Originally Posted by Wikipedia

Despite long intervals between meals or the occasional consumption of meals with a substantial carb load, human blood glucose levels normally remain within a remarkably narrow range. In most humans this varies from about 80 mg/dl to perhaps 120 mg/dl (3.9 to 6.0 mmol/litre) except shortly after eating when the blood glucose level rises temporarily (up to 140 mg/dl in a non-diabetic).