Glycemic index of some traditional fortified staple meals on the postprandial blood glucose responses of Nigerian undergraduate students : an open-label study

Background: Staple meals, or meals that are eaten routinely, inexpensive, and are readily available, constitute a dominant portion of the standard diet in a given population. Most of the indigenous staple foods available are based on starchy foods, as is the case in Nigeria. The development of diabetes mellitus, obesity, cancer and cardiovascular disease (CVD) has been reported to be linked to the intake of high starchy foods. Consequently, there is a strong need to determine the glycemic index of commonly consumed fortified staple foods, as well as to determine the extent of their effects on the postprandial blood glucose responses of Nigeria undergraduate students. Methods: Fifteen volunteers, nondiabetic undergraduate students aged 20–25yrs, on which a standard oral glucose tolerate test was performed were selected randomly after excluding those with family history of diabetes, in addition to smokers and alcoholics. The subjects reported by 8 am at the study centre each day after overnight fasting (10 – 12hrs) with certain precautions for a period of 6 days for the different prepared test meals, including: the glucose tolerance test (control), beans, rice, yam, unripe plantain and garri stews. Fasting blood samples (2ml each) were collected from the prominent arm veins of each student prior to the eating of one of the test meals of each day. Each test meal contained 50g carbohydrate portion per meal. After each meal had been eaten, 2ml venous blood samples were collected at 30 minutes interval for 120 minutes each day from each student and put into the specimen bottles for blood glucose estimations. The random sugar was determined 2hours later. A glucometer was used for measuring the blood sugar using test strips. The mean values of postprandial glucose blood sugar for each test meals from the randomly selected volunteered students were obtained. The glycosylated haemoglobin in the blood of the subjects was determined by the formulae method. Functional Foods in Health and Disease 2016; 6(7): 414-424 Page 415 of 424 Results: The mean glycosylated haemoglobin of the students was 4.7%±0.002, with fasting blood sugar of 89.02±4.41mg/dl. The ratio of protein and fat contents of the serving portion containing 50g carbohydrate were highest in unripe plantain stew 7.84g and 5.31, respectively, but were lowest in yam stew 4.19g for protein and 2.02 for fat in beans vegetable stew. The glycemic index of the commonly consumed fortified staple test meals was highest in rice stew (107.7± 8.4), followed by yam stew (102.4±1.8), garri and stew (101.4±11.8), beans stew (86.9±6.7), and unripe plantain stew (81.8±8.4) in that order. The carbohydrate content of the commonly consumed fortified staple test meals was highest in garri with stew (68.2±0.2g) and lowest in unripe plantain stew while the fibre content was highest in plantain stew (5.8±0.4g) and lowest in rice stew (2.8±0.12g). The mean blood oral glucose tolerance test of the students was below 120mg/dl, but had the mean peak after an hour interval (112.8±7.3mg/dl). The increment on the postprandial blood glucose after ingestion of the test meals was highest for garri and stew meal (93.1±2.4mg/dl), but lowest for unripe plantain stew meal (74.3±11.6mg/dl) after 120 minutes the test meals were ingested. Conclusion: Unripe plantain stew meal had the lowest glycemic index value, with lowest postprandial blood glucose response for the period of time the staple test meals were ingested. This could be attributed to the relatively higher level of fibre content of the unripe plantain than the other staple test meals.