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 intestinal absorption, endogenous synthesis, or maternal body stores. Arachidonic acid (AA) intake is frequently low in undernourished women, but milk secretion of this fatty acid is similar to that in well-nourished women.


OBJECTIVE
The objective was to evaluate the contribution of dietary and endogenously synthesized AA to its total secretion in the milk of women eating a low-fat diet.


METHODS
Ten lactating women who habitually ate a low-fat diet (17% of energy) received 2.5 mg [(13)C]linoleic acid (LA)/kg body wt orally 5 mo postpartum. LA and AA concentrations and (13)C enrichment were measured in milk samples 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 (13)C enrichment by isotope ratio mass spectrometry.


RESULTS
The cumulative 72-h recovery of [(13)C]LA in milk was 16.3 +/- 6.4% of the dose; only 0.01% of the label was found as [(13)C]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 absorption. Our results suggest that maternal body stores are the major source of milk LA and AA in these women.
Del Prado
M
M
Unidad de Investigación Médica en Nutrición, Instituto Mexicano del Seguro Social, México City.
Villalpando
S
S
Elizondo
A
A
Rodríguez
M
M
Demmelmair
H
H
Koletzko
B
B
D000328:Adult; D000886:Anthropometry; D016718:Arachidonic Acid / Q000008:administration & dosage* / Q000096:biosynthesis* / Q000378:metabolism; D002247:Carbon Isotopes; D002849:Chromatography, Gas; D018752:Diet, Fat-Restricted; D005260:Female; D006801:Humans; D007700:Kinetics; D007774:Lactation / Q000378:metabolism*; D019787:Linoleic Acid / Q000008:administration & dosage* / Q000378:metabolism; D011939:Mental Recall; D008895:Milk, Human / Q000737:chemistry*; D012424:Rural Population; D013053:Spectrophotometry
D002247:Carbon Isotopes; D016718:Arachidonic Acid; D019787:Linoleic Acid