ITHACA, N.Y. -- A diet based on wheat foods such as pasta, bread and cereal may be contributing to this nation's soaring rates of diabetes, obesity, high blood pressure, high cholesterol and coronary heart disease, according to a new Cornell University study.
On the other hand, rice-based diets, and to a lesser extent fish and green vegetables, appear to lower the level of blood values associated with the risk of these diseases. These findings, published in the January 1996 issue of the American Journal of Clinical Nutrition, come from the Cornell-China-Oxford Project on Nutrition, Health and Environment, a massive survey across the far reaches of China that investigates more diseases and dietary characteristics than any other study to date.
In 3,250 Chinese women living in widely dispersed rural counties, the researchers examined the relationship of various foods with a specific set of biochemical blood tests that have been shown to be commonly linked with diabetes, obesity, high blood pressure and coronary heart disease -- otherwise collectively known as the "insulin resistance syndrome."
"We found that the pattern of blood biochemistries of people in the northern part of China who eat a predominantly wheat- based diet resemble those in people with insulin resistance," said Jeffrey Gates, who has a doctorate in health sciences and works in Cornell's Division of Nutritional Sciences; he collaborated with T. Colin Campbell, the Cornell biochemist and director of the China project, Banoo Parpia, Cornell research associate, and Chen Junshi of the Chinese Academy of Preventive Medicine in Beijing.
This pattern includes higher insulin, higher triglycerides, and lower sex hormone binding globulin (a measure of insulin resistance).
"The Chinese women in the south, on the other hand, eat a rice-based diet and have a pattern of blood values that would be considered low risk," Gates added.
In the past couple of decades, many studies have pointed to insulin as being a common factor linking such diverse disorders as high blood pressure, diabetes and coronary heart disease. Recent research also has discovered that sex hormone binding globulin (SHBG), a relatively unknown blood protein, is a reasonably good indicator of insulin resistance. Low levels of SHBG are consistently linked to high levels of insulin in the body. Sustained high levels of insulin are, in turn, associated with the development of the chronic diseases mentioned above.
The Cornell researchers, therefore, looked at SHBG, triglycerides, cholesterol, insulin, testosterone, glucose and 21 different food groups. Factors commonly associated with insulin resistance, such as meat consumption, smoking, and weight were controlled for in the analysis.
"Though other foods such as fish and green vegetables were associated with changes in blood parameters studied, the strong effects of rice and wheat on SHBG were remarkable and unexpected," Gates said. "Women in the northern, wheat- eating counties consistently had low HDL levels, high triglycerides, and low SHBG, all suggestive of insulin resistance. Evidently, rice and wheat can have significantly different effects on the important biochemical parameters we measured." Interestingly, both the rice and wheat consumed in these Chinese regions are semi-refined. Gates stressed, however, that while rice and wheat appear to make the biggest impact on SHBG and insulin, certain other foods in the Chinese meal also have an important effect on SHBG and insulin changes in the blood, and thus ultimately, on those diseases associated with insulin resistance.
Gates speculates that "the differing effects of wheat and rice on SHBG and insulin may be due to the difference in amylose content, a particular kind of starch." Other researchers have found that some rice varieties have higher amylose content than wheat; some rices, on the other hand, have comparable levels.
"Several recent studies have shown that starches with higher amylose content slow down glucose absorption and thus reduce the insulin response of the meal," Gates added. "Clearly, the effects of wheat or rice on insulin response must not be isolated from the important influence of other dietary and lifestyle factors such as fat and exercise. However, this study lends support to the idea that certain starches may play an important role in the development of insulin resistance and thus increase an individual's risk for diabetes, hypertension, and coronary artery disease."