Seafood Wins Over Hearts
by Connie Guttersen, RD PhD,
author of the Sonoma Diet
Seafood is one of the top choices on many menus. Now a recent study finds a new reason for it to win over the hearts of diners. Dr. Connie Guttersen reviews the May '07 research on omega 3 and heart rhythms.
Electrifying Surprises Behind Health Benefits of Omega 3s.
Omega 3 fatty acids have been linked to a wide range of health benefits, including reduced risk of cardiovascular disease, certain cancers, good development of babies during pregnancy, and improved behavior and mood. A new study, led Christine Chrysohoou from the University of Athens, finds that fish consumption (such as one that is part of a Mediterranean Diet) is linked to an improvement of electrical properties of heart cells – meaning heart rhythms. This is an interesting area of study, referred to as electrophysiology. The heart's electrical cycle, measured by an electrocardiogram (ECG or EKG) reflects the electrical activity that controls the contraction of the heart and its heat beat.
Chrysohoou's study, published in the American Journal of Clinical Nutrition, May 2007, concluded that fish intake provides anti-arrhythmic properties. The researchers enrolled 3042 people (1514 men and 1528 women) with an average age of 45. The diets were evaluated using a self administered, validated food frequency questionnaire. Daily or weekly intake of 156 different foods was recorded, along with alcohol consumption, and physical activity. The study showed that people eating more than 300g oily fish per week (2 portions) had a 30% lower chance of exhibiting an abnormal QT interval--thus, their risk of heart disease was much lower. The QT interval is a measurement made by the electrocardiogram, which is related to the heart beat. An abnormal QT interval may cause a sudden uncontrollable heart rhythm, known as arrhythmia.
Similar results have also been published in a study by Harvard researchers who reported that the mechanism behind omega 3 oils and heart rate is due to the electrical signals affected by the flow of sodium and calcium in the ion channels. On the surface of each muscle cell in the heart are tiny pores called ion channels. Ion channels open and close to let electrically charged sodium, calcium and potassium atoms (ions) flow into and out of the cell. This generates the electrical activity of the heart, which causes each cell to contract.
Normally, the electrical activity spreads from one heart cell to the next in an orderly and coordinated way to allow the heart to pump blood. During each normal heartbeat, the muscle cells in the upper chambers of the heart, the atria (AY-tree-uh), contract. The contraction pumps blood from the atria to the ventricles. Then the muscle cells in the ventricles contract, pumping blood from the ventricles to the lungs and the rest of the body. This coordinated contraction of the atria and ventricles represents one normal heartbeat. It is within this metabolic process that omega 3 have a stabilizing effect. This is quite different than the protective role omega 3 oils have been recognized for previously, such as their lipid or blood pressure lowering abilities or even their antithrombotic effects. TOP
Omega 3 and Omega 6 Are Out Of Balance
Omega 3 fatty acids have been a part of the human diet for millennia. In history, the ratio of omega 6 (seed oils) to omega 3 fatty acids in the diet was 1:1. The ratio in the United States today has risen to 10:1 due to an overall decrease in consumption of omega 3 fatty acids and the widespread use of vegetable oils rich in linoleic acid. It is documented that competition between the omega 6 and the omega 3 is not beneficial for omega 3 metabolism under the current ratio. Substituting more monounsaturated fatty acids for the omega 6 oils can be a strategy for improving the metabolic environment for omega 3 fatty acids since there is not a known competition between these two fatty acid profiles.
| Linolenic Acid Content of Selected Vegetable Oils, Nuts, and Seeds, gm / tbsp |
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| Olive oil |
0.1 |
| Walnuts, English |
0.7 |
| Soybean oil |
0.9 |
| Canola oil |
1.3 |
| Walnut oil |
1.4 |
| Flaxseeds |
2.2 |
| Flaxseed (linseed) oil |
8.5 |
Adapted from USDA Nutrient Data Laboratory.
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A number of countries (Canada, Sweden, United Kingdom, Australia, and Japan) as well as the World Health Organization and North Atlantic Treaty Organization have made formal population based dietary recommendations for omega 3 fatty acids. Typical recommendations are 0.3 to 0.5 g/day of EPA + DHA and 0.8 to 1.1 g/day of alpha linolenic acid. The American Heart Association Dietary Guidelines include recommendations for at least two servings of fish per week and include recommendations for other food sources high in alpha linolenic acid. Evidence from prospective studies suggest that EPA + DHA supplementation ranging from 0.5 to 1.8 (either as fatty fish or supplements) significantly reduces cardiac mortality. Fish recommendations must also be balanced for the concerns about environmental pollutants, in particular PCB and mercury as described by federal and state advisories. TOP
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