ITHACA, N.Y. -- The long-term health benefits to Chinese and other Asian people who have traditionally existed on a primarily plant-based diet might be lost as more people in Asia switch to a Western-style diet that is rich in animal-based foods.
That conclusion is being drawn by some scientists after reviewing results from the latest survey of diets, lifestyles and disease mortality among Chinese populations -- this one comparing current dietary habits in Taiwan and mainland China -- and measuring them against a time when fewer meat and dairy products were available in rural China.
Preliminary results of "China Study II," the follow-up to the China-Oxford-Cornell Study on Dietary, Lifestyle and Disease Mortality Characteristics in 65 Rural Chinese Counties, or "China Study I," were discussed on June 16 at the Congress of Epidemiology 2001 in Toronto by T. Colin Campbell of Cornell, Sir Richard Peto of the University of Oxford, Dr. Junshi Chen of the Chinese Academy of Preventive Medicine and Dr. Wen-Harn Pan of Academia Sinica in Taiwan.
The Jacob Gould Schurman Professor Emeritus of Nutritional Biochemistry, Campbell also discussed China Study II today (June 25) at a press briefing on the Cornell campus.
"With the new data from mainland China, along with the fascinating new data from Taiwan now in hand, we will have the opportunity to explore dietary and disease mortality trends," Campbell says. "We will see how fast dietary changes in rural China -- preceded by earlier changes in Taiwan -- result in the development of Western diseases."
Some analyses of data from China Study I, which was conducted among thousands of rural families in mainland China, linked that population's low incidence of such Western health problems as cardiovascular disease, some cancers, obesity and diabetes to plant-based diets that were low in animal products. China Study I is now regarded as the most comprehensive study of diet, lifestyle and disease ever completed. Data from the study was first published in an 896-page monograph (1990) and resulted in more than 50 scientific publications.
Planned since 1987, China Study II was designed to re-survey the same mainland Chinese population as China Study I, in addition to a few new sites in mainland China and a new population of 16 counties in Taiwan. China Study II was directed by the three collaborators in the first study and by Dr. Win-harn Pan. When it started in 1987-88, it was the first collaborative research study between mainland China and Taiwan. Data from China Study II are now freely available at an Oxford University web site: http://www.ctsu.ox.ac.uk/projects/cecology1989/ .
Both surveys afford an opportunity to investigate the effect of dietary change from the typical plant-based diet of rural China to a Western-style diet that includes more animal-based foods, as consumed in urban China and in Taiwan. "Even small increases in the consumption of animal-based foods was associated with increased disease risk," Campbell told a symposium at the epidemiology congress, pointing to several statistically significant correlations from the China studies:
- Plasma cholesterol in the 90-170 milligrams per deciliter range is positively associated with most cancer mortality rates. Plasma cholesterol is positively associated with animal protein intake and inversely associated with plant protein intake.
- Breast cancer is associated with dietary fat (which is associated with animal protein intake) and inversely with age at menarche (women who reach puberty at younger ages have a greater risk of breast cancer).
- For those at risk for liver cancer (for example, because of chronic infection with hepatitis B virus) increasing intakes of animal-based foods and/or increasing concentrations of plasma cholesterol are associated with a higher disease risk.
- Cardiovascular diseases are associated with lower intakes of green vegetables and higher concentrations of apo-B (a form of so-called bad blood cholesterol) which is associated with increasing intakes of animal protein and decreasing intakes of plant protein.
- Colorectal cancers are consistently inversely associated with intakes of 14 different dietary fiber fractions (although only one is statistically significant). Stomach cancer is inversely associated with green vegetable intake and plasma concentrations of beta-carotene and vitamin C obtained only from plant-based foods.
- Western-type diseases, in the aggregate, are highly significantly correlated with increasing concentrations of plasma cholesterol, which are associated in turn with increasing intakes of animal-based foods.
Analyses of data from the China studies by his collaborators and others, Campbell told the epidemiology symposium, is leading to policy recommendations. He mentioned three:
- The greater the variety of plant-based foods in the diet, the greater the benefit. Variety insures broader coverage of known and unknown nutrient needs.
- Provided there is plant food variety, quality and quantity, a healthful and nutritionally complete diet can be attained without animal-based food.
- The closer the food is to its native state -- with minimal heating, salting and processing -- the greater will be the benefit.