Physics of a gymnast is very important for appearance on the competition, but also is crucial for performance, as an extra weight decreases the ability to perform certain movements and leads to injuries. The aim of the study was to reduce body weight of young female gymnast with minimum losses of muscle mass changing diet. Nineteen years old gymnast was involved in the study. Nutrition was examined using food questionnaire and food records. Body impedance analyzer Ioi 353 was used for body composition analysis and Heath-Carter method – for somatotype determination. Wingate and Sargent test were applied for anaerobic capacity determination. A low carbohydrate energy restricted nutritional plan for five days was developed. The subject reduced her weight by 2.1 kg. Her anaerobic capacity did not change significantly according to Wingate test (relative average power 2nd visit – 6 W/kg and 5th visit - 6.22 W/kg), but according to Sargent test (2nd visit – 3345.6 W and 5th visit – 4252 W) her power increased. The results clearly show that the person reduced the weight for about one month and the largest percentage being due to the loss of body fat and this did not affect the anaerobic capacity of the gymnast.