Short-term weight-reducing regimens were shown to influence fatty acid composition of serum lipids unfavorably. Adding long chain n-3 polyunsaturated fatty acids (n-3 LC PUFA) to a low-calorie diet (LCD) could avoid these changes. The aim of this study was to examine the effect of a short-term in-patient weight-reducing regimen including LCD with yogurt enriched by low doses of n-3 PUFA (n-3 LCD). The enriched yogurt contained 790 mg of fish oil, predominantly eicosapentaenoic (20:5n-3; EPA) and docosahexaenoic (22:6n-3; DHA). Forty obese women were randomly assigned to the group consuming LCD and joghurt either with or without n-3 enrichment. Following the 3-week diet in the n-3 LCD group a significantly higher increase in the proportion of n-3 LC PUFA (sum of n-3 FA, EPA and DHA) in serum lipids was confirmed. In phospholipids (PL) a significant difference in the sum of n-6 fatty acids was found, a decrease in the n-3 LCD group and an increase in LCD group. Significantly higher increase in the PL palmitate (16:0) was shown in the LCD group. The results suggest that low doses of n-3 fatty acid enrichment can help to avoid unfavorable changes in fatty acid composition in serum lipids after a short-term weight-reducing regimen.