Influence of dietary linoleic acid intake with different fat intakes on arachidonic acid concentrations in plasma and platelet lipids and eicosanoid biosynthesis in female volunteers

Background/Aim: N-6 fatty acids are considered to promote diseases
prevalent in industrialized countries and characterized by an
increased eicosanoid biosynthesis from arachidonic acid (AA). We
investigated the impact of the linoleic acid (LA) intake on AA
levels in humans. Methods: Six healthy female volunteers (age range
2334 years) were given liquid formula diets (LFD) devoid of AA for
6 weeks, providing a constant intake of zero energy% (LFD 0:
protein 15%, carbohydrates 85%) or 20 energy% (LFD 20: protein 15%,
carbohydrates 55%, fat 30%) LA, for 3 weeks each. Fatty acids of
plasma cholesteryl esters and platelet lipids were determined each
week, and the prostaglandin biosynthesis was measured in 24-hour
urine samples. Results: LFD 0 increased (+31% of initial value) and
LFD 20 lowered (-30% of initial value) the percentage of AA in
plasma cholesteryl esters and platelet lipids. Moreover, absence of
dietary AA lowered the percentages of AA in plasma (-31% week 0 vs.
week 6) and platelet (-11%) lipids, indicating a low transformation
of LA. LFD 0 reduced urinary metabolite levels of prostaglandins D,
E, and F in 24-hour urine samples (-48%, p < 0.001) within 24 h,
but did not significantly affect platelet aggregation (-10%) and
thromboxane formation (-25%). LFD 20 significantly lowered platelet
aggregation (-25%) and thromboxane formation (-43%). The
prostaglandin metabolite levels increased during the first 10 days,
declined thereafter, and were lower than the preexperimental values
at the end of the 3-week period. Conclusions: The results show that
dietary LA does not increase the AA levels in plasma or platelet
lipids and does not persistently contribute to prostaglandin
biosynthesis which is increased by AA intake with Western diets.