In the first-ever study of its kind, omega-3s from fish packed a much stronger anti-cancer punch, versus omega-3s from plant sources.

The study — from Canadian researchers — was conducted in experimental rodents, so its findings may or may not translate fully to humans.

University of Guelph professor David Ma led the team, whose work suggests that that seafood-source omega-3s are eight times more effective at inhibiting the development and growth of breast tumors.

Dr. Ma explained why they conducted the study: “There is evidence that both omega-3s from plants and marine sources are protective against cancer, and we wanted to determine which form is more effective.”

To learn more, search our website for “omega-3 cancer”.

Omega-3 fats: Not created equal
There are two distinct types of omega-3 fatty acids:

  • “Short-chain” omega-3 ALA from plants.
  • “Long-chain” omega-3 EPA and DHA from seafood and algae.

Humans only require long-chain omega-3s — EPA and DHA, especially DHA — which are critical to optimal health and to our very survival.

Our bodies can convert plant-source omega-3 ALA into EPA and DHA, but it’s a very inefficient process: see “Key facts about plant- and seafood-source omega-3s”, below.

The richest sources of omega-3 ALA are flaxseed, canola oil, walnuts, dark leafy greens, soy oil, and hemp oil.

(Flaxseed oil may be the richest food source of omega-3 ALA, and flaxseed abounds in polyphenol-type antioxidants known as lignans, whichgut bacteria metablize into weakly estrogenic compounds that may curb the risk of postmenopausal breast cancer.)

Grass-fed and pastured meats or poultry provide significantly more ALA than standard, grain-fed livestock, but the amounts remain quite small.

The only substantial sources of omega-3 EPA and DHA are seafood, fish or krill oil, algae, and phytoplankton.

Study finds seafood-source omega-3s eight times more protective
The University of Guelph team fed the different types of omega-3s to mice with a highly aggressive form of human breast cancer called HER-2 (Liu J et al. 2018).

About 25% of women with breast cancer have HER-2 breast tumors, which have a generally poor prognosis.

The Canadian team fed the mice diets enriched with either plant or fish oils, beginning in utero:

  • 10% flaxseed oil (high in omega-3 ALA)
  • 10% safflower oil (high in omega-6 fats)
  • 7% safflower + 3% flaxseed oil (high in omega-3 ALA)
  • 7% safflower + 3% fish oil (high in omega-3 DHA and EPA)

Safflower oil is very high in omega-6 fatty acids, and has virtually no omega-3 ALA, while flaxseed oil is very high in omega-3 ALA, and very low in omega-6 fatty acids.

“The mice were exposed to the different omega-3s even before tumors developed, which allowed us to compare how effective the fatty acids are at prevention,” said Dr. Ma. “It’s known that EPA and DHA can inhibit breast tumor growth, but no one has looked directly at how effective these omega-3s are compared to ALA.”

His team found the diets enriched with omega-3 fish oil reduced the size of mammary tumors by about two-thirds (60% to 70%) and reduced the number of tumors by about one-third (30%).

In contrast, higher doses of the plant-source omega-3 ALA were required to deliver the same benefit as the omega-3 fish oil.

Omega-3s discourage and fight cancer by turning on genes associated with the immune system and blocking tumor growth pathways, said Dr. Ma.

As he said, “It seems EPA and DHA are more effective at this. In North America, we don’t get enough omega-3s from seafood, so there lies an opportunity to improve our diet and help prevent the risk of breast cancer.”

We should note that breast cancer isn’t the only form that omega-3s appear to undermine — and that omega-3s have been shown to enhance the efficacy of standard cancer therapies.

(Search our website for “omega-3 cancer”, “omega-3 colon”, “omega-3 prostate”, and see Omega-3s May Enhance Certain Cancer Therapies, Fish Fats May Boost Breast Cancer Drug, Omega-3s May Fight Breast Cancer Fatigue, and Omega-3s Cut Cancer-Caused Wasting.)

Based on the doses given in the study, Ma said, people should consume two to three servings of fish a week to enable the same effect.

Dr. Ma made a key point: “Seeing the significant benefits omega-3s can have in combatting a highly aggressive form of breast cancer means omega-3s will likely be beneficial for other types of cancer.”

His point was reinforced by recent research from the University of Illinois, whose authors found that molecules formed when the body metabolizes omega-3 fatty acids — called endocannabinoid epoxides — stemmed the growth and spread of bone cancer in rodents (Roy J et al. 2018).

The Illinois study involved mice with osteosarcoma: a bone cancer that's notoriously difficult to treat.

The scientists found that omega-3-derived endocannabinoid epoxides slowed the growth of the bone tumors and their blood supply, curbed spread of the cancer cells, and prompted them to commit “suicide” (apoptosis).

Key facts about plant- and seafood-source omega-3s
Omega-3 DHA is critical to brain and eye function, while omega-3 EPA and DHA are both important to control of inflammation.

All seafood provides both DHA and EPA, but the levels and proportions can vary significantly among species.

Most people can only convert a small proportion of plant-source ALA into EPA and DHA, with the conversion rate ranging from 1% to 10%. (The body readily converts DHA to EPA, but cannot convert DHA into EPA nearly as efficiently.)

The conversion rate depends on several factors:

America’s “omega imbalance”
The standard American diet provides a very high, unbalanced ratio of omega-6 fatty acids to omega-3 fatty acids — from about 10:1 to 15:1 — versus the 1:1 to 3:1 ratio that humans ate until very recently.

This gross imbalance stems from the widespread use of cheap, omega-6-laden vegetable oils — soy, corn, safflower, sunflower, and cottonseed — in homes and in packaged, restaurant, and processed foods. (See “Which oils are best?”, below.)

And there’s steadily growing evidence that diets high in omega-6 fatty acids promote chronic inflammation, which in turn promotes cancer, cardiovascular disease, diabetes, dementia, and arthritis.

For example, see Breast Cancer Tied to Omega Imbalance … Again.

Which oils are best?
Oils high in omega-3 ALA and/or monounsaturated oleic acid make the best choices.

These include canola (choose non-GMO), extra virgin olive oil, macadamia nut oil, and "high-oleic" safflower and sunflower oils.

In recent years, many food and vegetable oil manufacturers have shifted from regular to high-oleic sunflower oil, which is extracted from seeds bred to contain much less omega-6 fat, and much more monounsaturated oleic acid.

Oleic acid also predominates in olive, macadamia nut, and avocado oils, and is considered metabolically “neutral” because it neither raises nor reduces inflammation.

The only way to be sure you’re getting high-oleic sunflower oil is to choose a brand — usually a “natural food” brand that discloses this fact.

(To minimize their omega-6 fat content, Vital Choice foods that include sunflower oil invariably employ high-oleic or mid-oleic sunflower oil.)

You can also find high-oleic safflower oil, but it usually has substantially more omega-6 fatty acids and less oleic acid, versus high-oleic sunflower oil.

Likewise, so-called “mid-oleic” sunflower oil has substantially more omega-6 fatty acids, and less oleic acid, versus high-oleic sunflower oil.


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