Effect of a 24-hour food-and-water fast on viscosity of whole blood and plasma.

As a result of abstaining from food and water for 24 h during the midsummer Tishah-b'Ab fast, blood viscosity increased by 16.5% in 27 subjects studied; plasma viscosity increased by 10.3% in nine; hematocrit, by 3.1% in 27; serum total protein, by 6.3% and albumin, by 7.7%, both in 29 subjects. These changes were statistically significant. Plasma fibrinogen did not increase significantly. Fasting-induced changes could impair blood supply to vital organs in patients with vascular insufficiency.