The glycemic index of indigenous South African foods

Abstract

Carbohydrates have important physiological effects and contribute about half of the total energy in the diet. It is known that not all carbohydrates have similar effects and that digestion and absorption differs in different starch sources. Starches are not all equal in their effects on blood glucose and lipids (Wolever, 1997). The glycemic index is a new concept which defines starches by their ability to raise or lower blood glucose when compared to a standard such as bread. The African diet is known for its high carbohydrate content (Walker, 1995). The glycemic and insulin indices of indigenous South African foods/meals were determined in this study. A sample of 37 healthy student volunteers (18 males and 19 females) aged 23 .3±2.38 years, body mass index 22.7±2.32 kg/m2 , and a fasting capillary glucose of3 .9±0.77 mmol/L were selected. Three subjects repeated the test to make the sample size 40. The subjects were divided into four groups of ten. Each group was allocated white bread as a standard and three other dishes/meals. The following dishes/meals were used: samp, samp and beans, dried bean stew, mabella porridge with sugar, mabella porridge without sugar, fermented sorghum porridge (ting), acid added sorghum porridge, soft mealiemeal porridge with sugar, soft mealiemeal porridge without sugar, stiff mealiemeal porridge with Dk.aka (Cucurbitaceae, Momordica balsamina L. ), and stiff mealiemeal porridge with dried bean leaf stew. The individual portion of each meal contained 50 g carbohydrate. These dishes/meals were prepared in individual portions using traditional methods of cooking. Each subject visited the research centre five times. Each visit was allocated a different dish/meal with bread repeated twice. The subjects were provided with a pre-evening meal consisting of stiff mealiemeal porridge and sour milk. They arrived at the research centre after an overnight fast. A

fasting blood sample was collected before they consumed the food over 10 minutes, then at 15, 30, 45, 60, 90 and 120 minutes. Blood samples were analysed for glucose and insulin concentrations. Glycemic and insulin indices were then calculated based on areas under the curves using computerised programs. Statistical analysis was done using the Newman-Keuls multiple comparison method. Both males and females had an adequate nutrient intake. The percentage contribution to energy was 53% for females and 55% for males from carbohydrate, 15% from protein for both sexes, 28% for females and 25% for males from fat. The use of indigenous foods was variable with maizemeal used daily and wild vegetables rarely. ...