Influence of Processing Methods on the Glycaemic Index and Nutritional Properties of Yam-Based Products for Diabetic Consumers in Lagos State

The rising prevalence of type 2 diabetes mellitus in urban Nigeria, particularly in Lagos State, has intensified interest in the glycaemic index of staple foods as a dietary management tool. Yam, a primary carbohydrate staple in South West Nigeria, can be processed in diverse ways that differentially affect its glycaemic index and nutritional composition. This study investigated the influence of boiling, roasting, frying, pounded yam preparation, and flour production on the glycaemic index and nutritional properties of white yam (Dioscorea rotundata) sourced in Lagos State. Human glycaemic index testing was conducted with fifteen healthy volunteers according to International Organisation for Standardisation 26642:2010 guidelines using glucose as reference food. Proximate composition, total starch, resistant starch, and dietary fibre were determined for each product. Results showed that boiled yam had a glycaemic index of 74, pounded yam 85, roasted yam 68, fried yam 62, and yam flour 52. Resistant starch content was highest in yam flour (4.8 percent of dry weight) and lowest in pounded yam (0.9 percent). Dietary fibre was significantly reduced in pounded yam due to processing intensity. Frying increased fat content substantially (from 0.3 to 8.6 percent) despite reducing glycaemic index through surface crust formation. The study provides glycaemic index data to support dietary guidance for diabetic consumers in Lagos State and recommends yam flour as the most glycaemically favourable yam product for diabetes management. Keywords: glycaemic index, yam, diabetes, processing, Lagos.