background: Furosemide inhibits the sodium potassium chloride cotransporter (NKCC2) in the thick ascending limb of the loop of Henle and increases urinary water and sodium excretion. This study investigates the effect of furosemide on body composition estimated with multifrequency bioimpedance spectroscopy (BIS) technique and urinary proteins from NKCC2. methods: This study is a randomized, placebo-controlled, crossover study where healthy subjects received either placebo or 40?mg furosemide on two separate occasions, where body composition with BIS, renal function, proteins from tubular proteins that mediate sodium and water transport, and plasma concentrations of vasoactive hormones were measured before and after intervention. results: We observed an expected increased diuresis with a subsequent reduction in bodyweight of (-1.51?±?0.36?kg, p?