American Journal of Preventive Medicine
Volume 29, Issue 4 , Pages 322-323, November 2005

Fish, Health, and Sustainability

  • Anthony J. McMichael, PhD
    • ,
  • Colin D. Butler, PhD

      Affiliations

    • Corresponding Author InformationAddress correspondence to: Colin Butler, PhD, National Centre for Epidemiology and Population Health, Australian National University, Canberra ACT Australia 0200.

National Centre for Epidemiology and Population Health, Australian National University, Canberra, Australia

Article Outline

 

Health risk assessment has become an increasingly sophisticated and policy-supportive procedure over the past several decades. The advent of a common currency with which to calibrate disparate risks to health has enabled a much more integrated approach to this topic area. Unresolved debates about “disability” or “quality-of-life” weightings aside, the availability of disability-adjusted life years (DALYs) and quality-adjusted life years (QALYs) has potentiated meaningful comparison of population health risks.

The set of papers in this issue by Teutsch, Cohen, and their colleagues1, 2, 3, 4, 5, 6 provides a well-presented example of this swings-and-roundabouts risk assessment. There is now plenty of evidence that the consumption of fish, either as part of a Mediterranean-type (or Japanese) diet or as a specific food item, reduces the risk of cardiovascular disease. More specifically, there is much animal experimental evidence and some human evidence that the long-chain polyunsaturated (omega-3) fatty acids—popularly referred to as fish oils—reduce various pathophysiologic abnormalities in heart, blood vessels, and blood, including anoxic ventricular arrhythmia, atherogenesis, hypertension, and blood clotting.

Fish consumption, most probably because of the fish oils, is also beneficial to the developing fetal and infant brain (and perhaps to the ageing brain). However, we also know, especially in the wake of the 1950s Minamata disaster, of the risks to the central nervous system posed by organic mercury as a contaminant in fish.7 In particular, as with environmental lead exposure, mercury exposure endangers neurocognitive development in both the fetus and the very young human.

The authors work through a series of scenarios in which the public responds differently to health messages about the health benefits and hazards of fish consumption. Their arithmetic is reassuring—but only if the public is given, and understands, the correct message about benefits and risks for women of childbearing age and for the population at large. The task for risk communicators is clear, and that must include individual epidemiologists discussing the results of their one recent study with journalists.

One key issue appears unaddressed, however. If subpopulations (such as women of childbearing age) reduce their consumption of fish with a high concentration of methyl mercury (MeHg), then will other groups (particularly the poor, including, perhaps in export market populations) increase their MeHg exposure? Teutsch, Cohen, and their colleagues1, 2, 3, 4, 5, 6 suggest that subsidies could be used to encourage the consumption of fish low in MeHg and high in n-3 polyunsaturated fatty acids (PUFAs). Putting aside discussion of economic plausibility, implementation of this proposal may well channel the consumption of less desirable, possibly toxic, fish toward poorer and less-informed populations, including perhaps women of childbearing age in developing countries. Indeed, even without subsidies, market forces, driven by the buying choices of better-informed populations, are likely to increase the consumption of less desirable fish by the poor, the population most vulnerable to any diminution of IQ points.

Health risk assessment must, for other reasons, now cast a wider net. The authors acknowledge, but do not explore, the wider ecologic impact of fish consumption. Eating fish may be good for health, but eating too many fish too fast is bad for the biosphere’s health, and therefore, in due course, for human health. This is not an issue that we had to consider several decades ago, when (in partial ignorance) over-exploitation was not an obvious issue. Today, however, we are manifestly jeopardizing fisheries around the world.8, 9 That nonsustainable practice will inevitably deplete the health-supporting properties of fish consumption for future populations everywhere, including for some of the world’s poorest but fish-dependent populations. Fish provide 17% of the total animal protein and 6% of all protein consumed by humans.8, 9, 10 Many coastal and riverine indigenous populations are particularly reliant on fish. In the Lihir Islands of Papua New Guinea, for example, fish consumption represents about 10% of recommended daily protein.11 Such populations cannot compete on the high seas with industrial fishing fleets, and are particularly vulnerable to local fish depletion.

Globally, marine fish and shellfish production has increased over fivefold, from around 20 million metric tons in 1950 to 105 million metric tons during the second half of the 20th century. However, the marine-fish catch has plateaued, and may even be in decline, while the size of the human population is continuing to expand. This leaves the expansion of aquaculture as the only way to maintain, or if possible increase, global per capita consumption of fish. Aquaculture already accounts for >25% of the total marine plus freshwater harvest. But fish farming itself entails some public health issues, including chemical contamination of fish, the promotion of antibiotic resistance, and the growing distortion of the lipid profile of caged fish, fed, increasingly, on land-grown crops.

The widespread practice of feeding wild-caught fish to farmed piscivorous fish increases production of some high-value species, but decreases the availability of fish for direct human consumption, on a per capita basis.12 To meet consumer demand for such fish, and at the same time to reduce the pressure on wild fish stocks, aquaculturalists are increasingly turning to land-based plants, such as grain, soybeans, lupins, and blended vegetable oils as staple fish food. However, because several of these crops are comparatively low in desirable long-chain fatty acids (especially n-3 PUFAs), the n-3 PUFA concentration of fish raised this way is likely to be lower than in their wild-caught cousins.13 Consequently, the n-3/n-6 PUFA ratio is also lower than what is thought to be optimum.14

Thus, the well-informed fish consumer of the future may wish to consider not only the likely MeHg and PUFA concentration of her meal, but its ecologic impact and—perhaps—whether his/her use of market power could unintentionally harm the health of others.

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References 

  1. Teutsch SM , Cohen JT . Health trade-offs from policies to alter fish consumption . Am J Prev Med . 2005;29:324
  2. Cohen JT , Bellinger DC , Connor WE , et al.   A quantitative risk-benefit analysis of changes in population fish consumption . Am J Prev Med . 2005;29:325–334
  3. König A , Bouzan C , Cohen JT , et al.   A quantitative analysis of fish consumption and coronary heart disease mortality . Am J Prev Med . 2005;29:335–346
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  5. Cohen JT , Bellinger DC , Shaywitz BA . A quantitative analysis of prenatal methyl mercury exposure and cognitive development . Am J Prev Med . 2005;29:353–365
  6. Cohen JT , Bellinger DC , Connor WE , Shaywitz BA . A quantitative analysis of prenatal intake of n-3 polyunsaturated fatty acids and cognitive development . Am J Prev Med . 2005;29:366–374
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  11. McMichael A, Scholes R, Palm C, Pereira E, Hefny M. Ecosystem services and human well-being. In: Millennium Ecosystem Assessment, ed. Multiscale assessments. Findings of the Sub-Global Assessments Working Group. Washington DC: Island Press, 2005 (in press).
  12. Naylor RL , Goldburg RJ , Primavera JH , et al.   Effect of aquaculture on world fish supplies . Nature . 2000;405:1017–1024
  13. Rondán M , Hernández MD , Egea MA , et al.   Effects of fishmeal replacement with soybean meal as protein source, and protein replacement with carbohydrates as an alternative energy source on sharpsnout sea bream, Diplodus puntazzo, fatty acid profile . Aquaculture Res . 2004;35:1220–1227
  14. Cordain L , Eaton SB , Sebastian A , et al.   Origins and evolution of the Western diet (health implications for the 21st century) . Am J Clin Nutr . 2005;81:50–54

PII: S0749-3797(05)00291-6

doi:10.1016/j.amepre.2005.07.033

American Journal of Preventive Medicine
Volume 29, Issue 4 , Pages 322-323, November 2005

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