Metabolic Impact of the Amount and Type of Dietary Carbohydrates on the Risk of Obesity and Diabetes

Abstract

The relationship between dietary carbohydrates and the current obesity and diabetes epidemic is the subject of intense renewed interest. Since glucose is an essential source of energy, with limited body stores, maintenance of blood levels and changes in its metabolism are strongly determined by the intake of carbohydrates in the diet. Depending on the individual genetic susceptibility and the impact of other risk factors, these metabolic changes can potentially deteriorate into manifest abnormalities with an important disease risk. In this review we focus on the impact of changing the quantity and quality of dietary carbohydrates on the biochemistry of fat synthesis and storage and on the metabolic abnormalities that can lead to overweight and obesity and to complications such as the metabolic syndrome and type 2 diabetes mellitus. Using simple illustrations of the metabolic pathways involved, we summarize current research on the following issues: ∞ Does an increase in dietary carbohydrates induce changes in blood lipids and an increase in body fat? ∞ Does a diet with a high glycemic index lead to higher energy intakes, obesity and a higher risk of developing type 2 diabetes mellitus? ∞ Is sucrose more obesigenic than starch? ∞ Does excessive consumption of food and drinks sweetened with fructose explain the current epidemic of obesity and diabetes? Despite convincing experimental data explaining the metabolic outcomes of excess consumption of these carbohydrate types, the evidence from dietary intervention studies has been undermined by methodological issues. Clear nomenclature and classification are still needed before this information can be applied to explain metabolic risks in each individual as well as to set up guidelines for the public health authorities and the food industry.