"This practice [removing honey and replacing it with sugar water] is supported by the common and misguided notion that honey taken from a hive can be replaced with sugar water as if the two are equivalent. They are not. Honey contains nearly 200 different substances, many of which are essential for the health of the colony. Simple sugar water contains two substances: sugar and water. Microscopy shows that bees fed sugar water have intestines that are shriveled and dull in comparison with bees fed honey, whose intestines are plump and shiny."
The full article is excellent: