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Effects of Dietary Weight Loss on Sympathetic Activity and Cardiac Risk Factors Associated with the Metabolic Syndrome

Laboratories of Cardiovascular Nutrition (N.E.S., P.J.N.) and Human Neurotransmitters (E.A.L., G.W.L., K.M., M.D.E.), Baker Heart Research Institute, Melbourne, Victoria 8008, Australia

Address all correspondence and requests for reprints to: Dr. Nora E. Straznicky, Cardiovascular Nutrition Laboratory, Wynn Domain, Baker Heart Research Institute, P.O. Box 6492, St. Kilda Road Central, Melbourne, Victoria 8008, Australia. E-mail: nora.straznicky{at}baker.edu.au.

Context: Weight reduction, the first line treatment for the metabolic syndrome, improves insulin sensitivity and associated metabolic and cardiovascular abnormalities, but there is a paucity of data regarding its effect on sympathetic nervous system (SNS) activity in this clinical setting.

Objectives: The objectives of this study were to test the hypothesis that dietary weight loss attenuates both insulin resistance and SNS activity and to examine the relationships between SNS activity and metabolic syndrome (MetS) components.

Design: This was a single-sample, repeated measures design study.

Setting: This study was performed at a tertiary referral center.

Participants: Twenty-three MetS subjects (age, 58 ± 2 yr; body mass index, 33.3 ± 0.8 kg/m²; mean ± SEM) were studied.

Intervention: A hypocaloric modified Dietary Approaches to Stop Hypertension diet (26% fat, 22% protein, and 51% carbohydrate; 100 mmol/d sodium) was consumed for 3 months.

Main Outcome Measures: The main outcome measures were postganglionic muscle sympathetic nerve activity (microneurography at a peroneal nerve), whole-body plasma norepinephrine spillover rate, spontaneous cardiac baroreflex function, and insulin sensitivity.

Results: The hypocaloric diet significantly reduced body weight by 7% and improved all MetS components. Norepinephrine spillover decreased from 877 ± 180 to 503 ± 39 ng/min (P = 0.005), and muscle sympathetic nerve activity decreased from 40.6 ± 2.1 to 34.6 ± 2.4 bursts/min (P = 0.01), whereas cardiac baroreflex sensitivity increased by 23.0 ± 8.0% (P = 0.02). The change in the norepinephrine spillover rate correlated positively and independently with the change in plasma leptin concentration (r = 0.49; P = 0.03).

Conclusion: Weight loss by a hypocaloric diet with moderate sodium restriction diminishes SNS activity in MetS subjects. This may be due to the consequences of decreased leptin concentration, enhanced insulin sensitivity, or improvements in cardiac baroreflex function.

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