Prostate : Excess Protein and Prostate Cancer

Harry Jackson Jr.

Researchers at Washington University are investigating a potential link between prostate cancer and excess protein in the diet.

They believe that reducing the amount of protein in the diet can control or even prevent prostate cancer. So they've started two studies to prove it.

Findings also may have implications in the prevention and treatment of colon and breast cancer, researchers say.

Dr. Luigi Fontana is the chief investigator on the study, "Does Protein Restriction Inhibit Prostate Cancer Growth?"

He's also co-director of the CALERIE Study, a national, federally funded look at the health effects of calorie restriction -- eating 20 percent to 30 percent fewer calories.

While working on the CALERIE Study, Fontana said researchers examined men who had reduced their calorie intake quite substantially. They found that protein intake was more important than calorie intake in regulating the circulating levels of a key hormone called insulin-like growth factor 1, or IGF-1.The hormone has been linked to the risk of developing prostate, breast and colon cancer.

The normal job of the hormone is to help cells grow. It's one of the reasons protein helps rebuild muscles.

But too much protein produced too much of the hormone, Fontana said. That extra hormone potentially helps prostate cancer cells grow, as well.


Now, researchers are ready to test the hypothesis in people. So a study on humans is looking for two sets of men: Those who have prostate cancer and are scheduled for surgery, and men who have recently had prostate cancer surgery but who continue to have detectable levels of prostate specific antigen.

With the first group, researchers will screen them, then place half of the men on a lower protein diet regimen, while the others will continue to eat a diet higher in protein.

"We'll provide breakfast, lunch and dinner for the people in the study," Fontana said. "For a month, they won't have to cook."

After the prostate surgery to remove the gland, 'subsequent tests will show if the diet reduced the aggressiveness of the cancer," Fontana said.

"Once we have the tissue removed, we can see if there are changes that suggest that we're doing the right thing," he said.

And for the men in the second group, half of them will eat a diet in which they get about 10 percent of total calories from protein. The others will continue to eat their usual diet, which is higher in protein.

"If there's any reading, that means there's still cancer cells in the body," Fontana said. "The PSA test is very reliable after surgery."

After a prostate gland is removed, there should be a zero PSA.

"If reducing protein intake makes the PSA numbers drop, this would suggest that we are positively influencing the course of their cancer," Fontana said.

Researchers will follow both groups for a year.


The findings could alter beliefs in several medical disciplines, Fontana said. One belief in the nutrition community was that eating a high-fat diet contributed to causing cancer.

The new research stands to show that too much protein is the culprit because it generates the excess IGF-1 that feeds some cancers. Saturated fat, fat from animals, got the blame, but it usually is part of a high-protein diet.

Indeed, the U.S. Department of Agriculture's, recent heir to, shows Americans need to eat smaller portions of protein and larger portions of fruits, vegetables and grains.

Fontana said federal statistics show that while protein should be around 10 percent of the diet, Americans eat 30 percent to 50 percent more than what is recommended; "too much meat and not enough vegetables, fruits, complex carbohydrates and other nutrients."

Fontana likens the discovery to how knowledge about heart disease and saturated fats emerged over the decades.

"In 1955, we didn't know anything about the link between diet and coronary heart disease," he said. "People were dying and we didn't know why. Then studies found that in places in the Mediterranean and parts of Asia people had lower rates of heart disease, because they were eating much less meat in their diets.

"They found that animal fats were linked with high cholesterol," he said. "Then, animal studies found that high cholesterol was bad for the arteries and the heart.

"It will be the same for cancer," he said.

He said he believes that if the studies prove his observations, the principle of tracking the effect of IGF-1 could be applied to fighting prostate, colon and breast cancers.

"Our hypothesis is that the higher incidence in prostate, breast and colon cancer in the United States is due to the constant, chronic, excessive protein intake in the diet," he said.

"It's potentially a major discovery similar to the association between animal fat and cholesterol."

"It has some public health implications," he said. "If we can slow or block prostate cancer by lowering protein intake it becomes one of the interventions."


The study is about 2 months old. Researchers are looking for volunteers.

Any man who has had prostate-removal surgery but who continues to have detectable PSA levels is eligible. They may be in the study for up to a year.

For the pre-surgery study, researchers are seeking otherwise healthy men with prostate cancer, who are scheduled for prostate cancer surgery. All medical and dietary assessments are provided free.

For more information about either study, call Mary Uhrich at 314-747-3180 or email

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