Effect of variable high fat diets on heart rate variability and selected modifiable cardiovascular risk factors.

Abstract

Background: Cardiovascular diseases are on the rise particularly in developing countries and multiple factors are responsible this alarming trend. Non-ideal dietary fats adversely affect the traditional cardiovascular risk factors. However, the effect on recently described cardiovascular (CV) risk factors like heart rate variability (HRV) is less studied. Unlike in the developed world, the effect of the variable locally consumed cooking fat types on CV risk profile are unexplored thus excluding a major avenue for intervention. Objectives: The aim of the present study was two-fold. Firstly, to determine the effect of variable high fat diets on HRV and selected modifiable CV risk factors. Secondly, to determine the chemical compositions of three locally available cooking fat types. Design: Experimental design. Setting: Department of Medical Physiology, University of Nairobi, Kenya. Study Animals: Male and Female Wistar rats aged 4-6 weeks. Methods: After acclimatization, forty animals will be divided into four groups to constitute the control(C) group and experimental groups 1(E1), 2 (E2) and 3 (E3). The control group will be fed on regular rat diet for 6 weeks. Fat enrichment (20%) of rat diet was prepared using locally sourced sunflower oil, palm oil and ghee and fed to groups E1, E2 and E3 respectively. Measurement of ECG, systolic blood pressure (SBP), fasting blood glucose and plasma lipid profile was done at baseline, and at three and six weeks. Fatty acid composition of the three fat types used will be determined using gas chromatography mass spectrometry (GC-MS). The experimental data were expressed as Mean +/- SD and analysed using repeated measures ANOVA. Significance level set at p < 0.05. Results: All groups were similar in characteristics at baseline. Six weeks later, E1 had lower BMI levels (p = 0.026) having recorded the least percentage weight gain (p = 0.017). Groups E1 and E3 demonstrated higher HRV as measured by RMSSD (p = 0.006). Similar differences were noted with NN20 (p = 0.04), NN50 (p = 0.04) and NN100 (p < 0.001). The HRV was inversely correlated with the heart rate (r = -0.654, p< 0.001) and the QTc interval (r = -0.681, p < 0.001). On evaluation of ECG parameters, E1 and E3 recorded shorter P wave durations (p < 0.05), PR intervals (p < 0.05) and QTc (p < 0.01). Moreover, E1 and E3 had smaller P wave amplitudes (p < 0.01) but larger Q wave amplitudes (p < 0.01). The groups were similar with regard to the QRS intervals and R, S and T wave amplitudes. For SBP, E2 and E3 ahd higher recordings (p < 0.01). No statistical differences were noted in the fasting blood glucose measurements. Experimental group 2 had statistically higher fasting plasma LDL-cholesterol (p < 0.01) and total cholesterol (TC) (p < 0.01). No statistical differences were noted in HDL, TGs and TChol/HDL ratio. Fat analysis by GC_MS showed sunflower oil had more unsaturated fatty acids than palm oil (72 μg/mg vs. 50 μg/mg). They both contained significant amounts of cholesterol (21.3 μg/mg vs. 5.8 μg/mg respectively) and TFA (70.8 μg/mg vs. 47.3 μg/mg respectively). Ghee contained highest levels of cholesterol (126.4 μg/mg), SFA (2836 μg/mg) and TFA (107.2 μg/mg). Conclusion: Heart rate variability, a marker of autonomic influence on the heart, is reduced by palm oil containing cooking fat. Sunflower oil not only maintains good HRV but also results in lower weights and BMI measurements, a shorter QTc on ECG, lower SBP measurements and lower LDL and total serum cholesterol levels. Despite having an otherwise good cardiovascular profile, ghee resulted in higher weight gain, BMI and SBP. Promotion of healthier cooking oil would result in good HRV and a better overall cardiovascular risk profile.