Dietary n-3 PUFA have many beneficial effects on cell and tissue function and on human health. In mammals the n-3 essential fatty acid α-linolenic acid (ALNA) can be converted into longer-chain (LC) n-3 PUFA such as EPA and DHA via a series of desaturase and elongase enzymes that are mainly active in the liver. Human studies have identified that males and females appear to differ in their ability to synthesise EPA and DHA from ALNA, with associated differences in circulating concentrations. Based on studies of women using the contraceptive pill or hormone-replacement therapy and of trans-sexual subjects it is suggested that sex hormones play a role in these differences. The rat has been used to investigate gender differences in n-3 PUFA status since this model allows greater dietary control than is possible in human subjects. Like human subjects, female rats have higher plasma DHA concentrations than males. Rats also respond to increased dietary ALNA in a way that is comparable with available human data. The concentrations of LC n-3 PUFA in rat plasma and tissues are positively associated with circulating concentrations of oestradiol and progesterone and negatively associated with circulating concentrations of testosterone. These findings suggest that sex hormones act to modify plasma and tissue n-3 PUFA content, possibly by altering the expression of desaturase and elongase enzymes in the liver, which is currently under investigation.

No abstract

In rats and humans, females have higher liver and/or plasma docosahexaenoic acid (DHA) content than males. We hypothesized that the effect of variation in total fat or essential fatty acid intakes on liver and plasma fatty acid composition would differ between sexes. Rats were fed a low-fat soybean oil (LFS), high-fat soybean oil (HFS), or high-fat linseed oil (HFL) diet for 20 d. There were significant sex differences in LFS rats in proportions of (n-3) and (n-6) fatty acids in plasma and liver contingent on lipid class. Significant diet x sex interactions were observed for eicosapentaenoic acid (EPA), DHA, and arachidonic acid (AA) status. HFL females had a higher proportion of EPA in plasma and liver phosphatidylcholine (PC), DHA in liver triacylglycerol (TAG), and AA in plasma PC than HFS and LFS females. These findings show that the effect of varying dietary fat intake on (n-3) and (n-6) long-chain PUFA (LCPUFA) status is modified by sex. Liver phospholipid and TAG fatty acid product:substrate ratios suggested greater Delta6 desaturase (Delta6D) activity in females than in males. The HFL diet induced higher Delta6D mRNA expression compared with the LFS or HFS diets and HFL females had 10% higher expression of Delta6D mRNA than HFL males. Together, these findings show that sex is an important determinant of the effect of variations in fat and fatty acid intake on LCPUFA status, which may have implications for recommendations for fat and fatty acid intake in humans.