Linoleic (LA) and alpha-linolenic (ALA) acids are the only truly essential N6 and N3\ud polyunsaturated fatty acids (PUFAs), and the precursors of arachidonicand\ud docosahexaenoic (DHA) acids, the most prevalent PUFAs in the mammalian brain.\ud Whilst main dietary sources of N6 are plant oils and red meat, the main sources of DHA\ud include seawater fish. This issue becomes apparent when considering typical\ud westernised diets. Furthermore, marine sources are currently threatened due to\ud overfishing and no sustainability. Here we investigated the serum, hypothalamus, liver\ud and white adipose tissues (WAT) fatty acid (FA) composition of rats fed a diet enriched\ud with either fish oil (FO) or soybean oil (SO). Whilst FO contains abundant DHA, SO\ud provides small amounts of ALA, alongside its important LAcontent. Fifteen 35-day old\ud Wistar rats were fed a control chow, or a diet enriched with FO (FOD) or SO (SOD) for\ud 8 weeks. Rats were sacrificed, trunk blood collected, hypothalamus, liver and WAT\ud dissected, and their FA composition analysed by gas chromatography. FOD increased\ud N3 content and SOD increased N6 content in all tissues. However, SOD significantly\ud increased DHAin hypothalamus and serum, a result not observed in other SOD tissues.\ud Whilst the SOD rats developed obesity, the FOD did not. SOD rats developed obesity\ud and imbalanced N6/N3 peripherally, but their hypothalamic N3 content was increased.\ud Such results further corroborate biomagnification and the preferential FAuptake by the\ud brain. Additional studies are necessary to investigate how nutrient-unbalanced diets\ud further affect brain metabolism.