Effect of Caloric Restriction and Protein Intake on Metabolism and Anabolic Sensitivity

Can Increased Dietary Protein Prevent the Suppression of Metabolism and Maintain Anabolic Sensitivity of Bone and Skeletal Muscle During Caloric Restriction?

The purpose of this study is to determine if an increased protein intake can attenuate the suppression of metabolic and anabolic hormones during caloric restriction

1. Preliminary testing

   Prior to the study start, participants will be weighed and body composition will be determined using calipermetry (7 sites) and bioelectrical impedance. Peak oxygen uptake (VO2peak) will be assessed using an incremental exercise test on a bicycle ergometer.

2. Randomization

   Participants will proceed through each of the following conditions lasting 5 days:

   CR-LP: Participants will be restricted to 30 kcal/kg FFM/day and protein intake will be low (0.8 g/kg BW/day).

   CR-HP: Participants will be restricted to 30 kcal/kg FFM/day and protein intake will be high (1.7 g/kg BW/day).

   CON: Participants will be in energy balance and consume 1.7 g protein/kg BW/day.

3. Diet Prescription

   Dietary energy intake will be controlled using clinical products and maltodextrin to meet target energy intakes. Participants will received calcium and Vitamin D supplementation throughout the study.

4. Exercise Prescription

   During all conditions, participants will conduct daily supervised exercise on a bicycle ergometer at an exercise intensity of 60% VO2peak. Exercise duration will be adjusted individually such that exercise energy expenditure will amount to 15 kcal/kg FFM/day. Additional exercise and intense physical activity will be prohibited.

5. Assessments

   The following assessments will be conducted prior to the start of each condition as well as upon completion of each condition: body weight and composition (impedance), fasting blood draw for assessment of metabolic and anabolic hormones, resting metabolic rate, aerobic fitness (VO2peak), and questionnaires.

6. Washout

Once a participant has completed a study condition, participant will be allowed a washout of at least 14 days to allow protein balance to return to baseline (Hoffer & Forse, 1990). During this time, participants will resume their regular diet and physical activity.

Inclusion Criteria:

• 4 hours/week of purposeful aerobic exercise over the last 3 months
• Body mass index: 19-25 kg/m2
• < 15% body fat

Exclusion Criteria:

• Cardiovascular disease risk factors that would result in greater than low risk
• Smoking
• Type I, type II diabetes, or history of high fasting glucose;
• History of high blood pressure and/or use of medication for hypertension;
• History of Dyslipidemia, or on lipid-lowering medication;
• Underlying health condition and/or use of medication that could interfere with any of our study outcomes.
• History or current diagnosis of a clinical eating disorder
• Failure to adhere to study protocol