Saturday, April 30, 2011

How Much Fish Oil Is Good?

Look at table 5 in this study:

Fatty Acid Composition Of Plasma Phospholipids And Risk Of Prostate Cancer In A Case-Control Analysis Nested Within The European Prospective Investigation Into Cancer And Nutrition, American Journal of Clinical Nutrition, 2008

It shows that high blood levels of the omega-3 fatty acid EPA was associated with increased risk for high-grade prostate cancer. As well, it shows an increased risk for high-grade prostate cancer with high levels of the omega-3 alpha-linolenic acid (the type of omega-3 found in plant sources such as flax and walnuts). (Some saturated fats also show increased risk for localized and advanced prostate cancers but I was more interested in the omega-3s right now.)

Just this week a study reported an increased risk for aggressive prostate cancer from high blood levels of the omega-3 fatty acid DHA.

There does seem to be something going on with omega-3 fats and more aggressive forms of prostate cancer. It's hard to tell just from these studies if the relationship involves intake. These are epidemiological studies so cause and effect is not clear. When it comes to cancer, we don't have the benefit of human intervention trials (which is why we don't know for certain if smoking causes lung cancer).
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Other Known Drawbacks To Omega-3 Fatty Acids

Omega-3 fatty acids can be immunosuppressive:Omega-3 fatty acids are associated with an increased risk for cardiac death:
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How Much Fish Oil Is Good?

The Japanese in Okinawa in 1950, some of the longest lived people in the world, were consuming fish at about 1% of their total calories - half an ounce a day. That's about one 3-ounce serving of fish a week.

Mainland Japanese in the 1950s were consuming fish at about 4% of their total calories - 62 grams or 2 ounces a day. Recent data1 show Japanese to be eating about the same as they did then, ~60 grams a day. Depending on the fish (e.g. catfish, tuna, mackerel), that's 100-200 mg omega-3 a day.

So, a gram of omega-3s a day is more than 5 times the amount the Japanese eat, and 20 times the amount older Okinawans ate. Given the evidence accruing for harm linked to higher intakes of omega-3, it seems prudent to limit consumption - both of fish and fish oil.
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1 Dietary Patterns And Cardiovascular Disease Mortality In Japan: A Prospective Cohort Study, International Journal of Epidemiology, 2007

6 comments:

Laurie Endicott Thomas said...

I would guess that the answer is zero. Gorillas don't fish. Even chimpanzees don't fish. Why should we imagine that people need to eat fish?

Bix said...

Well, we don't have to imagine. We could imagine. It would probably be better for the health of the planet, not to mention the health of the fish, if we didn't imagine.

Dr. Mel said...

There are plants and seeds that contain it too. And "weeds"--purslane contains more ALA than all other plants, and also a considerable amount of EPA.

ElDoubleVee said...

Orangutans fish, and eat the fish. They have perfected ways of grabbing fish from a stream and have been known to use tools to fish. I could foresee Chimpanzees eating fish if they were available in their habitat. Many mammals eat fish. Bears are notable salmon eaters.

Dr. Mel said...

Fascinating about orangutans, ElDoubleVee!

Laurie Endicott Thomas said...

The fact that other mammals eat fish is irrelevant. Dolphins are mammals that eat fish. Bears also eat fish, but biologically they are classified as true omnivores.

The point is that great apes can and often do get along just fine without eating fish. There is no reason to believe that human beings or even orangutans need to eat fish. Rather, there is evidence that adding animal-based foods of any kind to the human diet poses needless risks. http://www.ncbi.nlm.nih.gov/pubmed/9860369?dopt=Citation