Which of These Foods Will Stop Cancer? (Not So Fast)
Mr. Michelson is one of a growing number of people worried about cancer - because it is in their families or because they have seen friends suffer with the disease - who are turning to diets for protection. Cancer patients, doctors say, almost always ask what to eat to reduce their chances of dying from the disease.
The diet messages are everywhere: the National Cancer Institute has an "Eat 5 to 9 a Day for Better Health" program, the numbers referring to servings of fruits and vegetables, and the Prostate Cancer Foundation has a detailed anticancer diet.
Yet despite the often adamant advice, scientists say they really do not know whether dietary changes will make a difference. And there lies a quandary for today's medicine. It is turning out to be much more difficult than anyone expected to discover if diet affects cancer risk. Hypotheses abound, but convincing evidence remains elusive.
Most of the proposed dietary changes are unlikely to be harmful - less meat, more fish, more fruits and vegetables and less fat. And these changes in diet may help protect against heart disease, even if they have no effect on cancer.
So should people who are worried about cancer be told to follow these guidelines anyway, because they may work and will probably not hurt? Or should the people be told that the evidence just is not there, so they should not deceive themselves?
Dr. Barnett Kramer, deputy director in the office of disease prevention at the National Institutes of Health, said: "Over time, the messages on diet and cancer have been ratcheted up until they are almost co-equal with the smoking messages. I think a lot of the public is completely unaware that the strength of the message is not matched by the strength of the evidence."
[...]
Dr. Tim E. Byers, a professor of preventive medicine at the University of Colorado Health Sciences Center in Denver, was convinced that up to 20 percent of cancers were being caused by diet and he wanted to be part of the exciting new research that would prove it.
"I felt we were really on the cusp of important new discoveries about food and how the right choice of foods would improve cancer risk," Dr. Byers sad.
That was 25 years ago, when the evidence was pointing to diet. For example, cross-country comparisons of cancer rates suggested a dietary influence.
"For prostate cancer, if you look around the world, there might be 50-fold or greater differences in rates; they're huge," said Dr. Meir Stampfer, a professor of epidemiology and nutrition at the Harvard School of Public Health. "There are also big differences, many-fold differences, around the world for breast cancer and colon cancer."
And when people move from low risk countries to high risk countries, they or their children acquire the cancer rates of their new countries.
At the same time, some cancers were inexplicably becoming more common or, just as inexplicably, fading away in the United States.
In 1930, for instance, stomach cancer was the second leading cause of cancer death in women and the leading cause in men. Now, Dr. Stampfer says, stomach cancer is not even listed in the American Cancer Society's 10 leading cancers.
"So people think, 'What's happened in the past 70 years to make that change?' " he said. "Diet comes to mind."
[...]
Based on these indications, the cancer institute financed two studies on high-fiber diets and colon polyps. In one, 2,079 people were randomly assigned to eat low-fat high-fiber diets or to follow their usual diets. In the other, 1,429 people were assigned to eat high-fiber bran cereals or wheat bran fiber or to eat cereal and bars that looked and tasted the same but that were low on fiber. Fiber, the studies found, had no effect.
"We had high expectations and good rationale," Dr. Schatzkin said. But, he said, "we got absolutely null results."
Now, the largest randomized study ever of diet and cancer is nearing completion, involving 48,835 middle-age and elderly women. The women were randomly assigned to follow a low-fat diet with five servings a day of fruits and vegetables and two of grains or to follow their usual diet. The question was whether the experimental diet could prevent breast cancer.
The study is part of the Women's Health Initiative, a large federal project. When it began, the dietary fat hypothesis was ascendant. But after it was under way, other, less definitive studies failed to find any association between dietary fat and breast cancer.
The Women's Health Initiative diet study's results should be ready early next year, said its principle investigator, Ross L. Prentice, a biostatistics professor at Seattle's Fred Hutchinson Cancer Research Center.
And if it fails to find an effect?
Dr. Prentice said he would still wonder. Maybe what matters is diet earlier in life, he said, or maybe the women in the study did not stick to their diets.
Others say they suspect they were simply naïve about the cross-country comparisons that persuaded them in the first place.
"People drew inferences that were in retrospect overenthusiastic," Dr. Stampfer said. "You could plot G.N.P. against cancer and get a very similar graph, or telephone poles. Any marker of Western civilization gives you the same relationship."
Because of the striking differences in daily life between people in countries with high cancer rates and those in countries with low rates, diet may have nothing to do with the incidence of the disease, Dr. Schatzkin said. Or diet may play a large role but the questionnaires used to measure what people were eating might have been inadequate to find it.
"That's the problem." Dr. Schatzkin said. "We just don't know."
As for Dr. Byers, who once had such high hopes for the diet and cancer hypotheses, he says he is sadder now, but wiser. "The progress has been different than I would have predicted," Dr. Byers said.
Specific food can affect general health, he added, but as for a major role in cancer, he doubts it. He now believes that it is the amount of food people eat, not specific foods or types of foods, that may make a difference. "I think the truth may be that particular food choices are not as important as I thought they were," Dr. Byers said.
