NEW YORK (Reuters Health) - A diet that is low in fat and full of fiber, fruits and vegetables is a good idea in general, but it may not protect men against developing prostate cancer, US researchers report.

These findings appear on the tail of previous research that demonstrated that a high-fat diet is linked to an increased risk of advanced prostate cancer.

So what's a man to eat? Lead author Dr. Moshe Shike of the Memorial Sloan-Kettering Cancer Center in New York told Reuters Health that although these results suggest that eating well may not protect against prostate cancer, it nonetheless can have a powerful effect on the eater's general health.

"In spite of this study, the low-fat, high-fruit, high-vegetable diet is a healthy diet," Shike said.

This study "is by no means an indication not to follow this diet," he added.

In terms of the seemingly contradictory results between the current and previous findings, Shike noted that the two studies used different techniques to obtain their results. Specifically, in the first study, researchers asked men to remember their diets over the past 3 to 5 years, and not many people can recall their long-term eating habits with great detail, the researcher noted. In contrast, the current study followed the men over time, a technique considered to be more accurate by the research community, Shike said.

Shike's team measured the risk of prostate cancer in terms of rising levels of PSA, a protein produced by the prostate gland. Many cases of prostate cancer are only diagnosed when the disease is at an advanced stage, so doctors try to catch the cancer in its early stages by measuring PSA levels in the blood, with PSA spikes signaling a man may have the beginnings of prostate cancer.

The investigators obtained their findings by following a total of 1,350 men, half of whom received intense counseling to opt for a low-fat diet that was rich in fiber, fruit and vegetables. Shike and his colleagues then measured the men's PSA levels every year for 4 years, and noted when any study participant was diagnosed with prostate cancer.

Reporting in the September issue of the Journal of Clinical Oncology, Shike and his team note that most men who were asked to change their diets did so in the first year, and maintained their healthy habits throughout the study.

However, the authors also write that the healthy diet appeared to have no effect on how fast PSA levels increased in men, and just as many men from both dietary groups had elevated PSA blood levels throughout the study.

Furthermore, a similar number of men developed prostate cancer in the two groups--19 of those whose diet was unchanged, and 22 men who had adopted the healthy eating habits.

Based on these findings, if a middle-aged man decides to switch his diet to the one described in this paper, "that man cannot expect that this diet, if consumed for 4 years, will reduce his risk of developing prostate cancer," Shike said.

However, he noted that 4 years is not a very long period of time to study the life cycle of cancer. Consequently, it is possible that if a young boy were to adopt these healthy eating habits, the diet could reduce his risk of developing prostate cancer once he reaches middle age, Shike said.

In an accompanying editorial, Dr. Alan R. Kristal of Fred Hutchinson Cancer Research Center in Seattle, Washington, notes that the study findings appear sound, but may not present the whole picture of the influence diet has on the risk of developing prostate cancer.

"We should remember that this study does not address whether a low-fat and high-fiber dietary pattern affects very early processes in carcinogenesis, before a detectable increase in PSA would occur, nor does it address whether dietary change affects the development of invasive disease," he writes.

SOURCE: Journal of Clinical Oncology 2002;20:3570-3571, 3592-3598.

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