Effects of exercise on cardiovascular disease risk markers in South Asian versus White European men

Globally, cardiovascular disease (CVD) is a major cause for morbidity and mortality. Exaggerated postprandial lipaemia has been implicated in the development of atherosclerosis, and by lowering postprandial triacylglycerol (TAG) concentrations, atherogenic progression may be delayed. Many studies have revealed that exercise, in particular acute exercise, can attenuate postprandial TAG concentration. Most of this evidence relates to studies conducted in Western participants. South Asians are a population predisposed to CVD, and their adverse lipid profiles and physical inactivity may be among the underlying reasons. Hence, the studies described in this thesis examined the potential of acute bouts of exercise to favourably modify postprandial lipaemia and other CVD risk markers in young, healthy, South Asian men. The first experimental study described in this thesis compared the effect of 60 minutes of brisk walking on postprandial TAG concentration in 15 South Asian and 14 White European men. Trials were conducted over two days with exercise (or rest) taking place on day 1 and postprandial testing on day 2. A key finding from this study was that postprandial TAG, glucose and interleuklin-6 (IL-6) concentrations were elevated in South Asian compared with White European participants after consumption of high fat meals. This study also revealed a non-significant trend for brisk walking to reduce postprandial TAG concentrations in response to high fat meals in both groups. The second experimental study reported here examined the effect of 60 minutes of treadmill running at 70% of max on postprandial lipaemia and other CVD risk makers on the next day in 10 South Asian and 10 White European men. A significant main effect of trial was shown for postprandial TAG, IL-6 and soluble intercellular adhesion molecule-1 (sICAM-1), showing that TAG and IL-6 concentrations were lower on the exercise trial while sICAM-1 concentrations were higher on the exercise trial. In addition, ethnic group differences were observed for postprandial TAG, glucose and insulin concentrations indicating higher values in South Asians than White Europeans. A significant trial by group interaction effect was also observed for TAG, indicating a greater decrease after exercise in the South Asian men than the European men. In the third experimental study in this thesis the effect of 30 minutes of treadmill running on one day was compared with running for 30 minutes on three consecutive days in 11 South Asian men with regards to postprandial lipaemia. Neither a single bout of running nor three consecutive days of running influenced postprandial TAG in response to high fat meals when compared with the response on a control trial. It is not clear why exercise was ineffective in reducing postprandial lipaemia in this study but possibly the energy expenditure of exercise was insufficient to elicit change. The final experimental chapter described in this thesis combined the data from the first three studies. The objective of this chapter was to enhance the sample size in an effort to clarify the effects of acute exercise and to clarify the effects of ethnic group with respect to several fasting and postprandial CVD risk markers. The key findings were: 1) fasting and postprandial TAG and postprandial glucose concentrations were significantly reduced by exercise; 2) There were significant main effects of ethnic group for fasting high density lipoprotein cholesterol (HDL-C), total cholesterol/ HDL-C, IL-6 and systolic blood pressure (SBP), indicating lower values of HDL-C and SBP and higher values of total cholesterol/HDL-C and IL-6 in South Asian participants. Additionally, there were significant main effects of ethnic group for postprandial TAG and IL-6 indicating higher values in South Asian participants. Taken together, these data indicate that South Asians have an adverse CVD risk factor profile in comparison with White Europeans and this may explain, at least in part, their elevated risk of CVD. Importantly, the data produced within this thesis show for the first time that acute bouts of exercise can be effective for lowering postprandial plasma TAG concentrations in South Asians, at least transiently. Thus, exercise has the potential to serve as a non-pharmacological medicine in South Asians

Exercise and coronary heart disease risk markers in South Asian and European men

PURPOSE: South Asians have a higher than average risk of coronary heart disease. The reasons for this are unclear but physical inactivity and/or poor responsiveness to exercise may play a role. This study compared the effect of prior exercise on postprandial triacylglycerol (TAG), glucose, insulin, interleukin-6 (IL-6) and soluble intercellular adhesion molecule-1 (sICAM-1) concentrations in South Asian and European men. METHODS: Ten healthy South Asian men (i.e. nine Indian men and one Pakistani man) and 10 healthy European men aged 20 to 28 years completed two, 2-day trials (exercise and control) in a randomised-crossover design. On the afternoon of day 1 of the exercise trial, participants ran on a treadmill for 60 minutes at approximately 70% of maximal oxygen uptake. Participants rested on day 1 of the control trial. On day 2 of both trials participants rested and consumed high fat (57% of energy content) test meals for breakfast (0 h) and lunch (4 h). Fourteen venous blood samples were collected from a cannula between 0 h and 9 h for metabolic measurements. RESULTS: Three-way ANOVA identified higher (P < 0.05) postprandial TAG and insulin concentrations in South Asian versus European men. Exercise lowered postprandial TAG and IL-6 and elevated sICAM-1 concentrations. An interaction effect indicated a greater decrease (22 versus 10%) in TAG area under the concentration versus time curve after exercise in South Asian than European men. CONCLUSIONS: Postprandial TAG and insulin responses to high fat meals were elevated in these South Asian men but acute exercise was equally if not more effective for reducing postprandial lipemia in South Asian than in European men

The effect of prior walking on coronary heart disease risk markers in South Asian and European men

Purpose: Heart disease risk is elevated in South Asians possibly due to impaired postprandial metabolism. Running has been shown to induce greater reductions in postprandial lipaemia in South Asian than European men but the effect of walking in South Asians is unknown. Methods: Fifteen South Asian and 14 White European men aged 19-30 years completed two, 2-d trials in a randomised crossover design. On day 1, participants rested (control) or walked for 60 min at approximately 50% maximum oxygen uptake (exercise). On day 2, participants rested and consumed two high fat meals over a 9h period during which 14 venous blood samples were collected. Results: South Asians exhibited higher postprandial triacylglycerol (geometric mean (95% confidence interval) 2.29(1.82 to 2.89) vs. 1.54(1.21 to 1.96) mmol·L-1·hr-1), glucose (5.49(5.21 to 5.79) vs. 5.05(4.78 to 5.33) mmol·L-1·hr-1), insulin (32.9(25.7 to 42.1) vs. 18.3(14.2 to 23.7) μU·mL-1·hr-1) and interleukin-6 (2.44(1.61 to 3.67) vs. 1.04(0.68 to 1.59) pg·mL-1·hr-1) than Europeans (all ES ≥ 0.72, P≤0.03). Between-group differences in triacylglycerol, glucose and insulin were not significant after controlling for age and percentage body fat. Walking reduced postprandial triacylglycerol (1.79(1.52 to 2.12) vs. 1.97(1.67 to 2.33) mmol·L-1·hr-1) and insulin (21.0(17.0 to 26.0) vs. 28.7(23.2 to 35.4) μU·mL-1·hr-1) (all ES ≥ 0.23. P≤0.01), but group differences were not significant. Conclusions: Healthy South Asians exhibited impaired postprandial metabolism compared with White Europeans, but these differences were diminished after controlling for potential confounders. The small-moderate reduction in postprandial triacylglycerol and insulin after brisk walking was not different between the ethnicities