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Metabolism and the Evolution of the Human Brain

Well, happy belated New Year! Hope it's started off on the right foot for everyone. For this blog, December was a slower month, as expected, but earlier this week, we had a record-breaking day with almost 2000 pageviews! So definitely off to a good start for traffic at this site--and thanks always to my subscribers and visitors for your support.

So to get things rolling again here, let's start with a study that looked at how a change in metabolism helped the human brain evolve, and this relates to mitochondrial energy production, ketogenesis, and the like, so read on!

We know that genes and the environment both influence the metabolic processes that determine an organism's ability to survive and thrive in its environment. To illustrate the importance of metabolism for human brain evolution and health, researchers use the example of lipid energy metabolism (i.e. the use of fat [lipid] to produce energy) and the advantages that this metabolic pathway provides for the brain during environmental energy shortage.

In modern humans, lipid energy metabolism is a regulated multiple organs that link triglycerides in fat tissue to the mitochondria of many tissues, including the brain. There are three important control points, each of which are suppressed by insulin.
  1. Lipid reserves in fat tissue are released by lipolysis (the breakdown of fats) during fasting and stress, producing fatty acids (FAs) that circulate in the blood and are taken up by cells. 
  2. FA oxidation. Mitochondrial entry is controlled by carnitine palmitoyl transferase 1 (CPT1). Inside the mitochondria, FAs undergo beta oxidation and energy production in the tricarboxylic acid cycle (TCA, or otherwise known as the Krebs cycle) and respiratory chain. 
  3. In liver mitochondria, the HMG-CoA pathway produces ketone bodies for the brain and other organs. Unlike most tissues, the brain does not capture and metabolize circulating FAs for energy production. However, the brain can use ketone bodies for energy. 
The researchers then discuss two examples of genetic traits of metabolism that may be advantageous under most conditions but deleterious in others. A genetic variant prevalent in Inuit people may allow increased FA oxidation under nonfasting conditions (but also predispose to hypoglycemic episodes), and a "thrifty genotype theory," which suggests that energy expenditure is efficient so as to maximize energy stores (which in turn predicts that these adaptations may enhance survival in periods of famine but predispose to obesity in modern dietary environments).

Another shameless plug for my book, but I did discuss things like this, so if you find this type of stuff interesting...well, what are you waiting for?!  :)

Source: Metabolism as a tool for understanding human brain evolution: Lipid energy metabolism as an example

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