Carbohydrate Availability and microRNA Expression

Not Applicable

Completed

Lead Sponsor: United States Army Research Institute of Environmental Medicine

Brief Summary: This investigation will examine the impact of skeletal muscle glycogen stores on skeletal muscle and circulating microRNA expression and exogenous carbohydrate oxidation.

Primary Objective Determine the influence of carbohydrate availability (e.g., glycogen depletion and repletion) on skeletal muscle microRNA expression, and if changes in circulating microRNA are reflective of changes in skeletal muscle microRNA.

Secondary Objective Determine how initiation of exercise with adequate or low glycogen stores effects exogenous carbohydrate efficiency.

Detailed Description: Twelve, normal weight, healthy, physically active men and women will complete a glycogen depletion protocol, cycling at various intensities until failure. Participants will then consume a carbohydrate (CHO: 1 g/kg/hr) or an energy free control (CON) beverage matched for taste and color during the first 3-hr post glycogen depletion. For the remainder of the day participants will consume a diet designed to adequately (6.0 g CHO/kg/d) or inadequately (1.2 g CHO/kg/d) replenish glycogen stores. The following day participants will to complete 80-min of steady-state (\~60% VO2peak) cycle ergometry consuming carbohydrate at a rate of 1.8 g/min enriched with a stable isotope of carbon to determine exogenous carbohydrate efficiency when glycogen stores are low or adequate at the onset of exercise.

Following a minimum 7-d washout period volunteers will return to the laboratory to complete the second arm of the investigation. To ensure glycogen stores are similar between volunteers on testing day, 48-hrs prior to testing all volunteers will complete a glycogen depletion protocol and then consume a diet providing 6.0 g/kg/d carbohydrate to replenish glycogen stores.

Recruitment & Eligibility

Inclusion Criteria

Men and women aged 18 - 39 years
Weight stable (±5 lbs) for at least 2 months prior to the start of the study
Body mass index (BMI) between 18.5-30 kg/m2
Recreationally active based on assessment of physical activity history 2-4 days per week aerobic and/or resistance exercise
Refrain from taking any NSAIDS (i.e., aspirin, Advil®, Aleve®, Naprosyn®, or any aspirin-containing product for 10 days before and at least 5 days AFTER each muscle biopsy. (*Tylenol® or acetaminophen is ok to use if needed for discomfort)
Refrain from the use of alcohol and nicotine for the duration of the study
Females must be on contraception (e.g., oral birth control, NuvaRing®, Depo Provera®, etc.)
Supervisor approved leave status for federal civilian employees working within the US Army Natick Soldier Systems Center

Exclusion Criteria

Metabolic or cardiovascular abnormalities, gastrointestinal disorders (i.e., kidney disease, diabetes, cardiovascular disease, etc.)
Disease or medication (i.e., diabetes medications, statins, corticosteroids, etc) that affects macronutrient utilization and/or the ability to participate in strenuous exercise
Allergies or intolerance to foods (including but not limited to lactose intolerance/milk allergy), vegetarian practices, or medications (including, but not limited to, lidocaine or phenylalanine) to be utilized in the study
Anemia (HCT < 38) and Sickle Cell Anemia/Trait
Abnormal prothrombin time (PT)/ partial thromboplastin time (PTT) test or problems with blood clotting
Present condition of alcoholism, use of nutritional/sports supplements, anabolic steroids, or other substance abuse issues
Musculoskeletal injuries that compromise the ability to exercise
Blood donation within 8 weeks of beginning the study
Pregnancy

Primary Outcome Measures

Name	Time	Method
Fold Change in microRNA Expression From Baseline	24 hours	Determine the influence of low or adequate glycogen on expression of skeletal muscle and circulating microRNA. Expression of microRNA was determined using real time polymerase chain reaction analysis. microRNA expressions were calculated as a fold change relative to baseline.

Secondary Outcome Measures

Name	Time	Method
Exogenous Carbohydrate Oxidation	80 minutes	Determine how initiation of exercise with adequate or low glycogen stores effects exogenous carbohydrate efficiency. Exogenous carbohydrate oxidation was measured using an oral 13C-glucose isotope that was consumed in the study carbohydrate drink during steady-state cycling. Breath samples were collected during exercise and analyzed using isotope ratio mass spectrometry to calculate exogenous carbohydrate oxidation rates.