Marine omega-3 fatty acids (docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA)) have been shown to reduce breast cancer proliferation in cell and animal studies of breast cancer. DHA has also been shown to reduce bone metastasis in a mouse model of breast cancer. In addition, a high dietary omega-3 to omega-6 fatty acid ratio has been reported to protect against breast cancer risk, whereas low ratios increase risk. Fatty fish such as salmon are the best sources of marine omega-3 fats, but not all fatty fish are recommended for breast cancer patients and survivors.

Best types of fatty fish

The following fatty fish are recommended, both because of their relatively high levels of omega-3 fats and their relatively low levels of heavy metals such as mercury and other environmental contaminants:

Arctic char, wild
Herring
Lake trout
Mackerel
Salmon, wild
Sardines
Both smoked fish and pan or deep frying of fish should be avoided since these preparation methods introduce significant levels of carcinogenic polycyclic aromatic hydrocarbons (PAHs) or heterocyclic amines (HCAs).

While salmon and the closely-related Arctic char are recommended for consumption during chemotherapy, recent research suggests that herring, sardines, anchovies, mackerel, lake trout and similar fish should not be consumed the day before through the day after a chemotherapy treatment. In addition, these fish should be consumed only in moderation during the remaining days of each cycle. Fish oil supplements should not be consumed by those undergoing chemotherapy. Many fatty fish and fish oil supplements incorporate fatty acids that can induce resistance to a broad spectrum of chemotherapy drugs.

Other fatty fish

The following fatty fish and other seafood should be consumed infrequently (perhaps two times per month) despite their relatively high levels of omega-3 fats because of their high levels of heavy metals or other environmental contaminants, or salt:

Anchovies
Caviar
King mackerel
Shellfish
Tuna
Anchovies and caviar are salty whereas the other fish and shellfish tend to have high levels of mercury or other contaminants.

Omega-3 content of common fish

The marine fatty acid content of fish depends in part on their own food sources. Below is a list of common fish in approximate order of omega-3 fat content:

Salmon, wild
Mackerel
Salmon, farmed
Herring
Lake trout, wild
Bluefin tuna
Sturgeon, Atlantic
Sablefish (black cod)
Anchovy
Albacore tuna
Whitefish, lake
Arctic char, wild

Sardines
Bluefish
Whitefish
Mullet
Halibut
Striped bass
Mahi mahi
Pollock
Rockfish
Rainbow trout
Shark
Catfish

Carp
Cod
Flounder
Grouper
Haddock
Ocean perch
Red snapper
Swordfish
Pike, northern
Sole
Tilapia, farmed

The fish listed from catfish onwards are not significant sources of omega-3 fats.

Please see our article on how to optimize your breast cancer diet for information on what to eat during all stages of treatment and recovery.