Effects of Soy Protein and Creatine Supplementation on Certain Parameters in Men Performing Resistance Exercise

This study was designed as a randomized controlled trial. The study will be conducted with 54 male participants aged 18-35 years (CrM: 18, Soy: 18, Placebo: 18) who regularly attend gyms located in the Central district of Bitlis province and apply to the laboratory of Bitlis State Hospital. Data collection is planned between December 2025 and February 2026. Inclusion criteria for the study were determined as being between 18 and 35 years of age, engaging in regular resistance training for at least one year, having no metabolic diseases, not using regular medication, and not having used any dietary supplements in the last three months prior to the study. Exclusion criteria were defined as being under 18 or over 35 years of age, engaging in resistance exercise for less than one year, using tobacco and alcohol, using regular medication, having an allergy to soy protein, having a psychiatric disorder, and being female.

Voluntary individuals evaluated according to the inclusion criteria and deemed suitable for participation will be randomized using the 'Block Randomization' method. One-third of the individuals selected through the randomization method will be given creatine monohydrate supplementation, one-third soy protein supplementation, and one-third placebo. While all products to be used in our study are provided by a company with GMP (Good Manufacturing Practices) certification, products commonly consumed by athletes will be used, as stated in the literature summary. Creatine and soy protein are products that are widely used as dietary supplements in the market and are accepted as safe. Both products will be used within recommended dose limits. No invasive procedures will be performed on the participants in our study (no blood sampling will be conducted); participants who are routinely checked by a specialist physician will be included in the study.

A Personal Information Form, prepared by the researchers through a literature review, will be administered to the participating individuals using the face-to-face interview technique. The Personal Information Form questions consist of 15 open-ended and multiple-choice questions aimed at determining the individuals' general information, dietary habits, dietary supplement use, and nutrition and hydration status during training.

To evaluate the nutritional status of the participants, a consecutive three-day (two weekdays and one weekend day) dietary intake record will be taken at the beginning and end of the study. A three-day Food Record Form will be given to the participants during the first and fourth visits, and how to complete it will be explained to the individuals. After the records are collected, the amounts and contents of the consumed foods will be detailed and questioned by the participants and the researcher. In the evaluation of foods consumed at home, the book 'Food and Nutrition Photo Catalogue: Measures and Amounts' will be utilized. The portion contents of meals consumed by individuals outside the home will be calculated using the book 'Standard Food Recipes for Institutions Serving Mass Catering'. Dietary intake records will be analyzed using the BeBIS Nutrition Information System (Germany) 7.2 software, and the daily average energy and macro/micronutrient amounts consumed by the individuals will be determined.

Biochemical parameters to be used in the study will be obtained from the individuals' files within the scope of routine analyses performed during routine applications to Bitlis State Hospital. Hemogram values, creatine kinase, fasting blood glucose, total cholesterol, triglyceride, HDL cholesterol, LDL cholesterol, AST, ALT, ALP, iron, ferritin, and testosterone values of all individuals participating in the study will be used.

The study will consist of a total of four visits. On the day of the first visit, participants who volunteer to take part in the study will be informed about the research, informed consent forms will be completed, and forms for recording a three-day dietary intake record will be provided. The second visit will be conducted three days after the first visit; during this visit, the dietary intake records distributed in the first visit will be collected, and diet programs along with supplements will be distributed to the participants. The third visit will take place 53 days after the second visit. During the third visit, a three-day dietary intake record form will be distributed to assess the participants' compliance with the diet. The final visit will be conducted three days after the third visit. In the last session, the participants' three-day dietary intake records, BIA, skinfold thickness, body circumference measurements, and handgrip strength measurements will be obtained, and the study will be concluded.

Within the scope of the first and fourth visit monitoring, the body weight and body composition measurements of the individuals will be performed with the help of a Bioelectrical Impedance Analysis (BIA) device (Tanita BC 601, Japan). Measurements will be taken following a fast of at least 12 hours, after asking participants not to engage in heavy activity the previous day and not to consume drinks with diuretic properties such as tea and coffee. Metallic jewelry will be removed during the measurement. As a result of the measurement, the individuals' body weight (kg), body fat percentage, body fat mass (kg), fat-free mass (kg), and body muscle mass (kg) values will be determined. Skinfold thickness measurements will be taken from the biceps, triceps, subscapular, and suprailiac regions using a Holtain brand caliper. Participants' waist circumference and hip circumference measurements will be taken using a tape measure. Participants' handgrip strength measurements will be taken from both hands with three repetitions using a Herklotzn 120 kg (Germany) hand dynamometer. Participants will be asked to squeeze the dynamometer with all their strength, and the highest value obtained will be recorded. At the end of the study, initial measurement values and final measurement values will be compared between the groups.

The Personal Information Form will be completed for the participants, and the diets and supplements to be applied during the study will be given to the participants by the researchers. During the second visit, the REE (Resting Energy Expenditure) values of the individuals will be calculated by the researchers using the Mifflin-St. Joer calculation formula. The daily basic activities of the participants will be questioned by the researchers, and the physical activity coefficient will be calculated. As a result of the calculations made, the total energy requirement of each individual will be calculated, and the diets of the individuals will be planned according to the Dietary Guidelines for Turkey (TÜBER).

Among the nutritional supplements to be used in the research, 5 g/day of creatine monohydrate, which is recommended for the loading period and used in many studies in the literature, will be provided by dissolving it in 500 mL of water prior to exercise.

In a meta-analysis study conducted with soy protein, it was observed that the effective dose ranges used in the study were 10-53.3 g/day. However, in most studies conducted, the supplement dose was seen to be 22 g/day, and in our study, 22 g/day of soy protein supplement will be provided by dissolving it in 500 mL of water prior to exercise. For placebo supplementation, a powdered placebo content produced using maltodextrin by a company with GMP (Good Manufacturing Practices) certification will be used. Placebo supplementation will also be consumed by dissolving 25 g/day in 500 mL of water prior to exercise.

Periodic, free-weight resistance training will be applied to the individuals in the study for 8 weeks. Training will start on the first day of supplementation, and training programs containing all body muscles (4 days/week) will be applied. Each exercise session will end with a 10-minute treadmill warmup, 40 minutes of resistance exercise, and a 5-minute cooldown phase. The first day of training will consist of a total of 7 different exercises targeting chest and triceps muscles (Triceps: Triceps push down, lying dumbbell triceps extension, overhead triceps extension; Chest: Bench press, incline dumbbell fly, pec deck fly, chest dip). Each exercise will consist of 4 sets and 8-12 repetitions. The second day of training will consist of a total of 7 exercises involving back and biceps muscles (Back: Lat pulldown, chin up, pull up, deadlift; Biceps: Barbell biceps curl, seated dumbbell biceps curl, hammer curl). Each exercise will consist of 4 sets and 8-12 repetitions. The third day of training will consist of 5 exercises targeting shoulder muscles (overhead press, front raise, rear delt fly, full can). Each exercise will consist of a total of 3 sets and 10-15 repetitions. The fourth day of training will consist of a total of 7 different exercises targeting leg and abdominal muscles (Leg: Leg curl, squat, leg press, hamstring curl; Abdomen: Abdominal crunch, legs up crunch, side crunch). Each exercise will consist of a total of 4 sets and 8-15 repetitions. Individuals will be informed that they should rest for approximately one minute after each set.