The effect of modified fasting on blood pressure and sympathetic activity: a correlation?

The effect of a low calorie diet (200 kcal/0.8 MJ) composed of 50 per cent glucose and 50 per cent protein was studied on blood pressure and sympathetic activity in eight normotensive obese subjects. The study lasted 21 days; during the first seven days (period I) a weight maintaining diet was given; this was followed by 14 d (period II) of modified fasting (200 kcal/0.8 MJ). Sodium and potassium intakes of 20 and 80 mmol per d respectively were maintained constant throughout the study. In period I blood pressure decreased slightly until day 5; this occurred concomitantly with a marked natriuresis. Thereafter blood pressure and sodium excretion remained stable. No significant change was observed in the urinary excretion of total catecholamines, noradrenaline and 4-hydroxy-3-methoxy mandelic acid. From the start of period II blood pressure decreased markedly, together with a significant decrease in the urinary excretion of the catecholamines and 4-hydroxy-3-methoxy mandelic acid. Both blood pressure and urinary excretion of catecholamines and 4-hydroxy-3-methoxy mandelic acid stabilized after day 7 of period II. These changes preceded the maximal sodium diuresis of severe calorie restriction. The results suggest a primary role for the sympathetic system in the hypotensive effect of short term calorie deprivation although some influence of natriuresis cannot be excluded.