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Fried Fish and Heart Failure
Jacob Schor, ND, FABNO
June 20, 2011
Late last fall, I wrote an article suggesting that fried fish should replace the Chanukah staple food of fried potato latkas. My argument was that the holiday called for fried food and that both the practice of cooking fish in oil and the idea of eating it in combination with fried potatoes were originated in Jewish kitchens. My thinking at the time was that fish, even if fried was probably still a healthy food. Data from a study on fish and heart disease from a study published May 24 has made me rethink this idea. Unless new data refutes this current paper, and actually we are talking about a series of papers, next winter I will promote eating jelly doughnuts, the traditional Israeli choice, to eat on Chanukah. It may be a healthier choice than fried fish.
The study that has prompted my change of mind regarding fried fish was by Belin et al from ___ and is titled, “Fish intake and the risk of incident heart failure.” This was a retrospective study that compared reported dietary intakes of various types of fish and fish oil against incidence of heart failure over the course of ten years. Intake of baked or broiled fish, fried fish, omega-3 fatty acids and trans fatty acids (TFA) were determined from food frequency questionnaires.
Our general assumption that eating fish is good for your heart is still true but eating fried fish is worse for your heart than anyone might have thought.
Belin used the data collected from 84,493 participants in the Women's Health Initiative Observational Study (WHI-OS) for this study. The participants were all female, aged 50-79 and were of diverse ethnicity and background. The participants had been followed for an average of ten years ending in August 2008. They did not have heart disease at the start of the study.
Baked or broiled fish consumption was divided into 5 frequency categories: less than1 serving/month, 1-3/mo, 1-2/wk, 3-4/wk, and ≥5/wk. Fried fish intake was grouped into three frequency categories: less than 1 serving per month, 1-3/mo, and ≥1/wk. Associations between fish or fatty acid intake and incident heart failure were determined using Cox models adjusting for other risk factors for heart failure.
Fish is good for your heart as long as it is baked or broiled. Eating five or more servings of baked or broiled fish per week lowered the risk of having heart failure by 30% [hazard ratio (HR) of 0.70 (95% CI: 0.51, 0.95)]. This effect was attributed primarily to the consumption of dark fish particularly salmon, but also mackerel, and bluefish.
Fried fish is bad for your heart. Eating fried fish one or more times a week was associated with a 48% increase in risk for heart failure [HR of 1.48 (95% CI: 1.19, 1.84)].
No association was seen between consumption of omega-3 fish oil supplements or trans fatty acid intake with heart failure.
The concept that eating fish is good for the heart should not surprise our readers. It is now ‘common knowledge.’ The magnitude of the fried fish effect is a surprise and begs explanation. The data from this study suggest that a single serving a week of fried fish increases the risk of heart failure by almost 50%, while it takes five servings of fish cooked in a healthy manner to lower the risk and then by only 30%. Women who eat less than 1 serving of baked or broiled fish per month but have more than 1 serving of fried fish per week had a 2.3 fold higher risk for heart failure than women eating one serving of baked or broiled fish per week and less than 1 serving of fried fish per month (HR 2.28, 95%CI: 1.38, 3.75).
Holy Mackerel! It would be more accurate to say fried fish is bad for your heart rather than to say fish is good for your heart.
This current Belin paper isn’t the first study to report a negative impact from fried fish. They new to ‘ask the data’ about fried fish because of earlier but smaller studies. In 2005 Mozaffarian et al from Harvard Medical School reported a similar risk from eating fried fish. They had analyzed data from 4,738 adults older than 65, who had been tracked for 12 years. During that period 955 developed congestive heart failure. Subjects consuming baked or broiled fish 5 times per week had a 32% lower risk for heart failure, a result not far off from the current Belin study. Consumption of fried fish one or more times per week was associated with 35% higher risk. This fried fish number also was not far off from this new Belin study.
