Glycemic Index and Glycemic Load of Selected Staples Based on Rice, Yam and Cassava Commonly Consumed in Côte d’Ivoire ()
2. Material and Methods
2.1. Subjects
Ten healthy subjects were recruited to participate in the study. Subjects were physically examined by a medical doctor on the basis of the following criteria: age 18 to 55 years; body mass index 20 to 25 kg/m2 (WHO criteria); fasting blood glucose 4 to 7 mmol/L. Exclusion criteria were as follows: active gastrointestinal or metabolic disease (e.g. celiac disease), first-degree family history of diabetes, and a current course of medication. Pregnant and lactating women were also excluded. Subjects were staff and students from Nangui Abrogoua University. Ethical approval for the study was obtained from Medical Sciences Faculty of Abidjan. Subjects were given full details of the study protocol and the opportunity to ask questions. All subjects gave written informed consent prior to participation. All anthropometric measurements were made in the fasting state. Height was recorded to the nearest centimeter using a stadiometer (Seca Ltd, UK), with subjects standing erect and without shoes. Body weight was recorded to the nearest 0.1 kg, with subjects wearing light clothing and no shoes. BMI was calculated using the standard formula: weight (kg)/height (m2).
2.2. Test Foods and Preparation
Three starchy foods usually consumed with sauces by the Ivorian population were tested: pounded yam (foutou d’igname) with eggplant sauce (sauce gnagnan), Cassava paste (placali) with granulates palm nut sauce (sauce graine) and rice (riz blanc) with groundnut sauce (sauce arachide), were tested in the study. The ingredients of the test foods were purchased from Market of Port-Bouët in District of Abidjan (Côte d’Ivoire). A sample description and the preparation methods used, according to common practices in Côte d’Ivoire are described in Table 1.
2.3. Chemical Analysis
Laboratory of Food Biochemistry and Tropical Products Technology of Nangui Abrogoua University analyzed the chemical composition of the study meals. Each part of the meal (starchy food + sauce) were analyzed for moisture, fat, protein and total dietary fibre (gravimetric method) using standard AOAC methods [11]. Available carbohydrate was calculated by difference. Samples were analysed based on fresh matter. Moisture was determined by oven drying at 105˚C for 20 h. The protein content was estimated (nitrogen × 6.25) from quantitative analysis of nitrogen by using the Kjeldahl method. The fat was measured gravimetrically by extraction in diethyl ether and petroleum ether after acid hydrolysis. These analyses were carried out in triplicate.
2.4. Study Design
The protocol used was adapted from that described by Wolever et al. [12] and is in line with procedures recommended by the FAO/WHO [13]. Subjects tested the meals once each and the reference food (50 g glucose in 250 ml water, Glucose pur anhydre, COOPER, Place Lucien Anvert) three times in random order on separate days. 50 g of available carbohydrate for each test food sample was calculated from the results of the proximate analysis and the measured portion of the food was served to the subjects. The total amount served of each meal was adjusted to reach this level of carbohydrate. On the day prior to a test, subjects were asked to restrict their intake of alcohol and caffeine-containing drinks and to restrict their participation in intense physical activity (e.g. long periods at the gym, excessive swimming, running and aerobics). Subjects were also told not to eat or drink after 21 h the night before a test, although water was allowed, in moderation. The day of the test, subjects were studied in the morning after a 12 h overnight fast. After a fasting blood sample, subjects consumed the test meals in the laboratory in a randomized order at 1 - 2 week intervals. They were instructed to consume all the food served in a period of 15 min. All test meals and the reference food was served with 150 ml water. Further blood samples were taken at 15, 30, 45, 60, 90 and 120 min after starting to eat. Subjects remained sedentary during each session. Blood was obtained by finger-prick using the Glu-
Table 1. Processing and food preparation for the study.
colet 2 multipatient lancing system (Bayer Health Care). Blood glucose was measured using an automatic analyser (Ascensia Contours; Bayer Health Care).
2.5. Calculation of Glycemic Index and Glycemic Load
The GI was calculated using the method described by FAO/WHO [13] as the area under the blood glucose response curve of a 50 g carbohydrate portion of the test food expressed as a percent of the response to the same amount of carbohydrate from a standard food taken by the same subject. The area under the blood glucose response curve was calculated geometrically by applying the trapezoid rule [14]. When a blood glucose value falls below the baseline, only the area above the fasting level is included. The GI of each meal tested was taken as the mean (±s.e.m.) for the whole group. GI values were classified as high (70 - 100), intermediate (55 - 69), or low (<55) [15]. Glycemic Load for each food was determined by the method of Salmeron et al. [16]. In each individual glycemic load was calculated bay taking the percentage of the food’s carbohydrate content in a typical serving and multiplying it by its glycemic index value [17]. GL values were classified as low (≤10), medium (>10 to <20) or high (≥20) [18].
