Despite widely variable intervals between meals or the occasional consumption of meals with a substantial carbohydrate load, human blood glucose levels normally remain within a remarkably narrow range. In most humans this varies from about 82 mg/dl to perhaps 110 mg/dl (4.4 to 6.1 mmol/l) except shortly after eating when the blood glucose level rises temporarily up to maybe 140 mg/dl (7.8 mmol/l) or a bit more in non-diabetics. The American Diabetes Association recommends a post-meal glucose level less than 180 mg/dl (10 mmol/l) and a pre-meal plasma glucose of 90-130 mg/dl (5 to 7.2 mmol/l).
It is usually a surprise to realize how little glucose is actually maintained in the blood and body fluids. The control mechanism works on very small quantities. In a healthy adult male of 75 kg (165 lb) with a blood volume of 5 litres (1.3 gal), a blood glucose level of 100 mg/dl or 5.5 mmol/l corresponds to about 5 g (0.2 oz or 0.002 gal, 1/500 of the total) of glucose in the blood and approximately 45 g (1½ ounces) in the total body water (which obviously includes more than merely blood and will be usually about 60% of the total body weight in men). A more familiar comparison may help – 5 grams of glucose is about equivalent to a small sugar packet as provided in many restaurants with coffee or tea, with people using typically 1 to 3 packets per cup.
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