The Impact of a High-protein Diet on Energy Metabolism in Healthy Men

This study will be a randomized, controlled, cross-over trial of an acute nutritional intervention. The participants will be randomly assigned (1:1) to one of the following groups:

• Control group (CON). Those assigned to the CON will receive a diet composed of 55% of carbohydrate, 15% of protein, and 30% of lipid (similar to the North American dietary pattern [3]).
• High protein diet group (HP). Those assigned to the HP will receive a diet composed of 35% of carbohydrate, 40% of protein, and 25% of lipid constructed around a soy protein-based meal replacement (Almased®).

The diets given to participants in both groups will be eucaloric.

The following metabolic changes will be assessed between the diets:

• Energy metabolism (energy expenditure and substrate oxidation);
• Metabolic blood markers [glucose, insulin, lipid panel, peptide tyrosine-tyrosine (PYY), glucagon-like peptide-1 (GLP-1), ghrelin, leptin, free glycerol, and free fatty acids];
• Appetite sensations (hunger, satiety, fullness, and prospective food consumption).

Sample Size: A total of 18 participants will be able to detect an effect size of 1.41. The effect size was calculated based on changes in RQ (0.90 ± 0.04 in control group and 0.85 ± 0.03 in a high protein group) from a previously published study. Accounting for a 20% attrition rate (formula N=18/1-20%), the total sample size of 23 participants will have a power of 80% with a significance level of 5%. The sample size calculation was done using G*Power version 3.1.9.2.

Visit # 1 - Screening Visit: During the screening visit, the study coordinator will run through the study protocol and obtain written informed consent as well as participants' contact information. Eligibility to participate in the study will be based on set inclusion and exclusion criteria, completion of physical activity questionnaires, anthropometric assessment, bioelectrical impedance analysis (BIA), and analysis of biomarkers for kidney and liver function, electrolyte status, and thyroid-stimulating hormone.

Visit # 2 - Orientation Visit: During the orientation visit, participants will answer questions related to their health status and food preferences, will have their energy requirements assessed by an 1-hour WBCU test and will be provided an explanation about the run-in diet period. Body composition will also be assessed using dual energy X-ray absorptiometry (DXA) and air displacement plethysmography (ADP).

Visits # 3 \& 5 - Fitness Test \& Run-In Diet Visit: To standardize the exercise intensity while in the WBCU, participants will attend a fitness test visit prior to their first WBCU test visit. They will perform a submaximal exercise test on a treadmill (Freemotion Incline Trainer). The exercise test will begin at an individualized walking speed characterized as comfortable and sustainable. The incline will increase by 2% every three minutes until a RER of 0.9 has been achieved. During exercise, expired gases will be analyzed by a calibrated TrueMax® metabolic measurement system (ParvoMedics, Sandy, UT). To reproduce the same conditions during the WBCU exercise session, a breakfast identical to that provided inside the WBCU (CON Group) will be given to participants at 9 am and the treadmill test will start at 10:20 am. To determine the workload for the WBCU exercise session, each participant's respiratory exchange ratio (RER) will be plotted against their fitness test workload. The workload at which an RER of 0.85 occurred will be selected as the workload for the WBCU. We anticipate there will be a RER of 0.85 ± 0.03 during the WBCU control exercise session. The small difference may be due to factors such as the change in substrate oxidation throughout a 40-minute bout of exercise.

After the fitness test, participants will receive all the meals necessary to complete the 3-day run-in diet. This will standardize dietary intake among participants and minimize the effects of any eating style/behaviours on baseline data. The run-in diet will be a eucaloric diet and will have the same macronutrient distribution as of CON group diet (55% of carbohydrate, 15% of protein, and 30% of lipid). During this three-day run-in diet period, participants will be asked to abstain from any strenuous exercise, including endurance and/or resistance exercises. They can exercise (moderate) and drink coffee during the first and second days of run-in diet, but not during the third day.

Visits # 4 \& 6 - Whole Body Calorimetry Test Visits: Participants will complete a WBCU test visit twice during the study period, which will occur after the run-in diet periods. These visits will consist of two 32 hours (1.5 days) energy expenditure assessments inside the WBCU. During the 32-hour measurement period, participants of both groups (CON and HP) will be provided with a five-meal diet (breakfast, lunch, dinner, and two snacks) through an air-lock drawer system. The CON group will receive a diet composed of 55% of carbohydrate, 15% of protein, and 30% of lipid. The participants will receive breakfast, lunch, dinner and two snacks (afternoon and evening). The HP group will receive a diet composed of 35% of carbohydrate, 40% of protein, and 25% of lipid constructed around a soy protein-based meal replacement (Almased®). Participants will consume approximately 1 gram of Almased® per kg of body weight mixed with olive oil and low-fat milk (1% fat) in their breakfast, lunch and dinner. Two snacks (afternoon and evening) composed of approximately 1 gram of Almased® per kg of body weight mixed with apple juice and olive oil will also be provided. Amounts of low-fat milk, olive oil, and apple juice will be adjusted on an individual basis in order to achieve the desired macronutrient composition for the HP group. A variation of ± 2% for each macronutrient and ± 50 kcal/day will be considered.

The exercise session will be performed on the first morning (from 10:20 a.m. to 11:00 a.m.) spent in the WBCU. The session will be performed on a treadmill (BH T10 Pro Treadmill). The speed and grade of the treadmill will be set based on the fitness test as previously described.

Blood samples will be taken four times while participants are in the WBCU:

• Fasting on the first day (at 07:45 a.m.);
• After the exercise session on the first day (at 11:00 a.m.);
• Two hours postprandial on the first day (at 02:30 p.m.);
• Fasting on the second day (at 08:30 a.m.). The following blood markers will be analysed: glucose, insulin, lipid panel, PYY, GLP-1, ghrelin, leptin, free glycerol, and free-fatty acid. While participants are inside the WBCU, urine must be collected during the entire time. This is necessary to determine total nitrogen excretion, protein used by participant's body during the test day. Participants will be asked to rate their appetite sensations on a 100-mm visual analogue scale (VAS) immediately before and 30 minutes after each meal and snack provided in the WBCU in order to measure subjective appetite sensations (hunger, satiety, fullness, and prospective food consumption). Participants will be asked to wear an accelerometer around the wrist during sleep. The motion sensor will measure participants' activity patterns during sleep. A two week wash-out period between the WBCU test visits is needed to reduce the carryover effects of the interventions. A two week washout period is typical of feeding trials with soy isoflavone intervention [4, 5].

Statistical Analyses: Data distributions will be evaluated by the Shapiro-Wilk W-test. Parametric variables will be expressed in average and standard deviation and then converted into delta scores (i.e. post-pre values). To determine the differences among the variables analyzed after the intervention (within) and between CON and HP groups (between), Student's t-test or Mann-Whitney tests will be applied, according to data distribution. Pearson's correlation coefficients will be determined to assess whether there is a statistically significant correlation among the variables. All analyses will be performed using SPSS version 22.0, considering a critical significance value of 5%.