GOOD HEALTH MAGAZINE : Nutrition : CANCER, CALORIES & CONTROVERSY : ONE THIRD OF ALL CANCER DEATHS MAY BE RELATED TO WHAT WE EAT. YET IT’S UNCLEAR JUST WHAT PROMOTES THE DISEASE OR PROTECTS AGAINST IT.

A dozen women sat in a circle in a UCLA classroom one recent evening, hashing out the intricacies of fats--those insidious passengers in five-cheese risotto and creme brulee that may well be lurking behind the rising rates of certain cancers.

They were educated, accomplished women. They wore bifocals and blazers, badges of professional middle-age. But as the evening wore on, the conversation turned confessional: They talked about dessert the way recovering alcoholics talk about a drink.

Could you eat pumpkin pie without the crust? Could you use mozzarella in macaroni and cheese and have it not be stringy? What to do with that leftover stuffing beckoning from the freezer? Anyone know how many fat grams reside in a chicken- fajita pita?

Their monthly version of dietary group therapy is part of a nationwide research project looking into whether women can stick to a low-fat regimen. If they can, a larger study has been proposed to explore, over many years, whether a low-fat diet might cut one’s risk of cancer.

The outcome of even this first study remains unclear. As the participants tell it, they lurch between abstinence and overindulgence. But if they succeed in minimizing their fat intake, Marilyn Aronson, who conducted the UCLA session, believes there is much to be gained.

“Diet is not involved in every kind of cancer,” says Aronson, a clinical research nutritionist. “But I do believe that there are a lot of people suffering from cancer who might have been able to avoid it, or at least delay it, had they eaten differently.”

An estimated one third of all cancer deaths may be related to the food we eat. That’s as many as, perhaps more than, can be traced to tobacco. With some 485,000 cancer deaths in the United States each year, that means 160,000 people will die of cancers traceable to diet.

Yet, precisely what it is in foods that promotes cancer or protects against it remains unclear. The question is hotly debated. Most researchers agree that alcohol consumption and obesity play a central role in certain cancers. But beyond that, there is little consensus.

Dietary fats are a prime suspect. They have been linked to cancers of the colon, breast, prostate and lining of the uterus. But research on the relationship between fats and cancer is contradictory, and some experts believe the problem may be calories, not fats.

Fiber, too, has attracted much attention. Many believe it helps protect against colon cancer. Again, research findings conflict. Skeptics wonder whether to credit the fiber in high-fiber diets, or simply the diets’ relative paucity of fats.

Then there are vitamins. Foods rich in Vitamin C and Vitamin E may inhibit colon tumors, research suggests, while those containing Vitamin A and its precursors may protect against cancer of the lung. But are the vitamins themselves responsible, or is it something else in those foods?

Answering these questions is surprisingly difficult. One reason is that few people can recall in detail what they have eaten. Research subjects may remember what they swallowed yesterday, or last week, but not 15 years ago when perhaps it mattered most.

What’s more, some foods themselves are not well understood. Take fiber: There are more than half-a-dozen types. How much of each type is in which foods has begun to have been studied only recently. And even less is known about how each affects the body.

Finally, the process leading to cancer remains somewhat mysterious. It can take decades, involving factors that range from environment to genetics. How diet might influence that process--promoting or retarding it--has yet to be fully explained.

Nevertheless, experts say one thing is certain: Diet, like smoking, is one of the few cancer risk factors over which people have control. So experts have offered road maps for eating that may help protect against cancer, and certainly against other diseases.

Those guidelines--set forth over the past decade by the National Cancer Institute and American Cancer Society, the U.S. Surgeon General, the American Heart Assn. and the National Research Council--stress the following principles:

Avoid obesity. Drink alcohol only in moderation. Fats in the diet should account for no more than 30% of daily calories. The current American average is 40%.

Eat more foods high in fiber, such as whole-grain cereals, fruits and vegetables. The NCI recommends a daily fiber intake of 20 to 30 grams, rather than the current average of 11.

Be sure to include vitamin-rich yellow and dark-green, leafy vegetables; red, yellow and orange vegetables and fruits; citrus fruits, and juices made from any of those.

Limit salt-cured, pickled and smoked foods, which many researchers believe raise one’s risk of stomach and esophageal cancers. Minimize consumption of grilled or broiled foods that have become charred, since charring can produce carcinogens.

As some see it, our problems stem in part from the fact that our species evolved on the basis of a different diet than we now eat. For most of existence, humans subsisted on a high-fiber, low-fat diet. Only with industrialization came profound change.

According to Leonard A. Cohen, an expert on diet and breast cancer at the American Health Foundation in New York, prehistoric people got about 20% of their calories from dietary fats. They ate three times the fiber we eat and four times the Vitamin C, consuming a diet heavy in grains, vegetables and fruits.

That pattern prevailed until the Industrial Revolution some 2 1/2 centuries ago. With increasing affluence and changing tastes, fat consumption began to climb. Fiber intake dropped, consumption of refined sugars went up, consumption of complex carbohydrates down.

