Food related factors that affect the glycaemic response and glycaemic index of foods

Common modifiable risk factors such as unhealthy diet, physical inactivity and tobacco use associated with urbanization and lifestyle changes and an aging population, give rise to the intermediate risk factors such as overweight/obesity, hyperglycaemia, hypertension and hyperlipidaemia the stepping stones to the main chronic non communicable diseases (NCDs) such as heart disease, stroke, cancer, diabetes etc. Unhealthy dietary food habits especially increased intake of highly refined carbohydrates is identified as one major factor for the increase in nutrition related non communicable diseases (NCDs) in Sri Lanka. In this context glycaemic index (GI) of foods is important as this reflects how food carbohydrates affect the glycaemic response and thus energy intake and as GI can be used to select food ingredients, foods for consumption and also healthy food production. Analysis of different starchy foods commonly consumed by Sri Lankans clearly indicated that raw red or white rice or red or white (samurdhi) basmati elicited high GI. Parboiling decreased the GI. Mixed rice meal contribute to lower the GI decreased. The same observation was seen with bread where a mixed meal produced a lower GI. Hoppers, string hoppers and pittu when made with rice or wheat flour and consumed as a mixed meal produced high GIs. However, when millet flour was introduced to pittu the GI decreased to medium. Roti irrespective of flour variety used produced a low GI. Boiled legumes, Diascorea alata (purple) tubers and green leafy porridges produced low GI due to varied reasons. When considering the GIs obtained for different foods, the dietary components, processing method and particle size of flour used in food preparation were identified as major factors contributing to the different GIs. Food or meal components; i.e dietary fibre, moisture and protein contents affected the glyacemic response. The effect of increased dietary fibre and protein was responsible for the lower GI in mixed meals and legumes. The increased moisture in green leafy porridges contributed to decrease the GI. Wet processing (boiling) compared to dry processing (roasting) increased GI. This was clearly demonstrated by the high GI in pittu and string-hoppers which were wet processed and low GI in roti. Another factor that contributes to high GI was the particle size of the flour used in food preparations. This was seen when the GI of foods made with flour produced with different particle sizes elicited different GIs. Higher the particle size lower was GI. Extrusion also contributed to increase the GI of foods. However, the contribution of each of above factors to GI in each food would be different and will depend on the accompaniments added, the processing technique the food is subjected to and the properties of starch granular structure as well. Thus when selecting food, preparing meals or in industrial food production careful selection of foods or ingredients and combination of high GI foods with medium or low GI foods, controlling the processing and increasing the particle size could be used to control the carbohydrate intake and hence the glycaemic response which will prevent/control insulin resistance and associated complications leading to NCDs.