According to a review published by the British Medical Journal (BMJ), eating tuna, salmon, sardines or other oily fish once or twice a week reduces the risk of breast cancer.
Researchers based in China looked at 26 previously published studies covering more than 800,000 volunteers in the United States, Europe and Asia whose health was monitored and who gave details about their eating habits.
Oily fish is rich in n-3 polyunsaturated fatty acids, or n-3 PUFAs, which are involved in the immune system, blood-vessel activity and chemical messaging in the brain.
The analysis showed that women with a high intake of n-3 PUFAs had a %14 reduction in risk of breast cancer compared with those who had a low intake.
But the protective effect came only for fatty acids that come from fish, and not for ALA acids.
Those who showed the most benefit were women in Asia, whose diet was richer in fish than in Europe and America.
Every 0.1-gram increase in fish fatty acids per day was linked to a %5 reduction in breast cancer risk.