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News from the National Academies
Date: Feb. 15, 1996
Contacts: Dan Quinn, Media Relations Associate
Todd Bailey, Media Relations Assistant
(202) 334-2138; Internet <news@nas.edu>


EMBARGOED: NOT FOR PUBLIC RELEASE BEFORE 5 P.M. EST THURSDAY, FEB. 15


EXCESS CALORIES POSE MORE OF A CANCER THREAT
THAN 'NATURAL' OR SYNTHETIC CARCINOGENS IN FOODS


WASHINGTON -- Cancer-causing chemicals that occur naturally in foods are far more numerous in the human diet than synthetic carcinogens, yet both types are consumed at levels so low that they currently appear to pose little threat to human health, a committee of the National Research Council said in a report* released today.

The report says the greater cancer threat in the human diet today comes not from minor chemicals in food, but from diets too rich in calories and fats, or alcohol.

"While some chemicals in the diet do have the ability to cause cancer, they appear to be a threat only when they are present in foods that form an unusually large part of the diet," said committee chair Ronald Estabrook, chair, department of biochemistry, University of Texas Southwestern Medical Center at Dallas. "The varied and balanced diet needed for good nutrition -- including fruits and vegetables -- seems to provide significant protection from the natural toxicants in our foods."

Just how either type of chemical in foods causes cancer, however, still is not well understood. The report identifies research needed to shed light on the way diet contributes to cancer, the second leading killer in the United States, responsible for more than 500,000 deaths each year.

Historically, research and government regulation have focused on the relationship between cancer and the synthetic chemicals in foods, including trace amounts of man-made pesticides, flavoring and coloring agents, and preservatives. Many of these chemicals shown to cause cancer have been regulated out of the food supply.

More recently, however, researchers have begun to look at the comparative risk from chemicals that occur naturally and have found that some of these have the ability to cause or help spread cancer in laboratory animal tests. A few natural toxins, such as mycotoxins generated by fungi that often contaminate grains and nuts, are associated with elevated levels of cancer in humans.

The committee examined the potential of these natural carcinogens to cause cancer, comparing the risk they pose to the risk from synthetic carcinogens. It also examined "anticarcinogens," substances that are associated with lowering the occurrence of cancer. After assessing the data on more than 200 known carcinogens in food -- including 65 naturally occurring substances -- the committee determined that both naturally occurring and synthetic chemicals appear to cause cancer in similar ways and can be evaluated in the laboratory using the same methods. However, screening and research must be dramatically improved before scientists can understand the role that dietary chemicals play in causing cancer.

For example, the rodent bioassay, in which rats are fed high concentrations of an individual chemical, does not mimic human exposure conditions; the human diet contains a mixture of small amounts of thousands of chemicals, some of which may cause cancer and some that may help prevent cancer by acting as anticarcinogens. Rodents currently represent the best screening tool available for testing the ability of chemicals to cause cancer. But more sophisticated methods are needed to understand the link between dietary chemicals and cancer.

THE NEED FOR MORE KNOWLEDGE

Researchers lack sufficient knowledge about human exposure levels, about the ways chemicals induce or prevent cancer in humans, and about the concentrations of specific natural chemicals in foods. More naturally occurring chemicals should be tested on an individual basis for their ability to cause cancer, the committee said, with first priority given to those that have no nutritional value but are found in high concentrations in commonly consumed foods. Only a small fraction of the perhaps 1 million food chemicals that occur naturally have been tested so far, and some even have been shown to help prevent cancer.

To better understand the connection between dietary chemicals and cancer, the report also says:

> The mechanisms by which major dietary components like fat and calories cause cancer should be explored.

> Researchers must better define which foods protect against cancer, and how they do so.

> Improvements are needed in methods used to test chemicals for carcinogenicity, such as the rodent bioassay, and new tests using human genes, enzymes, cells, and tissues must be developed to screen chemicals quickly.

> Better data are needed on the concentrations of natural and synthetic compounds in food to estimate more precisely human exposure levels.

> Population-based studies must be improved by including better cellular and molecular markers to chronicle the damage done to cells by dietary chemicals. New markers are needed to shed light on the level of exposure to chemicals, and the damage such exposure can cause.

While knowledge of naturally occurring carcinogens and anticarcinogens is relatively new, more is known about the way excess calories -- including the fat component of those calories -- and excess alcohol contribute to cancer. These cancers may account for as many as one-third of all cancer deaths in the United States, the report says.

