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Fighting cancer without fat.

One out of eight.

Those are the chances that an American woman will get breast cancer during her lifetime. No other cancer comes close.

Researchers who study the links between diet and cancer have spent most of their time asking whether a low-fat diet can prevent the disease. But what about women who already have breast cancer?

A clear-cut answer won't be available for at least seven years, when a definitive trial is complete. But tantalizing pieces of evidence from studies of large populations, animals, and breast cancer patients suggest that eating less fat may increase the chance of surviving this all-too-common illness.



Like other clues linking diet to cancer, the first sign that fatty diets might impair breast cancer survival came from Japan.

"Japanese women have a 20 percent lower annual risk of recurrence than Americans," says Rowan Chlebowski of the UCLA School of Medicine. "That difference is comparable to the benefit of being treated with an anti-estrogen drug or chemotherapy."

So far, there's no proof that diet alone accounts for the difference - which is only seen in postmenopausal women.

Nor can researchers draw firm conclusions from studies that assess the diets of recently diagnosed breast cancer patients.

Several times, researchers have found that women who reported higher fat intakes were more likely to have advanced cancer when diagnosed, or to later have their cancer recur or spread.(1-3)

"But," explains Chlebowski, "it could be that cancers that spread could change a woman's metabolism, and that could lead her to eat a higher-fat diet."

In the last few years, scientists have found another reason to think that fat helps breast cancer spread: animal studies.


"Unlike in humans, metastasis in rats or mice is relatively rare," says Leonard Cohen of the American Health Foundation (AHF) in New York. "If you use a carcinogen to produce a tumor in rats or mice, it rarely spreads to other organs."

So to test whether diet - or anything else - encourages cancer to spread, some researchers use mice with defective immune systems. Others transplant tumors or inject millions of cancer cells into the bloodstream. In people, far fewer cancer cells travel that way.

"None of these models is perfect," says Cohen. "But when you add them all up, it's clear that we can affect the spread of tumors in animals by altering fat intake."

In some models, the more fat animals eat, the more quickly breast tumors grow or spread to their lungs. In other models, that's only true if the fat is rich in linoleic acid, the major fatty acid in polyunsaturated oils like safflower, corn, soy, and sunflower.

Granted, when you compare diets of different countries, a high incidence of breast cancer - though not necessarily a high recurrence rate - seems to be linked to diets high in saturated, not polyunsaturated, fats. But that link may not tell the whole picture.

"Both in Japan and the U.S., consumption of polyunsaturated oils has been increasing in recent years, while saturated fats have stayed flat," says the AHF's David Rose. "So one could argue that the increases in breast cancer could be attributed to increased linoleic acid."

And, although women whose breast cancers had spread by the time they were diagnosed sometimes reported having eaten more saturated fats, in other studies they reported eating more polys.(4,5)

The picture is even murkier when it comes to monounsaturated fats like olive oil. In a different animal model, says Elizabeth Boylan of Queens College in New York, "we found no statistically significant difference between [metastasis] on a low-fat versus a high-fat olive oil diet."

Kent Erickson of the University of California at Davis got similar results when he tested a specially formulated safflower oil that's rich in monounsaturated fats.

But few researchers are convinced that it's the polys - and not all fats - in most American women's diets that reduce their risk of surviving breast cancer. "None of the human studies have satisfactorily sorted out the ideal level of saturated versus unsaturated fats," says Erickson.


How could fats - or linoleic acid in particular - help tumors spread? There are several theories, says Erickson. For example, fats could:

* turn on genes that allow cancer cells to proliferate;

* make cancer cell membranes more fluid and pliable, enabling the cells to get out of small blood vessels and into the surrounding tissues;

* reduce the immune system's ability to kill cancer cells;

* create free radicals that damage healthy cells; or

* raise estrogen levels, which in turn could promote tumors.

By far the most popular theory is that linoleic acid increases the production of eicosanoids like prostaglandins, which may encourage cancer cells to proliferate.

Diets rich in linoleic acid make tumors metastasize, explains Erickson. "But if you put a prostaglandin blocker - like the drug indomethacin - in the animals' water supply, you can reduce the rate of tumor metastasis."

And there's another theory. A low-fat diet may improve survival by keeping women trim.

For postmenopausal women, says Rose, regardless of how much their cancers have spread at diagnosis, "obese women have a worse prognosis." And you don't have to be grossly overweight. "It's a sliding scale once you're beyond ideal weight," he adds.

Even if women aren't overweight before their cancers are diagnosed, there's an adverse effect of gaining weight after surgery.(1) "It's enough to negate the advantage of taking tamoxifen or chemotherapy," says Rose.

And studies show that women lose a few pounds on low-fat diets, even if they don't try to.

In the final analysis, it doesn't matter which theory explains how fat causes cancer to spread, as long as researchers can show that it does. And they're about to get their chance.


"A clinical trial is the only way to get unequivocal proof that dietary fat can influence the prognosis of breast cancer," says Leonard Cohen.

He ought to know. Along with Rose and American Health Foundation president Ernst Wynder, Cohen has been trying for years to convince the National Cancer Institute (NCI) to fund such a trial.

Doubts about feasibility were a major roadblock.

"At first no one believed you could get an American to accept and stay on a low-fat diet," says Cohen. "Now we know that is untrue. The Canadians, the Swedes, and we have shown that you can get women to stay on a low-fat diet for up to two years."

Last February, the NCI finally gave the go-ahead. For seven years, researchers in 20 centers around the country will follow 2,000 postmenopausal breast cancer patients classified as either stage I (no lymph nodes involved) or stage II (lymph nodes - but no other organs - involved). All will get standard therapy with the estrogen-lowering drug tamoxifen, and some will also get chemotherapy.

In addition, half will get advice based on national guidelines to cut fat to 30 percent of calories. The other half will be taught to eat a diet that's only 15 to 20 percent of calories from fat. "We'll push for 15 percent, but we'll be happy with anything less than 20 percent," says Cohen.

Rather than guess which fats are crucial, the researchers will cut them all. "If you target total fat intake," says UCLA's Chlebowski, "all types of fat will drop."

Should breast cancer patients eat a low-fat diet even before the trial's results are in? Yes, says the AHF's Rose.

"They should do it for reasons that are not limited to breast cancer, but to reduce the risk of cardiovascular disease and colon cancer, too."

(1) Breast Cancer Research and Treatment 20: 73, 1991. (2) Nutrition and Cancer 19: 1, 1993. (3) Journal of the National Cancer Institute 85: 6, 32, 1993. (4) Journal of the National Cancer Institute 80: 819, 1988. (5) Breast Cancer Research and Treatment 18: S135, 1991.



* Japanese women are about 20 percent more likely to survive breast cancer than American women, possibly because the Japanese eat less fat.

* A handful of studies in humans and animals suggests that diets high in any fats may help breast cancer spread, but a definitive answer is years away.

* In a trial that is just beginning, breast cancer patients MAII be taught to eat diets that get only 15 to 20 percent of calories from fat.
COPYRIGHT 1993 Center for Science in the Public Interest
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1993, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:less fat in the diet can increase survival rate for breast cancer
Author:Liebman, Bonnie
Publication:Nutrition Action Healthletter
Date:Jun 1, 1993
Previous Article:The problem with protein.
Next Article:Just the facts.

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