Testing the boundaries of recommended carbohydrate intakes: Macronutrient exchanges, carbohydrate quality and nutritional adequacy

Abstract

Aim:  The aim of this study was to explore the relationships between dietary carbohydrate, other macronutrients, carbohydrate quality and nutritional adequacy in the diets of free-living Australian teenagers, and to consider the implications for total carbohydrate recommendations.

Methods:  Using the Children's Nutrition and Physical Activity Survey (2007) database, the nutrient intakes of boys and girls aged 14–16 years were assessed by quintile of carbohydrate intake.

Results:  Carbohydrate intake was inversely associated with intakes of saturated fat, polyunsaturated fat, long-chain omega 3, monounsaturated fat and protein (for each association, P for trend <0.001). Carbohydrate intake was associated with increased intake of fibre in boys (P for trend <0.05) but not girls, the association being nonlinear. As carbohydrate intake increased, the densities of fibre, vitamin C, folate, thiamin and β-carotene declined and the density of sugar increased, implying a decline in carbohydrate quality. Nutritional adequacy was generally compatible with a wide range of carbohydrate intakes.

Conclusions:  In combination, the exchanges of carbohydrate for polyunsaturated fat, long-chain omega 3, monounsaturated fat and protein would be expected to increase coronary disease risk via several mechanisms. This implies that there may be a progressive increase in coronary risk as carbohydrate intakes increase across the Acceptable Macronutrient Distribution Range (AMDR), as the exchange of carbohydrate for saturated fat is now considered to be neutral for coronary risk. There is a case for lowering the upper and lower boundaries of the AMDR for carbohydrate intake as a strategy for chronic disease prevention. Lower boundaries would be unlikely to increase the risk for obesity or nutrient inadequacy.