Effect of a moderately energy- and salt-reduced diet on body compartments and blood pressure control in obese men with mild hypertension.

Ten middle-aged moderately obese men with untreated mild hypertension were studied during a 6-week weight maintenance period and a 9-week period on a diet containing 5 MJ when body mass decreased by 8.4 kg (SE 1.4). According to urinary sodium excretion there was a mean reduction of 89 mmol/day (SE 16) in sodium intake. Mean arterial pressure fell by 2.5 to 14.1 mmHg (95% confidence interval) which was correlated to the reduction of body mass. The sympathetic nervous activity diminished with decreasing noradrenaline excretion and heart rate. There were no changes in the renin-aldosterone system. Estimation of the body composition with a four-compartment model utilizing determinations of body mass, total body potassium and total body water (TBW) showed reductions of body fat (8.4 kg (SE 1.4] and body cell mass (BCM) (2.4 kg (SE 0.6], but not of TBW. Extracellular water (ECW) increased significantly as judged from ECW/BCM calculations. Plasma volume was determined by Evan's blue and did not change significantly. We suggest that the observed changes in body composition represent one aspect of the adjustment to a weight reducing diet, while blood pressure is lowered by another mechanism in the adaptive response to dieting, i.e. reduction in sympathetic nervous activity.