Another myth destroyedDear List
Juan Silva writes that omega-3 fatty acid content in oils of farmed fish is dependent on feed composition, species, and environmental conditions. This is also true of wild fish. A scan of the literature shows variation in composition both within farmed and within wild species as well as differences between the two classes. Van Vliet & Katan (American Journal of Clinical Nutrition, 1990, 51, 1-2), analysed lipids from wild and farmed trout, eel and Atlantic salmon and found that the ratio of omega-3 to omega-6 acids was lower in the farmed than in the wild. This lower ratio has been found in, some, but not all, species in which comparisons between farmed and wid has been made. This lower ratio of omega-3 to omega-6 has led to some claims that farmed fish are nutritionally inferior to the wild counterparts. This is of course nonsense as Charles Santerre has pointed out. The misunderstanding comes from the practice of expressing fatty acid composition of oils as percentages of the total. This is quite sensible from an analytical point of view, but is misleading from a nutritional point of view. What the nutritionist is interested in is the total intake per unit weight of a food item which will depend on both the proportion of omega-3 fatty acids in the oil, and the oil content of the food. Charles has provided this information for some species of fish. Scanning the Internet I see that an Iowa State University web page shows a table of omega-3 contents of some foods, including fish, but not differentiating between farmed and wild. I am a bit suspicious of some of the data for fish, but I haven't checked original sources of data.
I am in Jim Yonker's camp that it does not matter whether you eat wild fish or farmed fish as long as you eat some fish, the fattier the better. Reviews of the nutritional benefits of fish oils I have read point out that the typical diet in USA or Europe has less than the optimum content of omega-3 acids, and the recommended intake seems to be around 1g/day. Components of the diet other than fish contribute some omega-3 acids so 2-3 portions of salmon, farmed or wild, a week should boost intake to the recommended amount. This should please Jim, but if taken up by the whole population of the USA, I don't think there would be enough salmon to go around. The consumption of fish in the USA is about 20kg/person/year live weight equivalent, approximating to 25g/day edible portion. I would expect a high proportion of this to be lean species with lipid contents of less than 4%, and assuming the omega-3 fatty acid content was similar to that of oil in wild salmon, the average intake of omega-3 fatty acid in the USA diet from fish is in the order of 0.1g/day. The situation in Europe is similar, the per caput consumption in Europe, including Scandinavia is the same as in the USA. Given this large gap between actual and recommended consumption of omega-3 acids, any consistent differences between omega-3 contents of farmed and wild fish is a mere quibble.
Peter Howgate
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