In 2006, Mozaffarian’s group published a second study related to this fish business. Assuming that fish intake was associated with improved cardiovascular health, they looked for the physiologic effects behind the cardiovascular benefits. They compared dietary fish intake in 5,073 older adults against measurements of cardiac structure, function and hemodynamics. Eating canned tuna, broiled or baked fish was associated with lower heart rate, lower systemic vascular resistance and greater stroke volume and healthier diastolic function. In contrast, fried fish or fried fish sandwiches were associated with left ventricular wall motion abnormalities, a reduced ejection fraction lower cardiac output, a trend toward a larger left ventricular diastolic dimension, and higher systemic vascular resistance. While ‘nicely cooked’ fish was associated with desirable characteristics, fried fish was associated with structural abnormalities suggestive of systolic dysfunction and potential coronary atherosclerosis. As far as the authors could prove, “The observed inverse associations were independent of major lifestyle factors and potential dietary and non-dietary confounders.”
While there are a number of plausible explanations to explain the positive benefits of fish consumption, there are only weak theories to explain the negative impact of fried fish.
Maybe it’s the oil?
Fried fish, especially prepared away from home is likely cooked in oil that is used multiple times. Reusing frying oil increases the levels of trans fatty acids. In a 2000 study mice were fed mackerel fried in coconut oil. Rats fed fish fried in oil that had been reused multiple times had higher cholesterol and were more likely to show signs of kidney and liver damage.
If it were the trans fatty acids formed in the fish fry oil one would expect consumption of other fried foods, such as French fries to also increase risk. So far though these studies have not revealed an association between cardiovascular disease and other fried foods.
The explanation for the fried fish effect that seems the most plausible is that it isn’t the fish per se that is at fault. We want to believe that this is a causal relationship when it might not be. Rather fried fish consumption, may simply be a marker of a relatively unhealthy lifestyle. Study participants who had high fried fish consumption were more likely to have dyslipidemia. According to the Belin analysis, people who chose baked or broiled fish were younger than those who ate fried fish. The also had less diabetes, less atrial fibrillation (AF), less coronary artery disease, (CAD) lower systolic blood pressure (SBP), lower body mass index (BMI), had more physical activity, higher education, consumed more fruits and vegetables DHA/EPA and less saturated and trans fatty acids. Those who consumed more fried fish were pretty much the opposite; they were more likely to have AF, CAD, SBP, higher BMI, less exercise, lower education, lower fiber intake, lower fruit and vegetable intake, higher total energy intake, higher intake of SFA, TFA. They were more likely to smoke.
Thus it may not be that the fried fish itself is at fault. Instead eating fried fish may be a litmus test that indicates an unhealthy life style, which is more likely to lead to heart disease.
Though as attractive as this theory might be, the studies that could support this idea have not.
For example, A 2009 paper that reported omega 3 intake from non-fried fish is inversely associated with interleukin – 6 and c-reactive protein levels found that these associations were “... independent of age, body mass index, physical activity, smoking, alcohol consumption, and dietary variables.” They could be wrong.
It is possible that the explanation for these effects is from ‘unmeasured dietary and non-dietary factors such as mercury or other contaminants in the fish.
Guallar et al from Johns Hopkins reported in 2002 that high mercury levels doubled risk of myocardial infarction (MI) and theorized this counter-action to the cardiovascular benefits of fish might complicate the analysis of fish and heart disease data.
The data have certainly not been consistent. More is not always better when it comes to fish. Researchers from University of Alabama analyzed data from a Swedish cohort of 36, 234 women and found that moderate consumption of fatty fish (1-2 times per week) was associated with a 30% lower heart failure (HF) risk, but more frequent servings were not as beneficial, lowering HF by only 9% for 3 servings/week or less. Could it be that with higher fish consumption, mercury overload comes into play?
The studies have been inconsistent in finding a correlation between mercury in fish and cardiovascular disease. Plante and Babo responded to Guallar’s assertion with data from a Japanese city of 50,000 where most of the population appear to have very elevated mercury, yet do not show higher MI risk than the general population that has acceptable levels of mercury.
