From
The New York Times SCIENCE Tuesday, May 8, 1990 - by Jane E. Brody
Introduction
In the `Grand Prix' of epidemiology, scientists tracked eating habits of
6,500 Chinese.
Early findings from the most comprehensive large study ever
undertaken of the relationship between diet and the risk of developing disease
are challenging much of American dietary dogma. The study, being conducted in
China, paints a bold portrait of a plant-based eating plan that is more likely
to promote health than disease.
The study can be considered the Grand Prix
of epidemiology. Sixty-five hundred Chinese have each contributed 367 facts about
their eating and other habits that could ultimately help them and Americans preserve
their health and prolong their lives. The data alone fill a volume of 920 pages,
to be published next month by Cornell University Press.
First Findings
Among the first tantalizing findings are these:
Obesity is related more to
what people eat then how much. Adjusted for height, the Chinese consume 20 percent
more calories than Americans do, but Americans are 25 percent fatter. The main
dietary differences are fat and starch. The Chinese eat only a third the amount
of fat Americans do, while eating twice the starch. The body readily stores fat
but expends a larger proportion of the carbohydrates consumed as heat. Some of
the differences may be attributable to exercise. The varying levels of physical
activity among the Chinese were measured, but the data have not yet been analyzed.
Reducing dietary fat to less than 30 percent of calories, as is currently
recommended for Americans, may not be enough to curb the risk of heart disease
and cancer. To make a significant impact, the Chinese data imply, a maximum of
20 percent of calories from fat -- and preferably only 10 to 15 percent -- should
be consumed.
Eating a lot of protein, especially animal protein, is also
linked to chronic disease. Americans consume a third more protein than the Chinese
do, and 70 percent of American protein comes from animals, while only 7 percent
of Chinese protein does. Those Chinese who eat the most protein, and especially
the most animal protein, also have the highest rates of the "diseases of
affluence" like heart disease, cancer and diabetes.
A rich diet that
promotes rapid growth early in life may increase a woman's risk of developing
cancer of the reproductive organs and the breast. Childhood diets high in calories,
protein, calcium and fat promote growth and early menarche, which in turn is associated
with high cancer rates. Chinese women, who rarely suffer these cancers, start
menstruating three to six years later than Americans. Dairy calcium is not needed
to prevent osteoporosis. Most Chinese consume no dairy products and instead get
all their calcium from vegetables. While the Chinese consume only half the calcium
Americans do, osteoporosis is uncommon in China despite an average life expectancy
of about 70 years, just five few years less than the American average.
These
findings are only the beginning. Dr. T. Colin Campbell, a nutritional biochemist
from Cornell University and the American mastermind of the Chinese diet study,
predicts that this "living laboratory" will continue to generate vital
findings for the next 40 to 50 years.
The study, started in 1983 to explore
dietary causes of cancer, has been expanded to include heart, metabolic and infectious
diseases. Dr. Chen Junshi of the Chinese Institute of Nutrition and Food Hygiene
organized the survey to cover locations from the semitropical south to the cold,
arid north.
Exacting, Labor-Intensive Study
The extensive volume of
raw data and its counterpart on computer tape will be available to any scientist
to use as raw material for medical research.
It is an exacting, labor-intensive
study, initially financed by the National Cancer Institute, that probably could
not have been done anywhere except China. For nowhere else can accurate mortality
statistics be combined with data from people who live the same way in the same
place and eat the same foods for virtually their entire lives.
Nowhere else
is there a genetically similar population with such great regional differences
in disease rates, dietary habits and environmental exposures. For example, cancer
rates can vary by a factor of several hundred from one region of China to another.
These large regional variations in China highlight biologically important relationships
between diet and disease.
The Whole Diet Panoply
And nowhere else could
researchers afford to hire hundreds of trained workers to collect blood and urine
samples and spend three days in each household gathering exact information on
what and how much people eat, then analyzing the food samples for nutrient content.
"The total cost in U.S. dollars of this project -- $2.3 million plus
600 person-years of labor contributed by the Chinese Government -- is a mere fraction
of what it would have cost to do the same study here," Dr. Campbell noted.
And unlike typically circumscribed American studies that examine one characteristic
as a factor in one disease, the Chinese investigation "covers the whole diet
panoply as it relates to all diseases."
Dr. Mark Hegsted, emeritus professor
of nutrition at Harvard University and former administrator of human nutrition
for the United States Department of Agriculture, said: "This is a very, very
important study -- unique and well done. Even if you could pay for it, you couldn't
do this study in the United States because the population is too homogeneous.
You get a lot more meaningful data when the differences in diet and disease are
as great as they are in the various parts of China."