Those dietary changes, combined with a less active lifestyle, are believed to have been responsible for the increased size of modern people, Cohen says. They also account for the rise in obesity, earlier maturation, cardiovascular disease and cancer.

Our diet has changed faster, it appears, than our physiology can adapt.

“In a sense, then, modern people are living in a biological time warp,” Cohen wrote in 1987. “Their Stone Age physiology contends daily with a 20th-Century diet to which it is poorly adapted.”

How exactly might dietary changes influence cancer risk?

Researchers believe that the cancer process has several stages. As Cohen describes it, it is triggered by an initiator, such as a carcinogen or a virus. The initiating agent permanently damages the body’s genetic material. A mutation results, setting the stage for the possible development of cancer.

Later, some other agent, known as a promoter, picks up the process, causing the damaged cells to multiply and create a tumor. Some elements in the diet, such as fats, may be promoters, researchers say. Others, like vitamins, may help derail the process.

The most widely studied of those nutrients is fat. Evidence from animal studies in the 1940s first suggested that fats might increase a person’s cancer risk. Rodents fed high-fat diets in those and subsequent studies proved more likely than others to develop mammary tumors.

Then researchers began noticing international differences: People in countries with high-fat diets had higher breast-cancer rates. And those emigrating from low-fat to high-fat countries quickly took on the breast-cancer rate of their new home.

One hypothesis goes like this: Fats influence levels of hormones, such as estrogen. Estrogen appears to be important in the development of breast cancer. By raising estrogen levels, fats in the diet may increase a woman’s breast-cancer risk.

A similar hypothesis exists for prostate cancer, which, some studies indicate, also is influenced by dietary fats. Some researchers suspect that fat promotes prostate cancer by increasing levels of the hormone testosterone in the blood.

But in the case of breast cancer, some researchers are skeptical.

“The problem is, there are a lot of things that go along with eating fat--like sitting down, having early menarche and having Cadillacs,” says Malcolm Pike, a professor of preventive medicine at the University of Southern California.

ight something else in our lifestyle be to blame?

To try to eliminate such confounding factors, researchers narrowed their focus. They began studying differences in breast-cancer rates in the United States. They looked at Seventh Day Adventists, who avoid eating meat. They studied nurses, hospital patients, pre- and post-menopausal women.

Their findings have been mixed. Some studies have found an association between fat and breast cancer; others have not. One large study of women nurses found no more breast cancer among nurses who ate the most fat than among those who ate the least.

There are several possible explanations. Differences in fat intake in the United States may be too slim to produce measurable differences in cancer risk. Or, studies may have been designed in such a way as to be unable to flush out a connection, even if one exists.

For example, most of the studies have been retrospective. That is, they recorded and analyzed diet after the fact. Researchers have interviewed women with and without breast cancer, attempting to piece together how the women ate in the past.

But, as noted, people have great difficulty recalling what they eat. (One study found that people recalled correctly less than half the time.) What’s more, researchers say, fat is an especially problematic nutrient to estimate with accuracy.

Inaccuracy tends to be a neutralizing force. Researchers have studied its impact using hypothetical cases. Even in cases where associations exist, researchers have found that incorrect measurement tends to obscure, rather than exaggerate, real links.

Then there’s the possibility that fat, or fat alone, is not the culprit.

David Kritchevsky, associate director of Philadelphia’s Wistar Institute, the nation’s oldest biological-research institute, believes that the real issue is calories. Our high calorie intake and low calorie expenditure has elevated our cancer risk, he theorizes.

In one study, Kritchevsky and others fed one set of rats five times the fat, but 25% fewer calories, than they fed a control group of rats. The lower-calorie rats, despite their high-fat diet, developed significantly fewer tumors.

“The major thing is calories,” contends Kritchevsky, who believes that people may be able to reduce much of the risk from a high-calorie diet by burning off more calories. “Maybe the answer (to the nation’s high rate of breast cancer) is to eat 20% less.”

The issue of colon cancer and fat is similarly contentious.

Some researchers have concluded that a high-fat diet doubles one’s risk of colon cancer. Others have found similar associations. One study linked meats, specifically, to the disease. Others have found no connection.

One theory is that fats might promote colon cancer by stimulating bile acids, which have been found to promote tumors in animals. (Some experts suggest that dietary calcium, by neutralizing the bile acids, might counteract that effect.)

But many questions remain: Which types of fats are especially problematic? Is total calorie intake more significant than fat? Can burning a lot of calories help? Finally, what is the effect of any interaction between fats and dietary fiber?

Fiber, which is plant material that is resistant to digestion, first attracted attention in the early 1970s. Researchers working in Africa noticed that African men on high-fiber diets had relatively low rates of death from colon cancer.

Since then, that association has been explored extensively. The results, predictably, are conflicting. Of 40 studies in one review, 32 found that fiber cut one’s risk of colon cancer. Six were equivocal, or found no association, and two found that fiber increased the risk.

Why should fiber work against colon cancer?

