The postprandial blood glucose concentration : as influenced by some changes in type and amount of carbohydrate in the meal and by post meal slow walking

Abstract

Background The burden of obesity, type 2 diabetes (T2D) and cardio-vascular diseases (CVD) is rapidly increasing worldwide. Impaired glucose tolerance (IGT), in which the blood glucose level is higher than normal but not as high as in diabetes, is also a major public health problem. People with IGT have a higher risk of developing T2D and CVD, and especially the magnitude and duration of the postprandial blood glucose concentration (PPG) seems of crucial importance. In Norway, immigrants from Pakistan have a high prevalence of T2D, especially women. The International Diabetes Federation (IDF) suggests that reducing PPG is important for achieving HbA1c goals, probably even more important than control of the fasting level. IDF further states that there is a progressive relationship between plasma glucose levels and CVD risk well below the diabetic threshold. Thus, reducing the post meal glucose levels could be important for T2D/CVD prevention. Therefore, it seemed of interest to study to what extent moderate meal changes would influence PPG in a group of diabetes prone female Pakistani immigrants. Since previous studies in healthy ethnic Norwegians had shown a PPG-blunting effect of light post meal physical activity, we wondered if the very low intensity activity (slow walking) usually practised by these women, would have a similar effect.

Aim The main aim of this thesis was to investigate the extent to which moderate variations in the amount and type of carbohydrates in a meal, and post meal slow walking, might acutely modify the PPG in female Pakistani immigrants living in Oslo, Norway.

Method Applying a cross-over design, 31 female Pakistani immigrants living in Oslo were recruited from participants of the completed InnvaDiab Study to participate in experiments where their blood glucose concentration was measured every 15 min for 2h after intake of various amounts and types of a carbohydrate food, either while resting after the meal or doing very light post meal walking of two durations. The carbohydrate rich meals included three different types of bread (regular bread, and pea fibre enriched bread with two levels of rapeseed oil), cornflakes with milk, and chick peas with onion and tomato.

Results Intake of an amount of pea fibre enriched bread containing 25 g CHO attenuated the postprandial peak glucose value (PV, p<0.05), the Incremental Area Under the glucose vs. time Curve (IAUC, p<0.05) during 15 to 75 min, the glycemic profile (GP, p<0.05), and increased the duration of satiety (p<0.05), as compared with intake of regular bread with 25 g CHO. There was no difference between fibre enriched bread with or without rapeseed oil in PV, Incremental peak value (IPV) or IAUC. Satiety ratings after intake of 25 g CHO in regular coarse bread was 7-23 % lower than corresponding ratings after intake of 25 g CHO in the fibre enriched breads at all observation time points from 60 to 120 min (p < 0.05 for all time points). A sustained elevated PPG was found after intake of cornflakes providing 75g available CHO. When reducing the cornflake intake to obtain 25g CHO we found reductions in PV of 11% (p=0.008) and IAUC of 51% (p=0.003). IAUC was reduced by 40% (p=0.001) in response to halving the amount of bread. PPG was also appreciably lowered after intake of 50g CHO given as cooked chick peas spiced with tomato and onion, compared to the same amount of available CHO as corn flakes with milk. Change to chick pea type of CHO resulted in a 15.7% reduction in PV (p=0.0001), and 50.9% reduction in IAUC (p=0.0001), and increased the time to reach PV (TTP), on average by 20 min (p=0.006), and the glycaemic profile (GP) by 73.5% (p=0.002). The order of post meal blood PV to one CHO type (amount) corresponded well with the response order to another CHO type (amount) (r>0.9, p<0.001). When resting after intake of 50g CHO, the blood glucose concentration increased during the first 30 to 45 min, reaching a maximum value of 9.1 mmol/L after 45 min Then the glucose concentration decreased but was still about one mmol/L higher that at baseline at the end of the experiment, i.e. at 2h. When 20 min very slow post meal walking was performed after intake of the same meal the mean PV was lowered by 8.2% (NS), and time to reach the PV was delayed, on average by 19 min (p=0.002). These effects of walking were strengthened when the postprandial walk was increased to 40 min. In this latter experiment the time to reach PV from zero time (TTP) was delayed by 25 min (p=0.001) and the PV was lowered by 16.3% (p=0.001). Additionally, after postprandial walking, the blood glucose concentration approached baseline levels after 2h. A significant reduction (p<0.05) in systolic blood pressure (SBP), but not diastolic blood pressure, was observed in response to 40 min postprandial walking as compared with resting after the meal.

Conclusion In diabetes prone subjects the PPG can be appreciably blunted both by reducing the quantity and changing the quality of the ingested carbohydrates, and by light post meal walking. The study suggests that there are “high- and low responders” to a carbohydrate load, below the blood glucose threshold indicating diabetes.