The fish/mercury/heart disease theory sunk a bit further earlier this year. Wennenberg et al in a January 2011 paper looked at the relationship between low or high fish consumption, methyl-mercury, selenium and omega-3 levels with the risk for MI. This was a case-control study nested within the northern Sweden cohort in which data and samples were collected prospectively. Data from 431 cases of MI were compared against 499 matched controls. While low selenium, high mercury and low omega-3 fats were correlated with increased risk for MI, no correlation was seen for fish consumption.
What is it about fried fish? Could it be the fried potatoes that are almost always served alongside fried fish? In the current Belin 2011 study, consumption of other fried foods was tracked and independent associations were looked for but not found for total fried foods, French fries, fried potatoes, fried rice, fried cassava, fritters, or fried chicken intake. Fried food did not increase cardiovascular risk in the Belin data. Yet fried fish did.
My personal guess, a guess that is to date unsubstantiated by anything I have read in the literature, is the interaction between the transfatty acids in the oil, which trigger reactive oxygen damage in the body and the polyunsaturated fatty acids in the fish, which make the body more susceptible to oxidative reactions, that are to blame. But really, we don’t have a decent explanation yet.
If you eat fried fish often, this is not good; you are at higher risk for heart disease. Whether this is from the fried fish itself, or because you flunked the ‘fried fish litmus test for healthy lifestyle’ is not clear. In case it is the fried fish that is to blame, it would be wise to eat it less often. For those of you who will only eat fish when it is fried, you should forget about that idea that eating fish is good for your heart.
Back to the idea about promoting jelly doughnuts for Chanukah…. I’m not sure we are ready to go there yet. Perhaps those potato pancakes and sour cream were the healthier choice after all.
Fried Fish for Chanukah December 2010
Belin RJ, Greenland P, Martin L, Oberman A, Tinker L, Robinson J, et al. Fish Intake and the Risk of Incident Heart Failure: The Women's Health Initiative. Circ Heart Fail. 2011 May 24.
Mozaffarian D, Bryson CL, Lemaitre RN, Burke GL, Siscovick DS. Fish intake and risk of incident heart failure. J Am Coll Cardiol. 2005 Jun 21;45(12):2015-21.
Mozaffarian D, Gottdiener JS, Siscovick DS. Intake of tuna or other broiled or baked fish versus fried fish and cardiac structure, function, and hemodynamics. Am J Cardiol. 2006 Jan 15;97(2):216-22. Epub 2005 Nov 21.
Ammu K, Raghunath MR, Sankar TV, Lalitha KV, Devadasan K. Repeated use of oil for frying fish. Nahrung. 2000 Oct;44(5):368-72.
He K, Liu K, Daviglus ML, Jenny NS, Mayer-Davis E, Jiang R, et al. Associations of dietary long-chain n-3 polyunsaturated fatty acids and fish with biomarkers of inflammation and endothelial activation (from the Multi-Ethnic Study of Atherosclerosis [MESA]). Am J Cardiol. 2009 May 1;103(9):1238-43.
Guallar E, Sanz-Gallardo MI, van't Veer P, Bode P, Aro A, Gómez-Aracena J, et al. Mercury, fish oils, and the risk of myocardial infarction.
N Engl J Med. 2002 Nov 28;347(22):1747-54.
Levitan EB, Wolk A, Mittleman MA. Fatty fish, marine omega-3 fatty acids and incidence of heart failure. Eur J Clin Nutr. 2010 Jun;64(6):587-94. Epub 2010 Mar 24.
Plante M, Babo S. Mercury and the risk of myocardial infarction. N Engl J Med. 2003 May 22;348(21):2151-4; author reply 2151-4.
Wennberg M, Bergdahl IA, Hallmans G, Norberg M, Lundh T, Skerfving S, et al. Fish consumption and myocardial infarction: a second prospective biomarker study from northern Sweden. Am J Clin Nutr. 2011 Jan;93(1):27-36.