Nutrition guru pokes huge holes in omega-3/prostate study
Jonny Bowden, PhD, CNS is a best-selling authority on nutrition and health whose advice* flows from hard science and common sense ... and he has a sharp eye for pseudo-science.
He kindly permitted us to republish his critique of the new study – Media Madness: Fish Oil Supplements and Prostate Cancer – which appears in Dr. Bowden's Huffington Post column.
Harvard prostate cancer expert calls new study “weak, at best”
Anthony D'Amico, M.D., is professor of Radiation Oncology at Harvard Medical School and chief of Genitourinary Radiation Oncology at the Brigham and Women's Hospital and Dana-Farber Cancer Institute.
He's co-authored more than 140 peer-reviewed publications on the detection and treatment of prostate cancer, and he has co-edited four urologic oncology textbooks.
In a recent radio interview about the new study, he opined that the “… scientific strength of it is weak, at best,” and explained one key reason why:
“…these types of studies are not cause and effect; that is, if you take the fish oil you're going to get an aggressive or some kind of prostate cancer … [so] you try to adjust for that association, for all the things you know can cause prostate cancer.”
“They tried this, but they didn't do it properly...they left out some very important risk factors for prostate cancer ... from a scientific standpoint that's what makes this association [between omega-3 DHA blood levels and higher risk for prostate cancer] extremely weak and possibly false.”
*See our Dr. Jonny Bowden Healthiest Foods pack, designed to his specifications.
- The authors admit they don't know why omega-3s – which display anti-cancer effects across the board – would promote prostate tumors. This is especially true given that, in the authors' words, the men in the study had “very low concentrations of [omega-3s]”.
- Japanese men had much lower rates of prostate cancer from 1960-2000, compared with men from the U.S., UK, France, or Italy, despite eating much more fish ... hence, much more omega-3 DHA as well (Marugame T, Mizuno S 2005).
- The authors' conclusion that omega-3s raise prostate risks is based on a truly insignificant 0.2% difference in the proportion of omega-3 fatty acids in red blood cells between the men who developed prostate cancer (4.66%) and those who did not (4.48%). And the range in those groups nearly overlapped: the range in men who developed prostate cancer ended at 4.55% while the range in men who did not get prostate cancer started at 4.56%, and the range in men who got high-grade cancer started at 4.51%. This may pass a statistical test, but it doesn't pass the "smell test".
- Men who drank heavily, ate more (proven-unhealthful) trans fats, and smoked had lower rates of aggressive, high-grade prostate cancer ... yet the authors did not conclude that men should smoke, drink more alcohol, and eat more trans fats.
- The blood measure they used – plasma phospholipid fatty acids – is an unreliable gauge of omega-3 levels, developed more than 50 years ago. According to Dr. Bibus, a single fish meal or fish oil supplement will raise the proportion of omega-3s in a person's total phospholipid fatty acids dramatically ... and the men's blood was drawn only once, at the outset of the seven to 12-year study.
- It's entirely possible that the men who developed prostate cancer were generally less healthy, and were taking fish oil supplements.
- Although the authors tried to eliminate “confounding” diet and lifestyle factors that would muddy the waters, it is notoriously hard to do that. And it appears that they authors did not account for the confounding effects of selenium and vitamin E, which were the targets of the original SELECT study. These supplements are implicated in prostate cancer. (Alpha-tocopherol is just one of eight parts of vitamin E, but is the most common supplemental form of "vitamin E". It depletes the body of other vitamin E components, which may be why it is linked to higher prostate risks.)
- As the authors admitted, “Expressing fatty acids as weight proportions could create spurious results because an increase in the percentage of one type of fatty acid requires a decrease in others”. And their justification for dismissing this factor doesn't pass muster: “… however, given the very low concentrations of [omega-3s], it is unlikely that their variability, which is strongly related to dietary intake, would be strongly affected by proportions of other phospholipid fatty acids.” But decades of research on fatty acids analysis suggests that this assertion is a stretch, at best.
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