Document 654gqLN4vBr82zR9nJYya4Bn3

Science URL 05101 Diet/cancer recommendauons debated Controversy over dtet/cancer link points up dtfHcutttes of formulating public poHcy guidelines from incomplete or uncertain rosoarch data Jeffrey L. Fox C&EN, Washington The search for causes and the con sequent efforts to develop preven tive measures against cancer involve a wide range of experts--basic biol ogists, nutritionists, toxicologists, ep idemiologists, clinicians, and policy planners, just to name a few of the influential participants. They are a fractious lot. Hence, their achieve ments, despite arising out of efforts directed at a common goal, often are presented piecemeal and some times are contradictory. The policy goals the experts recommend thus come across as being less than coherent. Recent attempts to develop a pol icy on diet and cancer provide an example of the difficulties experi enced when experts address this wor thy goal. This limited, but by no means easy, project falls within a broader framework in which the issue of major causes and contributors to cancer incidence is being studied. That issue bean directly on diet. Yet, there has been little agree ment--indeed, there often is outright disagreement--about which prob lems deserve emphasis, never mind which dangers demand immediate correction. Within this context, an ad hoc committee of the National Research Council, which is pari of the Na tional Academy of Sciences in Wash ington, D.C., was set up to develop dietary recommendations to lower the rise of cancer in the U.S. (C&EN, June 21, page 4). The project was begun at toe request of the National Cancer Institute, which itaelf formu lated recommendations in 1979. Those recommendations, however, were based on a relatively quick sur vey of the scientific literature and also on hunches and personal judg- ments of Arthur C. Upton, then head of NCI. NRC's charge was to de velop guidelines based on a more thorough analysis of available data, including any recent studies, and to recommend areas for research. The NRC committee has met the first part of its obligation by put ting together a substantial report (more than 250 pages in length) and by issuing a set of "interim7' guide lines that are remarkably similar to those issued by NCI a few years ago. A second report, establishing priorities for future dietary and can cer research, is expected to be com pleted in another year. Essentially, the NRC report holds that most common cancers poten tially are preventable since they are determined more by "habit, diet, and custom," rather than by genetic fac tors. However, "it is not now possi ble and may never be possible to specify a diet that protects all peo ple against all forms of cancer," the report says. Its goal, then, is to present guide lines for a diet "consistent with good nutritional practices and likely to reduce the risk of cancer." These guidelines call for a reduction in con- MEWS ANALYSIS sumption of fats from the present level of about 40% of the average person's caloric intake to about 30%. This means a reduction in the con sumption of fatty cuts of meat, whole-milk dairy products, and cook ing oils and fats. In addition, Amer- Rmearchers closing In on basics of malignancy nesaarchars studying cancer at the cellular level are growing Increasingly confidant that they're close to making fundamental and important discoveries about the nahre of malignancy. That confidence sterna from many conver gent observations of the drcurscited sat of genes found m soma tumorcausing viruses and in oertaln maftgwnt cads from animals. Recently, researchers at several laboratories. Inducting the National tostkutoe of Haafto In BetoaetM. Md., Cold Spring Hvbor Laboratory on Long letond In New York, MsssacUestls Institute of Technology In Cambridge, and Harvard metical school in Boston, have mounted an enormous effort to understand how toeea genes ere related, hoping to loom from toat what they do to make normal cals become maftgwnt Last year, It stiN was an open question whether these two subsets of genes were truly related (C&EN, Mvch Id, 1961. page 16). Now the adandets studying them beSave toe vkal and anfenaAcsl gsnss to be ctoesly related. If not identical. In their detailed molecular sfruchree. These similarities also extend to genes found in some human ceis-- Inctudtog oeNs that are considered nor mal as wei as cads toet are frankly malignant Most of toese genes share the prop erty of "transforming cells," that is. of changing the characteristic jyowth pattern of a normal cell to the uncontrotied growth typical of a cancer call. Such genes exert this effect whan in troduced into tost ceis, usually a par ticular type of mouse cell. Just how tosss panes franstorm cads remains a mystery. Tbs genes do en code for a protein, which seems Im portant for malignant transformation, to soma Instances, that protein to an ac tive. membrane associated "kinase," meaning ft can transfer phosphoric add residues from nucleotide phosphates (usually guanotine triphosphate) typi cally to Used or to other proteins. Whetoer such enzymic activity to crucial to fransfbrmetion stM to unknown, but seams Ifcety. An Important conviction to that these genes are ubiquitous, and their activity In normal cads either to carefully mod ulated or nil. When moved about from one cell type to another, these genes can become activated--sometimes thanks to delberate biochemical tin kering by scientists, and other times poesl>iy Just by being In another place. The exact way In which control over toese genes Is exerted, and how it's lost, could be pivotal to maNgnsncy. M CAEN June 2S, 1W2 URL 05102 icans should eat more fruits, vege tables, and whole-grain cereal prod ucts, especially those rich in vitamin C and in carotene. Dietary supple ments of individual nutrients found in these foods should be avoided, the committee cautions, because they may be toxic in high doses. The