The Quest For the Best N6:N3 Ratio. Swine Study Suggests: 5:1 is Healthy, 1:1 Will Also Cut Fat and Build Muscle

Yes, this study is about omega-3s, but it is not about the beneficial effects of fish oil.

Ok, I see you are totally excited, so I am not going to beat around the bush for long: According to a soon-to-be-published study from the Hunan Provincial Engineering Research Center of Healthy Livestock, Institute of Subtropical Agriculture at the Chinese Academy of Sciences  a 5:1 ratio of n-6:n3 (as in omega-6 to omega-3) is good enough to keep pigs healthy.

Kicking out another couple of grams of omega-6 fatty acids, on the other hand, had pretty intriguing effects on the body composition of the ninety-six male cross-bred (Large White£
Landrace) pigs who happened to weigh about as much as an average human being (another advangate, of swine - HED calculations are not necessary; learn more).
Lineseed or soybean - that makes all the difference

I hope you did not already start popping fish oil, while you are reading this. After all, in this case the glorified residual waste from the fishery industry did not contribute to either the health or weight loss benefits Duan et al. observed in their pigs who were fed one of the four isoenergetic diets with n6:n-3 PUFA ratios of 1:1, 2·5:1, 5:1 and 10:1 for 2 months.

Table 1: Ingredients, nutrient and fatty acids composition of the diets the pigs received; † vitamin premix (Duan. 2013)

As the ingredient profiles of the different diets (table 1) tell you the major source of omega-3 fatty acids was lineseed oil. The latter is basically devoid of long-chain omega-3 fatty acids (EPA & DHA). Instead, it contains the short-chain variety aka alpha-linolenic acid that is often laughed at in the health and fitness community as being the useless precursor to the powerful "fish oils" EPA and DHA (note: the level of DHA was identical in all diets!).

So, no fish oil, just ALA

Although the allegedly more potent LC-PUFAs were missing, the changes in body composition and the overall improvement (=reduction) of the activity of the potentially pro-carcinogenic PI3K-alpha gene and the fat storage genes FATP-1 and PPAR-gamma (learn more about PPAR-gamma) were still impressive.

If you take a closer look at the data in figure 1, though, you will realize that the effects on body composition require a reduction to 2.5:1, better 1:1 to become significant.

Figure 1: Feed conversion rate, muscle mass, adipose tissue mass, lean to fat mass ratio expressed relative to the levels of the pigs in the 5:1 n6:n3 group after 2 months on the different diets (Duan. 2013)

At the same time there is a clear relationship between increased adiposity and the amount of soybean oil in the pig diets. Thank god that the USDA in their incredible wisdom lists it among the top dietary sources for fat *sarcasm*.

Ah, I'd better not get political here, but let me point out one thing: In view of the currently available scientific evidence it borders physical injury resulting from negligence that the "guidelines" do not put an emphasis on the reduction of the the crazily high n-6:n-3 ratio of the Standard American Diet (16-17:1).

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Unlike this pig study, a previous rodent study suggests you should pick EPA over DHA over ALA for weight loss purposes (learn more)

Bottom line: This is one of the most convincing well-controlled animal studies we have that would support that the purportedly "paleolesque" 1:1 ratio of n-6:n-3 fatty acids entails highly significant health benefits,  even if those omega-3 fatty acids don't come from fish, but from lineseed oil.

One thing we must not forget, though, is the fact that the beneficial changes in health and body composition were brought about by the concomittant reduction in omega-6 and increase in omega-3 fatty acids. Simply drinking a bottle of lineseed or cod liver oil everyday could thus do more harm than good, because with ~3g of oil per 100g the diet was also low in total fat and almost devoid of saturated fats and whether the same results would occur in a high fat scenario is beyond what the study at hand can tell us.

References:

• Duan Y, Li F, Li L, Fan J, Sun X, Yin Y. n-6:n-3 PUFA ratio is involved in regulating lipid metabolism and inflammation in pigs. Br J Nutr. 2013 Aug 15:1-7. [Epub ahead of print]
• Miller ER, Ullrey DE. The pig as a model for human nutrition. Annu Rev Nutr. 1987;7:361-82. Review.