When a person\'s glucose and glycogen stores are depleted, which can occur due t

Question

When a person's glucose and glycogen stores are depleted, which can occur due to fasting or due to a diet consisting largely of fat (like eskimo diets), the body produces its energy by breaking down triglycerides into fatty acids. Fatty acids can be then converted to Acetyl-CoA, which can consequently enter the citric acid cycle, generating ATP.

Now normally when a cell does not receive sufficient oxygen to undergo its natural processes, it usually breaks down glucose anaerobically to generate ATP and lactic acid. However, in the case where the body is running off fatty acids (e.g. fast, or fat/protein only diet), how does the body respond to such anaerobic situations?

Explanation / Answer

You are correct in thinking that fatty acids cannot be metabolised anaerobically. However, in the type of metabolic state that you are describing, blood glucose will be maintained by the liver to support tissues or cells which are more or less dependent upon anaerobic metabolism. The classic example of such a cell type is the red blood cell which as no mitochondria and so cannot use the TCA cycle. The brain is also heavily dependent upon glucose.

The liver exports glucose that it has produced via gluconeogenesis from amino acid skeletons, as well as from glycerol produced as a result of fat metabolism.

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