The MacNeil/Lehrer Report; Diet and Cancer

[Tease]

ROBERT MacNEIL [voice-over]: A national panel of top scientists reports that what you eat may determine whether you get cancer.

[Titles]

MacNEIL: Good evening. Twenty years ago scientists concluded there was a link between cigarette smoking and lung cancer although they couldn't prove it at the time. All the same, they advised Americans that if they stopped smoking they would probably reduce the risk of getting lung cancer. Today, the results of a major study were released making a similar connection between diet and cancer. A panel of scientists assembled by the National Academy of Sciences concluded that diet appears to play a role in most common kinds of cancers. The Academy suggested that making some changes in diet -- in particular, eating less animal fat and more fruits and vegetables -- might prevent some cancers. In fact, the report suggested that by changing its diet this nation might reduce its cancer rate by as much as one third. The study found immediate critics, some charging it went too far, others not far enough.The American Meat Institute condemned the diet recommendations, saying they were based on insufficient evidence. Tonight, what is the evidence linking cancer and diet, and how should Americans react to it? Jim?

JIM LEHRER: Robin, today's report contains no promises of cancer-free lives for those who eat right, even for those who religiously follow its own dietary guidelines. Most everything is framed in terms of possibilities and probabilities, not certainties. But even so, the guidelines are rather specific: on eating fats -- linked by studies to cancer of the breast, prostate and large bowel -- the recommendation is to cut fat consumption from its current 40% of the average American diet to 30%. That means primarily eating less meat, whole dairy products and cooking oil. It also suggests minimizing the consumption of salt-cured, salt-pickled and smoked foods, connected through foreign studies to cancer of the esophagus and stomach. Such foods include sausage, bacon, bologna, hot dogs, smoked fish and ham, among many, many others. In addition, the report says there may be a link between the excessive drinking of alcohol and cancer of the upper gastrointestinal and respiratory tracts, particularly when the drinking is combined with cigarette smoking. It recommends drinking only in moderation. On the positive side the major suggestion is to eat fruits and vegetables and whole-grain cereal products every day, particularly citrus fruits, spinach, carrots, cabbage, brussels sprouts, sprouts, broccoli, tomatoes and cauliflower, among others, that contain vitamins A and C, which appear to inhibit certain forms of cancer. The chairman of the study committee which put out all of this advice today is Dr. Clifford Grobstein, a professor of biology and public policy at the University of California at San Diego. Doctor, in general terms, how strong is the connection between diet and cancer?

Dr. CLIFFORD GROBSTEIN: I think probably the best answer to that is that it is strong enough to give ground to consider modification of diet on the part of individuals and also in terms of public health measures. It is not strong enough, it seems to me, to cause alarm, certainly not hysteria. The opportunity, I think, is presented, according to the evidence that we've compiled, to make modifications that may reduce the incidence of cancer and to some degree, for individuals, to reduce the likelihood of their getting it.

LEHRER: But the key word here is "may," is that right, in every category?

Dr. GROBSTEIN: Well, as was emphasized in the summary at the beginning, we are talking probabilities. We are looking at data that are largely statistical in nature, whether it has to do with --

LEHRER: Rather than scientific, right?

Dr. GROBSTEIN: No, they're scientific, but they are scientific in the sense that we are looking at populations of people in most instances. There are studies, of course, that involve individual comparisons of individual persons. But overall I would say, both in the studies or the results of looking at human populations, and also in our animal experiments, we are looking at results that are based on numbers, and therefore we can only speak of probabilities. And we can't speak of certainties, and we can't make forecasts about particular individuals from the information that we've been reviewing.

LEHRER: Let's go through some of the specifics. How would you rate the validity of the link between fatty foods and cancer?

Dr. GROBSTEIN: Well, I think our committee feels that that is probably the one that they have the greatest confidence in, and I'd like to explain why. There are two general kinds of information that were reviewed in this report. One has to do with what I spoke of a moment ago, that is, how human populations -- what the incidence of cancer is in human populations, what is known technically as epidemiologic studies. Those studies give clear indication of a correlation between dietary factors and especially with respect to fats and particular forms of cancer. On the other side we have experiments with animals largely coming to be done because of the clues that were offered by looking at populations. Those experiments, of an entirely different sort, now, and dealing with animals and not human populations -- they show results that are confirmatory of the impression that one gets looking at populations. Beyond that there is now a mechanism that is suggested by which fats may cause or increase the incidence of certain forms of cancer.

