The aim of this study was to examine changes in fatty acid composition of serum phosphatidylcholine, cholesteryl esters and triacylglycerols and in that of adipose tissue. Material and methods: Subjects of the study were 34 obese women who were on a low calorie diet for a short period (28 days, 3 420 kJ/day). The serum lipid profile was measured by standard biochemical methods and fatty acid analysis of serum lipids and adipose tissue was performed using capillary gas chromatography. Results: The diet used reduced the body mass (from 92.6 ± 11.4 to 86.3 ± 11.3 kg). BMI (from 34.2 ± 3.3 to 31.9 ± 3.3 kg/m 2), fat and fat free mass (from 42.6 ± 10.5 to 39.2 ± 9.9 kg, and from 48.9 ± 6.7 to 45.9 ± 5.7 kg, resp.), waist/hip circumference ratio (from 0.84 ± 0.06 to 0.78 ± 0.18) and waist circumference (from 102.5 ± 10.1 to 97.9 ± 10.4 cm). We also observed an altered lipid serum profile: lower levels of total cholesterol (from 5.29 ± 0.82 to 4.62 ± 0.93 mmol/L), HDL-cholesterol (from 1.02 ± 0.18 to 0.90 ± 0.16 mmol/L), phospholipids (from 2.69 ± 0.36 to 2.34 ± 0.32 mmol/L), lipoprotein (a) (from 0.23 ± 0.34 to 0.16 ± 0.25 g/L), apolipoprotein A-I (from 1.35 ± 0.23 to 1.09 ± 0.22 g/L) and apolipoprotein B (from 0.82 ± 0.12 to 0.72 ± 0.13 g/L). The diet resulted in an increased content of saturated and decreased content of n-6 polyunsaturated fatty acids in serum, phosphatidylcholine and cholesteryl esters; the content of n-3 polyunsaturated fatty acids decreased only in cholesteryl esters. Serum triacylglycerols had a lower content of saturated and higher content of monounsaturated fatty acids vs the state before the diet. A decrease of the n-3 polyunsaturated fatty acid content was observed in adipose tissue. Conclusion: As a result of body mass reduction by a short-time low calorie and low fat diet, the polyunsaturated fatty acid content tends to decrease with concomitantly increased saturated fatty acid content. The appropriate fat content of the diet should be considered in the further stages of treatment.

        Key words: obesity, low caloric diet, serum lipids, fatty acids, adipose tissue.