Carbohydrate quality and health: new evidence for driving dietary choices

Abstract

The growing prevalence of chronic diseases, such as obesity and type 2 diabetes (T2D), is an important public health concern and the development of strategies for reducing and preventing this real epidemic is of primary importance. Among the factors able to modulate the reduction of risk of chronic diseases and mortality, diet is certainly among the most relevant and modifiable. Carbohydrates play a fundamental role in this framework, as they are the major components in our diet. Recently, carbohydrates have received some negative publicity and their link to human health has been largely questioned. However, evidence suggests that the carbohydrates role in the incidence of chronic diseases depends both on their quantity and quality. In this scenario, the carbohydrate-quality concept needs to be considered as parameter to follow within the jungle of healthy dietary choice. Different tools have been proposed to classify carbohydrate foods based on their quality. Among them, the content of dietary fibre, the solid or liquid form, the ratio whole grain/refined, the glycaemic index (GI) and the glycaemic load (GL) emerge as the most investigated. Despite being one of the most studied and applied, the use of GI is still under debate, and its contribution to weight management still needs some robust confirmation. For this reason, more studies, and in particular long-term studies, are needed to evaluate the effect of carbohydrate quality toward human health to identify the best dietary recommendations for the population. On the basis of these considerations, the aim of this Doctoral Thesis were: i) to provide data on GI, GL, and macronutrient composition of breakfast foods commonly consumed in Italy; ii) to explore whether the addition of fat-rich sauces (tomato sauce and pesto) may affect GI values and glycaemic responses of low GI (spaghetti) and medium-high GI (rice) carbohydrate-rich foods, and to infer if the health effects of low GI foods may be preserved also in the context of mixed meals; iii) to investigate the role of pasta consumption (as an easily implementable low GI carbohydrate dietary choice) on weight loss and weight loss maintenance in healthy obese adults, in the framework of a hypocaloric diet; iv) to investigate the effect of a long-term low GI or high cereal fibre diets on weight reduction and on the subsequent maintenance of a reduced weight in overweight and obese adults with T2D. The evidence from these studies suggests that high quality carbohydrate foods may have a positive impact on health. In particular, i) the substitution of commonly consumed Italian low-medium GI breakfast items, high in saturated fat and sugar and low in fibre, with other low-GI, low-saturated fat breakfast alternatives would help the population to meet nutritional recommendations; ii) the difference in postprandial glycaemic response and GI between a low GI foods (spaghetti) and a higher GI food (rice) was preserved when tomato sauce and olive oil were added as a source of fat, but not after the addition of pesto, where the quantity of fat was higher. However, lowering the postprandial response with the addition of fat, which lead to an increase in energy, should not be considered as a viable strategy; iii) the consumption of high quality carbohydrate foods, such as pasta, in the framework of a hypocaloric diet was effective in a 6-month weight loss program in healthy obese adults, as well as in improving glycaemic and lipidemic profiles, iv) ad libitum consumption of a low GI or a high cereal fibre diet resulted effective in a 3-year BMI reduction in T2D overweight and obese subjects. In the short period, the low GI diet induced a more relevant reduction in BMI, and a greater benefit on glycaemic control, when compared to the high cereal fibre diet. In conclusion, the findings of this Doctoral Thesis contribute to shed light on the importance of selecting high quality carbohydrate foods as one of the possible strategy to increase the overall quality of the diet. The evidence emerging from this thesis links the consumption of low GI and high fibre foods, such as fruits, vegetables, legumes and wholegrain products, to a strong positive impact on health. In particular, the choice of high quality carbohydrate foods influences acute post-prandial glycaemic control, and may represent a valuable strategy in the framework of weight loss and weight management in healthy obese, and in overweight and obese type 2 diabetics.