A new study says, eating salmon or other fatty fish just once a week can help reduce men's risk of heart failure.
However, the effect of fatty fish and marine omega-3 fatty acids can be seen only in men.
The study provided no evidence that taking food supplements containing marine omega-3 fatty acids made any difference. The men in this study, which is published in Europe's leading cardiology journal, the European Heart Journal, obtained most of their marine omega-3 fatty acids from the food they ate.
Researchers in the USA and Sweden followed 39,367 Swedish men, aged between 45-79, from 1998 to 2004. They recorded details of the men's diet and tracked the men's outcome through Swedish inpatient and cause-of-death registers.
During the period, 597 men without a history of heart disease or diabetes developed heart failure, of which 34 died.
The researchers found that men who eat fatty fish, such as herring, mackerel, salmon, whitefish and char, once a week were 12 percent less likely to develop heart failure compared to men who never eat fatty fish.
Although this association with fatty fish did not reach statistical significance, the researchers also found a statistically significant association with the intake of marine omega-3 fatty acids (found in cod livers and other fish oils); men who consumed approximately 0.36 grams a day were 33 percent less likely to develop heart failure than men who consumed little or no marine omega-3 fatty acids (0.15-0.22 grams a day).
The men were divided into five groups depending on their intake of fatty fish, with the first group consuming none, or very little, and the fifth group consuming the most, three of more servings of fatty fish a week.
The researchers found that while the middle group, which eat one serving of fatty fish a week, had a 12 percent reduced risk compared to the men who never eat fatty fish, the men in the next two groups, who eat either two servings a week or three or more servings a week, had nearly the same risk as the men who eat none.
The researchers also divided the men into five groups based on their intake of marine omega-3 fatty acids. Again, the same U-shape was seen, with the middle group who consumed 0.36 grams a day of fatty acids having a 33 percent reduced risk of heart failure, while the men who consumed more (either approximately 0.46 grams per day or approximately 0.71 grams per day) had a risk similar to men who consumed none or very little.
Dr. Emily Levitan, a cardiology research fellow at Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, USA, who led the research, said: "Our study shows that a moderate intake of fatty fish and marine omega-3 fatty acids is associated with lower rates of heart failure in men, but that the men did not gain a greater benefit by eating more of these foods.
"The apparent U-shaped relationship of fatty fish and marine omega-3 fatty acids with heart failure was unexpected. The higher rate of heart failure in men who consumed the most fatty fish or marine omega-3 fatty acids compared with moderate consumption may be due to chance. Alternatively, these may be men in poor health who ate more fish to try to improve their ill-health, and therefore the fatty fish and fatty acids appear to be risk factors for heart failure. I suspect this is the most likely explanation, but we cannot be certain from our data."