Reduced dietary fat intake increases parasympathetic activity in healthy premenopausal women

1. Hypercholesterolaemia has been associated with decreased heart rate variability, a measure of cardiac parasympathetic activity. However, the effect of perturbation of the lipid profile on autonomic function has not been examined systematically. 2. The effects of short-term dietary lipid modification on autonomic function are studied in 25 normotensive, non-smoking, premenopausal women with normal bodyweight. Subjects consumed either a low (L, 25%) or high fat (H, 40%) diet for 2 weeks in an open, randomized, cross-over manner with a 2 week washout. 3. Baroreflex sensitivity was determined by gating beat-to-beat heart period (RR) interval and continuous non-invasive blood pressure recordings. Heart rate variability measures of cardiac parasympathetic nervous system activity were obtained in the time (standard deviation of RR intervals, root mean square of successive differences (rMSSD)) and frequency (high frequency power) domains. All assessments were made at the same timepoint in the menstrual cycle. 4. Both low-density lipoprotein-cholesterol and high-density lipoprotein-cholesterol decreased significantly (P < 0.05) with increased dietary fat intake (H, 2.7 +/- 0.1 vs L, 2.2 +/- 0.1; H, 1.3 +/- 0.1 vs L, 1.1 +/- 0.1 mmol/L, respectively) as did mean arterial pressure (H, 78.1 +/- 1.5 vs L, 74.3 +/- 1.5 mmHg). Weight was unchanged by dietary lipid intake (H, 62.6 +/- 8.5 vs L, 62.3 +/- 8.3 kg, P = NS). 5. There was a significant increase in rMSSD (H, 29.6 +/- 3.4 vs L, 38.8 +/- 6.4 msec, P < 0.05) and natural logarithm of high frequency power following low fat diet (H, 4.4 +/- 0.2 vs L, 4.8 +/- 0.3 msec2, P = 0.01). Baroreflex sensitivity also increased following the low fat diet (H, 13.91 +/- 2.2 vs L, 16.9 +/- 3.2 msec/mmHg, P = 0.23). 6. Short-term dietary lipid modification can significantly increase cardiac parasympathetic nervous system activity in healthy premenopausal women. These changes in autonomic status appear to be independent of changes in bodyweight and may be of clinical relevance considering the prognostic implications of heart rate variability in cardiovascular disease.