I just read in Fanatic Cook (< http://fanaticcook.blogspot.com/2010/04/psa-testing-cant-detect-prostate-cancer.html >) that a study has shown that:
"There is some evidence that a diet higher in fat, especially animal fat, may increase the risk of prostate cancer."
Since we, as believers in the Paleo worldview, presumably place eating animal fat as one of the core principles of our diet, will this more likely lead to us (in a statistically significant way at least) getting prostate cancer?
Considering how common and dangerous prostate cancer is, are the (theoretical longevity?) benefits of paleo worth the prostate cancer trade-off?
Anyone know any more details about this study so we can see if we should trust it, and how significant the causation is is?
asked byMorgan (1670)
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on April 13, 2010
at 05:41 PM
The studies cited thus far are all observational and only show an association. They do not explain the mechanism. You are (unconsciously and because you're being lead by the nose by good ol' bad journalism) jumping to a causative relationship when none has been established, especially when you ask the question, "Did cavemen all die of prostate cancer?"
Keep a few things in mind:
1) Not everyone who eats animal fat gets prostate cancer. Thus there is no 1:1 causative relationship in the same way that getting hit with a baseball bat in the head with a certain force will break your skull or being irradiated with a certain dose will kill you.
Lesson: Never mistake association/correlation for causation. Establishing which event causes another is not a trivial task in human health, and it's very easy to put the cart before the horse when just working with observations.
2) The people who were studied were eating, generally speaking, the standard american diet and thus there are all sorts of confounding factors. The paleo approach is, almost entirely, based on saying, "This is observed in modern man on a modern diet; what if we didn't eat a modern diet?" It's possible that to get prostate cancer, you need to eat animal fat AND X, where X is not typically present in a hunter gatherer society.
Lesson: Never forget confounding factors; simple relationships are usually not that simple in reality. (don't forget to apply this to your favorite paleo dogma either)
To quote the NY Times article:
Both the writers of the editorial and the authors of the new study pointed out that the relationship between fat intake and the promotion of prostate cancer was complex and in need of much further research. Dr. Giovannucci said, "The findings need to be confirmed in similar prospective studies in different populations, and more research is needed into how animal fats might promote prostate cancer."
3) They cite "alpha-linolenic acid from animals" as the fat causing the highest cancer risk, but earlier in the article they claim that omega-3 fatty acids are anti-cancer. This is somewhat bizarre since alpha-linolenic acid is an omega-3 fatty acid typically associated with plant sources, not animal sources.
In the course of searching for some clarification, I came across a study from 2006 which directly contradicted that observation: http://www.psa-rising.com/blog/2006/06/alpha-linolenic-acid-no-impact-on-prostate-cancer/
So here we have two large studies, one asserting one thing, another saying in essence, "No association."
Lesson: Verify the details.
NOTHING in human health is simple. Even the basic logic of avoiding neolithic foods can only reach the status of a heuristic, not a principle. Something like "eat animal fat -> get prostate cancer" just doesn't pass the nuance smell test.
on April 12, 2010
at 07:33 PM
Keep in mind that there are studies to support pretty much any opinion someone has. You have to take a look at who they were testing and what they ate and their lifestyle. The majority of people eat the standard American diet and exercise very little, so basing results off of what they eat and what it can hold in store for them in terms of disease is not applicable to people eating paleo and working out.
Also, do they distinguish as to what kind of animal fat? If it's conventionally-raised meat, then sure, you are going to have some problems, especially when it is combined with eating alot of grains and sugars. But if it's grassfed, then you are getting vital nutrients and minerals, and avoiding the toxins that are in the fat of conventionally-raised meat. Picking apart many studies reveals that they are poorly conducted and more often than not the funding for them is coming from a source that will skew the results.
on April 12, 2010
at 06:14 PM
So the National Cancer Institute slips in the sentence
"In addition, there is some evidence that a diet higher in fat, especially animal fat, may increase the risk of prostate cancer."
in this article on PSA testing: http://www.cancer.gov/cancertopics/factsheet/Detection/PSA without quoting any references. Bix then quotes that on very pro-vegetarian biased blog. I'm not impressed.
Somebody linked an article in the comments that does a fairly extensive review of existing studies looking into the link between dietary fat and prostate cancer and finds the evidence inconclusive. http://www.escholarship.org/uc/item/5q1808ts?display=all
on April 19, 2010
at 01:55 PM
There is a good overview of prostate cancer risk factors from CANCER RESEARCH UK: http://info.cancerresearchuk.org/cancerstats/types/prostate/riskfactors/
"No modifiable risk factor for prostate cancer has been identified and therefore, at present, there is insufficient evidence on which to base a prevention strategy. The established risk factors are age, family history and ethnicity.
Many other factors have been studied but the evidence is inconclusive. One reason for this may be that different factors are involved in the development and promotion of aggressive disease compared to non-aggressive disease, making epidemiological studies of prostate cancer particularly complex.
Interpretation of prostate cancer risk factors has been further complicated in the PSA era, when identification of many prostate cancers is dependent on a threshold PSA level, which in turn is affected by other exposures such as body mass. This blurs the distinction between ???cases??? and ???controls??? leading to the possibility of PSA-detection bias."
Strangely the only factor that actually reduces risk is type 2 diabetes...
"The risk of prostate cancer was significantly lower, by 16% in the most recent meta-analysis, among men with diabetes mellitus than among those without this condition but why this is so is not clear."
There may be a genetic link between the two. Otherwise its all rather inconclusive.
on April 12, 2010
at 06:29 PM
There's a very obvious paleo answer to all this: look at our history and look at the alternatives to a high fat diet. If this study did hold any ground wouldn't we see serious prostrate problems in populations with a high saturated fat intake?