Doctors have puzzled over the complex relationship between fat and prostate cancer for years as studies have produced apparently conflicting results.
Now, two new papers suggest that obesity affects different subtypes of prostate cancer in different ways.
In a study of nearly 70,000 men that was released last week in Cancer Epidemiology, Biomarkers & Prevention, researchers found that being obese increased the risk of aggressive cancers by 54%. Yet obesity decreased the risk of developing "low-grade" tumors by 14%. Men in the study who lost 11 or more pounds were about half as likely as the others to develop aggressive cancers, says author Carmen Rodriguez, an epidemiologist at the American Cancer Society.
Results from the other paper, published in October, were similar: Obese men had a 78% increase in the risk of very aggressive tumors, but an 18% decrease in the risk of low-grade tumors, says Howard Parnes, a prostate cancer expert at the National Cancer Institute.
The studies reinforce the notion that prostate cancer is not a single cancer but a family of diseases, each fueled by different chemicals, Parnes says. Obese men tend to have less testosterone, known as the male hormone, but more estrogen, often called the female hormone, Parnes says. Abdominal fat also affects levels of insulin, a hormone that helps the body process sugar.
Doctors have long seen testosterone as the villain in prostate cancer, Parnes says, and treat advanced cases of the disease by blocking that hormone. The truth may be more complex. These hormones may interact differently with each subtype of cancer, fueling the growth of some while slowing others.
Michael Morris, a prostate cancer specialist at New York's Memorial Sloan-Kettering Cancer Center, says neither study was designed to answer questions about obesity and prostate cancer. Because of these limitations, doctors can't say for sure that obesity caused a change in the men's risk of prostate cancer.
Still, Parnes says, the studies suggest that by losing weight, "you'd have a benefit not only for prostate cancer, but also for your heart."
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