From The April 2000 Issue of Nutrition Science News
People who eat more unrefined carbohydrates have lower insulin levels and, therefore, a lower risk of heart disease, according to the 10-year Coronary Artery Risk Development in Young Adults study that tracked the evolution of risk factors among young adults in four parts of the country.
David Ludwig, M.D., Ph.D., of Children's Hospital in Boston studied 2,909 healthy adults, both black and white, ages 18 to 30. The study population was divided into five smaller groups according to a ratio of dietary fiber to caloric intake. Among both blacks and whites, the higher the ratio, the lower the insulin levels.
Elevated circulating insulin levels are thought to contribute to several heart disease risk factors including high blood pressure, obesity and high LDL cholesterol levels. A meal high in refined carbohydrates is quickly absorbed, and sends insulin levels soaring. Unrefined carbohydrates such as whole grains, starchy vegetables or fruit remain in the stomach longer, which delays insulin increases.
These results raise the interesting possibility that fiber may play a greater role in determining cardiovascular disease risk than total or saturated fat, says the author.
This study did not determine the dietary source of fiber or whether it was soluble or insoluble. Nor did researchers assess the nutrients found in fiber, such as phytochemicals, magnesium or vitamin E.
Journal of the American Medical Association 1999 (Oct 27); 282 (16): 1539–1546
Ludwig DS, Pereira MA, Kroenke CH, Hilner JE, Van Horn L, Slattery ML, Jacobs DR Jr
Department of Medicine, Children's Hospital, Boston, Mass 02115, USA.
CONTEXT: Dietary composition may affect insulin secretion, and high insulin levels, in turn, may increase the risk for cardiovascular disease (CVD).
OBJECTIVE: To examine the role of fiber consumption and its association with insulin levels, weight gain, and other CVD risk factors compared with other major dietary components.
DESIGN AND SETTING: The Coronary Artery Risk Development in Young Adults (CARDIA) Study, a multicenter population-based cohort study of the change in CVD risk factors over 10 years (1985-1986 to 1995-1996) in Birmingham, Ala; Chicago, III; Minneapolis, Minn; and Oakland, Calif.
PARTICIPANTS: A total of 2909 healthy black and white adults, 18 to 30 years of age at enrollment.
MAIN OUTCOME MEASURES: Body weight, insulin levels, and other CVD risk factors at year 10, adjusted for baseline values.
RESULTS: After adjustment for potential confounding factors, dietary fiber showed linear associations from lowest to highest quintiles of intake with the following: body weight (whites: 174.8-166.7 lb [78.3-75.0 kg], P<.001; blacks: 185.6-177.6 lb [83.5-79.9 kg], P = .001), waist-to-hip ratio (whites: 0.813-0.801, P = .004; blacks: 0.809-0.799, P = .05), fasting insulin adjusted for body mass index (whites: 77.8-72.2 pmol/L [11.2-10.4 microU/mL], P = .007; blacks: 92.4-82.6 pmol/L [13.3-11.9 microU/mL], P = .01) and 2-hour postglucose insulin adjusted for body mass index (whites: 261.1-234.7 pmol/L [37.6-33.8 microU/mL], P = .03; blacks: 370.2-259.7 pmol/L [53.3-37.4 microU/mL], P<.001). Fiber was also associated with blood pressure and levels of triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and fibrinogen; these associations were substantially attenuated by adjustment for fasting insulin level. In comparison with fiber, intake of fat, carbohydrate, and protein had inconsistent or weak associations with all CVD risk factors.
CONCLUSIONS: Fiber consumption predicted insulin levels, weight gain, and other CVD risk factors more strongly than did total or saturated fat consumption. High-fiber diets may protect against obesity and CVD by lowering insulin levels.