LEHRER: What do you mean by that, sir?

Dr. GROBSTEIN: I mean that there is now a track, so to speak, that you can trace from fats through the production of biosalts and biosteroids to their conversion in the intestine to other substances, and some of those substances appear to be ones that will cause cancer. And therefore there is a track from fat in the diet to the incidence of cancer in the colon. Now, I say there is that track and I say there is that mechanism suggested. It's not regarded as fully established. But the evidence for it is increasing, and when scientists have correlations among sets of data that come from different sources, and then they begin to think that this is reflecting in reality.

LEHRER: What about the evidence that says eating certain kinds of fruit and vegetables may inhibit certain cancers. Is that as convincing as that on the fats?

Dr. GROBSTEIN: I would say that in the sense that I was just talking about, not quite. That is, the information with respect to fruits and vegetables and so on comes pretty largely from population studies. The animal studies that correlate with it are based upon individual constituents that are isolated from it, say, vitamin A or vitamin C. There is a correlation between the two kinds of observations that we're not at all sure yet whether the particular substances that are being looked at experimentally are the total explanation of why fruits and vegetables have the effects that they do.

LEHRER: I noticed that while you recommend eating foods that have vitamin A and C, you do not recommend -- quite the contrary -- taking vitamin supplements of A and C. Why not?

Dr. GROBSTEIN: Well, looking at vitamin A, for example, we know that excessive amounts of vitamin A can be toxic, and therefore it would not be a good idea to recommend that vitamin A be taken in large amounts. Vitamin C, there are some more questions as to whether in large amounts it's toxic. But I think our primary concern is that we think in terms of the complexes of components that foods are, and the complexes of foods that diets are, rather than to think in terms of simple fixes involving particular compounds that may be abused by being overused.It is possible to do that. So our feeling is that at the present time our knowledge entitles us to talk about, make recommendations about foods. We're still a little concerned about making recommendations about compounds that are used as pharmacologic agents.

LEHRER: Thank you. Robin?

MacNEIL: Now a view from a private-sector researcher studying the prevention of major diseases. Dr. Ernst Wynder is founder and president of the American Health Foundation. Dr. Wynder took part in some of the first research linking smoking to lung cancer. First of all, what's your opinion of the Academy committee's report?

Dr. ERNST WYNDER: Well, I would like to congratulate Dr. Grobstein. I think it's a vert thoughtful report and very appropriate recommendations that both we as a scientific community and I think we as a public can learn from and live by.

MacNEIL: Would you go any further than they do, from your own experience and knowledge, in recommending diet changes?

Dr. WYNDER: No, what they recommend is more or less what we would also recommend, and a word that I like to introduce here is the word "prudent." Dr. Grobstein kind of inferred that the recommendation we're making is prudent. In other words, we may not have all the evidence in, and the report indicates we may never have all the evidence in, simply because nutritional studies are more difficult than some studies, perhaps, with pure carcinogens. But the prudent thing is --

MacNEIL: Carcinogens are agents which cause cancer.

Dr. WYNDER: Which cause cancer. But the prudent recommendation is to modify our diet, particularly because our colleagues concerned with reduction of heart disease have already been on the record to make similar recommendations.

MacNEIL: You're saying that if you followed these recommendations you might also do yourself some good in the area of heart disease?

Dr. WYNDER: That's correct. There is perhaps one other point. You know, sometimes even though we say we are what we eat, most of us in medical school haven't learned much about nutrition. Our public gets confused because we hear all kinds of things from food faddists and others about the kind of diet we ought to eat and how quickly we can lose weight. But one point I like our audience and my colleagues to reflect on is something I call the anthropology of nutrition, namely, when we first came on this earth we came largely on this earth as vegetarians, no doubt eating a very small percentage of our total calories in fat. And therefore we're given metabolic pathways to deal with that type of dietary intake. And we are kind of suffering from metabolic overload, and Dr. Grobstein mentioned that we are producing too many bile acids which may well relate to colon cancer. And dietary fat, for instance, also affects our hormonal milieu. So there are many metabolic parameters that go into disarray as we eat too many particular fat calories.