By adding bulk, it may decrease the concentration of carcinogens in fecal matter that come in contact with the lining of the colon. Also, by speeding up so-called “intestinal transit time,” it may minimize that contact between carcinogens and intestinal tissue.

But fiber is more complicated than was initially recognized. Many early studies measured only the crude fiber, rather than the total fiber, in foods. Researchers say those studies underestimated the amount of fiber being consumed.

Now, in a laboratory in Madison, Wis., researchers are analyzing the fiber content in foods. They are meticulously isolating and extricating half a dozen types of fiber and preparing a fiber profile of 400 common foods.

For each food, they are identifying nine attributes--a testament to the complexity of fiber: total, soluble and insoluble dietary fiber values; the amounts of various types of fiber--hemicellulose, pectin, mucilage, cellulose and lignin; and, for oats and barley, the gum content.

About 150 foods have been analyzed so far, says Judith Marlett, a registered dietitian and professor of nutritional sciences at the University of Wisconsin. Within the next few years, she and her co-workers expect to produce a chart for use in research studies and in designing diets.

Still, the physiological effects of each type of fiber remain unknown. And some researchers remain doubtful that fiber itself is especially beneficial. High-fiber diets tend also to be low in fat and heavy on fruits and vegetables, which are high in beneficial micronutrients, including vitamins and minerals.

Among fruits and vegetables, research interest has focused in particular on dark-green, leafy vegetables and so-called cruciferous vegetables such as Brussels sprouts, cabbage and mustard greens, as well as red, yellow and orange fruits and vegetables.

Many are high in Vitamin A and its precursor, beta carotene, a form of pigment found in carrots, tomatoes and green, leafy vegetables. People who regularly eat those foods appear to have a relatively low risk of lung cancer. Some research suggests they also protect against prostate, bladder, esophageal and stomach cancer.

he evidence on lung cancer is especially striking, researchers say. In general, studies have found that smokers and former smokers who took in relatively little beta carotene were nearly twice as likely to develop lung cancer as those in the studies who consumed the most.

Research also suggests that beta carotene from fruits and vegetables, rather than Vitamin A from animal sources, carries the greatest protective benefit for people who have smoked (who are at the greatest risk of getting lung cancer). But it is not known whether the advantage is greatest for heavy smokers or for light smokers and ex-smokers.

It is unclear, too, whether other micronutrients might be responsible for the benefit of fruits and vegetables. But lack of food-composition data in the past has prevented epidemiologists from focusing on the contributions of pigments other than beta carotene.

“We don’t know if you should take beta carotene or be eating a can of spinach,” says Dr. Brian Henderson, director of the Norris Comprehensive Cancer Center at USC and a prominent researcher of diet and cancer. “You know, maybe Popeye was right.”

Finally, there are several other links between diet and cancer being explored:

There is some evidence, though contradictory, suggesting that Vitamin C and Vitamin E may slow the development of colon cancer. And there are suggestions that Vitamin C may protect against stomach cancer, perhaps by blocking the formation of certain carcinogens called nitrosamines.

Consumption of salt-cured and salt-pickled foods has been tied to cancers of the stomach and mouth. They contain nitrates and nitrites that can form nitrosamines, which have been linked to cancer of the mouth and stomach.

Broiling and grilling over an open flame can produce carcinogenic hydrocarbons when fat comes in contact with flames or hot coals. For that reason, health experts recommend wrapping food in foil when barbecuing and keeping it a good distance from the coals.

Many of the questions about diet and cancer remain unresolved because of the difficulty of designing studies capable of producing unambiguous results.

For example, because a nutrient is associated in a study with an increased risk of cancer does not necessarily mean that it is responsible for that increase.

To eliminate those shortcomings, researchers have resorted to studies of animals, manipulating their diets to simulate human experience. But whether it is really possible to extrapolate from findings on animals remains unclear.

In hopes of overcoming many of the limitations of past research, a group of researchers has proposed a massive federal study of women and cancer. As many as 32,000 middle-aged women would be recruited and followed closely for a decade, perhaps more.

Half would remain on their current diets. The other half would be placed on a low-fat diet. Advocates of the controversial trial predict that a diet in which only 20% of calories came from fat could reduce the incidence of breast cancer alone by 50%.

(The monthly meetings led by Marilyn Aronson in Los Angeles are part of a smaller study exploring the feasibility of conducting such a trial.)

But the trial, predicted to cost more than $100 million, would be the most expensive ever funded by the federal National Cancer Institute. And many researchers question whether even a project of that magnitude could provide conclusive results.

They wonder whether altering diet in middle age would produce a measureable reduction in cancer risk, or whether it would be necessary to start in young adulthood, or earlier, to prove that a low-fat diet would make a difference.

Proponents of the study--such as Ross Prentice, director of the division of public-health sciences at the Fred Hutchinson Cancer Research Center in Seattle--contend that the study is warranted. Without it, they say, the issue of diet and cancer may never be resolved.

“What I’m worried about is that we simply may never get the answer” to whether dietary fat contributes to the high cancer rates in the United States, Prentice says. “I’m not at all sure that other studies likely to be done will give us clear answers.”