Although the American Heart Association and similar organizations endorse this idea, in 2009 Jenkins et al questioned its wisdom on two bases: the weakness of evidence for benefits of fish and fish oil intake, and the strength of evidence that global fisheries are collapsing and unable to support current, let alone increased, use of fish and fish oils.
"The main problem with this advice is that, even at current levels of fish consumption, fisheries globally have reached a state of severe crisis (Figure 1).5-8 Already, the demand from affluent and developing economies, particularly newly affluent China, cannot be met by the world's fisheries.6 Moreover, declining catches are increasingly diverted toward affluent markets rather than local ones, with dire consequences for the food security of poorer nations, islands and coastal communities.9"
Uncertain health benefits of fish and fish oil
Jenkins et al point to a number of problems with the evidence supporting use of fish and fish oils:
1. Healthy subject effect: "....fish eaters generally have healthier lifestyles than the rest of the population. They exercise more, smoke less and have better diets.11–13" This makes it very hard to determine whether the better health found among people eating more fish is due to their fish consumption, or to these other habits.
2. Inconsistent results: Some interventional studies show benefits from increased intake of fish and fish oils, while others do not, and some, such as DART-2, showed harm, with an increased risk of cardiac death among men who took fish oils.
3. Vegetarians appear to have a lower risk of cardiovascular disease and death therefrom, despite avoiding fish and fish oils, suggesting that non-fish dietary factors play a larger role.
4. We have little evidence supporting the use of fish and fish oils for metabolic syndrome, diabetes, or neurological or autoimmune diseases, or even for neurological development.
Regarding the neurological argument, although Jenkins et al do not mention this, Sanders reviewed the available literature and reported that "There is no evidence of adverse effects on health or cognitive function with lower DHA intake in vegetarians." In addition, Beezhold et al found a lower incidence of depression among vegetarians than among omnivores, despite lower intake of omega-3 fatty acids among the former. They reported that "participants with low intakes of EPA, DHA, and AA and high intakes of ALA and LA had better mood," contradicting the hypothesis that depression results from insufficient intake of pre-formed long-chain omega-3 fatty acids.
Declining Fish Stocks
Jenkins et al report:
"In contrast to the uncertainty over the value of omega-3 fish oils in the scientific literature, there is little doubt about the gravity of the fisheries crisis and the prospect of ongoing collapses of fish stocks. There is scientific consensus about the rapid worldwide decline of fish stocks. Notably, and despite increasing fishing effort, global catches have been in decline since the late 1980s (Figure 1A),5 and the number of collapsed stocks has been increasing exponentially since 1950 (Figure 1B).8,47,48 There are also over 100 confirmed cases of extinctions of marine populations in the world's oceans.49"
"When projected forward, these trends imply the collapse of all commercially exploited stocks by midcentury.7,8 Yet the dire status of fisheries resources is largely unrecognized by the public, who are both encouraged to eat more fish and are misled into believing that we still sail in the sea of plenty.50 Indeed, the species that Westerners are supposed to eat in increasing amounts have stocks that are already under tremendous pressure (e.g., yellowfin tuna, the basis of the much recommended North American “tuna-fish sandwich”51) or that have collapsed, sometimes spectacularly, such as cod off the coast of northeastern Canada.52"
According to an article in the National Geographic, large fish stocks have declined 90 percent since 1950.
On November 2, 2006, Richard Black of the BBC reported on a study published in Science: "There will be virtually nothing left to fish from the seas by the middle of the century if current trends continue." Black reported:
Steve Palumbi, from Stanford University in California, one of the other scientists on the project, added: "Unless we fundamentally change the way we manage all the ocean species together, as working ecosystems, then this century is the last century of wild seafood."
In short, the drive to eat more fish and fish oils will only accelerate the rate of destruction of marine ecosystems.
At the very least, our hunger for fish and fish oils will leave future generations with a world wherein they will be unable to eat cod liver oil or fatty fish even if they needed to, because there just won't be any left in the oceans.
Perhaps people eating increased amounts of seafood will suffer the same fate as ocean fish. Seafoods commonly contain chemical contaminants that appear to impair fertility, including mercury, PCBs, PEs, and others.
Rozati et al found, among Indian men:
"PCBs were detected in the seminal plasma of infertile patients but absent in fertile controls (Table 1)."
"...a comparison between fish-eaters and non fish-eaters, irrespective of the dwelling revealed higher PCB concentrations and significantly lower total motile sperm counts in fisheaters than in non fisheaters (Tables 2,3)."
"Fish-eating urban dwellers had the highest PCB concentrations, followed in order by fish-eating rural dwellers, non fish-eating urban dwellers with an exclusively vegetarian diet and non fish-eating rural dwellers with an exclusively vegetarian diet. The total motile sperm counts in these men were inversely related to their PCB concentrations, being the least in fish-eating urban dwellers followed by fish-eating rural dwellers, non fish-eating urban dwellers with an exclusively vegetarian diet and non fish-eating rural dwellers with an exclusively vegetarian diet (Tables 2)."
Another study reported:
“The lowest levels of p,p'-DDT+p,p'-DDE and PCBs were found in milk from lacto-vegetarians and the highest levels in milk from mothers who regularly consumed fatty fish from the Baltic.”Norén K. Levels of organochlorine contaminants in human milk in relation to the dietary habits of the mothers. Acta Paediatr Scand. 1983 Nov;72(6):811-6.