I am told over and over that the brain is dependent on glucose and its dangerous to run low carb. This is the primary concern of doctors, medical students, dietitians, midwives and most people, but not biochemists.
Let’s explore some religion to break a myth.
Is God (in whatever form that is) stupid enough to make our most important organ, the brain, dependent on only one fuel source of glucose? Surely not.
On my recent trip to Vanuatu I was looking through a 1996 textbook of physiology. There it all was on page 22 of a 1148 page textbook – in the Introduction to Physiology chapter. We are not even in the ‘fine print’ area!
Here’s some basic biochemistry, and it’s not even new.
The mitochondria is the engine of the cell. It will process a variety of fuel sources into Acetyl-CoA which then enters the Krebs cycle and converts into ATP – Adenosine Tri phosphate. ATP is found in all living tissue and provides energy for virtually all physiological processes. We are completely dependent on that ATP – it is life itself.
That mitochondria is like a teenager looking for food. It doesn’t care where the Acetyl CoA comes from, as long as it’s there.
Acetyl-CoA can be made from glucose from carbohydrate, ketone bodies (fatty acids) from fat and amino acids from protein. The mitochondria is a hybrid engine and it will run efficiently on these different fuel sources.
Any cell that has mitochondrion will need Acetyl-CoA. Every cell in the brain has mitochondria. Every cell. As a result every brain cell can run along on ketones and low carb. That’s what happens if you skip a meal, fast overnight or longer. It’s all just perfectly designed to keep our brains functioning.
There are only 2 cells in the body that are dependent on glucose. They don’t have mitochondria and they do require glucose. Have a think about that….and it’s not the brain. That glucose can be formed from a low carb diet or the liver by gluconeogenesis conversion of protein to glucose.
The myth of 140 grams of carbohydrate required per day is just another myth. There is no absolute requirement for ingested carbohydrate and I cannot find any evidence from where that ‘magical’ or ‘imaginary’ figure of 140 grams has come from. I have been told that it was estimated at a conference once and has become urban folklore!
The only cells that are dependent fully on circulating (not ingested) glucose are the erythrocytes (red blood cells) and some cells in the kidney (thin cells of the loop of Henle). Both of these cells lack mitochondria. No mitochondria means no hybrid engine. These two cells are uniquely dependent on glucose but get plenty of fuel from the glucose that the liver produces every day.
So when the next person says that the brain is dependent on glucose there is only one response…..
Do you really think God was stupid enough to make the brain, our most important organ to be dependent on one fuel source?
And certainly not on just glucose.