UCLA Study Finds Low-Fat Diet Slows Prostate Cancer Growth in Lab Models
A low-fat diet may help men with aggressive prostate cancer better fight their disease and live longer, according to researchers at UCLA's Jonsson Cancer Center who showed that a diet low in polyunsaturated fats slowed cancer growth and increased survival times in lab models.
The study appears in the Feb. 15 issue of the peer-reviewed journal Cancer Research. The study is part of the Jonsson Cancer Center's Specialized Program of Research Excellence in prostate cancer, a federally funded program created to find better ways to prevent, detect and treat this disease, which will strike more than 220,000 American men this year alone.
Laboratory mice with advanced human prostate cancer that were deprived of the hormone testosterone were fed a diet low in polyunsaturated fats and remained in remission about twice as long as mice fed a diet with a much higher fat content, the study found. The mice on the low-fat diet also lived nearly twice as long as those on the high-fat diet, said Dr. William Aronson, a Jonsson Cancer Center researcher and the study's lead author. Additionally, levels of PSA — which measures the amount of prostate cancer present — were markedly lower in the mice fed a low-fat diet.
Aronson called the results "very significant," but cautioned that large studies need to be conducted in humans to ensure the results can be translated from mice to men.
"These results provide a sound basis for clinical trials evaluating the impact of dietary fat reduction in prostate cancer patients on hormone therapy," said Aronson, an associate clinical professor of urology. "This new finding tells us that a low-fat diet can impact cancer growth and survival times in laboratory mice. We need to understand why, and duplicate the results in humans."
The research by Aronson and his UCLA colleagues studied polyunsaturated fats, derived from corn oil and found in the baked goods and fried foods popular in the American diet. The team wanted to create a lab environment that would mimic a human population, specifically men with advanced prostate cancer treated with hormone therapy.
Standard treatment for advanced prostate cancer is to stop production of the hormone testosterone, which drives cancer growth. Called androgen-deprivation therapy, this treatment works for a time. However, many men then develop cancers that are androgen independent, meaning the cancers grow despite low levels of testosterone. Once that happens, hormone therapy is no longer effective and few other treatment options are available, Aronson said.
In the Jonsson Cancer Center study, laboratory mice with human prostate cancer were divided into three groups. One group was fed a high-fat diet containing about 42 percent of calories from polyunsaturated fats. A second group of mice was castrated — to mimic men on androgen-deprivation therapy — and fed a diet containing 42 percent of calories from fat. The third group of mice, also castrated, was fed a low-fat diet, with about 12 percent of calories coming from fat. All three groups ate the same number of calories, Aronson said.
The UCLA research team found that the uncastrated mice in the high-fat diet group had tumors that grew rapidly and the animals died quickly from the cancer. Tumor growth in the castrated mice being fed a high-fat diet stabilized for a time — mirroring what happens to men with advanced prostate on hormone therapy. As expected, and as often happens in humans, the cancers in this mice group then began to grow again. Meanwhile, the castrated mice on a low-fat diet went twice as long before their cancers became androgen independent and began to grow again. Additionally, survival times were significantly longer in the low-fat diet group, and tumor size was much smaller than those found in mice on a high-fat diet, Aronson said.
"This study may help us solve a clinical problem, how to prevent or delay androgren independence," Aronson said. "Maybe men on androgen-deprivation therapy, if they eat a low‑fat diet, might prolong the effectiveness of their hormone therapy."
Doctors have been recommending a diet low in fat for some time, based on epidemiological studies offering evidence that such eating habits may help prevent certain cancers. This study is the first to show that a low-fat diet may help hormone therapy work better and longer, Aronson said.
"Now we need to do more detailed laboratory studies to find out how the fat intake is affecting the growth of the androgen-independent cancers," Aronson said.
Human studies are several years away, Aronson said. However, men with prostate cancer can switch to a low-fat diet now and perhaps reap some benefit. Aronson suggests patients reduce their intake to about 15 to 20 percent of calories from fat and combine that with daily exercise; for example, taking a brisk walk or doing aerobic activity for 30 minutes every day. Men also should eat more tomato products, particularly tomato paste, and make sure the fat they do eat contains omega-3 fatty acids, the type found in fish oils.
"I think dietary fat reduction, coupled with high fiber intake from fruits and vegetables in a variety of colors, can truly have an impact on prostate cancer prevention, and in combination with existing treatments, perhaps increase survival times for patients," Aronson said.
UCLA's Jonsson Comprehensive Cancer Center is composed of 240 cancer researchers and clinicians engaged in cancer research, prevention, detection, control and education. One of the nation's largest comprehensive cancer centers, the center is dedicated to promoting cancer research and applying the results to clinical situations. In 2003 the center was named the best cancer center in the Western United States by U.S. News & World Report, a ranking it has held for four consecutive years.
For more information on the Jonsson Cancer Center, visit www.cancer.mednet.ucla.edu/.