AbstractThe present study was undertaken in an attempt at unravelling the mechanisms involved in alteration of water and electrolyte balance occurring in the obese during fasting and refeeding. After a short control period, 8 obese patients were submitted to total fasting for 7 days, after which they received 200 g glucose orally in 1 dose each morning for 3 consecutive days. The intake of sodium and potassium was kept constant throughout.Body weight reduction during fasting was far in excess of what could be ascribed to negative caloric balance, on account of fluid and sodium chloride losses. Conversely, carbohydrate refeeding was associated with sodium chloride and water retention.Urinary sodium excretion exceeded intake during fasting despite the fact that aldosterone secretion rate (ASR) almost doubled, rising from 160 to 280 μg/24 h. After aldosterone was administered i.v. over 3 hours on the penultimate day of fasting, sodium excretion dropped from 62 to 22 mEq/24 h. Cortisol levels in plasma and urine remained normal during fasting.Unlike what was seen before the fast, glucose administration after 7 days without food resulted in a prompt decrease in sodium (from 34 to 6 mEq/24 h) and potassium (from 48 to 17 mEq/24 h) excretion; ASR and Cortisol values did not change appreciably at that time. Bicarbonate administered in order to correct the acidosis resulting from starvation, failed to reverse the negative sodium balance.After the fast, a marked deterioration of glucose tolerance was observed, despite an excessive insulin response, since plasma immunoreactive insulin levels at 3 hours were 2.5 times higher than those obtained during the control period.The hypothesis is raised that the accompanying sodium retention might be, at least in part, due to this increased insulin secretion