Abstract
A high prevalence of diabetes exists globally and in particular in Saudi Arabia. Several dietary and lifestyle factors are implicated although dietary carbohydrates (CHOs) have a key role in influencing diabetes risk. The physiological impact of CHOs on postprandial blood profiles can be measured in vivo or predicted from in vitro digestion rates. This thesis examined the relationship between CHO digestibility in vitro and CHO bioavailability in vivo by assessing a variety of UK and Saudi Arabian foods. Our hypothesis was that traditional Saudi foods could have better health impacts on blood glucose and insulin levels. The CHO digestibility method of Englyst was established to determine rapidly available glucose (RAG) and slowly available glucose (SAG) parameters. RAG and SAG were determined for some food standards, and some Saudi and UK foods. Also, glycaemic and insulinaemic indices (GI and II) of Saudi Arabian Hassawi Rice and dates were tested using FAO/WHO protocols and compared with Uncle Ben's rice and dates with Arabic coffee respectively. Once the RAG, SAG and GI values for some Saudi and UK foods were determined, the role of the SAG index was assessed in terms of its ability to differentiate between two meals with essentially identical macronutrient contents and GI values. Our results demonstrated the method for RAG and SAG measurements to be reproducible and to show good agreement with the observations in the literature. In terms of GI and II values for Hassawi rice and Uncle Ben's rice, no significant differences were observed between the two types of rice in terms of plasma glucose responses, however, a lower insulin response were noted for Hassawi rice (p<0.007). For Arabic coffee consumed with dates, there was an increase in glucose response at 45 and 60 min (p<0.05) although the insulin response was not significantly affected. For the high and low SAG meals, despite the similarity between the two meals it was evident that the high SAG meal resulted in a modestly lower incremental area under the glucose curve (p=0.21) and a lower insulin response, particularly at 45 min (p=0.053). In conclusion, these studies showed that some traditional Saudi foods could have beneficial effects in terms of plasma glucose and insulin responses. Furthermore, RAG and SAG values can be used as important predictors of GI. Nevertheless, the SAG value can show important metabolic differences between the impact of foods with the same GI. The observations for staple foods may be important for people with diabetes in Saudi Arabia.