Contribution of dietary and newly formed arachidonic acid to human milk lipids in women eating a low-fat diet

Background: Polyunsaturated fatty acids in milk are derived from direct int estinal absorption, endogenous synthesis, or maternal body stores. Arachido nic acid (AA) intake is frequently low in undernourished women, but milk se cretion of this fatty acid is similar to that in well-nourished women. Objective: The objective was to evaluate the contribution of dietary and en dogenously synthesized AA to its total secretion in the milk of women eatin g a low-fat diet. Design: Ten lactating women who habitually ate a low-fat diet (17% of energ y) received 2.5 mg [C-13]linoleic acid (LA)/kg body wt orally 5 mo postpart um. LA and AA concentrations and C-13 enrichment were measured in milk samp les collected before and after the tracer application. Total lipid, LA, and AA contents were determined in diet composites, Fatty acids were assessed by gas chromatography and C-13 enrichment by isotope ratio mass spectrometr y. Results: The cumulative 72-h recovery of [C-13]LA in milk was 16.3 +/- 6.4% of the dose; only 0.01% of the label was found as [C-13]AA. The calculated transfer of dietary LA and AA into milk was 32.8 +/- 18.0% and 11.8 +/- 6. 6%. respectively. AA originating from conversion of dietary LA contributed only 1.1% to the total milk AA secreted. Conclusions: Little milk AA originates from conversion of LA; 70% of LA and 90% of AA secreted in milk were not derived from direct intestinal absorpt ion. Our results suggest that maternal body stores are the major source of milk LA and AA in these women.