Staff: Dr. ssa Rosalba Giacco, Dr. Gennaro Clemente, Dr. Domenico Cipriano

No Staff: Dr.ssa Lara Bruno

Collaborator from other Istitutions: Dr. M. Mancini, Prof. G. Riccardi

Our scientific activity focuses mainly on:

• The effects of dietary carbohydrates on postprandial plasma glucose and lipid metabolism in humans,
• Validation of non invasive methods to study gastric emptying rate and
• Identification of early metabolic markers of predisposition to obesity.

Synthesis of the research lines :

1) Importance of chemical and physical structure of foods on postprandial metabolism and possible mechanisms of the anti-hyperglycemic activity of soluble fiber: viscosity, colon fermentation and physical structure.

We have shown that different foods with similar content of carbohydrates (in terms of chemical composition in all macronutrients) induce very different glycemic responses. These studies have enabled us to classify foods based on their glycemic response in vivo as "Low Glycemic Index" foods (i.e. pasta, parboiled rice, potato dumplings etc.) and "High Glycemic Index" foods (i.e. bread, potatoes, pizza, hard toasted bread) (R.Giacco et al. Br J Nutr, 2001). Our results represent an important innovation since they have clarified that carbohydrate-rich foods need to be characterized not only by their chemical composition but also by their physiological properties. This allows us to choose foods that induce healthy metabolic effects and to identify technological processes that enable the preservation and development of food characteristcs beneficial for human health. Concerning the mechanisms accounting for the anti-hyperglycemic activity of soluble fiber, we have shown that viscosity of a fiber-rich food (i.e.biscuits fortified with glucomannan, the most viscous type of soluble fiber) improves plasma glucose response only if consumed in large quantities (relevant for a pharmacological rather than nutritional approach); conversely, when the viscosity of a fiber-rich meal is within the range observed for common naturally fiber-rich food (i.e. a portion of legumes), it plays a less important role. The metabolic effects of bacterial fermentation in the human colon have been studied supplementing a meal with Resistant Starch (RS) (a carbohydrate that is not viscous but, like fiber, is fermented by colon bacteria in short-chain fatty acids). The meal containing RS significantly reduced the postprandial plasma glucose levels compared to the placebo. This effect was mediated by an increase in plasma acetate concentrations (R.Giacco et al., Diab Nutr Metab, 1998). Another factor involved in the anti-hyperglycemic activity of soluble fiber is the physical structure that fibers give to foods: indeed they surround the starch granules reducing the accesibility of amylolitic enzymes and slowing starch digestion. This mechanism explains why naturally fiber-rich food improve the glycemic response to a meal better than food supplemented with fiber (R.Giacco, G.Clemente et al. Nutrition Rewievs 2003).

2) Study of role of gastric emptying rate on plasma glucose and lipid metabolism utilizing the ultrasound B-Mode ecography.

We have validated the gastric emptying rate using ultrasound B-Mode ecography against the gold standard method (scintigrafic method) before studying the dietary components able to influence gastric emptying rate (i.e. solid or liquid form of foods, protein, fiber and lipid). The results of our studies show that both fiber and protein slow down gastric emptying rate. Concerning dietary fat, we have shown that dairy products with different physical structure (butter, milk and mozzarella cheese), when consumed in portions with the same quantity of fat, differently affect gastric emptying rate (G.Clemente, R Giacco et al. Nutr Met Cardiovasc Dis 2003).

3) Early metabolic markers of predisposition to obesity.

We have shown that healthy, normal weight young male adults with a strong family history of obesity and thus at high risk to become obese have higher insulin-sensitivity levels and reduced postprandial lipid oxidation compared to healthy, normal weight young men, without family history of obesity (R.Giacco, G.Clemente et. al. IJO, 2003).