Our goal was to determine the effects of 3-week low carb (LC) diet on body composition and physical performance in healthy adult women, who were physically active at least 3 months before the start of our experiment. The experiment have successfully completed ten subjects, with an average age of 29,3 ± 7,9 years and average body mass index of 26,4 ± 3,9. We measured body mass, the percentages of fat mass and muscle mass and the circumferences of the waist and hips. The tests for physical performance were back squats with 5 repetition maximum strength test, maximum number of pushups and rows on suspension trainer in 2 minutes and best 2000 m time on indoor rower. The average caloric intake of control and LC diet was very similar (1467 : 1446 kcal), while the percentages of macronutrients intake were very different (carbohydrates: 41,0 : 15,4 %; fats: 39,0 : 60,0 %; proteins: 20,0 : 24,5 %). LC diet lowered the body mass (– 1,3 kg), fat mass (– 0,8 kg), while maintained muscle mass and also lowered the circumference of belt (– 2,1 cm) and hips (– 0,9 cm). Physical performance tests have shown slight improvement after LC diet but the differences were not statistically significant, so we conclude that LC diet did not impair strenght and endurance in our subjects.