Fried, Broiled, or Baked Fish?

Summarized by Robert W. Griffith, MD
March 13, 2006

Introduction

We've been told for some years now to eat more fish. It's good for the heart - there's less risk of an abnormal rhythm, sudden cardiac death, stroke, and heart failure. The next question, of course, is 'what sort of fish'? Salmon, mackerel, tuna, and halibut are usually high on the list; they yield more omega-3 polyunsaturated fatty acids, which seem to be the critical factors.

The next question - how should the fish be prepared? Could heart health be linked with differences in cooking, and thus help explain just how dietary fish is beneficial? Boston scientists have studied this, and reported in the American Journal of Cardiology, here's a summary.

What was done

The Cardiovascular Health Study was started in 1989. More than 5,000 men and women over 65 from 4 different communities were randomly selected to participate, and undergo extensive baseline evaluations aimed at defining cardiac health.

Food frequency questionnaires were used to determine how often they consumed various specified foods, including tuna fish, other fish (broiled or baked), and fried fish or fish sandwiches (fried fish burgers). Participants had to choose between 5 levels of frequency, ranging from 4 or fewer times a year to 5 or more times a week.

The cardiac evaluations included heart rate, blood pressure, and three types of echocardiography (2-dimensional, Doppler, and M-mode transthoracic). These allowed assessment of the heart's structure, function, and hemodynamics.

What was found

For the purpose of analysis, the participants were classified as either consuming tuna and other fish that was broiled or baked, or fried fish and fish sandwiches; we'll call these 'tuna/other fish' and 'fried fish', respectively.

Cardiac structure and systolic function: tuna/other fish was not linked to changes of cardiac structure, except for a trend towards a smaller left ventricular size. Fried fish, on the other hand, was linked with several measures of reduced systolic function¹.

Hemodynamics: tuna/other fish was associated with a lower heart rate, lower systolic and diastolic blood pressure, and increased blood output per beat (stroke volume). Fried fish was linked with less obvious effects on blood pressure, lower cardiac output, and higher resistance in the peripheral circulation (systemic vascular resistance).

What these results may mean

The authors of the study interpret these findings in the following way: eating tuna/other fish was linked to improved hemodynamics (lower heart rate and blood pressure, increased cardiac output), whereas fried fish was associated with structural changes suggesting some heart malfunction and potential coronary artery atherosclerosis. They go on to theorize that the findings would account for the some of the beneficial effects of fish oil in preventing abnormal heart rhythms. Earlier studies have shown that fried fish intake is sometimes linked to non-fatal MI, atrial fibrillation, and heart failure.

It might be thought that lifestyle factors could also play a role in this study. Thus tuna/other fish eaters were slightly younger, more often female, and had a higher education level than fried fish eaters, factors that we know are often associated with improved general nutrition and greater physical activity; however, the differences between cardiac results for tuna/other and fried fish eaters persisted after adjustments were made for these factors.

The next steps are, of course, to determine the factor, or factors, in tuna and other baked or broiled fish that have positive effects (probably omega-3 type fish oils) and what it is in fried fish meals that are so harmful. (Could it be the French fries?)

Source

• Intake of tuna or other broiled or baked fish versus fried fish and cardiac structure, function, and hemodynamics. D. Mozaffarian, JS. Gottdiener, DS. Siscovick, Am J Cardiol, 2006, vol. 97, pp. 216--222

Footnotes
1. The cardiac cycle is divided into two parts - systole and diastole. During systole, the heart ventricles contract, ejecting blood out of the heart and into the arteries. Next, the ventricles relax, and re-fill with blood to prepare for the next contraction; this is called diastole.

Related Links
Omega-3s, the Heart-Healthy Fats
Eat More Fish for Irregular Heartbeat?
High Blood Levels of Omega-3s May Lower Your Risk of Death

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