Diabetes mellitus: It is caused due to insulin deficiency or hyperfunctioning of beta cells of Islets of Langerhans of the pancreas. Urine is sweet to taste (glycosuria) due to the presence of sugar. Due to the presence of sugar, there is a failure in normal osmotic reabsorption of water by kidney tubules. Due to the breakdown of lipids, ketone bodies in the body fluids increase and as a result release out through urine (ketonuria).