In the first part
of the study, 100 people from each of 65 counties throughout China each contributed
367 items of information about their diets, lives and bodies. The responses from
residents of each county were then pooled to derive county wide characteristics
that could be measured against the area's death rates for more than four dozen
diseases.
By matching characteristics, researchers derived 135,000 correlations,
about 8,000 of which are expected to have both statistical and biological significance
that could shed light on the cause of some devastating disease.
In the poorer
parts of China, infectious diseases remain the leading causes of death, but in
the more affluent regions, heart disease, diabetes and cancer are most prominent,
Dr. Campbell said.
Adding Taiwan to the Research
Although from an overall
perspective of nutrient composition the Chinese diet is more health-promoting
than ours, he said, there are some important limitations that result from a lack
of economic development.
"Food quality and variety are not as good as
ours," he explained. "With limited refrigeration, bacteria and mold
contamination is more common, large amounts of salt and nitrites are used to preserve
foods and hot spices are used to mask off-flavors."
The study is now
being expanded and revised. New mortality rates are being gathered to update the
original mortality data from the early 1970's and to reflect causes of death for
100 million people in the late 1980's. The original 6,500 participants are being
resurveyed and people from 12 counties in Taiwan are being included in the expanded
survey, which will also measure many socioeconomic characteristics.
"We
want to see how economics change and health factors follow," Dr. Campbell
explained in an interview. "Taiwan should be interesting because it is intermediate
between the United States and China in nutrient intake and plasma cholesterol
levels. And since the Taiwanese gene pool is more like the Chinese, we can study
the relative contributions of genetics and diet to risk of disease."
Cholesterol as Disease Predictor
Dr. Campbell continued: "So far we've
seen that plasma cholesterol is a good predictor of the kinds of diseases people
are going to get. Those with higher cholesterol levels are prone to the diseases
of affluence -- cancer, heart disease and diabetes."
Contrary to earlier
reports that linked low blood cholesterol levels to colon cancer, the Chinese
study strongly suggests that low cholesterol not only protects against heart disease
but also protects against cancer of the colon, the most common life-threatening
cancer among Americans. In China, mortality rates from colon cancer are lowest
where cholesterol levels are lowest.
Over all, cholesterol levels in China,
which rage from 88 to 165 milligrams per 100 milliliters of blood plasma, much
lower than those in the United States, which range from 155 to 274 milligrams
per 100 milliliters of plasma.
"Their high cholesterol is our low,"
Dr. Campbell noted. He said the data strongly suggest that a major influence on
cholesterol levels and disease rates is the high consumption of animal foods,
including dairy products, by Americans.
Basically a Vegetarian Species
"We're basically a vegetarian species and should be eating a wide variety
of plant foods and minimizing our intake of animal foods." he said.
The Chinese have already begun to capitalize on these findings, using them to
develop national food and agricultural policies that will promote health.
"Usually, the first thing a country does in the course of economic development
is to introduce a lot of livestock," Dr. Campbell said. "Our data are
showing that this is not a very smart move, and the Chinese are listening. They're
realizing that animal-based agriculture is not the way to go."
The plant-rich
Chinese diet contains three times more dietary fiber than Americans typically
consume. The average intake in China is 33 grams of fiber a day, and it ranges
as high as 77 grams in some regions. Dr. Campbell found no evidence to suggest
that diets very high in fiber are in any way deleterious to nutritional well-being.
While American scientists worry that fiber may interfere with the absorption
of essential minerals like iron, no reason for concern was found among the Chinese.
Rather, those with the highest fiber intake also had the most iron-rich blood.
Iron From Vegetables
The study also showed that consumption of meat
is not needed to prevent iron-deficiency anemia. The average Chinese adult, who
shows no evidence of anemia, consumes twice the iron Americans do, but the vast
majority of it comes from the iron in plants.
Nor are animal products needed
to prevent osteoporosis, the study showed. "Ironically," Dr. Campbell
noted, "osteoporosis tends to occur in countries where calcium intake is
highest and most of it comes from protein-rich dairy products. The Chinese data
indicate that people need less calcium than we think and can get adequate amounts
from vegetables."
Another common health concern that could prove to
be a red herring is the fear that aflatoxin, which is produced by a mold that
grows on peanuts, corn and other grains, causes liver cancer. Rather, the Chinese
study strongly indicates that chronic infection with hepatitis B virus and high
serum cholesterol levels are the primary culprits.
Among other intriguing
findings are a relationship between infection with herpes simplex virus and coronary
heart disease and a relationship between infection with the yeast candida and
nasopharyngeal cancer.