Nutritionally-induced changes in parasympathetic function

It is possible to quantify the input of the parasympathetic nervous system to heart rate variability in man by the spectral analysis of heart rate variability. This is done by noninvasive, computerized electrocardiography over several minutes of observation. Earlier studies from this laboratory demonstrated that when body weight of obese or nonobese subjects is increased 10% or decreased below usual body weight, there are accompanying changes in autonomic function, as measured by alterations in heart rate variability. The clearest of these changes is an abrupt decline in parasympathetic function with increase in body weight, and an increase in parasympathetic activity as body weight declines, and when new, lower body weights are maintained. Recently, it has been possible to examine this phenomenon by a pharmacologic dissection of the autonomic input to heart rate variability. The separate input of each branch of the nervous system to cardiac variability, as well as the intrinsic heart rate, is measured by this approach. The subjects studied to date have been few, but there is confirmation of a major change in parasympathetic function with weight alteration whereas sympathetic changes are small.