The low-energy protein diet providing 1559 kJ is the first accurately defined diet for the treatment of obesity in the CSSR. The daily amount contains 4.0 g fat, 33.0 g protein, 50.0 g carbohydrate, 5.6 g fibre and daily recommended allowances of vitamins. The diet is enriched with potassium, magnesium and iron. The low-energy protein diet was used for a period of 28 days in the treatment of 49 obese patients aged 40.49 +/- 1.39 years whose initial weight was 110.14 +/- 3.41 kg and the BMI 39.44 +/- 1.13. The therapeutic regime comprised in addition to the diet adequate physical exercise of aerobic character and training of correct eating behaviour. Four weeks treatment led to a significant decline of body weight (by 10.60 +/- 0.46 kg) and a significant drop of the BMI (by 3.65 +/- 0.16). Men lost more weight than women. In women a substantial drop of the body weight (90.5%) was due to reduction of body fat, while in men adipose tissue participated by 60.0% in the loss. During the fourth week of treatment a positive nitrogen balance was achieved, obviously due to adequate physical exercise. The waist/hip ratio was not affected by treatment in either group. The therapeutic regime influenced favourably some risk factors of ischaemic heart disease. In addition to a significant drop of the systolic and diastolic blood pressure a significant decline of total cholesterol, triacylglycerols and serum insulin occurred. There was a concurrent decline of the urinary C-peptide excretion. The therapeutic regime involving the low-energy protein diet was well tolerated by the patients. The incidence of side effects during treatment was less frequent than in treatment by intermittent fasts. No disorders of the cardiac rhythm were recorded during treatment.