Sunday, January 27, 2013

Making the Right Fish Choices: Fatty Acid Contents of 33 Different Fish Species. Plus: What Are the Implications?

Pollachius virens (Photo: Tino Strauss) is king, when it comes to the n:3/n:6 ratio, but with <1% of fat you will still be hard pressed to get tons of omega-3s from eating pollock... but is more really better, let alone necessary?
I have already broached the issue of the differences in the fatty acid composition of fish - even those of the same species - in past articles such as the one(s) on fish as a potential source of mercury in your diet (read more). When I saw the recent paper by Claudia Strobel, Gerhard Jahreis and Katrin Kuhnt in Lipids in Health and Disease, I thought that it was about time to supply you with some real data on the actual n:3/n:6 ratio of different fish and its implications for the purported health benefits and anti-obesity effects of regular fish intake. Is there a "super fish" or is it as so often a matter of "mixing and matching" to achieve the right balance?

Fish? Of course, I have fish & chips or fish sticks every other day!

I guess I don't have to tell you that both the fish part of "fish and chips", as well as the "healthy" fish sticks that are pretty popular at least among German kids, should actually be sold at the bakery, right? I mean the ratio of the bread crumb coating to the pressed fish fillets inside, is hilarious and in view of the fact that these products are 'pre-fried' with cheap vegetable oil before they end up in the freezer cabinets of supermarkets all around the world, you cannot avoid the increased (partially oxidized) omega-6 intake, even if don't (as most people do) fry them at home.

So, if the fast-food version of "fish" is not an option to gear your polyunsaturated fatty acid ratio more towards the n-3 side of things, which fish shall you go for? Well, according to the data the scientists from the Friedrich Schiller University in Jena, Germany, collected Pollachius virens is the n3:n6 king among the seven most frequently consumed fish species, which are herring, tuna, pollock, alaska pollock, salmon, rainbow trout and iridescent shark (at least according to Strobel, 2013).
Figure 1: Content of EPA & DHA, other omega-3 and the sum of omega-6 fatty acids in percent of total fat of the 33 tested species in the study; ordered according to n3:n6 ratio, fish with the highest n3:n:6-ratios on the left; note: the anchovies and sardines were in a tin with oil and while they were drained before the analysis this will have decreased the n-3:n-6 ratio (data calculated based on Strobel. 2013)
On the other hand, the total fat content of pollock (<1%) is so low that you will be hard pressed eating enough of it to elicit any significant health effects. As far as the most frequently consumed fish species go, this does bring us back to our good old friend, the salmon.
Figure 2: Comparison of fatty acid content in g/100g of wild and farmed salmon (left) and respective omega-3 to omega-6 ratios (right; based on Strobel. 2013)
Unfortunately "salmon" does not equal salmon, these days. The dripping orange stuff you can buy for a few bucks (the orange color is artificially added to the feed by the way) at every supermarket, for example, is farmed salmon and contains only 2-3x more omega-3 fatty acids than omega-6s. The reddish, lean cuts of wild salmon on the other hand, have a 12-13x higher relative omega-3 content and in fact almost no omega-6 fatty acids (0.05g / 100g). With 0.53g /100g omega-3 fatty acids, wild salmon is yet just like pollock not the "bulk" source of omega-3 fatty acids you would be looking for, if you fell for the stupid idea that you could undo the damage you are doing by eating tons of (oftentimes oxidized) omega-6 fatty acids by simply throwing an even greater amount of omega-3s into the equation.

So what do we make of all that information?


The very latest on the effects of fish consumption on body weight comes from a study in the latest issue of the British Journal of Nutrition and shows that there is no effect of higher intakes of total, lean or fatty fish on 5-year risk of becoming obese in the 344,757 male and female participants of the European Prospective Investigation into Cancer and Nutrition (Jakobsen. 2013). Now, this does not exclude the existence of non-body weight related benefits, but it certainly puts the myth of the "anti-obesity" effect of fatty fish into perspective. After all, every 10g of additional high fat fish in the diets of the female study participants was associated with a 5x more pronounced increase in body weight than an equal amount of low fat fish. The general trend towards increasing BMIs was yet countered by none of the two.
In view of the fact that we are suffering from a relative deficiency in omega-3 fatty acids, only (relative to the exubarant amount of omega-6 fatty acids the average Westerner consumes on a daily basis), I see the data presented in this post not as a "shopping guide", but rather as a means to conduct a reality check of how realistic it really is that someone who follows a no fast- and convenient-food diet and keeps a non-neurotic eye on his overall n-6 intake will benefit from omega-3 intakes in the multiple gram range.

Specifically when it comes to supplementation, previous trials such as Filaire et al. did in fact find increases in oxidative stress in perfectly healthy athletes (judo) in response to 6 weeks on 600mg EPA + 400mg DHA per day (Filaire. 2010). If you also take into consideration that these negative effects on lipid oxidation were not ameliorated by higher alpha-tocopherol (vitamin E) levels, the message this and other studies are sending is clear: The putative increase in omega-3 requirements is a result of an abnormally high intake of omega-6 fatty acids.

The easiest way to escape any negative effects while still reaping the benefits therefore is to reduce (not totally avoid!) the intake of omega-6 fats (specifically from processed foods) - full stop! If you do that by incorporating a large variety of whole foods into your diet and include grass-fed beef, dairy from pastured cows and, obviously, fish on a regular basis, you won't have to increase your intake of omega-3 fatty acids by picking the orange colored, disgustingly tasting, fat dripping farmed salmon from the super market over its delicious red wild cousin, just because it has 4.5x more omega-3 fatty acids.

Bottom line: It's food quality and fatty acid ratios that make the difference; not the absolute numbers of allegedly good and bad fats, carbs and whatever else has recently fallen victim to the over-generalization that appears to be necessary to render dietary advice suitable for the masses. If there is any one thing that's to blame for the health crisis these days, it's this kind of black-and-white thinking that's behind the overgeneralized and faulty "expert advice" which is by no means propagated exclusively via supposedly unreliable sources on the Internet.

References:
  • Filaire E, Massart A, Portier H, Rouveix M, Rosado F, Bage AS, Gobert M, Durand D. Effect of 6 Weeks of n-3 fatty-acid supplementation on oxidative stress in Judo athletes. Int J Sport Nutr Exerc Metab. 2010 Dec;20(6):496-506.
  • Jakobsen MU, Dethlefsen C, Due KM, May AM, Romaguera D, Vergnaud AC, Norat T, Sørensen TI, Halkjær J, Tjønneland A, Boutron-Ruault MC, Clavel-Chapelon F, Fagherazzi G, Teucher B, Kühn T, Bergmann MM, Boeing H, Naska A, Orfanos P, Trichopoulou A, Palli D, Santucci De Magistris M, Sieri S, Bueno-de-Mesquita HB, van der A DL, Engeset D, Hjartåker A, Rodríguez L, Agudo A, Molina-Montes E, Huerta JM, Barricarte A, Amiano P, Manjer J, Wirfält E, Hallmans G, Johansson I, Khaw KT, Wareham NJ, Key TJ, Chajès V, Slimani N, Riboli E, Peeters PH, Overvad K. Fish consumption and subsequent change in body weight in European women and men. Br J Nutr. 2013 Jan;109(2):353-62.
  • Strobel C, Jahreis G, Kuhnt K. Survey of n-3 and n-6 polyunsaturated fatty acids in fish and fish products. Lipids Health Dis. 2012 Oct 30;11:144.