If you get your nutrition factoids from headlines, you might have recently concluded that omega-3 fats cause prostate cancer.
FACT: omega-3 fats are nutrients. That means, your body absolutely needs them to function properly. It doesn’t make much evolutionary sense for the human body to require a substance that actually causes disease. If that were the case, humans would have died out long ago.
Nevertheless, ignorant journalists pumped up this story, because, well, they can. Journalists aren’t nutrition experts, and have no ability to sort through poor study design. They don’t understand that “association does not equal causation“. All they care about is a big screaming sensational headline.
Here’s an example of the kind of junk conclusions that are possible when you believe “association equals causation”: Every human that ever lived breathed air. They all eventually die. Therefore air causes death.
This omega-3 study fits that same pattern. The study surveyed men who had prostate cancer and tested their blood for omega-3 fats. Results: men with more omega-3 in their blood had more risk for prostate cancer.
Here’s what they didn’t bother to think about:
- Men diagnosed with prostate cancer may have started doing things they thought would help, such as taking omega-3 supplements or eating more salmon. What else were they doing that wasn’t measured? Taking herbs or chemotherapy medications that affected omega-3 metabolism as a side effect?
- The differences in blood levels that supposedly correlated with higher cancer risk were incredibly small. As one critic noted, you could have a temporary increase just from eating fish for lunch. Which brings up another problem:
- The whole study was based on just one blood draw. Leaving the numbers open to random variation based on what someone ate for lunch, having no relevance to long term blood levels.
Here’s an interesting fact, courtesy of National Geographic Magazine: members of the Karuk tribe, who lived along the Klamath River in Oregon long ago, ate more than a pound of salmon a day. Every day. Do the math: that adds up to roughly 5-6 grams of omega-3 fats every single day of a Karuk’s life. Most omega-3 supplements contain a comparatively measly 1/2 gram per day. There is no record that the Karuk tribe, or any other of the numerous Arctic tribes that had very high daily intake of omega-3 from salmon, herring, sardines, seal or other ocean mammals, had any history of a prostate cancer epidemic. Why not?
There’s a more obvious and contemporary comparison to make, mentioned by many of the critics of this junk study: if omega-3 causes prostate cancer, why isn’t there an epidemic of prostate cancer in Japan? Denmark? Sweden? What about the cod-liver-oil-swilling Norwegians? In fact, people in these countries are considerably healthier than in the US.
The only way to prove a link between omega-3 and prostate cancer is to find large numbers of male subjects, preferably by age 18, and sign them up for a life long study. One group gets omega-3 and/or eats salmon, flax, canola oil and walnuts frequently. One group cannot consume omega-3 or eat any high fat ocean fish or walnuts or canola oil or flax or anything that contains any of those. For 50+ years. In fact, because these diet restrictions are so draconian, all the subjects will likely have to be confined to a facility that provides all their food in measured portions. Keep track of who gets prostate cancer and who doesn’t. Then we’ll know. Anyone want to volunteer?