Macronutrient intake and glucose tolerance - Pregnancy

Nutrition Research Newsletter, March, 2004

The fed state of normal pregnancy is characterized by prolonged hyperglycemia and hyperinsulinemia. Research has shown that insulin sensitivity in late pregnancy falls from between 45% and 70% to values similar to those of nonpregnant individuals with type 2 diabetes. Glucose intolerance during pregnancy is a result of the inability to produce a sufficient amount of insulin as pregnancy-related insulin sensitivity decreases. Gestational diabetes mellitus (GDM) and impaired glucose tolerance (IGT) are serious and common concerns in pregnancy. The prevalence of GDM in the US population is estimated to be 1% to 4%. In some populations, IGT has been shown to have a rate 2 times that of GDM. Substantial evidence exists that diet is linked to the development of glucose intolerance. Diets high in fat and lower in complex carbohydrates are recognized as risk factors for the development of type 2 diabetes. In the present study, researchers sought to evaluate the influence of dietary fat and carbohydrate consumption during pregnancy on the development of IGT and GDM in both isocaloric and nonisocaloric diets. If specific patterns of caloric or nutrient intake influence the development of glucose intolerance during pregnancy, dietary guidelines that incorporate these patterns would provide a low-cost and effective way to reduce risk.

Data from the Pregnancy, Infection, and Nutrition (PIN) Study--a prospective cohort study designed to identify determinants of preterm delivery in central North Carolina--were used for this analysis. Subjects included 1698 women. Dietary intake was assessed during the second trimester using a food-frequency questionnaire. Women were classified into 1 of 3 glucose categories: GDM, IGT, and normal glucose tolerance.

The overall prevalence of IGT and GDM in the cohort was 2.6% and 5.2%, respectively. The addition model showed that adding 100 kcal from carbohydrates to the diet was associated with a 12% decrease in the risk of IGT and a 9% decrease in the risk of GDM. The substitution model showed that substituting fat for carbohydrates (per each 1% of total calories) resulted in a significant increase in the risk of both IGT and GDM. The findings suggest that in an isocaloric diet, an increase in carbohydrate intake as a percentage of energy with a simultaneous decrease in fat intake as a percentage of energy significantly reduces the risk of glucose intolerance. Furthermore, increasing carbohydrates without decreasing fat and thus not controlling for total energy intake also significantly reduces the risk of both IGT and GDM. Future studies must try to separate out the composition of carbohydrate and fat that is associated with decreased risk.

T. Saldana, A. Siega-Riz, L. Adair. Effect of macronutrient intake on the development of glucose intolerance during pregnancy. Am J Clin Nutr 79:479-486 (February 2004) [Correspondence: AM Siega-Riz, Carolina Population Center, CB No. 8120 University Square, University of North Carolina at Chapel Hill, Chapel Hill, NC 27516-3997. Email: am_siegariz@unc.edu]

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