Landmark study that put vegetables on the preventive-medicine map also finds fishy diets cut cancer and heart disease rates
by Craig Weatherby
Back in the early 1980’s, Cornell University Professor T. Colin Campbell, Ph.D. led the famed Cornell-Oxford-China Study, whose results put vegetable-heavy, low-meat diets in the preventive-health spotlight.
Better known as “The China Project”, analysis of data from this huge epidemiological study is ongoing. In fact, it represents the most comprehensive and scientifically powerful investigation of the links between diet and disease in medical history.
The China Project’s results form the firm foundation of the now widely accepted theory that diets high in vegetables help prevent cancer and heart disease. Recent arms of the study indicate that much of the credit belongs to vegetables’ characteristic antioxidants (see "Early China Project analysis", below).
Analysis of China Project data finds fish heart-healthy
Three years ago, Dr. Campell and his co-authors published their analysis of fish-consumption data from the Phase I of the study, which involved a survey of 6,500 subjects in 65 rural counties.
They compared the fatty acid and antioxidant composition of the participants’ red blood cells with the participants’ health status and their self-reported fish consumption.
Those who ate the most fish—and therefore had the highest blood-cell levels of omega-3 DHA—had the lowest blood triglyceride levels and the lowest rate of cardiovascular disease (CVD).
In addition, those who had the highest blood-cell levels of omega-3 DHA also had the lowest rates of most chronic diseases, and DHA appeared to be more protective than the two other omega-3s in fish oil: EPA and DPA.
As expected, those who ate the most fish also had the highest levels of omega-3s in their red blood cells.
Interestingly, these two positive correlations—lowest triglycerides and rates of cardiovascular disease—were even stronger among those had the highest combined levels of DHA and oleic acid: the monounsaturated fat found most abundantly in olive oil and macadamia nut oil, which is also abundant in the peanut oils commonly used in Chinese cooking.
Those who ate the most fish also had the highest blood levels of the antioxidant, anti-mercury mineral selenium—of which fish are the richest food sources—and the highest blood levels of glutathione peroxidase.
(Glutathione peroxidase is a selenium-containing antioxidant that protects our cell membranes. Accordingly, the body’s self-generated “antioxidant network”—in which glutathione peroxidase plays a key part—depends heavily on the presence of adequate dietary selenium.)
As Dr. Campbell’s team concluded, “These results demonstrate the protective nature of fish consumption and DHA … This finding suggests the protective effect of fish consumption as validated by red cell DHA is universal. The protective effect is, therefore, most likely to be due to the fundamental properties of docosahexaenoic acid [DHA] in cell function.”
Early China Project analysis boosted antioxidants’ anti-cancer reputation
In the early 1990’s members of the China Project compared the levels of various antioxidants obtained from study participants’ blood, and compared those levels with rates of cancer (Chen J et al 1992).
They found that the people with the highest blood antioxidant levels had the lowest risk of cancer: a fact that may go a long way toward explaining the low cancer rates the very first China Project data analyses found among Chinese people who ate exceptionally vegetable-rich diets.
Vitamin C was the most protective anti-cancer antioxidant, overall. High levels of selenium—again, fish are the richest food sources—were associated with a reduced risk of esophageal and stomach cancers. Beta-carotene was found to exert protective effects, especially against stomach cancer.
China Project called the “Grand Prix” of diet-disease studies
Unlike studies conducted in the developed world, where everybody eats more or less the same foods in similar proportions, The China Project took place in rural China, where, at the time, almost all people still spent their entire lives near their places of birth eating locally produced foods prepared in accordance with regional culinary customs.
And there were also dramatic differences in the prevalence of disease among the various regions of rural China. Rates of various cardiovascular diseases differed up to 20-fold, and cancer rates often varied even more.
These wide differences in diets and disease rates made rural China the ideal place to explore relationships between lifestyle factors and degenerative disorders like cancer, diabetes, and heart disease.
These unique attributes led The New York Times to term The China Project the “Grand Prix” of diet-disease studies.
When its initial results were published in 1990, they indicated that a majority of all cancer and cardiovascular disease cases could be delayed into advanced old age by adopting plant-based diets low in meats.
The original survey was undertaken from 1983 through 1984, with the first results published in 1990. Blood, urine and food samples were obtained for analysis, while questionnaire and 3-day diet information was recorded.
The international team returned to China in 1989 and to conduct the larger China Study II, which included more people (more than 10,000 adults with families), more counties (including Taiwanese counties), and more measurements.
Since then, they’ve published many papers on the relationship of foods and dietary patterns with disease, with mountains of data left to analyze.
Their key findings to date are these… note that “animal products” refers only to meats and dairy foods, not to seafood:
- Disease patterns in much of rural China tend to reflect those prior to the industrial revolution in the U.S., when cancers and cardiovascular diseases were much less prevalent.
- American men’s rate of death from heart disease is 17 times higher than the rate among rural Chinese men.
- Chronic degenerative diseases (cancers, cardiovascular diseases, diabetes, etc.) occur where diets are richer in animal products and higher in total fat.
- These degenerative diseases were clustered in urbanized, industrialized Chinese counties, where more animal products are consumed. (Affluence induces people to eat more meat, since it is a higher-status food.)
- Small additions of animal based foods to an otherwise plant-heavy diet raise the risk of heart and other degenerative diseases.
- Increasing intake of plant protein is associated with increasing body height, but plant-based diets high in protein (as from combining soybeans and rice) can also produce “big” people.
- In rural China, animal protein intake constitutes about one percent of total calorie intake, compared with an average of 10 percent of calories in the US.
- Rates of osteoporosis are much lower in China, even though calcium intakes are much lower.
- Obesity is far less prevalent in China than in the US, even though they consume about 30% more total calories.
And thanks to the recent, fish-focused analysis of China Project data, we can now add seafood to the list of dietary factors that make Chinese people in some regions healthier than the average American.
- Wang Y, Crawford MA, Chen J, Li J, Ghebremeskel K, Campbell TC, Fan W, Parker R, Leyton J. Fish consumption, blood docosahexaenoic acid and chronic diseases in Chinese rural populations. Comp Biochem Physiol A Mol Integr Physiol. 2003 Sep;136(1):127-40. Review.
- Chen J, Geissler C, Parpia B, Li J, Campbell TC. Antioxidant status and cancer mortality in China. Int J Epidemiol. 1992 Aug;21(4):625-35.