Non-linear assessment of heart rate variability in ovo-lactovegetarians, vegans and omnivores during oral glucose tolerance test

Abstract

Although the health benefits of vegetarian diets have been well documented, the exact mechanisms of health benefits of vegetarian diets on the cardiovascular system remain unclear. Autonomic nervous system (ANS) activity is influenced by food ingestion. Carbohydrate but not fat or protein ingestion affects the cardiac ANS by increasing the sympathetic activity. In this study we aimed to investigate the cardiac ANS activity in 7 ovo-lactovegetarians, 8 vegans and 5 omnivores by means of heart rate variability (HRV) non-linear (Poincaré plot and fractal dimension - FD) analysis. Heart rate (HR) was recorded continuously at baseline and during oral glucose tolerance test (OGTT-75 gr of glucose) (90 min) by using Polar S810 HR monitor. The series of consecutive R-R interval (tachogram) in function of beat numbers was extracted, linearly interpolated and resampled at 2 Hz for further processing. Non-linear parameters of HRV were calculated at baseline and during OGTT. This study demonstrated in all three groups, both at baseline and during the OGTT, a similar value of RR interval as well as a not significant difference of FD, which is considered as a possible indicator of complexity of inputs to HR controllers. On the contrary, the Poincaré plot analysis revealed, both at baseline and during the OGTT, a difference in the SD1 and SD2 parameters values, comparing omnivores to vegetarians and vegans, with the highest values in omnivores. At baseline and during the OGTT (30 min) the SD1 and SD2 parameters in normalized units (n.u.) as well as the SD1/SD2 ratio, as expression of vagosympathetic balance, were statistically different between omnivores and vegans. In conclusion, non-linear Poincaré plot analysis suggested a different cardiac ANS function in vegans and ovo-lactovegetarians in comparison to omnivores at baseline as well as during the OGTT. © 2008 Springer-Verlag.