To eat fish or not to eat fish? This question seems to have a lot of people floundering these days. Two new scientific reviews of the health effects of fish intake made a big splash this Fall, when they were released on the same day.
On October 17, 2006, the Institute of Medicine (IOM) published Seafood Choices: Balancing Benefits and Risks, its summary of current knowledge on the health benefits of fish and the potential risks from contaminants such as methylmercury, dioxins, and polychlorinated biphenyls (see the executive summary at: http://fermat.nap.edu/execsumm_pdf/11762.pdf). The same day, a literature review on much the same topic was published in the Journal of the American Medical Association (Mozaffarian D, Rimm EB. JAMA. 2006; 296: 1885–1899).
Both publications offer positive messages about the health effects of omega-3 fatty acids, abundant in fish and seafood. The IOM report arrives at no firm conclusions about whether regular fish consumption prevents disease, but its general message is that fish is a healthy food with minimal risks. The JAMA authors, however, seem certain the health benefits outweigh any risks.
Drs. Dariush Mozaffarian, of the Harvard School of Public Health, and Eric Rimm, of Brigham and Women’s Hospital, found that intake of fish oil equivalent to one or two servings of fish per week was associated with a 36% decrease in risk of death from coronary heart disease and a 17% drop in total mortality. They also concluded that the evidence is supportive of omega 3’s as important to early brain development.
These benefits, they contend, far outweigh any risks from contaminants. “Avoidance of modest fish consumption due to confusion regarding risks and benefits could result in thousands of excess CHD deaths annually and suboptimal neurodevelopment in children.” Dr. Mozaffarian has said the risks associated with PCBs and dioxins in fish are “greatly exaggerated,” and that “seafood is likely the single most important food one can consume for good health.”
The IOM’s recommendations are more conservative and less definite. The document “confirms that eating fish and shellfish may reduce people’s overall risk for developing heart disease. It is not certain whether this is because substituting the lean protein of seafood for fatty cuts of meat reduces consumers’ intake of saturated fat and cholesterol or because of the protective effects of omega-3 fatty acids.” The report also indicates that, “maternal consumption of omega-3 fatty acids from seafood can contribute to vision and cognitive development in infants and lengthen the duration of gestation.”
IOM acknowledges potential risks from methylmercury, dioxins, and PCBs, but notes that, “reliable data on the distribution of some contaminants is lacking, and there is little evidence on how beneficial effects of seafood might counteract some of the risks from contaminants.”
Both reports include caveats about contaminant exposure for special populations, particularly childbearing or nursing women, and they urge caution for people who fish and eat their own catches from potentially polluted inland waters.
At this point, data are pretty supportive of the notion that at least weekly fish consumption, along with increases in fruits, vegetables and whole grains, will promote good cardiovascular health. On a population basis, prevalence of coronary artery disease is considerably lower in Mediterranean and Pacific Rim countries than in the US, at equivalent cholesterol levels. Common to these cultures is a diet high in fruits, vegetables, legumes, whole grains, nuts, fish and mono- and polyunsaturated oils.
The Lyon Diet Heart Study tested the effect of a modified Mediterranean diet on cardiovascular risk after first myocardial infarction. After an average of 46 months, subjects on the diet had 72% fewer cardiovascular events and 60% lower all-cause mortality (Kris-Etherton P, Eckel RH, Howard BV, et al. Circulation. 2001; 103: 1823–1825). These findings were reproduced with an Indo-Mediterranean diet, cutting cardiovascular events by 45% and sudden cardiac death by 66% (Singh RB, Dubnov G, Niaz MA, et al. Lancet. 2002; 360: 1455–1461).
Omega-3 fatty acids from fish affect CHD outcomes by decreasing triglycerides, inhibiting fibrinogen, and by reducing platelet aggregation, inflammation, and blood pressure. There’s some evidence they can prevent ventricular arrhythmias. Omega-3s also improve arterial compliance, endothelial function, heart rate variability, and mood. Most of the prospective, controlled intervention trials with either cold-water fish or omega-3 supplements have shown reduced cardiovascular events. But there may be genetic polymorphisms, and only certain patients may benefit from omega-3 fatty acids, as was suggested in a study of post-angioplasty restenosis (De Lorgeril M, Salen P. Nutr Metab Cardiovasc Dis. 2003 Dec; 13(6): 345–348).
The new seafood reports are getting mixed reviews from environmental activists, concerned that both the IOM and the Harvard authors are too facile in dismissing ocean pollution as a public health issue.
Food industry critic, Dr. Marion Nestle, author of Food Politics and the recent What to Eat, refers skeptically to the “very sunny Harvard study,” and equates its emphatically positive message with pitches that tout “miracle foods.” Jane Houlihan, of the Environmental Working Group, an advocacy group, is quoted as saying, “the Harvard study reads like an advertisement for the seafood industry.”
Both reports have come under criticism from the Consumers Union. In addition to raising concerns about the failure of either report to fully address the risks of mercury in tuna, the consumer organization has also stated, “we are also concerned that both reports dismiss concerns about PCBs in most fish.”
Another advocacy group representative, Rebecca Goldburg, PhD, of Environmental Defense, claims “the high degree of certainty [about fish’s health benefits] in one report and the extreme caution in the other … will make people more confused than ever.”
It is this writer’s opinion that the health benefits of fish and fish oil are clear, and that the only caution is that they be chosen from fish known to be low in mercury, dioxin and PCB content. Fish to be avoided for their high mercury levels are shark, marlin, swordfish, large tuna, large halibut, and moonfish (opah). For more on this topic, log on to www.holisticprimarycare.net and search “Omega-3.”
Michael Traub, ND, is past president of the American Association of Naturopathic Physicians, and was named that organization’s 2006–07 “Physician of the Year.” He practices in Kailua-Kona, Hawaii.