The study was funded by the National Institute for Environmental Health Sciences, the U.S. Environmental Protection Agency, the National Cancer Institute, the U.S. Food and Drug Administration, the American Industrial Health Council, and Nabisco Foods Group.

The National Research Council is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering. It is a private, non-profit institution that provides independent advice on science and technology issues under a congressional charter.

A committee roster follows.

*The report, Carcinogens and Anticarcinogens in the Human Diet: A Comparison of Naturally Occurring and Synthetic Substances, is available from the National Academy Press at the mailing address in the letterhead; tel. (202) 334-3313 or 1-800-624-6242. The cost of the report is $44.95 (prepaid) plus shipping charges of $4.00 for the first copy and $.50 for each additional copy. Reporters may obtain copies from the Office of News and Public Information at the letterhead address (contacts listed above).

# # #
[Internet availability: This news release is available on the World Wide Web at <http://www.nas.edu>; via Gopher at <gopher.nas.edu>; and via FTP at <ftp.nas.edu/pub/>.]


NATIONAL RESEARCH COUNCIL
Commission on Life Sciences
Board on Environmental Studies and Toxicology

Committee on Comparative Toxicity of Naturally Occurring Carcinogens

Ronald W. Estabrook, Ph.D.1,2 (chair)
Virginia Lazenby O'Hara Professor of Chemistry and Chairman, Department of Biochemistry
University of Texas Southwestern Medical Center
Dallas

Diane Birt, Ph.D.
Professor
Eppley Institute
University of Nebraska Medical Center
Omaha

Gary P. Carlson, Ph.D.
Professor of Toxicology
Department of Pharmacology and Toxicology
School of Health Sciences
Purdue University
West Lafayette, Ind.

Samuel M. Cohen, Ph.D.
Professor and Chairman
Pathology and Microbiology Department
University of Nebraska Medical Center
Omaha

Eric E. Conn, Ph.D.1
Professor Emeritus of Biochemistry
Section of Molecular and Cell Biology
Division of Biology
University of California
Davis

Norman R. Farnsworth, Ph.D.
Director, Program for Collaborative Research in the Pharmaceutical Sciences
College of Pharmacy
University of Illinois
Chicago

David W. Gaylor, Ph.D.
Director of Biometry Staff
National Center for Toxicological Research
U.S. Food and Drug Administration
Jefferson, Ariz.

Richard L. Hall, Ph.D.
Consultant
Baltimore

John Higginson, M.D.
Clinical Professor (retired)
Department of Community and Family Medicine
Georgetown University Medical Center
Washington, D.C.

Ernest Hodgson, Ph.D.
William Neal Reynolds Professor and Head, Department of Toxicology
North Carolina State University
Raleigh

Laurence N. Kolonel, Ph.D.
Director, Epidemiology Program
Cancer Research Center
University of Hawaii
Honolulu

Daniel Krewski, Ph.D.
Acting Director
Bureau of Chemical Hazards
Health Canada
Ottawa, Ontario

Charlene A. McQueen, Ph.D.
Associate Professor
Department of Pharmacology and Toxicology
College of Pharmacy
University of Arizona
Tucson

Michael W. Pariza, Ph.D.
Director, Food Research Institute
Department of Food Microbiology and Toxicology
University of Wisconsin
Madison

Janardan K. Reddy, M.D.
Professor and Chairman, Department of Pathology
Northwestern University Medical School
Chicago

I. Glenn Sipes, Ph.D.
Professor and Head, Department of Pharmacology and Toxicology
College of Pharmacy
University of Arizona
Tucson

Bernard M. Wagner, M.D.
President
Wagner Associates Inc.
Millburn, N.J.

Paul B. Watkins, Ph.D.
Director, Clinical Research Center
University of Michigan
Ann Arbor

I. Bernard Weinstein, M.D.2
Director, Columbia-Presbyterian Cancer Center, and
Professor of Medicine, Public Health, Genetics, and Development
College of Physicians
Columbia University
New York City

Lauren Zeise, Ph.D.
Chief, Reproductive and Cancer Hazard Assessment Section
Office of Environmental Health Hazard Assessment
California Environmental Protection Agency
Berkeley


RESEARCH COUNCIL STAFF

J. David Sandler
Staff Officer

(1) Member, National Academy of Sciences
(2) Member, Institute of Medicine