Epidemiological and clinical trial evidence indicates that n-6 polyunsaturated fatty acid (PUFA) intake is cardioprotective. Nevertheless, claims that n-6 PUFA intake promotes inflammation and oxidative stress prevail. This narrative review aims to provide health professionals with an up-to-date evidence overview to provide the requisite background to address patient/client concerns about oils containing predominantly unsaturated fatty acids (UFA), including MUFA and PUFA. Edible plant oils, commonly termed vegetable oils, are derived from vegetables, nuts, seeds, fruits and cereal grains. Substantial variation exists in the fatty acid composition of these oils; however, all are high in UFA, while being relatively low in saturated fatty acids (SFA), except for tropical oils. Epidemiological evidence indicates that higher PUFA intake is associated with lower risk of incident CVD and type 2 diabetes mellitus (T2DM). Additionally, replacement of SFA with PUFA is associated with reduced risk of CVD and T2DM. Clinical trials show higher intake of UFA from plant sources improves major CVD risk factors, including reducing levels of atherogenic lipids and lipoproteins. Importantly, clinical trials show that increased n-6 PUFA (linoleic acid) intake does not increase markers of inflammation or oxidative stress. Evidence-based guidelines from authoritative health and scientific organisations recommend intake of non-tropical vegetable oils, which contain MUFA and n-6 PUFA, as part of healthful dietary patterns. Specifically, vegetable oils rich in UFA should be consumed instead of rich sources of SFA, including butter, tallow, lard, palm and coconut oils.

There is an increased use of vegetable oils containing n-6 fatty acids (FA) in aquafeeds, and several trials indicate that there might be an increased requirement of EPA and DHA for Atlantic salmon when they are fed higher dietary n-6 FA. With a limited supply of EPA and DHA for production of aquafeeds, it is important to know how to efficiently use these FA to maintain growth and health of the fish. In the present trial, three diets containing equal amounts of n-3 FA (about 7·7 % of total FA) and different n-6:n-3 FA ratios (about 1, 2 and 6), as well as one diet with n-6:n-3 FA ratio at about 1 but twice as much n-3 FA, were fed to Atlantic salmon. Despite constant dietary n-3, increasing dietary n-6 led to significantly reduced n-3 in tissue polar lipids. Interestingly, EPA was significantly reduced while DHA was not. Maintaining a stable n-3 content in the polar lipids when increasing dietary n-6 FA was only obtained by simultaneously increasing the dietary n-3 content and with this maintaining the same n-6:n-3 FA ratio. Polar lipid n-6 FA in tissues thus primarily reflected the dietary n-6:n-3 FA ratio and not the absolute dietary n-6 FA content. Neutral lipids, on the other hand, reflected the dietary absolute levels of both n-3 and n-6 FA. This study indicates that a better use of dietary EPA is achieved by keeping the dietary n-6:n-3 FA ratio low.

n-6 Fatty acids have been shown to exert pro-adipogenic effects, whereas n-3 fatty acids work in opposition. Increasing intakes of linoleic acid (LA; n-6) v. α-linolenic acid (ALA; n-3) in Western diets has led to the hypothesis that consumption of this diet during pregnancy may be contributing to adverse offspring health. This study investigated the effects of feeding a maternal dietary LA:ALA ratio similar to that of the Western diet (9:1) compared with a proposed ‘ideal’ ratio (about 1:1·5), at two total fat levels (18 v. 36 % fat, w/w), on growth and lipogenic gene expression in the offspring. Female Wistar rats were assigned to one of the four experimental groups throughout gestation and lactation. Offspring were culled at 1 and 2 weeks of age for sample collection. Offspring of dams consuming a 36 % fat diet were approximately 20 % lighter than those exposed to an 18 % fat diet (P < 0·001). Male, but not female, liver weight at 1 week was approximately 13 % heavier and had increased glycogen (P < 0·05), in offspring exposed to high LA (P < 0·01). Hepatic expression of lipogenic genes suggested an increase in lipogenesis in male offspring exposed to a 36 % fat maternal diet and in female offspring exposed to a low-LA diet, via increases in the expression of fatty acid synthase and sterol regulatory element-binding protein. Sexually dimorphic responses to altered maternal diet appeared to persist until 2 weeks of age. In conclusion, whilst maternal total fat content predominantly affected offspring growth, fatty acid ratio and total fat content had sexually dimorphic effects on offspring liver weight and composition.

