title: Effects of high-carbohydrate and high-fat dietary treatments on measures of heart rate variability and sympathovagal balance.
abstract: OBJECTIVE
  We tested the hypothesis that respiratory quotient (RQ) determines sympathovagal balance associated with metabolism of stored and dietary energy substrates.
  
  
  METHODS
  Six 18-20 year-old African-American males were studied after two control pretreatments of fasting and post-treatments of metabolizing high-fat and high-carbohydrate beverages. RQ, heart rate (HR), energy expenditure (EE) and blood pressure (BP) were recorded at rest and repeated 1 h-3 h after ingesting isocaloric high-carbohydrate and high-fat beverages. Sympathovagal modulation of HR was quantified by the low frequency/high frequency (LF/HF) ratio from fast Fourier transform (spectral) analysis of the electrocardiogram RR intervals during paced breathing at 0.2 Hz. Significance of differences of peak post-treatment values from controls was evaluated by analysis of covariance and of correlations by linear regression at P<0.05.
  
  
  RESULTS
  The high-carbohydrate and high-fat treatments increased RQ, EE, HR and LF/HF with significant interactions between covariates. LF/HF values were not significant after eliminating covariance of RQ, EE and HR for the control vs. high-fat and for the high-fat vs. high-carbohydrate and after eliminating covariance of EE and HR for the control vs. high-carbohydrate treatments. Across the RQ values, correlations were significant for EE and LF/HF.
  
  
  CONCLUSIONS
  These findings imply that high RQ and sympathetic modulation produced by metabolizing carbohydrate is associated with high resting energy expenditure. We conclude that respiratory quotient may be an important determinant of the LF/HF ratio in the heart rate variability spectrum, likely, by a respiratory chemosensory mechanism.
authors.affiliation: Department of Physiology & Biophysics, Howard University Graduate School of Arts & Sciences, Washington, DC 20059, United States. rmillis@howard.edu
authors.forename: Richard M
authors.initials: RM
authors.lastname: Millis
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Austin
authors.forename: Vernon
authors.initials: V
authors.lastname: Bond
authors.forename: Mezbah
authors.initials: M
authors.lastname: Faruque
authors.forename: Kim L
authors.initials: KL
authors.lastname: Goring
authors.forename: Brian M
authors.initials: BM
authors.lastname: Hickey
authors.forename: Raymond
authors.initials: R
authors.lastname: Blakely
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Demeersman
mesh_terms: D000293:Adolescent; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D004041:Dietary Fats / Q000008:administration & dosage*; D004734:Energy Metabolism / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D008297:Male; D013564:Sympathetic Nervous System / Q000187:drug effects* / Q000502:physiology; D014630:Vagus Nerve / Q000187:drug effects* / Q000502:physiology; D055815:Young Adult
chemical_list: D004040:Dietary Carbohydrates; D004041:Dietary Fats