Toward this end, Allott et al examined dietary intake from 1,854 men diagnosed with prostate cancer. They separated men into low/intermediate risk vs. high aggressive cancers defined using AUA/NCCN criteria as Gleason sum ≥ 8 (grade group 4 or 5), or PSA >20 ng/ml, or clinical stage T3/4. In total, 17% of the men had high-risk cancers. Their specific question related to saturated fat, which commonly occurs in animal meat. They broke patients into tertiles (i.e. thirds) based upon amount of saturated fat intake adjusting for total amount of fat intake. They found that increased saturated fat intake was associated with greater risk of aggressive cancers, but only among men not taking a statin. Among men taking a statin, there was no link between saturated fat intake and prostate cancer aggressiveness. They also found that increased cholesterol intake correlated with increased risk of aggressive cancer, but only among white men and not black men.
Before thinking about the meaning of the results, we must first acknowledge the limitations. The study only included men with cancer. Thus, we cannot address what a diet may look like that could prevent cancer in the first place. Second, men were asked their diet after they were diagnosed. This is important in that men with bad cancers may better remember their bad diet vs. men with lower risk cancer that feel reassured that though they have cancer, they are unlikely to die from it. This is an epidemiological issue called “recall bias”. Third and finally, associations do not mean causation. In other words, simply because increased intake of saturated fat was associated with more aggressive cancers does not mean that saturated fat causes more aggressive cancers. However, it does give us a hint of where to look.
What can we take away from these findings? The fact that the results for saturated fat disappeared among people taking a statin suggests a more complex link likely involving cholesterol. As saturated fat is most often from animal meat, which contains high cholesterol, it is possible that statins “protect” people from the adverse effects of animal meat intake by lowering cholesterol. Indeed, higher cholesterol was linked with higher aggressive prostate cancer, although only among white men (an interesting observation that requires further study). However, as statins also have anti-inflammatory properties, perhaps the saturated fat results in inflammation that is squelched by the statins. Alternatively, these results may have nothing to do with saturated fat, but rather reflect other lifestyle factors associated with higher saturated fat intake (i.e. intake of other foods, higher intake of meat – and charred meat in general, physical activity levels, etc.).
Like most well done epidemiological studies, the study by Allott et al. gives us some good clues of where to look, but no definitive answers. In the meantime, we can take stock in that there are now two well established modifiable risk factors for prostate cancer death: smoking and obesity. Avoiding both seems like fairly safe advice. Beyond that, the search continues for the optimal way of life to maximize overall health while simultaneously reducing prostate cancer deaths.
Written by: Stephen Freedland, MD Editor-in-Chief, Prostate Cancer and Prostatic Diseases Cedars-Sinai Medical Center, Los Angeles, CA
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