|Does a (very) high fish oil diet entail the risk of going rancid - in spite of all its short-term health benefits?|
This article is about balance!
By now, you should have realized that this post is all about balance, the critical balance of 'stable' saturated and 'unstable' (poly-)unsaturated fatty acids - not in your diet, but in cells & tissue.
This is not an "anti-fish oil article" or anti-omega-3 article! It's an article to remind you not fall for the prominent black-and-white thinking and to falsely equate balance with mediocrity.Recent evidence of the importance of these numbers comes from a study that was conducted by researchers from the INRA UMR in Montpelier, France (Feillet-Coudray. 2013). It is, as you may have suspected, a rodent study. With a study duration of 12 weeks and the aspiration to investigate the long-term effects of diets containing 50 or 300 g lipid/kg in the form of either lard or fish oil, this was yet more than a concession to financial constraints.
In the life of a rodent, three months are equivalent to several human years (some sources would say 5 years, but I would not bet on that). A similar study in man would thus take several years - years in the course of which all study participants would have to be locked away in a metabolic ward to ensure that they eat nothing but what the scientists serve them.
|Figure 1: Total fatty acid (FA) composition of the LIVER and MUSCLE (mg FA/g tissue; Feillet-Coudray. 2013)|
No changes in muscle fatty acid make-up. How Come?
Apropos changes! If you look a the data in Figure 1 you will realize that the fatty acid make-up of the musculature in the study by Feillet-Coudray et al. did not change at all. In view of the significant changes in the fatty acid composition of the liver, this appears to be counter-intuitive and if we recall the study design and results of the previously cited study by Ayre et al. (1997) probably a result of the comparatively high omega-6:omega-3 ratio of the purported "fish oil" diet, which contained only 15g of omega-3 fatty acids per kg, and a whopping 21.7g of omega-6s. With an additional 25g of monounsaturated and 27.4g of saturated fats it is thus by no means an "omega-3", let alone "fish oil" diet as the one in the Airy study, which lead to major performance impairments in muscular endurance (and probably strength, which was yet not measured in the Ayre study | learn more).
|Figure 2: Fatty acid composition of the test diets (Feillet-Coudray. 2013)|
Not exactly representative of the contemporary diets, but still meaningful
From a scientific point of view the significant, but still small differences may be a limitation. From a practical point of view, the omega-3 : omega-6 ratios are however more realistic than those of a real 'fish oil only' diet:
- CONTROL & LARD ~ 7:1 vs. FISH ~ 3:2
- SAD ~ 15:1 vs. HIGH N3 ~ 1:1 - 3:1
You do not necessarily want to supplement daily, not in spite of, but rather because a recent Cambridge study shows that, compared to weekly administration, daily administration of fish oil supplements leads to an increased incorporation of eicosapentaenoic acid and docosahexaenoic acid into platelets and mononuclear cells in humans (Browning. 2014). Obviously, this doesn't mean that the same will be the case for the liver, but it clearly supports my previous recommendation to do prefer eating fish twice a week over supplements.As close as the FISH diet may be to the often hailed "optimal 1:1" ratio, the CONTROL and LARD diets both contain much more omega-3s / less omega-6s than the SAD diet. Against that background it's actually quite astonishing that
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- all rats developed liver steatosis associated with moderate liver injury when fed the 30 % lipid diets
- the rats in both the CONTROL and FISH group did so without getting obese (only the rats "on" the 30% LARD diet became obese; 11% higher body weight, 32% more body fat)
- both FISH (+30%) and LARD (+103%) had elevated insulin levels compared to the rodents on the 30% CONTROL diet; despite higher insulin levels, the effective glucose uptake in the FISH group was normal, while it was already compromised in the LARD group
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"[...] was increased with the fish-oil diet in comparison with the mixed and the lard diets. Within the 5 % lipid diets, the liver TBARS level was increased by 22 % with the fish-oil diet compared with the mixed diet, whereas within the 30 % lipid diets, the liver TBARS level was increased by 104 % with the fish-oil diet compared with the mixed diet." (Feillet-Coudray. 2013)It turned out that there was a direct correlation of pathological lipid oxidation and the amount of omega-3 fatty acids in the liver (p < 0·001; r = 0·319). Accordingly, the...
"glutathione peroxidase activity was decreased with the fish-oil 30 % lipid diet in comparison with the lard 30 % lipid diet" (Feillet-Coudray. 2013)The answer to the the question I raised in the caption of the image in the title of this article, i.e. "Does a (very) high fish oil diet entail the risk of going rancid - in spite of all its short-term benefits?" is "Yes, it does!".
- Ayre KJ, Hulbert AJ. Dietary fatty acid profile affects endurance in rats. Lipids. 1997 Dec;32(12):1265-70 (learn more)
- Browning, Lucy M., et al. "Compared with Daily, Weekly n–3 PUFA Intake Affects the Incorporation of Eicosapentaenoic Acid and Docosahexaenoic Acid into Platelets and Mononuclear Cells in Humans." The Journal of nutrition (2014): jn-113.
- Feillet-Coudray C, Aoun M, Fouret G, Bonafos B, Ramos J, Casas F, Cristol JP, Coudray C. Effects of long-term administration of saturated and n-3 fatty acid-rich diets on lipid utilisation and oxidative stress in rat liver and muscle tissues. Br J Nutr. 2013 Nov;110(10):1789-802.