MacNEIL: To put that in slightly more simple terms, does that mean that modern man, with a high standard of living, tends to eat a lot more meat than he was ever used to in a simpler condition, and it overloads the system?

Dr. WYNDER: Yeah, particularly also because modern man tends to sit all the time, like for instance the four of us now. And when we sit we don't burn too many calories. So I think to our students we sometimes say look at the biological reasonableness of a finding. And what the committee has found and recommended is entirely reasonable as we understand biological phenomena.

MacNEIL: You were one of those involved in very early research, as I said, into the connection between smoking and lung cancer. Is the link between diet and cancer as strong and direct as that? I mean, can cancer-causing agents be found in food?

Dr. WYNDER: Well, first of all, the committee reports, and we concur, that the main way in which diet enhances our risk for cancer doesn't so much relate to specific carcinogens, like aflatoxin in mouldy foods or nitrosamines or polysaturate or maybe hydrocarbons in charcoaled meat, but rather lies in macronutrients which affect biological parameters. So in a way nutrition acts largely as a tumor modifier, or you may say tumor enhancer, of cancer cells that may be initiated by a totally different process. But the fact is that our data suggest that if our fat intake would be lower, and in part as we eat less fat we also ought to eat more fresh fruit and vegetables, more vegetable proteins, and in all of this process the responsible food industry can be of help. They are already producing leaner meat. They are already producing low-fat milk and leaner cheeses. So I think the food industry should listen to that and see how they can cooperate with these recommendations and make all the profit in the world, and yet provide better foods to the public. I'd like to make one final point. It was the German philosopher Kant who once said we've got to make decisions sufficient on the base of action, but insufficient to satisfy our intellect. And I think this report kind of deals with this kind of philosophy.

MacNEIL: Well, thank you. Jim?

LEHRER: Another opinion of today's findings and recommendations from another leading cancer researcher. He is Dr. John Higginson, who has been studying the connection between cancer and diet as well as other environmental and health factors for more than 30 years. He headed the World Health Organization's international agency for research in cancer for 16 years, and is now a senior scientist with a Washington-based pathological research group run by a consortium of 15 universities. Doctor, how do you rate the evidence linking diet to cancer?

Dr. JOHN HIGGINSON: Taken as a whole I believe that diet is very significantly related to a high proportion of human cancers, especially in females. However, when one comes down to specifics, a fat, vitamins, etc., one runs into more problems of just how strong the evidence is.

LEHRER: Well, let's go through. Do you think Dr. Grobstein and his group went too far in what they say the links are in these various areas?

Dr. HIGGINSON: I don't think one can ever say anybody goes too far in this because they gave all the caveats necessary on this wide-ranging and excellent report.But what one man might regard sufficient to be a strong positive guideline, another might be more hesitant about. For example, I have a greater belief and emphasis on the fiber side than the Academy report. It rather emphasized fat.I feel evidence, for example, is stronger for the role of fiber in cancer of the large intestine, for example.

LEHRER: Well, what do you feel about what they say about fat? You just don't think the evidence is there to go even as far as they did?

Dr. HIGGINSON: I would believe fat is very significantly related to cancer. I don't know how. What I feel is that the data that we do have on human populations is such as to have very many inconsistencies, and it may not be quite so straightforward as just saying reduce total fat. For example, in Finland, the intake of fat is very, very high, much higher than in Copenhagen, yet the incidence of colon cancer is about half that in Copenhagen, and there's a much lower breast rate. Both these cancers are related, with good reason, to fat. This would suggest that the relationship is not too simple. On the other hand, there is no question, from the point of view of heart disease, that reducing fat is important and in fact in the U.S. has been shown to have a major impact over the last 15 years.

LEHRER: So, in other words, if people want to eat less fat to improve their possibilities in terms of catching heart disease, fine, but you don't think the evidence is there for them to do it solely in an attempt to reduce cancer, correct?

