Sunday, October 09, 2005

Diet-induced weight loss and cardiac autonomic nervous system - Obesity and Cardiac Factors

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Diet-induced weight loss and cardiac autonomic nervous system - Obesity and Cardiac Factors
Nutrition Research Newsletter, Oct, 2003

Severe obesity is associated with increased total mortality with a concomitant increased risk of sudden death. In the Framingham study, the risk of sudden cardiac death with increasing weight was encountered in both genders, and the annual sudden cardiac mortality rate in obese men and women was estimated at approx. 40 times higher than the rate of unexplained cardiac arrest in a matched nonobese population. Obesity and the cardiac autonomic system are intrinsically related. A 10% increase in body weight is associated with a decline in parasympathetic tone, accompanied by a rise in mean heart rate, and conversely, heart rate declines during weight reduction. This is of importance because increment in heart rate has been shown as a marker associated with increased mortality. Also, liquid protein diets have been associated with potentially life threatening arrhythmias Because elevated plasma free fatty acid (FFA) concentrations, which are often encountered in obesity, may play a role in arrhythmogenesis and there may be an association between FFA concentration and premature ventricular complexes (PVCs), it is of clinical importance to evaluate the impact of a high-fat (HIF) diet on autonomic cardiac modulation and arrythmogenicity in severe obesity after weight loss.

Because a diet rich in carbohydrates is associated with decreased FFAs, the purpose of the present study was to evaluate the influence of an HIF and high-carbohydrate (HC) diet regimen on both cardiac autonomic nervous system modulation and the presence of arrhythmias in reduced-obese individuals. Eight severely obese subjects (BMI greater than or equal to 40 kg/[m.sub.2]) underwent a three-month weight loss program followed by a three-month reduced-weight maintenance regimen. Thereafter, each subject was admitted for an inpatient period of 17 days on two separate occasions. A high-carbohydrate (60%) or high-fat (55%) diet of appropriate energy content for weight maintenance was prescribed during each inpatient phase. Heart rate variability was derived from a 24-hour Holter monitoring system in all subjects during their inpatient stay. Cardiac Holter monitoring was performed at three occasions, including the 2nd night of a two overnight calorimetry chamber stay.

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After the diet regimen, there was a 10% decrease in weight. There was no significant change in systolic and diastolic blood pressure, arrhythmias, glucose, insulin, total cholesterol, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, respiratory exchange ratio, and resting energy expenditure between experiments. Mean heart rate was lower after weight loss compared with baseline. After weight loss, there was an increase in the parasympathetic indices of heart rate variability showing and increase in cardiac vagal modulation.

The findings of the present study suggest that weight loss is associated with significant improvement in autonomic cardiac modulation through enhancement of parasympathetic modulation, which clinically translates into a decrease in heart rate.

P Poirier, T Hernandez, K Weil, T Shepard, R Eckel. Impact of Diet-Induced Weight Loss on the Cardiac Autonomic Nervous System in Severe Obesity. Obes Res 11(9):1040-1047 (September 2003). [Correspondence: Paul Poirier, Associate Professor of Pharmacy, Institut Universitaire de Cardiologie et de Pneumologie, Laval Hosptial, 2725 Chemin Sainte-Foy, Sainte-Foy. Quebec, Canada, GIV 4G5. E-mail: Paul.Poirier@crhl.ulaval.ca]

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