For the first time, there is evidence that eating tuna, both albacore and light, and dark fish at least once a week can slow the narrowing of arteries in postmenopausal women. The effect was particularly strong in women with diabetes, according to a new study published in the September issue of the American Journal of Clinical Nutrition.

The study -- based on work supported by the U.S. Department of Agriculture and the National Heart, Lung and Blood Institute -- reported that women who ate one or more servings of tuna or dark fish per week had less change in the diameter of their coronary arteries compared with women who ate these fish less than once a week. As heart disease progresses, arteries become more clogged, and this reduces blood flow to the heart. Women who ate fish at least once a week also had fewer new lesions in their arteries than women who ate fish less often.

One important finding of the study was that women with diabetes who ate fish twice or more per week had nearly 60% less narrowing of their arteries compared with those who ate fewer than two servings of fish a week. This observation is especially important for diabetic women, because their risk of heart disease is two to three times greater than non-diabetic women. This study comes at a time when diabetes, a major factor for heart disease, is on the rise in the U.S., and is usually accompanied by obesity, another major risk factor for heart disease.

Women in this study participated in the Estrogen Replacement and Atherosclerosis trial and were deemed suitable for a cohort study on fish consumption and atherosclerosis. Participants underwent coronary angiography (an X-ray examination of the blood vessels of the heart) both at the beginning of the study and after three years to determine changes in the diameter of their coronary arteries, and to detect coronary lesions.

"While there is a strong link between fish intake and heart health, this study provides the first evidence suggesting that tuna and other dark fish can slow the progression of atherosclerosis in older women, especially those with diabetes," said Joyce Nettleton, D.Sc., R.D., author of Omega-3 Fatty Acids and Health and a member of the Tuna Nutrition Council, which advises U.S. Tuna Foundation on nutrition and public health matters. "It's important to note that this study doesn't suggest that eating fish can prevent disease, but it may significantly retard atherosclerosis in women."

The health benefits of fish are attributed to the high levels of n-3, or omega-3 fatty acids. Evidence suggests that dietary omega-3s might slow down the atherosclerotic process, which can be fatal. Populations that consume more omega-3 fatty acids have significantly lower cardiac mortality, especially sudden death, and people who eat fish appear to have less heart disease.

Of the top 10 most commonly consumed fish in the U.S., canned tuna and salmon have the highest levels of the omega-3 fatty acids according to the U.S. Department of Agriculture (USDA) Nutrient Database.

The study found that women who ate one or more servings of tuna or dark fish per week had smaller changes in the minimum diameter of their coronary arteries than women who consumed other fish. This finding is likely attributable to the higher omega-3 content of dark fish, but may also be related to the preparation of tuna and dark fish versus the preparation of white fish, which is often fried in trans or saturated fats and served with other fried foods such as potatoes.

"The best way to reap the benefits of fish is to eat dark, fatty fish, such as canned tuna, and prepare fish in a healthful way, such as broiling or baking. Most of us should simply eat more of it," Nettleton said. According to Nettleton, the average American eats about 15 pounds of fish a year, compared with about 70 pounds of poultry.

Recognizing the many health benefits associated with dark fish consumption -- including the positive influence on brain and heart function -- health organizations such as the American Heart Association and the American Dietetic Association recommend that people eat two servings a week of fish, especially fatty fish, such as canned tuna.