Glycemic index and glycemic load: standardisation of method, new mechanisms of action, effects on energy metabolism and on new markers of cardiovascular disease risk

Abstract

In the present doctoral research, different aspects of glycemic index and glycemic load were investigated. We observed interlaboratory variability in GI measurement and studied GI and GL effects on health aspects. Firstly, there is evidence that one needs controlling and collecting analyses from different laboratory for optimizing GI methodology. The standardization is the groundwork if the aim is glycemic labelling of food products. There is, in fact, sufficient evidence to support labelling on the grounds of benefit for diabetic persons, considering also the growing incidence of diabetes in developed and developing countries. However, caution should be exercised in food choice based solely on GI or GL because LGI and GL foods may be energy dense and contain substantial amounts of sugars or undesirable fat that contribute to the diminished glycemic response but not necessarily to good health outcomes. It seems appropriate that, when GI or GL are used to guide food choice, this should only be done in the context of other nutritional indicators and when values have been measured in a large group of individuals (Livesey et al. 2008, Mitchell 2008, Howlett and Ashwell 2008). Moreover, there is evidence for a positive effect of LGI meal to i) improve glucose tolerance during a subsequent meal; ii) to increase post prandial metabolism and iii) to protect liver and, indirectly, heart health. However, not all the mechanisms of action are completely clear. The second meal effect seems more a consequence of fermentable carbohydrates than low GI. Apparently, a LGI specific effect remains to be substantiated by other investigations. The effect of GI on energy metabolism results straight, but it should be confirmed by a long-term study, since controversial results have been reported in the literature. Finally, there is a direct relation between GI and liver steatosis, in particular in subjects who already suffer of impaired glucose disposal. The results observed in this thesis are in good agreement with the International Life Sciences Institute workshop on glycemic response and health, held in Nice, France (6–8 December 2006) (Howlett and Ashwell 2008). In summary, LGI diets improve glycemic control especially in individuals with impaired glucose tolerance and diabetes; the intake of high GI carbohydrates (from both grain and non-grain sources) in large amounts is associated with an increased risk of heart disease in overweight and obese even when fibre intake is high, but this requires further confirmation in normal-weight. GI and GL are useful parameters to be considered in the choice of foods for individuals with diabetes or impaired glucose regulation, and they may also be relevant for normoglycemic individuals with insulin resistance or metabolic syndrome; unavailable fermentable carbohydrate, independent of GI, seems to have a relevant effect on health outcome.