Effects of Food Processing Methods on Diets Proximate Nutrient Composition and Glycemic Profile in Male Type 2 Diabetic Subjects

This experimentally-controlled designed study investigated the effects of selected food processing methods: boiling, flouring, frying, pounding and roasting on proximate nutrient compositions of white yam (Diascorea rotundata)-based diets and postprandial glycemic profiles in male type 2 diabetic Nigerians. Proximate composition of yam meals (raw and processed) and 50g digestible carbohydrates of served portions were determined and analyzed using standard methods of food analysis. The glycemic index (GI) was determined using 20 volunteers (10 type 2 diabetic patients and ten healthy (control) subjects; age range 30-70 years) who consumed served portions of each processed meals containing 50g digestible carbohydrates. Postprandial capillary blood glucose concentrations taken half hourly for two hours using glucometer were used to construct the mean incremental glycemic response (GR) curve from which the GI was calculated. Product of each processing method was classified into low or high GI diet based on the international GI classification of foods while the glycemic profile to each processed meal was based on the pattern of the mean postprandial glycemic responses. Fibre, protein and calorie contents of the processed yam meals increased significantly (P≤0.05) compared with the raw meal while their ash and moisture contents decreased according to the degree and extent of exposure to heat. Roasting of yam gave the highest GI (93.3±4.0%) while frying gave the lowest GI (36.2±2.7%). Postprandial glycemic response patterns (glycemic profile) varied with the different processing methods: High-GI meal induced quick GR with robust (undesirable) glycemic profile while low-GI meal caused delayed GR with low (desirable) glycemic profile. Methods of food processing improved or worsened glycemic profile in type 2 diabetic Nigerians depending on their degree and extent of alteration of food proximate composition, glycemic index values and the postprandial glycemic responses. Dietary recommendation for diabetics should focus both on the source of carbohydrates and the processing method(s) which favor low-GI diets and desirable impact on glycemic profile.