Acute Fasting Increases Vagal Tone and Reduces Ambulatory Arterial Pressure

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Department of Kinesiology and Integrative Physiology


Obesity is a chronic metabolic disorder associated with increased risk of cardiovascular disease, and intermittent fasting might mitigate risk. Intermittent fasting creates a negative energy balance that results in weight loss, but the cardiovascular benefits of fasting have not been studied thoroughly. The purpose of this study was to investigate the influences of an acute 24-hr fast on cardiovascular control and hemodynamics. Ours was a randomized, crossover design with autonomic testing occurring 3-hrs postprandial (fed) and 24-hrs postprandial (fast). A standardized meal was provided for both conditions. 24-hrs before autonomic testing participants wore an ambulatory blood pressure (ABP) cuff which recorded 3 brachial pressures per hr during the day and 2 pressures per hr at night. 24-hour ABP was averaged and compared via a paired t-test (N=17, 6 Female; fed vs. fasted). 3 participants did not meet inclusion criteria of at least 20 valid day and 7 valid night recordings. Twenty young (23±0.7 yrs), normotensive, non-obese (25±0.8 BMI), participants completed the autonomic test. We measured blood glucose (GLU), ketones (β-OHB), and triglycerides (TRG) to confirm a successful fast. With subjects in a supine position during the autonomic test, we recorded the ECG and beat-to-beat arterial pressure (finger plethysmography). Cardiovagal baroreflex sensitivity (cvBRS) was determined by beat-to-beat changes in R-R interval (RRI) and systolic pressure (SAP) using the sequence method. Only sequences with linear r values >0.7 were accepted (cvBRS-up N=18; cvBRS-down N=20). Spectral analysis was used to assess heart rate variability. The high frequency (HFnu; 0.15-0.40 Hz) and low frequency (Lfnu; 0.04-0.15 Hz) components were normalized to total power. Subjects rested quietly for 10 min while breathing in time to a computer display prompting them to breathe at a frequency of 15 breaths/min. The last 8 min of the autonomic test were averaged and compared via a paired t-test (N = 20, 7 Female; fed vs. fasted). Data are expressed as mean±SE. P-values ≤ 0.05 were considered significant and are indicated by an asterisk (*). Changes in TRG, GLU and β-OHB with fasting were consistent with expectations: TRG and GLU decreased (TRG; 114±11 fed vs. 68±6* mg/dL fast)(GLU; 99±3 fed vs. 80±2* mg/dL fast), and β-OHB increased (β-OHB; 0.13±.03 fed vs. 0.57±.12* mmol/L fast). Overall SAP and diastolic (DAP) ABP decreased in the fasted condition (SAP;111±1.5 fed vs. 109±1.5* mmHg fast) (DAP; 66±1.4 fed vs. 64±1.5* mmHg fast). During the autonomic test, RRI, cvBRS-up, cvBRS-down, and HFnu increased, and LFnu decreased in the fasted condition. (RRI; 991±35 fed vs. 1053±45* ms fast)(cvBRS-up 19.5±3 fed vs. 26.4±6* ms/mmHg fast) (cvBRs-down; 15.3±1 fed vs. 21.5±3* ms/mmHg fast) (HFnu; 54.4±3 fed vs. 61.4±4* a.u. fast) (LFnu; 45.6±3 fed vs. 38.6±3* a.u. fast). Our results suggest that acute fasting may convey cardioprotective benefits through enhanced vagal tone and reduced 24-hr ambulatory arterial pressure.

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The FASEB Journal Physiology