2.6. Statistical Analysis
Statistically significant differences between measurement parameters and samples were verified with one-way analysis of variance using the Statistical Product and Service Solutions Software (SPSS version 17.0, Chicago, USA). The Tukey’s honesty significant differences (HSD) multiple range tests used to determine the differences between group means at the 95.0% confidence level.
3. Results
3.1. Proximate Composition of Test Meals
The macronutrient composition of the test meals is presented in Table 2. Proximate composition showed that the fiber (11.9 ± 0.3 g) and fat (32.3 ± 0.0 g) content of cassava paste with granulates palm nut sauce were very much highest than those of pounded yam with eggplant sauce and rice with groundnut sauce. However, rice with groundnut sauce has the highest protein (15.8 ± 0.1 g) content of all three test foods.
3.2. Descriptive Characteristics
Ten healthy subjects were recruited are 7 men and 3 women with 20.5 ± 1.7 kg∙m−2 on average body mass index (BMI) and 28.5 ± 2.1 years on average age. Normal readings of the standard glucose used in the clinical chemistry analyser ranged from 4.0 - 6.4 mmol/L glucose. The initial blood glucose obtained from the normal subjects for all test foods did not exceed 6.0 mmol/L glucose (Table 3). No significant differences were observed between subjects for the fasting blood glucose (p > 0.05).
3.3. Blood Glucose Response, GI and GL of Test Meals
The mean blood glucose responses up to 120 min following ingestion of the three meals and glucose are shown in Figures 1, 2 and 3. Fasting blood glucose levels did not differ before the treatments. The blood glucose levels for both the pounded yam with eggplant sauce and rice with groundnut sauce were significantly lower at 15 min than the glucose (p < 0.05). At 30, 45, 60 min, only the rice with groundnut sauce was significantly lower than the glucose (p < 0.05). The reference food (glucose), pounded yam with eggplant sauce and cassava paste with granulates palm nut sauce showed significantly higher glucose responses compared to those of rice with ground-nut sauce (Area Under the Curve, AUC: mean ± s.e.m.; mmol × min/L: 83.8 ± 26.3 vs. 186.5 ± 60.5; 174.5 ± 56.0 and 159.4 ± 50.9 for rice with groundnut sauce, glucose, pounded yam with eggplant sauce and cassava paste with granulates palm nut sauce; p < 0.05, respectively, see Table 4). Although, pounded yam with eggplant sauce and cassava paste with granulates palm nut sauce blood glucose dynamics was increased, they did
Table 2. Nutrient composition of foods tested, per 50 g available carbohydrate portion.
Table 3. Descriptive characteristics of study participants at study entry*.
Figure 1. Glycemic profile (mmol/L) for 120 min after consumption of glucose (
) and pounded yam with eggplant sauce (
) tested in normal subjects (n = 10). Points at the same time interval and bars with different letters are significantly different (p < 0.05), data are mean ± s.e.m.
Figure 2. Glycemic profile (mmol/L) for 120 min after consumption of glucose () and cassava paste with granulates palm nut sauce (
) tested in normal subjects (n = 10). Points at the same time interval and bars with different letters are significantly different (p < 0.05), data are mean ± s.e.m.
Figure 3. Glycemic profile (mmol/L) for 120 min after consumption of glucose () and rice with groundnut sauce (
) tested in normal subjects (n = 10). Points at the same time interval with different letters are significantly different (p < 0.05), data are mean ± s.e.m.
not differ significantly from reference food (p < 0.05). GI data of the pounded yam with eggplant sauce, cassava paste with granulates palm nut sauce and rice with groundnut sauce were significantly different (p < 0.05) with 94 ± 4, 86 ± 1 and 45 ± 3 respectively (Figure 2). The GLs (mean ± s.e.m.; g) were 46.9 ± 1.9; 42.8 ± 0.7 and 22.6 ± 1.5 for the pounded yam with eggplant sauce, cassava paste with granulates palm nut sauce and rice with groundnut sauce respectively (Table 4). All test meals have a GL significantly different (p < 0.05).
4. Discussion
According to the official classification of GI [17], data showed that rice with groundnut sauce presented a favourable glycemic response, ranking as foods with a low GI (GI = 45).
The GIs of pounded yam with eggplant sauce and cassava paste with granulates palm nut sauce were high and ranging to 94 and 86 respectively. The American Dietetic Association (ADA) reviewed the evidence of glycemic index as a nutrition therapy intervention for diabetics and acknowledged that low glycemic index foods may reduce postprandial blood glucose levels and asserted that there is sufficient.evidence of long term benefit to recommend using low glycemic index diets as a primary strategy in meal planning [19]. On this base, the rice with groundnut sauce produces a lower increase of the plasma glucose concentration, as a result of slower rates of gastric emptying and digestion of carbohydrate in the intestinal lumen [12]. Data provides evidence that rice with groundnut sauce with low GI could be an ideal food for diabetic diets. So, rice with groundnut sauce releases gradually from glucose, which avoids an important “glycemic peak” and reduce the risk of diabetes mellitus. That appears on
Table 4. AUC, glycemic index/load and classification of tests foods.