Dr. HIGGINSON: Provided that they keep their intake of fat down to such that they are reasonably slim and not getting obese so it's not part of an obesity problem, I am not prepared to be too dogmatic that they are going to affect their cancer pattern. It may well be that this will be proven high, but we may find that fat is a parameter indexing something else in the diet.

LEHRER: Would you be dogmatic on the positive suggestion of eating fruits and vegetables, particularly those that have vitamin A and C?

Dr. HIGGINSON: Yes, because I feel it's part of a healthy diet. It's a very dld -- all these recommendations are 30, 40, 50 years old, and one does it and one has good theoretical reasons for doing it. Therefore, one prudently will do it and recommend it.

LEHRER: But here again you don't believe that eating those foods will necessarily inhibit cancer, right?

Dr. HIGGINSON: Possibly not for me speaking as an individual. Maybe taken in a mass population it may have an effect in the totality. We don't know enough to say that A will be helped and B not.

LEHRER: What about the recommendation to -- the term that the panel used was minimize the eating of smoked foods, salt-cured and salt-pickled foods. What's your feeling on that?

Dr. HIGGINSON: Again, that is hypothesis supported by experimental and other data. Again, if one examines populations, one can produce evidence that is inconsistent with the hypothesis. This is the unfortunate situation.

LEHRER: Well, Dr. Higginson, you've been involved in this kind of work for 30 years now. Forget what the -- well, don't forget it, but put aside for a second here, for a moment, what Dr. Grobstein's panel said today, and narrow strictly on cancer from your point of view. What diet would you recommend if you wanted to reduce cancer and reduce the chance of getting cancer?

Dr. HIGGINSON: My answer is I would have to go along with the recommendations of the committee because the total picture is such that you're not entitled to say, "Don't do it; forget it." On the other hand, you can say that it is a guideline, but it does indicate that we should go into it in a real decent research manner now. We've been talking about it for 30 or 40 years. Maybe the fact that people start doing something may enable us to start putting some of these shaky data on a decent basis.

LEHRER: But basically you think the data is still very shaky, right?

Dr. HIGGINSON: Not shaky so much as uncertain.

LEHRER: All right, thank you. Robin?

MacNEIL: How do you reply to Dr. Higginson, Dr. Grobstein, about the fat connection particularly?

Dr. GROBSTEIN: Well, I think that what Dr. Higginson says is quite correct. The committee points out that we are dealing with an area of considerable uncertainty, and we would expect that people might make different judgments on the basis of the information that we currently have available. I think that one has to keep in mind that when one is trying to turn scientific facts which are necessarily incomplete with respect to practical problems into practical advice, that there necessarily is an element of judgment. I completely agree that the circumstances are such that none of the things that the committee has said are rigorously demonstrated as they would be in what we call basic science. But we have in the back of our minds, I think all of us, being able to use knowledge as soon as it will be useful to us. I think in respect to cancer, we have in mind especially the long period of time over which cancer develops, and we know that some of the things that are happening now -- some of the foods, for example, that are being consumed or some of the cigarettes that are being smoked -- are going to produce cancer 20 or 25 years from now.

MacNEIL: Can I ask Dr. Higginson this? Did I understand you to say it may turn out to be that it isn't fat itself. I think the word you used was that it's a parameter indexing something else. Does that mean fat may be an agent that precipitates another activity? What did you mean by that?

Dr. HIGGINSON: Well, the trouble is, people that have a high-fat diet have high-protein diets, and they tend to eat more meat. There is quite a number of other parts of the diet that go along with that. They even tend to eat more fruit and certain other things. And this has been demonstrated a number of studies. So it may well be that it's either theoretically possible the carrying of fat of very micro-constituents induce enzymes that induce -- sorry, chemicals that induce enzymes in the body, steroids that come from other things -- the whole thing is highly complex.

MacNEIL: What's your comment on that, Dr. Wynder?

