The study will be conducted using a randomized, double-blind, placebo-controlled, crossover study design. Approximately 10 healthy men and 10 healthy women between the ages of 18 - 39 years of age will be recruited to participate in this study. Prior to beginning the study, all participants will sign an IRB-approved informed consent document and complete a healthy history questionnaire to determine study eligibility. All participants will report to the laboratory for all study visits between 0600 - 1000 hours. Prior to each of the seven study visits, participants will be asked to abstain from exercise, tobacco, nicotine, and alcohol for 24 hours and observe an overnight (8 - 10 hours) fast including caffeine. Study visit 1 will be a screening visit where participants will first sign an IRB-approved informed consent document. To determine eligibility, participants will then complete a health and medical history form and have their height and weight assessed along with their resting heart rate and blood pressure. If determined eligible, study participants will allowed to exercise within 24 hours of each study visit. On one occasion prior to study visit 1, study participants will be required to record their food and fluid intake for the three days prior to each study visit and instructed to replicate this diet prior to each visit. To assist in replicating their food intake, participants will be given pre-packaged frozen meals of their choosing. All meals will provide similar amounts of energy, carbohydrates, fats, and proteins. Participants will be instructed to follow an overnight fast whereby no food or fluid with calories will be consumed for the 8 to 10-hour period prior to each study visit. Water intake will be encouraged during this time for appropriate hydration status. Upon arrival for each subsequent study visit, participants will again have their body mass determined and they must be determined to be weight stable (defined as having a body mass within 2% of their previous study visit body mass). Resting heart rate, blood pressure, and body composition will then be assessed (only study visit 2) using a bio-electrical impedance analyzer (BIA). After assessment of body mass, resting heart rate, and resting blood pressure, study participants will donate their first of six venous blood samples. From there, participants will complete a series of assessments evaluating various perceptual indicators using the profile of mood states (POMS) and anchored 100-mm visual analog scales. Finally, participants will then have their resting metabolic rate determined using a metabolic cart. Upon determination of baseline resting metabolic rate, participants will be assigned in a randomized, double-blind, placebo-controlled, crossover fashion to ingest one of seven supplement conditions. One condition will be a non-energetic placebo (maltodextrin) while the other six supplemental conditions will be a 200 mg dose of caffeine, 100 mg paraxanthine, 200 mg paraxanthine, 300 mg paraxanthine, a combination of caffeine (200 mg) + paraxanthine (200 mg), and a 200 mg dose of 1-methylxanthine. All supplements will be orally ingested with 8 fluid ounces of cold tap water. The order of administration for all interventions will be randomized using a random allocation software to ensure randomization and to avoid order effects. After ingestion, participants will complete all assessments in an identical fashion 30, 60, 90, 120, and 180 minutes after ingestion of their assigned supplement. All study visits will take place between 0600 - 1000 hours. It is anticipated that follow-up study visits will be scheduled 3 - 7 days apart from each other after all dietary and exercise controls have been observed.