The Effect of High-carbohydrate Intake on Substrate Utilization in Postmenopausal Women

Abstract

LEARNING OUTCOME: To determine if changes in piasma lipoprotein concentrations that occur in response to high-carbohydrate, low-fat (HCLF) intake may be associated with or result from changes in substrate utilization.By implementing three diets which replaced energy from fat with carbohydrate, stepwise, over a 16-week period, we assessed the metabolic effects of a controlled increase in carbohydrate consumption in postmenopausal women. Substrate utilization was assessed by analysis of plasma metabolites [e.g. lactate, free glycerol (FG), and free fatty acids (FFA)] as well as respiratory quotient (RQ) measurements at baseline and three different timepoints throughout the study. Fasting insulin and glucose concentrations were measured to assess insulin sensitivity. Following the increase in carbohydrate consumption, mean fasting insulin concentration decreased nearly 24% and was accompanied by a concurrent drop in fasting glucose levels. Fasting RQ measurements, plasma FFA and FG concentrations following intervention did not significantly shift from baseline concentrations. Mean total-, low-density lipoprotein- and high-density lipoprotein-cholesterol were reduced an average of 5%, 9% and 13.5% of baseline values, respectively. Both plasma triglyceride (TG) and lactate were markedly elevated relative to baseline. Plasma lactate and TG correlated significantly at two of four timepoints, with plasma TG concentrations higher in those with higher plasma lactate levels. Our results suggest that during increased carbohydrate consumption, glucose oxidation increases, resulting in increased concentrations of plasma lactate. Thus, HCLF intake may promote lipogenesis by enhancing the levels of lipogenic precursors, such as lactate. The increase in lipogenesis induced through HCLF intake by increased lipogenic precursors causes the endogenous synthesis of FFA which in turn increases plasma TG. Additional research is warranted to more clearly define the relationship of increased production of lactate, a lipogenic substrate, to hypertriglyceridemia and increased plasma TG and cardiovascular disease risk in postmenopausal women.