I can’t salmon the strength

(Apologies to Andrew Hussie for the title)

There are any number of articles that could reasonably be written about companies putting profits before customer safety and the dangerous of over-intensive farming to the environment. The Guardian‘s particularly sad Comment is Free offering today – “Who dares question the industrial food system over GM salmon?” – however is not one of them.

Genetically modified salmon is deemed safe for human consumption – despite higher levels of a suspected carcinogen

As you can possibly guess, the subheadline doesn’t tell the whole story, as the article admits halfway down.

The [FDA] also found that even though the genetically altered salmon carry elevated levels of insulin-like growth factor-1 (IGF-1), a suspected carcinogen, those levels are so minute that they pose no health risk.


In fact, if you read the FDA report (PDF), they said even more than that. First of all – and most importantly – they found that “there did not appear to be a statistically significant difference between the mean IGF1 level for the GE [genetically engineered] and non-GE salmon” (p. 69) – on average, if you eat these salmon, your IGF-1 intake will be the same as usual. Instead, the increase was only in the maxima. The FDA’s experiments, admittedly, were not as rigorous as they could be, as a relatively small number of fish were tested – a small enough number that a single outlier was able to throw the whole thing off. In this case, it was a genetically engineered salmon with IGF-1 levels of 18.428 ng/ml (Table 16, p. 69). From the small sample, there’s not a lot you can say, but given that the second placed GE salmon had a IGF-1 concentration of 11.578 ng/ml and the average is 9.263 ng/ml, it looks like they may have just found an unusual fish.

Secondly, even if we did assume that the 18.428 ng/ml fish was relatively common, this is less than the average IGF-1 concentration in beef – according to Table 18 (p. 71), cattle plasma has a mean IGF-1 of 50.5 ng/ml. Pasteurized milk, which humans consume far more of than salmon, contains 8.2 ng/ml – not much less than the mean for GE-salmon. In fact, the report finds (p. 72-74) that even if someone with a salmon-heavy diet were to switch from eating wild salmon to farmed GE salmon, they found that, at the very upper bound – i.e., assuming they ate nothing but the 18.428 ng/ml salmon, this would increase the daily IGF-1 intake by 1.2 µg per day – 0.1% of the total eaten or produced by the body.

Finally, the hormones produced by salmon are not believed to be “homologous” to human hormones – in laboratory experiments, the hormones were not able to bind to human growth hormone receptors (Appendix C, p. 161). All the experiments I could find looking at carcinogenicity of IGF-1 used human hormones – as the New York Times article says, it’s not clear whether IGF-1 can even enter the bloodstream when consumed instead of being produced in the body.

The article does try to dismiss this point with a slippery slope argument:

The substance occurs naturally in salmon and other animal products, and the agency tells us that the genetically altered fish contains only a tiny amount more. Yet, by considering such matters one at a time, the FDA may well be introducing us to many tiny risks that start adding up to a very real risk.

Of course, on average, at least within the bounds of statistical significance, it doesn’t contain any more IGF-1 than wild salmon. But more to the point, the FDA doesn’t “consider such matters one at a time“. The FDA report specifically looks at the average diet of an American teenage boy – the group most likely to be at risk from excess growth hormone – and considers where GE salmon falls in the context of the average daily consumption, which is more than can be said for this article.

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