guidelines also call for mini mizing consumption of salt-cured, salt-pickled, and smoked foods, and limiting the consumption of alcohol, particularly by those who smoke, to moderate levels. The NRC guidelines, mild and general though they may be, are eliciting much the same criticism as did their NCI predecessors. Those criticisms come from many differ ent camps. Some must be taken as the obvious outcry of special inter est groups who have something tan gible at stake should NRC's sugges tions become widely implemented. Those interest groups, including meat processors and distributors, naturally have the right to protect their turf. Yet, in matters affecting public health, surely even the spe cial interest groups owe the experts a fair hearing. For example, the American Meat Institute faults NRC for relying on studies that compare dietary habits of people in different countries. A similar organization, the National Meat Association, takes NRC to task for "taking a simplistic approach to a very complex question/' The as sociation also criticizes the "almost steady stream of contradictory state ments coming from the scientific community," calling it "perplexing and confusing to the public." Some defenders of NRC's efforts may discount such criticisms, no matter what their intrinsic validity might be; they judge them on the basis of who's issuing them. But crit icisms also are emanating from within the scientific camp, even, iron ically, from scientists who sit on other NAS committees and boards. Over the long term, such plural ism probably is healthy in the search for truth. Meanwhile, though, it can be perplexing not only to the pub lic, but also to the news media and to members of the scientific com munity who genuinely are interested in maintaining coherence in thought and purpose. Robert E. Olson is a biochemist at St. Louis University school of medicine and a member of the NAS Food & Nutrition Board. He is crit ical of the recent NRC report as he has been a critic of past reports pertaining to diet and disease. "We OrobtMn: no concmr-froo mo were accused of being too conserva tive," he tells C&EN, referring to a report on dietary influences on heart disease prepared by FNB two years ago. "This [NRC] report... is more flamboyant and liberal about chang ing diet. My feeling is the evidence Unking diet to cancer is weaker than that for heart disease." The problem of differences among scientists is very much a question of what evidence anyone considers ac ceptable. The NRC committee states in its report that scientifically valid data "are provided by three major sources: epidemiological studies on human populations; experimental studies on animals; and in-vitro tests for genetic toxicity." Critics, includ ing Olson, simply don't agree with mat premise. "I'm surprised, espe cially with [the committee's] use of epidemiologic research," be says, call ing it "hardly proper" to apply such results toward making "sweeping" changes in diet Thus he calk the report "premature" and says that any general recommendations about diet ought to be backed by data from clinical trials. Olson's suggestion is sound from a scientific standpoint but undoubt edly impossible from a practical one. Many dietary effects on cancer are believed to be subtle--contributory rather than directly causative. The scope that would be needed to test, for example, whether reductions in fat intake affect cancer incidence goes way beyond the limits of most clinical triak. The question of time is central to the disputes that develop over can cer policy. Olson, for instance, ar gues that, in most matters concerning public health policy, lack of speed may be a virtue. On one level, there is a risk that the public will be de ceived into following new practices that will do them no good, he says. And at another level, adopting such practices might cause harm. Specif ically, he says that reductions in in take of animal fat may deprive some people of needed nutrients, particu larly people who are recovering from disease or children who are growing rapidly. "Tins research is relatively young," says Clifford Grobstein, chairman of the NRC committee and professor of biology and public policy at the University of California, San Diego. "We have resisted overoptimistic statements... but recognized that we should try to put what we learn to use as soon as possible." This notion--that new knowledge be used "soon" in formulating pol icies--represents a fundamental point of difference between groups within the scientific community.jit ako is perhaps the most crucial dif ference underlying the two reports issued by FNB ana NRC. Oddly enough, for all the criticism it is drawing, the NRC report is hardly a radical document. Urging people to eat more fresh fruit, vege tables, and whole grains--welcome though such recommendations may be--is not all that different from what children are told in U.S. schook. And cutting back on fat in take, a virtue touted indirectly by clothing designers, also U by now common wisdom that is transmitted by way of the medical community. Ironically, no one seems to question the right of family doctors to tell their otherwise healthy patients to shed extra weight by cutting back on dietary fats. NRC's study--the result of a care ful weighing of dozens, perhaps hun dreds, of published studies--certain ly deserves to have some impact, especially when measured against its formidable competitor, the many ad vertising devices affecting what peo ple eat.lt would seem peculiar sim ply to ignore--or worse, dismiss--the compilation of so many carefully ex ecuted studies while deferring whole hog to the endless entreatments from commercial advertisements to buy and consume all manner of foods. The scientists whose interests reside solely in improving public health can't remain silent indefinitely against that din in hopes that some day scientific certainty will arrive. June 28.1982 C&EN 27