## 5 Conclusions  
In summary, we provide direct evidence that reduced EA in male trained endurance athlete by 50% results in poor endurance performance, worse explosive power and altered lactate metabolism. It negatively affects wellbeing and eating behaviours. The TFEQ and Wellbeing questionnaire are useful tools for detection of changes and seem to be more sensitive than blood changes. Drastic reductions of EA could lead to poor eating behaviours and we suggest EA should be lowered by no more than 25% in order to avoid potential eating disorders. This is the first study providing direct evidence that EA is correlated with testosterone, meaning that EA was measured and not estimated. It is also the first to prove that performance can be affected before health detrimental effects occur. This implies the necessity for further research in EA in males. The findings also suggest that the threshold for LEA in men is above 15 kcal/kg FFM/day. The practical application of this study is that male athletes should aim for optimal EA when striving for results. Drastic changes in EA have harmful effect on performance as early as in 14 days, which should be of great interest for coaches in endurance disciplines when considering body mass optimisation in athletes. Finally, whether mREE/pREE could be used in future as a surrogate marker for suboptimal EA needs more evidence.  
The following are available online at [[https://www.mdpi.com/article/10.3390/app11188618/s1](https://www.mdpi.com/article/10.3390/app11188618/s1)]([https://www.mdpi.com/article/10.3390/app11188618/s1](https://www.mdpi.com/article/10.3390/app11188618/s1)), Supplementary File S1: Table S1: Inclusion criteria for participants, Figure S1: Flowchart of enrolment, Supplementary File S2: Table S2: Well-being subjective questionnaire with scoring system, Supplementary File S3: Table S3: Subjective assessment of 50% EA reduction from all 12 participants, Figure S2: Differences in EEE before intervention and during the 50% EA reduction state, Figure S3: The calculated EEE for 50% EA reduction compared to the achieved EEE for each of the 12 subjects, Figure S4: Time and EEE divided into training modalities as measured in 50% EA reduction intervention.  
Conceptualization, I.J., N.K., S.R., methodology I.J.; N.K.; S.R., formal analysis I.J., investigation I.J.; resources, I.J.; data curation, I.J.; writing--original draft preparation, I.J.; writing--review and editing, I.J., N.K., S.R.; supervision S.R.; funding acquisition I.J. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Slovenian Research Agency grant number P5-0147. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.  
The study was conducted according to the guidelines of the Declaration of Helsinki. National medical ethical approval was acquired before the start of the study (No. 0120-202/2020/5).  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study  
Data Availability Statement: Additional Data are available upon reasonable request.  
The authors declare no conflict of interest.