Integrating Quantitative Energetics Determines the Microbiome's Contribution to Energy Balance

Inclusion criteria

• Able to communicate meaningfully with the investigator and legally competent to provide informed written consent
• Age 18 - 45 years, inclusive
• Weight stable (+/- 3 kg) during the 6 months prior to enrollment
• BMI ≤ 30 kg/m2

Exclusion criteria

• History or presence of cardiovascular disease (unstable angina, myocardial infarction or coronary revascularization within 6 months, clinically significant abnormalities on EKG, presence of cardiac pacemaker, implanted cardiac defibrillator)
• History of type 1 or type 2 diabetes
• Bleeding disorders
• Acute or chronic infections
• Hepatitis and/or cirrhosis
• Severe asthma or chronic obstructive pulmonary disease
• Renal insufficiency or nephritis
• Thyroid dysfunction (suppressed TSH, elevated TSH if symptomatic, elevated thyroid stimulating hormone (TSH) if asymptomatic)
• Uncontrolled hypertension (BP >160 mmHg systolic or >100 mmHg diastolic)
• Prior bariatric surgery
• Inflammatory bowel disease or malabsorption, swallowing disorders, suspected or known strictures, fistulas or physiological/mechanical GI obstruction, history of gastrointestinal surgery, Crohn's disease or diverticulitis
• Participants with strict dietary concerns (e.g. vegetarian or kosher diet, multiple food allergies, or allergies to food we will provide them during the study)
• Current use of polyethylene glycol (e.g. Dulcolax, Miralax, Gavilax)
• Cancer within the last 3 years (except non-melanoma skin cancer or treated cervical carcinoma in situ)
• History of depression within < 5 years from screening visit or which, in the opinion of a medical investigator, will impact the participant's ability to complete the study
• History of eating disorders
• Cushing's disease or syndrome
• Untreated or inadequately controlled hypo- or hyperthyroidism
• Active rheumatoid arthritis or other inflammatory rheumatic disorder
• Pregnant or nursing females or females less than 6 months postpartum from the scheduled date of collection.
• Tobacco use within the past 3 months
• Metal implants (pace-maker, aneurysm clips) based on Investigator's judgment at Screening.
• Unable to participate in MRI or MRS assessments due to physical limitations of equipment tolerances (e.g. MRI bore size) based on Investigator's judgment at Screening.
• Unable to tolerate MRI/MRS imaging or claustrophobia.
• Nickel allergy.
• Had major surgery, donated or lost 1 unit of blood (approximately 500 mL) within 4 weeks prior to the pretrial (screening) visit.
• Intolerance to acetaminophen use.
• History of regular alcohol consumption exceeding 7 drinks/week for female participants or 14 drinks/week for male participants (1 drink = 5 ounces [150 mL] of wine or12 ounces [360 mL] of beer or 1.5 ounces [45 mL] of hard liquor) within 6 months before screening.
• Anemia (hemoglobin <12 g/dl in men, <11 g/dl in women)