Fish and PUFA consumption are thought to play a role in mental health; however, many studies do not take into account multiple sources of PUFA. The present study analysed data from a sample of 935 randomly selected, population-based women aged 20–93 years. A validated and comprehensive dietary questionnaire ascertained the consumption of n-3 and n-6 PUFA. Another assessed fish and energy intake and provided data for a dietary quality score. The General Health Questionnaire-12 (GHQ-12) measured psychological symptoms and a clinical interview (Structured Clinical Interview for DSM-IV-TR Research Version, Non-patient edition) assessed depressive and anxiety disorders. Median dietary intakes of long-chain n-3 fatty acids (310 mg/d) were below suggested dietary target levels. The only PUFA related to categorical depressive and anxiety disorders was DHA. There was a non-linear relationship between DHA intake and depression; those in the second tertile of DHA intake were nearly 70 % less likely to report a current depressive disorder compared to those in the first tertile. The relationship of DHA to anxiety disorders was linear; for those in the highest tertile of DHA intake, the odds for anxiety disorders were reduced by nearly 50 % after adjustments, including adjustment for diet quality scores, compared to the lowest tertile. Those who ate fish less than once per week had higher GHQ-12 scores, and this relationship was particularly obvious in smokers. These are the first observational data to indicate a role for DHA in anxiety disorders, but suggest that the relationship between DHA and depressive disorders may be non-linear.

The present study quantifies the relationships between diet fatty acid profile and fatty acid composition of rat skeletal muscle phospholipids. Young adult male Sprague–Dawley rats were fed, for 8 weeks, on one of twelve moderate-fat diets (25 % of total energy) differing only in fatty acid profile. SFA content ranged from 8–88 % of total fatty acids, MUFA 6–65 %, total PUFA 4–81 %, n-6 PUFA 3–70 % and n-3 PUFA 1–70 %. Diet PUFA included only essential fatty acids 18 : 2n-6 and 18 : 3n-3. The balance between n-3 and n-6 PUFA (PUFA balance) in the diet ranged from 1 : 99 to 86 : 14 % n-3 PUFA:n-6 PUFA. The slope of muscle phospholipid composition plotted against diet composition quantifies the response of muscle membrane composition to dietary fat (0, no response; 1, complete conformity with diet). The resulting slopes were 0·02 (SFA), 0·10 (PUFA), 0·11 (MUFA), 0·14 (n-3 PUFA) and 0·23 (n-6 PUFA). The response to PUFA balance was biphasic with a slope of 0·98 below 10 % diet PUFA balance and 0·16 above 10 %. Thus, low diet PUFA balance has greater influence on muscle composition than 18-carbon n-3 or n-6 PUFA individually. Equations provided may allow prediction of muscle composition for other diet studies. Diet PUFA balance dramatically affects muscle 20 : 4n-6 and 22 : 6n-3. This may have significant implications for some disease states in human subjects.

In this study, the intake of n-6 and n-3 PUFA of pre-school children in Flanders, Belgium, was evaluated, and recommendations to address the very low intake of long-chain PUFA are presented. Food consumption data (based on parentally reported 3 d dietary records obtained from October 2002 to February 2003) of 661 children (338 boys, 323 girls) between 2·5 and 6·5 years of age and the PUFA concentrations obtained from various food composition databases were used. The actual PUFA intake levels were compared to Belgian, European and American recommendations. Only the intake of linoleic acid (LA) fell within the recommended ranges. Margarine, bread, biscuits and chocolate products contributed most to LA intake. The intake of α-linolenic acid (LNA) was low compared to the recommendations and was obtained mostly from the consumption of margarines and fatty sauces. This resulted in a high LA/LNA ratio. The intake of all long-chain PUFA was far below the recommended levels. Meat and meat products were the most important sources of arachidonic acid. Consumption of fish and other seafood was very low, though these were the most important sources of long-chain n-3 PUFA. In conclusion, Flemish pre-school children should consume more n-3-rich products in order to increase their LNA intake and decrease their LA/LNA ratio. Furthermore, the replacement of meat products rich in SFA by poultry would increase the arachidonic acid intake. As well, fatty fish consumption needs to be increased, as it is a rich source of long-chain n-3 PUFA.