Dr. WYNDER: Well, I'd like to make two comments, one specifically, the point made by my colleague John Higginson about Finland. We looked at this in Finland and we went to Cupio in Finland, collected stool, brought it back to this country and analyzed it. And what we found, that in spite of a high-fat diet, the rate of colon cancer appeared to be low because of a high integral diet. Their fiber gave them a great amount of stool bulk, which in our opinion dilutes bile acid metabolites. And here is one area where I might not entirely agree with the panel because I feel certain kinds of fibers that lead to increased stool bulk are protective. But the final point I'd like to make --

MacNEIL: Does that mean that you can eat a lot of fat, but provided you also eat a lot of fiber? That it neutralizes it?

Dr. WYNDER: No, I like to be good on all fronts, if I can say, and furthermore the fiber story seemingly does not apply to breast cancer and perhaps not even to coronary disease. But the other point I wanted to make, in this democracy of ours we make scientific policy and we make recommendations to the public on the basis of majority of opinion, and I think it's quite important for the audience to know that Dr. Grobstein and his colleagues met for months and months, and went over all the testimonies of scientists on all sides of the fence, so to speak, and therefore their conclusion and their recommendation are made based upon all of these scientific inputs that they have. So sooner or later in a democracy the majority of scientific opinion must rule.

MacNEIL: Thank you. Jim?

LEHRER: Is this kind of a consensus a political decision that was arrived at by your committee?

Dr. GROBSTEIN: That's an interesting question. Primarily, no. Primarily we examined the scientific information and we made scientific judgments. But as I indicated, those judgments involve a certain degree of uncertainty.

LEHRER: What I'm really asking, Doctor, is this, toput it very simply. Are your fellow panel members, who are also maybe going to be interviewed tonight or tomorrow about this, are they saying the same things you're saying? Are they saying, "Well, I agree here, but I disagree there and we had to reach a consensus. I lost the vote there," or what?

Dr. GROBSTEIN: The last thing that I would try to do is to forecast the behavior of individuals, even scientists. But I will say that we discussed this matter very carefully, and I think this report is not only a consensus of the members of the committee, but it is essentially a unanimous one. I would not expect that there would be more differences of opinion expressed by the members of the committee that you're hearing tonight from Dr. Higginson, Dr. Wynder and from me. That is, we have certain differences as individuals in our judgments. Keep in mind that the committee consisted of a very diverse group of people in terms of their professional background.

LEHRER: How many were there altogether?

Dr. GROBSTEIN: Twelve, 13. Epidemiologists, molecular biologists, pharmacologists, pathologists, so on. Each of these comes at this from a different direction so that we have many perspectives being put together, and the process of reaching a consensus is not easy, and it is not the case that all of the members, I'm sure, on any particular point, would say exactly the same thing in the same way. It's not a chorus. But I think that they are all in agreement on the major recommendations of the report.

LEHRER: Dr. Higginson, you said quite strongly that not enough research has been done to draw a lot of conclusions. Are there studies underway now that will eventually clear this up?

Dr. HIGGINSON: The National Academy of Science -- the National Cancer Advisory Board recently reviewed this particular problem and strongly recommended a marked intensification on research in nutrition. But our basic problem is people are having great difficulty in, (a), finding trained manpower and knowing the right type of experiments to do in what's a terribly difficult field.

LEHRER: Well, what do you think would be the most significant experiment? What is the most critical need in terms of finding out information on this?

Dr. HIGGINSON: I think the critical need is accurate ways of measuring diet that people actually take, following those people, and being prepared to follow them for a long time, as was done in the heart study in Framingham.

LEHRER: But it's going to take a long time?

Dr. HIGGINSON: And you can run the experiments at the same time. They will give you guidelines, and they will help; you'll bring the two together.But I think we must be prepared to help our children. And the other thing, never forget, the diet starts acting before -- long before the first year one. It starts acting in utero, and this may be the important point in diet. For many cancers, what happens before 14, rather than what happens after 14.

LEHRER: All right, thank you. Robin?

MacNEIL: Yes, Dr. Higginson, Dr. Grobstein and Dr. Wynder, thank you all very much for joining us. Good night, Jim.

LEHRER: Good night, Robin.

MacNEIL: That's all for tonight. We will be back tomorrow night. I'm Robert MacNeil. Good night.