Mr. Michelson is one of a growing number of people worried about cancer - because it is in their families or because they have seen friends suffer with the disease - who are turning to diets for protection. Cancer patients, doctors say, almost always ask what to eat to reduce their chances of dying from the disease.
The diet messages are everywhere: the National Cancer Institute has an "Eat 5 to 9 a Day for Better Health" program, the numbers referring to servings of fruits and vegetables, and the Prostate Cancer Foundation has a detailed anticancer diet.
Yet despite the often adamant advice, scientists say they really do not know whether dietary changes will make a difference. And there lies a quandary for today's medicine. It is turning out to be much more difficult than anyone expected to discover if diet affects cancer risk. Hypotheses abound, but convincing evidence remains elusive.
Most of the proposed dietary changes are unlikely to be harmful - less meat, more fish, more fruits and vegetables and less fat. And these changes in diet may help protect against heart disease, even if they have no effect on cancer.
So should people who are worried about cancer be told to follow these guidelines anyway, because they may work and will probably not hurt? Or should the people be told that the evidence just is not there, so they should not deceive themselves?
Dr. Barnett Kramer, deputy director in the office of disease prevention at the National Institutes of Health, said: "Over time, the messages on diet and cancer have been ratcheted up until they are almost co-equal with the smoking messages. I think a lot of the public is completely unaware that the strength of the message is not matched by the strength of the evidence."
[...]
Dr. Tim E. Byers, a professor of preventive medicine at the University of Colorado Health Sciences Center in Denver, was convinced that up to 20 percent of cancers were being caused by diet and he wanted to be part of the exciting new research that would prove it.
"I felt we were really on the cusp of important new discoveries about food and how the right choice of foods would improve cancer risk," Dr. Byers sad.
That was 25 years ago, when the evidence was pointing to diet. For example, cross-country comparisons of cancer rates suggested a dietary influence.
"For prostate cancer, if you look around the world, there might be 50-fold or greater differences in rates; they're huge," said Dr. Meir Stampfer, a professor of epidemiology and nutrition at the Harvard School of Public Health. "There are also big differences, many-fold differences, around the world for breast cancer and colon cancer."
And when people move from low risk countries to high risk countries, they or their children acquire the cancer rates of their new countries.
At the same time, some cancers were inexplicably becoming more common or, just as inexplicably, fading away in the United States.
In 1930, for instance, stomach cancer was the second leading cause of cancer death in women and the leading cause in men. Now, Dr. Stampfer says, stomach cancer is not even listed in the American Cancer Society's 10 leading cancers.
"So people think, 'What's happened in the past 70 years to make that change?' " he said. "Diet comes to mind."
[...]
Based on these indications, the cancer institute financed two studies on high-fiber diets and colon polyps. In one, 2,079 people were randomly assigned to eat low-fat high-fiber diets or to follow their usual diets. In the other, 1,429 people were assigned to eat high-fiber bran cereals or wheat bran fiber or to eat cereal and bars that looked and tasted the same but that were low on fiber. Fiber, the studies found, had no effect.
"We had high expectations and good rationale," Dr. Schatzkin said. But, he said, "we got absolutely null results."
Now, the largest randomized study ever of diet and cancer is nearing completion, involving 48,835 middle-age and elderly women. The women were randomly assigned to follow a low-fat diet with five servings a day of fruits and vegetables and two of grains or to follow their usual diet. The question was whether the experimental diet could prevent breast cancer.
The study is part of the Women's Health Initiative, a large federal project. When it began, the dietary fat hypothesis was ascendant. But after it was under way, other, less definitive studies failed to find any association between dietary fat and breast cancer.
The Women's Health Initiative diet study's results should be ready early next year, said its principle investigator, Ross L. Prentice, a biostatistics professor at Seattle's Fred Hutchinson Cancer Research Center.
And if it fails to find an effect?
Dr. Prentice said he would still wonder. Maybe what matters is diet earlier in life, he said, or maybe the women in the study did not stick to their diets.
Others say they suspect they were simply naïve about the cross-country comparisons that persuaded them in the first place.
"People drew inferences that were in retrospect overenthusiastic," Dr. Stampfer said. "You could plot G.N.P. against cancer and get a very similar graph, or telephone poles. Any marker of Western civilization gives you the same relationship."
Because of the striking differences in daily life between people in countries with high cancer rates and those in countries with low rates, diet may have nothing to do with the incidence of the disease, Dr. Schatzkin said. Or diet may play a large role but the questionnaires used to measure what people were eating might have been inadequate to find it.
"That's the problem." Dr. Schatzkin said. "We just don't know."
As for Dr. Byers, who once had such high hopes for the diet and cancer hypotheses, he says he is sadder now, but wiser. "The progress has been different than I would have predicted," Dr. Byers said.
Specific food can affect general health, he added, but as for a major role in cancer, he doubts it. He now believes that it is the amount of food people eat, not specific foods or types of foods, that may make a difference. "I think the truth may be that particular food choices are not as important as I thought they were," Dr. Byers said.
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