Starvation blood glucose levels

Even after 5—6 weeks of starvation, blood glucose levels are still in the range of 65 mg/dl. 

Even during a prolonged fast, blood glucose levels do not decrease dramatically. After 5 to 6 weeks of starvation, blood glucose levels decrease to only approximately 65 mg/dL (Table 31.2). 

The first hormonal signal found to comply with the characteristics of both a satiety and an adiposity signal was insulin [1]. Insulin levels reflect substrate (carbohydrate) intake and stores, as they rise with blood glucose levels and fall with starvation. In addition, they may reflect the size of adipose stores, because a fatter person secretes more insulin than a lean individual in response to a given increase of blood glucose. This increased insulin secretion in obesity can be explained by the reduced insulin sensitivity of liver, muscle, and adipose tissue. Insulin is known to enter the brain, and direct administration of insulin to the brain reduces food intake. The adipostatic role of insulin is supported by the observation that mutant mice lacking the neuronal insulin receptor (NDRKO mice) develop obesity. 

The extract from Colin Blakemore s book provides a vivid account of the behavionral consequences of a low blood glucose level. This is because the brain uses glucose as the only fuel, except in prolonged starvation. Problems also arise if the blood glucose level increases well above the normal. An increase of only about twofold above the... 

To provide an alternative fuel to glucose during starvation. Indeed, fatty acid oxidation restricts the rate of glucose utilisation, which maintains the blood glucose level, via a regulatory mechanism known as the glucose/ fatty acid cycle (Chapter 16). 

When the blood glucose level falls and the liver s glycogen reserves are also exhausted, the liver still has the capacity to synthesize glucose via gluconeogenesis from amino acids that are supplied from protein breakdown. Under starvation conditions the liver forms increasing amounts of ketone bodies (see fig. 18.7). This is due to elevated concentrations of acetyl-CoA, which favor the formation of ketone bodies. The ketone bodies are secreted and used as a source of energy by other tissues, especially those tissues like the brain that cannot catabolize fatty acids directly. 

C. Blood glucose levels during prolonged fasting (starvation)... 

B. In the absence of insulin, a person with IDDM will behave metabolically like a person undergoing prolonged starvation except that blood glucose levels will be elevated. Lipolysis in adipose tissue will produce fatty acids, which will be converted to ketone bodies in the liver. 

Brain cannot use fats for energy instead, brain has a specific requirement for glucose. Under conditions of starvation, however, when blood glucose levels decrease, brain can adjust to use ketone bodies, which can be derived from fatty acids. 

A 70-kg human can store at most the equivalent of 6700 kJ of energy as glycogen. This source of blood glucose will be exhausted just a few hours after a meal. Because it is critical for brain function that blood glucose levels be maintained near 4.4 mM, the organism adapts metabolically during starvation to increase the use of fuels other than carbohydrate. 

See also Maintaining Blood Glucose Levels, Response to Starvation, Action of Insulin, Action of Glucagon, Peptide Hormone Synthesis... 

C. Blood Glucose Levels during Prolonged Fasting (Starvation)... 

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