Study links diet to prostate cancer

Prostate cancer strikes nearly a quarter-million American men each year — more than any other cancer except skin cancer. But while scientists are still not certain what causes it, they suspect diet and obesity somehow play a role.

Now a very small clinical trial by Seattle researchers is offering tantalizing glimpses into that link.

The pilot study, involving eight local men recently diagnosed with prostate cancer, found that dramatically cutting back on dietary fats and carbohydrates and/or calories actually alters the levels of genes in prostate tissues that can potentially regulate cancer growth.

The researchers did not attempt to identify the cancer's culprit. But the study, published Wednesday in the October issue of the journal Cancer Epidemiology, Biomarkers and Prevention, suggests that whatever its cause, prostate cancer may respond quickly and markedly to significant changes in weight and diet.

Strikingly, the changes occurred after four of the men spent just six weeks on a low-fat, low-carb diet, said Dr. Daniel Lin, assistant professor of urology at the University of Washington and the paper's lead author.

"Imagine what could happen in four years or even 40 years," Lin said.

Scientists don't exactly understand the mechanism between cancer and excess weight or diet. But the link exists, said Marian Neuhouser, the paper's co-author and a scientist at the Fred Hutchinson Cancer Research Center in Seattle.

One explanation may be that body fat synthesizes hormones, such as estrogen, that raise the risk of certain cancers, Neuhouser said. Fat cells also trigger low-grade inflammation in the body, and that also could be a risk factor for some cancers, she said.

One argument for a dietary or environmental cause of prostate cancer, Lin said, is that it's much less common in Asia than in the United States — but Asian men get it more often after immigrating here.

Still, only a few definitive risk factors for prostate cancer are known, including age, race and family history.

Lin cautioned that the latest study was extremely small and did not measure whether the cancer progressed more slowly among the men in the low-calorie group. Also, those men consumed an average of 1,500 calories a day — 40 percent less than the men in the control group who stuck to a "standard American diet" rich in fat and carbohydrates.

Researchers found significant differences in about 30 out of 7,000 genes in the two groups of prostate-tissue samples. Though few in number, Lin said the affected genes included important ones, such as genes that control cell growth or cellular repair, both of which can influence cancer development.

Kyung Song: 206-464-2423 or ksong@seattletimes.com