2.3.2. Development of Endurance Skills

The plan consisted of a 30-min run at constant heart rate (at approximately 70% max TF or around 130–140 heart beats/minute).

#### 2.3.3. Supervision of Adherence to Training and Diet Protocols

Overall adherence to diet was checked once weekly by a nutritionist. Furthermore, adherence to CKD was evaluated through urinary ketone measurements performed twice daily and by measurement of blood β-hydroxybutyrate at the end of the study.

Training compliance was monitored through mandatory check-in procedures in a gym, and also by a sport tester for aerobic performance (TomTom Runner Cardio, TomTom, The Netherlands).

#### *2.4. Post-Intervention Testing*

Data collection procedures were the same as baseline testing procedures. To ensure reliability, power measures and performance testing were completed by the same researcher as at baseline for each subject. In addition, subjects conducted their testing at the same time and with the same personal researcher as pre-testing. Results from all tests were compared to the individual's baseline values and provided to the subjects after data analysis.

#### *2.5. Statistical Analysis*

Statistical analysis was performed using Sigma Stat software (SPSS Inc., Chicago, IL, USA). Graphs were drawn using SigmaPlot 13.0 software (SPSS Inc., Chicago, IL, USA). The results are expressed as mean ± standard deviation (SD). Differences of body composition (body fat %, weight, BMI, lean body mass, and fat mass), biochemical, and strength or aerobic performance parameters between CKD and RD were evaluated using one-way ANOVA followed by Holm-Sidak test. Paired t-test was used for the assessment of intra group differences as appropriate. Statistical significance was assigned to *p* < 0.05.

#### **3. Results**

## *3.1. The Influence of Cyclical Ketogenic Reduction Diet vs. Nutritionally Balanced Reduction Diet on Anthropometric and Biochemical Parameters*

Both CKD and RD decreased body weight (Figure 2), body fat mass and body mass index with comparable effects of both approaches (Table 1). Lean body mass and body water content was significantly reduced by CKD (Figures 3 and 4 and Table 1) while it was not influenced by RD.


**Table 1.** Anthropometric and biochemical parameters of subjects on cyclical ketogenic reduction diet or nutritionally balanced reduction diet at baseline and after 8 weeks of diet.

Data are mean ± SD. Statistical significance is from One-way ANOVA and paired *t*-test (V1—baseline testing vs. V2—testing after 8 weeks of diet). \* *p* < 0.05 vs. V1. BMI: Body mass index; CK: Creatine kinase; LDH: Lactate dehydrogenase; β-OH-butyrate—β-hydroxy-butyrate. NS: Not significant. NA : not avalible.

**Figure 2.** Individual responses of body weight for subjects before and after 8 weeks of cyclical ketogenic reduction diet (CKD) and nutritionally balanced reduction diet (RD). Statistical significance is from paired *t*-test \* *p* < 0.05 vs. baseline.

**Figure 3.** Individual responses of lean body mass for subjects before and after 8 weeks of cyclical ketogenic reduction diet (CKD) and nutritionally balanced reduction diet (RD). Statistical significance is from paired t-test \* *p* < 0.05 vs. baseline.

**Figure 4.** Individual responses of body water weight for subjects before and after 8 weeks of cyclical ketogenic reduction diet (CKD) and nutritionally balanced reduction diet (RD). Statistical significance is from paired t-test \* *p* < 0.05 vs. baseline.

None of the diets significantly affected serum concentration of creatine kinase or lactate dehydrogenase (Table 1), liver tests, urea, creatinine, or circulating lipids (data not shown). β-hydroxy-butyrate significantly increased in CKD group while it was unaffected in subjects on reduction diet (Table 1).
