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102 7.33 Brain Macronutrient Metabolism

Fatty acid breakdown does not occur to any great extent in the brain because of the low activity of an enzyme in the beta-oxidation pathway limits the pathway’s activity1. Compared to the extrahepatic tissues as a whole, in the brain the following pathways are not performed or are not important:

Glycogen synthesis and breakdown

Lactate synthesis

Fatty acid synthesis and breakdown

Triglyceride synthesis and breakdown

Protein synthesis and breakdown

These pathways are crossed out on the figure below.

Figure 7.331 The metabolic pathways that are not performed or important in the brain compared to extrahepatic tissues as a whole are crossed out2

Fatty acid breakdown does not occur to any great extent in the brain because low activity of an enzyme in the beta-oxidation pathway limits the activity of this pathway2.

By removing those pathways the only pathways left are:

Glycolysis

Ketone body breakdown

Figure 7.332 Brain metabolic capability1

Thus, due to its limited metabolic capabilities, the brain needs to receive either glucose or ketone bodies to use as an energy source.

References & Links

1. Yang SY, He XY, Schulz H (1987) Fatty acid oxidation in rat brain is limited by the low activity of 3-ketoacyl-coenzyme A thiolase. J BIol Chem 262 (27): 13027-13032.

2. http://en.wikipedia.org/wiki/File:CellRespiration.svg

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