Influence of glycemic load on HDL cholesterol in youth

Nutrition Research Newsletter, March, 2005

Traditionally, relations between diet and blood lipids were examined in terms of the main food groups: fat, protein, and carbohydrate. Dietary carbohydrate is usually further divided into simple sugars and complex carbohydrate. In terms of their postprandial metabolic and hormonal responses, however, many complex carbohydrates are little different from simple sugars, and it makes considerable sense, therefore, to classify carbohydrates according to postprandial glucose responses. This can be conveniently expressed in terms of "glycemic index" for either glucose or white bread. Glycemic load reflects both the glycemic index of dietary carbohydrate as well as the amount of carbohydrate ingested. The purpose of this study was to examine for relations between diet and conventional lipids factors in a group of youth who displayed a wide range of cholesterol values and hence a broad range of fat, protein, and carbohydrate intake.

Subjects were healthy males and females, aged 11 yr to 25 yr. Some of the subjects had attended the Pediatric Lipid Clinic at the Children's Hospital of Wisconsin because of hyperlipidemia or a family history of coronary disease. Other subjects had responded to advertisements inviting their participation, irrespective of blood lipids or family history of coronary disease. Because of this recruitment strategy, participants exhibited a broad range of blood lipids and body mass index z scores. Subjects attended the Clinical Research Center on the day of the study in the fasting state after a 12 hr fast. After signing informed consent, subjects underwent a brief physical examination, including height, weight, and blood pressure.

Study participants, and their parents when appropriate, were instructed by the research dietitian on how to record food intake for 3 day (2 weekdays and 1 weekend day). The completed food diaries were reviewed with the subject by the same dietitian who used food models to document quantities. Mean dietary constituents were estimated as grams per day and percentage carbohydrate, fat, and protein as the percentage of daily calories. The glycemic index of each food was multiplied by the carbohydrate content of that food, and the sum of those values provided the average daily glycemic load. Milk fat and milk protein from milk alone were also estimated, as well as dairy fat and dairy protein from the dairy products milk, cheese, yogurt, and ice cream.

The only significant correlation between dietary constituents and blood lipids were with HDL cholesterol. Significant correlation with high-density lipoprotein (HDL) cholesterol was evident for glycemic load, glycemic index, total sugars, total carbohydrate, and fructose. Stepwise multiple regression analysis was performed, and glycemic load was the only independent predictor of HDL cholesterol, accounting for 21.1% of its variation.

Interpretation of data from this study highlights a possible concern of dissecting dietary influences on cardiovascular disease. In this study, glycemic load was moderately correlated with many other dietary constituents, including total, saturated, monounsatured, and polyunsatured fats; total protein; and milk protein. Glycemic load was not a component of most previous dietary studies, and this raises the possibility that a true relation between glycemic load and various aspects of cardiovascular disease was incorrectly ascribed to other dietary factors.

In conclusion, this study demonstrates an inverse relation between glycemic load and HDL cholesterol in a group of hyperlipidemic and normolipidemic older children, teenagers, and young adults. HDL cholesterol is well recognized as an important independent coronary risk factor in healthy individuals and those with coronary artery disease. A causal relation in this instance cannot be excluded. It is suggested that lipid-lowering diets have the potential for inducing unfavorable consequences on blood lipids. Counseling on lipid-lowering diets should be provided only by trained professionals, and advice on appropriate carbohydrate needs should be an integral component of this counseling.

A Slyper, J Jurva, J Pleuss, R Hoffmann, D Gutterman. Influence of glycemic load on HDL cholesterol in youth. AJCN 81(2):376-379 (February 2005) [Correspondence: A Slyper, Department of Pediatrics, Loyola University Medical Center, 2160 South First Avenue, Maywood, IL 60153. E-mail: aslyper@lumc.edu]