August 6, 2002
     Prostate Cancer

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Changing diet may slow progression of prostate cancer

SEATTLE -- Aug. 6, 2002 (Cancer Digest) -- New research suggests that fat and calcium themselves may not cause prostate cancer, as previously thought, but instead may fuel its progression from localized to advanced disease.

A fat-laden diet and high calcium consumption have long been suspected risk factors for prostate cancer, however, the research team led by Dr. Alan Kristal of the Fred Hutchinson Cancer Research Center in Seattle found that while high intake of dietary fat and calcium is associated with an increased risk of clinically significant, advanced prostate cancer, it apparently has no impact on risk of early-stage disease.

"Our findings clearly show decreased risk for late-stage disease in men with diets that are low in fat and moderate in calcium, perhaps because these diets slow progression of prostate cancer into more aggressive disease," said Kristal in a prepared statement. "For men diagnosed with early-stage prostate cancer, this finding could be important because it suggests that moderating fat and calcium consumption may reduce the risk of cancer recurrence following treatment."

Results of this population study appear today's issue of Cancer Epidemiology, Biomarkers and Prevention, a journal of the American Association for Cancer Research. The National Cancer Institute and Fred Hutchinson funded the research.

This study looked at the association of total calorie, fat, calcium and vitamin D intake on prostate-cancer risk among 1,200 Seattle-area men ages 40 to 64. More than 60 percent of the participants were under age 60. Half of the men had been recently diagnosed with prostate cancer and the other half were healthy, randomly selected Puget Sound-area residents who served as a comparison group.

The men were interviewed about their dietary habits three to five years prior to diagnosis (or an equivalent time frame among the comparison group). They also completed a detailed dietary questionnaire that asked how much and how often they consumed certain foods and dietary supplements.

While previous studies have examined similar dietary factors on overall prostate-cancer risk, few studies have looked specifically at risk comparing early with advanced disease.

Kristal and colleagues found that men who ate lower-fat diets, with fat accounting for no more than 30 percent of their daily calorie intake, had half the risk of late-stage cancer than men who consumed more fat. However, there were no associations of fat intake with early-stage disease.

Saturated fats (found in meat and dairy fat) and monounsaturated fats (found in certain oils, such as olive and peanut) were associated with an increased risk of advanced prostate cancer. Polyunsaturated fats (found in certain oils, such as safflower and canola) were not. Consumption of omega-3 fatty acids (found in fatty fish such as salmon and mackerel) also did not have an impact on overall prostate-cancer risk, contrary to experimental studies in cell cultures that have suggested there may be a protective effect.

The U.S. Department of Agriculture's Dietary Guidelines for Americans recommends no more than 30 percent of total daily calories from fat. For example, a person who needs 2,000 calories a day based on their height, weight and activity level would want to aim for no more than 600 calories from fat, or 65 grams (1 gram of fat has 9 calories, compared to only 4 calories in a gram of carbohydrate or protein).

One reason that low-fat diets could reduce the risk of prostate cancer is because they reduce blood levels of circulating male hormones such as testosterone. Growth of the prostate, and perhaps growth of prostate cancer, is fueled by male hormones.

The researchers also found the risk of advanced prostate cancer was 112 percent higher - more than double - among men who consumed the most calcium (more than 1,200 mg per day, equivalent to four or more glasses of milk) as compared to those who got the least (fewer than 500 mg). It didn't matter whether the calcium came from food or supplements. "For regional/distant disease, there were consistent trends for increased, independent risks from both dietary and supplemental calcium," the researchers wrote.

The only dietary risk factor that appeared to carry equal weight among men with both early and advanced prostate cancer was the amount of total calories consumed, regardless of fat.

"Total energy intake was significantly associated with risk for both localized and advanced disease," said Kristal, who is also an associate professor of epidemiology at the University of Washington School of Public Health and Community Medicine.

Men who ingested the most calories each day more than doubled their risk of localized prostate cancer (a 115 percent increased risk) and nearly doubled their risk of advanced prostate cancer (a 96 percent increased risk) compared to men who consumed the fewest calories.

While there is no effective treatment for advanced prostate cancer, localized disease can be treated by surgically removing the prostate or with radiation therapy. While almost all men diagnosed with early-stage prostate cancer survive for more than five years, only 34 percent of men diagnosed after the disease has spread to distant organs are alive after five years, according to the American Cancer Society.

"As more and more men are diagnosed with early stage disease due to the widespread use of the PSA (prostate-specific antigen) screening test, it becomes increasingly important to consider how dietary or lifestyle changes could decrease their risk of cancer recurrence," said Kristal.