Nimm's Journal, 03 September 2013

One of the most pervasive ideas in the diet-health sphere, and to some extent even in the scientific literature, is that when you eat rapidly digesting carbohydrate, this causes an increase in blood glucose and insulin, followed by hypoglycemia (the "crash"). This low level of blood glucose then causes hunger and cravings. It's a simple, logical idea that has virtually no scientific support.

Hypoglycemia definitely causes hunger and food cravings (3). That isn't in question. The problem is that the level of hypoglycemia that causes hunger (below 51-65 mg/dL depending on the study; 3, 3B) is rare in non-diabetics, no matter what kind of carbohydrate they eat. For example, Dr. Ludwig's study reported that participants had an average fasting glucose of 88 mg/dL. This is a normal level of fasting glucose. At the lowest level of the HGI group's post-meal "crash", they had a blood glucose of 85 mg/dL-- a trivial 3 mg/dL below fasting, and nowhere near hypoglycemic. The LGI group had a blood glucose of 95 mg/dL, only 10 mg/dL higher than the HGI group. Could a difference in blood glucose this small account for measured differences in hunger? Probably not, given that previous studies have struggled to find satiating effects of much higher levels of blood glucose in humans.

The unfortunate reality is that there is no compelling evidence that blood glucose fluctuations within the normal range cause differences in hunger and food intake.