal: \<5.7, prediabetes: 5.7-6.4, diabetes: \>6.4). Each participant must meet all the inclusion criteria and none of the exclusion criteria at screening in order to participate.

Participants that meet the initial qualifying criteria will visit the study center for a screening meeting. The participant and a member of the research team will meet in a private office to discuss the informed consent form. The informed consent form will be provided to the participant for their review, the study will be described in full detail and any questions the interested participant has will be encouraged and responded to. If they choose to participate in the study, they will be asked to sign the consent form providing written consent. The participant will be informed that even though they signed the consent form, their participation in the study is dependent on anthropometric measures and diet and medical questionnaire answers to determine if they meet the study criteria.

If the participant provides consent, they will be provided with questionnaires including Automated Self-administered 24-hour Dietary Assessment Tool (ASA24®),and medical history. All collected samples and data will be coded to maintain participant anonymity. Participants will be given a small volume of Study Product to screen for tolerance of the bitter tasting Study Product. Height, weight and body composition using bioelectrical impedance will also be measured. A1CNow+, Hba1c Blood monitor kit will be used to assess Hba1c score. Both body composition and Hba1c score to stratify participants to ensure various metabolic statuses are represented in the study population. The participant will then complete a 6 minutes Astrand Bike Test to determine the predicted VO2 Max. This test does not require fasting and uses only submaximal effort upon the participant to determine cardiometabolic status by an average heart rate at 6 minutes of pedaling at a moderate intensity. If the participant is eligible for the study and is still interested in participating then they will be scheduled to return to the study center for the testing visit.

Participants will report to the study center in the morning of the Test Day. Compliance with pre-test instructions (fasted \> 10h, no alcohol \>24h, no exercise \>24h, consumed pre-test food) will be confirmed study staff. Participants will complete a baseline Beverage Tolerability Questionnaire (BTQ). Participants will be asked to completely void their bladder and a sample will be analyzed for hydration status. Participants with samples reading greater \> 1.025 USG will be asked to drink 160z of water and retest again in 30 minutes. Participants will be provided with a container to void all urine during the study visit. This will be aliquoted for urine R-BHB analysis to assess the clearance of ketones in the body. A trained member of the study team will insert an IV cannula into a vein in the antecubital fossa to allow for repeated blood sampling. The cannula will be flushed with a small volume of saline after each sample withdrawal to maintain patency. At the same time as all whole blood samples, capillary blood samples will also be collected from a finger for real-time analysis of blood BHB and glucose concentration, using lancing device, commercially available test strips and a handheld monitor (KetoMojo, CA, USA).

Participants will then consume the C8 Ketone Diester Study Product. They will be given 5 minutes to consume the Product. After C8 Ketone Diester consumption, they will remain at the study center for \~4-5h, with blood sampling occurring at regular intervals (see Figure 2). A total of 7 whole blood samples (\~8 mL each) will be collected each Test Day. Capillary blood samples will be collected at the same time as whole blood samples. At the 4th hour finger stick, participants whose capillary ketones levels have not returned to baseline will be asked to stay for a 5th hour to assess the complete metabolism of the study product. Participants will complete satiety questionnaires each hour, and will complete a BTQ at the end of the Test Day.

Participants will be asked to minimize ambulatory movement during the Test Day. Non caloric beverages (i.e., water) will be permitted ad libitum and intake volumes will be recorded. At the end of the Test Day, the IV cannula will be removed and a dressing will be applied to the cannula site. Participants will be given a snack to consume.