the weakness of its hyperglycemic peak (6.5 ± 0.3 mmol/L at 45 min, Figure 3 Indeed, more gastric emptying is slowed down, more the waves of hypergly cemias postprandial are weak and absorption of carbohydrates set out again in time [20]. The GI value of rice with groundnut sauce is in the same order as those mentioned by Nientao et al. [21] which has showed low GI of rice (GI = 46). Besides, the values of the GI can vary according to the process of meals confection. For this purpose, Omoregie & Osagie [10] showed that the high GI (GI = 95) of food containing rice “Tuwo Shinkafa” is due to the rice which was crushed and cooked with water in order to obtain a pasta product. The glycemic response of pounded yam with eggplant sauce and cassava paste with granulates palm nut sauce showed that both foods raise blood glucose levels quickly and high. There are quickly converted into glucose, quickly digested and absorbed and in most cases a quick rise in insulin [22]. Hyperinsulinemia may also, over time, lead to insulin resistance via increases in the blood glucose concentration [7] and thereby increase the risk of type 2 diabetes and obesity [23]. GI data of these foods are similar to those of the “Tapioca”, (food based on cassava, GI = 81) [24] and lower than “N” gbô (food based on boiled yam, GI = 53 - 70) [5]. The difference on GIs of the three test meals was probably due to their biochemical composition. Indeed, GI of mixed meals is reduced by coingestion of protein, fiber or fat. The presence of large amounts of protein or fat may significantly reduce the glycemic response by increasing insulin secretion and slowing gastric emptying [25]. On this basis, the association of levels of fat, protein and fiber in foods provide contents of 20.2 g, 40.5 g and 50.1 g for the pounded yam with eggplant sauce, rice with groundnut sauce and cassava paste with granulates palm nut sauce respectively. In principle, the GI classification of foods should be: GI of pounded yam with eggplant sauce > GI of rice with groundnut sauce > GI of cassava paste with granulates palm nut sauce. This is not the case for the cassava paste with granulates palm nut sauce which have a high proportion of macronutrients, and GI high (GI = 86). This significant increase in the GI could be notably due to the carbohydrate fraction including physico-chemical characteristics of its starch.
Indeed, cassava paste with granulates palm nut sauce is the one that has the highest water content (396 ± 1.7%) among food (Table 2). As a result, the starch is gelatinized most. This high starch gelatinization has certainly inhibited the action of macronutrients and to increase the GI of the dish. Starch is more digestible, digestion is more rapid and high GI [5]. According to Mendosa [26], for a better control of glycemic response on diabetes mellitus management and its prevention, GI data must be associated to GL data. In this study, it’s appear that the GLs of foods were 47, 43 and 23 for pounded yam with eggplant sauce; cassava paste with granulates palm nut sauce and rice with groundnut sauce respectively. According to the official classification of GL [26], all the test meals have high GL (GL > 20 g). So, their consumption should be limited because they could increase the insulin response. Indeed, beyond the GL day labourer of 80 g, food can involve an important insulin secretion. And, more GL, the higher the food contains glycemic carbohydrate [26]. Therefore, rice groundnut sauce (GL = 23) is the food that has the highest low glycemic carbohydrate foods among the three tests. Thus, although all three tests foods can negatively influence health, rice with groundnut sauce would be the least aggressive to the body.
5. Conclusion
This study has provided GI and GL values for three common staple carbohydrate-rich foods in the Ivorian diet. The pounded yam with eggplant sauce and cassava paste with granulates palm nut sauce, which has high GI, and high GL are hyperglycemic foods these two (2) foods must be eaten in very small quantities. Rice with groundnut sauce is a low-GI food but its GL remains high. This meal, which seems to be advised to the diabetics diet must be consumed moderately. These data will serve as nutritional guidelines for the prevention and the management of diabetes mellitus in Côte d’Ivoire.
Acknowledgements
This work was financed within the Agricultural Productivity Program in West Africa (PPAAO/WAAPP 1B.) Don IDA N˚6260 CI et Don N˚TF 098014 CI by FIRCA (Fonds Interprofessionnel pour la Recherche et le Conseil Agricoles). In addition, the authors wish to thank Dr Abodo Jacko (Endocrinology and Diabetology Department; Universitary and Hospital Center of Yopougon, Abidjan) for his technical support and volunteers for their collaboration. We are grateful also for the helpful assistance of Yapi D. A., Gbakayoro J. B., Kroufie A., Degbeu C., Voho E. Alida Sandrine and Yapo G. Bruno.
Abbreviations and Acronyms
ADA: American Dietetic Association;
AOAC: Official Methods of Analysis;
AUC: Area Under the Curve;
BMI: Body Mass Index;
CHO: Carbohydrate;
FAO: Food and Agriculture Organization;
GI: Glycemic Index;
GL: Glycemic Load;
WHO: World Health Organization.
NOTES