The objective of this study was to evaluate changes in the concentrations of EPA and DHA in the erythrocytes and breast milk of a group of lactating women in the municipality of Sonsón (Antioquia) before and after receiving supplementation with these fatty acids for three months.In a quasi-experimental study, 11 lactating women were evaluated before and after EPA (100 mg) and DHA (250 mg) supplementation for three months. The consumption of omega-3 food sources was determined by simple frequency, anthropometry (weight, height) was performed, and the fatty acid profiles of erythrocytes and breast milk were determined with gas chromatography.Sonsón, Colombia.A group of lactating women in the municipality of Sonsón (Antioquia).Low consumption of foods that are sources of omega-3 fatty acids was found, as was low EPA and DHA content in erythrocytes and breast milk at the beginning of the study period. After supplementation, there was no significant change for EPA, however, there was a significant increase in DHA in both erythrocytes and breast milk; in addition, there was a decrease in the omega-6/omega-3 ratio.Supplementation with 250 mg of DHA increased its concentration in the blood and breast milk to levels approaching the recommended average DHA of 0.3%, where benefits have been seen for the mother.