Athlete nutrition is becoming an increasingly important factor on the path to achieving top results. Nutrients such as soluble fiber can alter the intestinal microbiota, resulting in metabolites with a positive effect on metabolism. Thus, the fibers become available, an additional source of energy to the host, have an anti-stress effect and delay the feeling of fatigue. The primary goal of the study is to determine the impact of soluble dietary fiber on increasing athletic efficiency, the secondary goal is to determine the impact of fiber on delaying fatigue. Subjects will be randomly divided into experimental and control group. The sample of variables will consist of genome microbiota genome sequencing data, measures to assess morphological characteristics, lower extremity explosive strength tests, and cardiovascular endurance. The statistical package SPSS will be used for data processing. The expected scientific contribution of this research is to expand the scientific knowledge about the importance of dietary fiber in the diet of athletes with the aim of improving sports performance.

Material, participants, methodology and research plan The material will be soluble fiber NUTRIOSE and placebo. Nutriose, derived from corn, is generally well tolerated and no allergic reactions are known. Participants will be made aware of this in informed consent. If, however, there will be any adverse reactions in participant, participant will withdraw from the study immediately.

The participants will be 14 adult, professional basketball players. The sample of subjects was determined by the size of the group in the same training process in order to exclude the influence of different training processes on the research results. Participants who have used antibiotics in the last 3 months, participants with type 1 and 2 diabetes, and also who have used other ergogenic aids in the last 30 days and still using them are excluded.

Participants will be randomly divided into two groups: the experimental group that will consume the tested fibers and the control group that will consume placebo. Design is a double-blind study where an independent statistician will be entrusted with the randomization of subjects into the two groups.

Sample variables:

Methods: dietary methods, anthropometric methods, fatigue assessment questionnaire and fecal samples analysis.

The sample of variables consists of: fecal sample for intestinal microbiota sequencing, measures to assess morphological characteristics (body height, body weight, triceps skinfold, subscapular skinfold, chest skinfold, abdomen skinfold, suprailiocristal skinfold, thigh skinfold, axillary skinfold, fat percentage calculated by the seven skinfolds algorithm).

Dietary methods will be used to control eating habits and fiber intake prior to testing and to control diet during testing. The methods will be a food diary (three-day) and as an unannounced control of daily food intake once a week will be a 24-hour dietary recalls. The three-day food diary will show diet and average fiber intake just before the start of testing and unannounced control of daily food intake as evidence of unchanged eating habits during the study. All collected dietary data will be processed using Croatian food tables in addition to American tables for all foods whose chemical composition is not available in national tables.

In assessing the athletic performance of basketball players, emphasis will be placed on the explosive power of the lower extremities (concentric and eccentric contractions). Anthropometric methods will use tests to assess vertical explosive power (squat jump, countermovement jump, one legged countermovement jump, maximal countermovement jump, continuous jumps with straight egs, continuous jump with bent legs) with Optojump system and explosive power - sprint (5m, 10m and 20m sprint) with the Powertimer Newtest system. Aerobic endurance tests (BEEP test with sound signal) and anaerobic endurance test (300 m (15x20)) with Powertimer Newtest system will be used to assess cardiovascular endurance. Laboratory measurements will be performed within the Sports Diagnostic Center of the Faculty of Kinesiology, University of Zagreb.

Fecal samples will be collected at the Faculty of Food Technology and Biotechnology, University of Zagreb. Analysis of the composition of the intestinal microbiota by DNA sequencing from fecal samples will be performed using an Illumina NGS device.

Participants will complete a questionnaire on a daily basis in subjective feeling of fatigue on a scale of 1 to 10 (rate of perceived exertion).

Participants will have a daily short questionnaire on: bloating, change in stool consistency, nausea and weakness.

Research plan:

The research lasts a total of 8 weeks. Initial measurements before the start of supplementation include anthropometric testing and taking the first microbiota sample. This is followed by taking another microbiota sample 2 weeks after the start of supplementation. Final measurements follow at the end of 4 weeks of supplementation that include anthropometric testing and taking a third microbiota sample. Finally, the fourth microbiota sample will be 4 weeks after the final and 8 weeks after the initial measurements, respectively. After getting acquainted with the basics of testing, participants will sign a consent to participate.

Three days before the initial testing, participants will be explained how collect feces and the collection containers will be distributed. Each participant will be subjected to a dietary method of measuring food intake, a three-day diet diary and unannounced controls of daily food intake, once a week. Initial measurements will begin by collecting fecal-sampled containers. After measuring the morphological characteristics, tests to assess explosive power and aerobic and anaerobic capacities will be approached. After the initial testing, during the regular competition season, the participants of both groups will continue the training process without the possibility of additional training or changes in the training process. The experimental group (n = 7) will consume 2x8.5 g/day of soluble dietary fiber over four weeks, while the control group (n = 7) will consume the same amount of placebo carbohydrates. The dose was determined by previous studies with a proven effect on the morphological characteristics of participants and without side effects.

Participants will be taken by the respondents after the training in the presence of the research leader, and on the day off they will send a picture of an empty bag in mobile phone application. This will resolve "compliance." The training process will be the same for both groups, and participants will be advised not to change their diet pattern for two weeks prior to the test as well as for the duration of the experiment. After each training session and basketball game, respondents will complete a questionnaire in subjective feeling of fatigue on a scale of 1 to 10 (rate of perceived exertion). The final measurements are equal to the initial ones.

Data processing methods:

The sample size in the study was estimated through a test power of 70 % and a significance level of 5 %. The statistical program SPSS (Statistical Package for the Social Science), version 17.0., SPSS, Inc. will be used for data processing. Descriptive statistical parameters of the monitored variables will be calculated: arithmetic mean (AS), standard deviation (SD), minimum (MIN), maximum (MAX) and range result (RAS) and curvature (KURT) and distribution asymmetry (SKEW), and normality distribution by the Kolmogorov-Smirnov test. Multivariate and univariate analysis of variance (MANOVA and ANOVA) will be used to analyze the effects of training between initial and final measurements within groups, as well as to analyze differences in effects between groups. In case of statistically significant differences between groups, Tukey post hoc analysis will be used to determine the difference between specific groups. All conclusions will be drawn at the level of statistical error p <0.05.

Inclusion Criteria:

• Professional basketball players from the same team participating in the same monitored training process

Exclusion Criteria:

• Diabetes or other chronic disease, taking sports performance enhancing drugs, taking antibiotics 3 months prior or during the course of the study

Program is used to make random selection and grouping of participants in two groups: experimental one receiving fiber and control one, receiving placebo. A research assistant who is not involved in study (neither design nor implementation) will pack prebiotic/placebo daily doses (20 grams/day) and provide nutritionist who is one of the investigators with doses for each participant. Only when the study is completed and all results processed will the information on who received fiber/placebo be released.