We always thought that fish are absolutely healthy food. Making fish as your menu a couple of times a week maybe could lower your risk for developing heart disease. But, researchers have found something else.

Instead of found that fish or the essential omega-3 fatty acids obtained primarily from seafood could reduce risk for diabetes, researchers suggest that eating 2 or more servings of fish a week may slightly increase diabetes risk.

Dr. Frank B. Hu from Harvard School of Public Health in Boston, Massachusetts, and colleagues explained, "Diet is a key factor in preventing the onset of diabetes in adults, but how omega-3 fatty acid intake impacts diabetes risk is still unresolved."

Among 152,700 women enrolled in the Nurses' Health Study and 42,504 men enrolled in the Health Professionals Follow-Up Study, researchers examined relationship between fish and omega-3 fatty acid intake and the development of diabetes.

Overall, during up to 18 years of follow up, 9,380 cases of adult-onset diabetes developed among these healthcare workers.

After adjusting for lifestyle and other dietary factors, plus body weight, family history of diabetes, and menopausal status and hormone use when applicable, Hu's team noted increased diabetes risk "in all cohorts" consuming higher levels of omega-3 fatty acids.

Relative to those who ate lesser amounts of fish, they found that diabetes was 1.17 times more likely among people who ate fish 2 to 4 times a week, and 1.22 times more likely among those who ate fish 5 or more times a week.

"Further study is needed to figure out the "clinical relevance" of the current findings and determine the mechanisms behind their observation that high fish intake may raise diabetes risk," the team said. They also emphasized that numerous studies have demonstrated beneficial effects of fish and omega-3 fatty acids on multiple risk factors associated with diabetes, and on heart disease as the major sequelae of diabetes.