*3.3. The Influence of Cyclical Ketogenic Reduction Diet vs. Nutritionally Balanced Reduction Diet on Spiroergometric Parameters*

Spiroergometric parameters are shown in Table 3. Respiratory exchange ratio decreased in subjects on CKD while it did not change in subjects on RD. None of other spiroergometric parameters were significantly affected in CKD group.


**Table 3.** The effect of cyclical ketogenic reduction diet and nutritionally balanced reduction diet on aerobic performance parameters.

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 TFmax—maximal heart rate; Rmax—respiratory exchange ratio; Wmax—peak workload; VEmax—maximal pulmonary ventilation; VO2 max/kg—peak oxygen uptake; VO2max/TF—peak pulse oxygen; Wmax.kg peak workload/kg; W170 max/kg—physical working capacity (at a heart rate of 170/min). NS: Not significant. NA : not avalible.

In contrast, in RD group peak workload, peak oxygen uptake/kg, peak workload/kg, and physical working capacity at a heart rate of 170/min increased after 8 weeks of intervention.

#### **4. Discussion**

The most important finding of this study is that eight weeks of regular aerobic exercise combined with exercise training complemented by two different dietary approaches—cyclical ketogenic reduction diet or nutritionally balanced reduction diet—significantly decreased body weight and body fat in healthy young men to a similar degree while having differential influence on body composition, strength parameters, and aerobic performance.

Despite comparable influence of both diets on body weight, we detected distinctions in their effects on body composition. In CKD group, the drop of body weight was due to a combination of decreased body fat, body water, and a slight, but significant, decline in lean body mass. On the contrary, in RD patients neither body water nor lean body mass were significantly affected and the weight reduction was predominantly due to body fat loss. The influence of ketogenic diet combined with different forms of exercise on body composition has been studied both in athletes and in patients with obesity and other comorbidities on numerous occasions. In some of the trials, isocaloric [24] or hypocaloric ketogenic diet [25] did not significantly change lean body mass while reducing body fat. On the contrary and in agreement with our current data, Perissious and colleagues found a reduction in lean body mass in patients with obesity undergoing exercise program while being on low carbohydrate diet [26]. Differential effect of ketogenic vs. nutritionally balanced diet under hyperenergetic conditions has also been described in a study in healthy men undergoing an eight-week resistance training program. Under these conditions, lean body mass increased only in control diet while it was unaffected in the ketogenic diet group [27]. Finally, ad libitum low carbohydrate ketogenic diet reduced body mass and lean body mass without compromising performance in powerlifting and Olympic weightlifting athletes [28]. In our study, a slight decrease in lean body mass did not impair strength parameters as compared to baseline values. Nevertheless, we have noted that in RD patients both lat pull-down and leg-press significantly increased after eight weeks of intervention as compared to no change in subjects on CKD.

While neutral effect of CKD on strength parameters in our study could have been expected based on the previously published data [29,30], we hypothesized that ketogenic diet could be more efficacious in improving endurance parameters as compared to nutritionally-balanced reduction diet as suggested by some previous trials [31]. The increasing popularity of ketogenic diets in endurance athletes is based on the hypothesis that predominant fat utilization over the use of carbohydrates may improve energy availability during endurance exercise along with accelerated recovery [10]. Bailey and Hennesy recently reviewed available data on the influence of ketogenic diet on endurance in athletes. They included seven studies into their analysis and concluded that limited and heterogenous findings prohibit definitive conclusions [16]. In our study, we found decreased respiratory exchange ratio in CKD groups after eight weeks of intervention as compared with no effect of RD suggesting a shift towards lipid oxidation, which is in agreement with the mode of action of ketogenic diet and previously published data [32]. However, none of the endurance parameters as measured by spiroergometry have been affected in CKD group. On the contrary, in RD group peak oxygen uptake and peak workload significantly increased after eight weeks of intervention. Our data suggesting lack of improvement of endurance performance by ketogenic diet go in similar direction with results published by Burke and colleagues in 2017 [33] and reproduced by the same group in 2020 [34] where they found decreased endurance parameters in elite race walkers after ketogenic diet. By contrast, in one of the early studies, low carbohydrate diet improved endurance times during moderate exercise in moderately obese patients along with significant reductions in body weight and body fat mass [35]. Nevertheless, despite more pronounced fat loss the improvement on endurance performance with low carbohydrate diet was comparable to that of high carbohydrate diet group.

When interpreted the results of our study within the context of currently published data it is important to consider its strengths and limitations. The randomized design and the good compliance of the subjects to dietary and treatment regimens can be consider strong points of our trial. On the other hand, the limitations include relatively short duration, low number of subjects and inclusion of only male participants.

Taken together our data are in general agreement with most of the previously published studies [36] showing little or no benefit of ketogenic diet on endurance capacity. However, it should be noted that contribution of fatty acids to metabolic response may differ with respect to duration and intensity of exercise [37,38], exact type of training and numerous other characteristics. The utilization of fatty acids increases with prolonged bouts of exercise of moderate intensity suggesting that ketogenic diet might be useful especially with longer duration of aerobic exercise.

#### **5. Conclusions**

In summary, our data show that in healthy young males undergoing resistance and aerobic training comparable weight reduction can be achieved with ketogenic and nutritionally balanced reduction diet. In RD group, improved muscle strength and endurance performance was noted relative to neutral effect of CKD on these parameters. Furthermore, CKD also slightly reduced lean body mass. Our study thus demonstrates that the cyclical ketogenic reduction diet effectively reduces body weight but is not an effective strategy to increase anaerobic or strength performance in healthy young men. All in all, further randomized studies of longer duration are still needed to explore whether the response to different diets is affected by long-term adaptation responses and whether it differs in males and females or subjects with various types and levels of fitness.

**Author Contributions:** Conceptualization, P.K., D.H., R.P.D., M.H., and Z.V.; methodology, P.K., I.L., Z.L., B.J.K., J.T., V.H., M.M., D.H., Z.V., and R.P.D.; writing—original draft preparation, P.K., M.H., and Z.V.; and writing—review and editing, all authors. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Funded by CZ-RO ("Institute for Clinical and Experimental Medicine—IKEM, IN 00023001") and RVO VFN 64165 to M.H.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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