Thanks guys.
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I have been taking an interest in Type 2 Diabetes recently and I have come to the conclusion that when God designed mammals he was mainly thinking about bears!
We eat food, it gets chewed up and passed into the stomach where chemicals are added then it goes to the small intestine by which time all the glucose has been extracted from the food and it is available for use. The small intestine works a bit like a "heat exchanger" but for glucose. It passes the glucose into the bloodstream.
That glucose is fuel and the brain gets first go at it. Many other cells need to be "unlocked" before they can accept the glucose fuel. The need for the "keys" is detected by the pancreas which issues the "keys". Those keys are insulin molecules. When a cell is unlocked it can accept glucose.
When no more glucose is needed it has to be removed from the bloodstream and the liver does that. If you need energy between meals the liver issues some of the glucose.
If even more food is consumed then the excess glucose is converted to fat. Remember: three meals a day is quite a modern thing. We could spend days finding the next buffalo in former times. If you have a build up of fat then it makes you insulin resistant which makes you hungrier. At that point, there is a positive feedback loop and you go into self-destruct mode: more insulin resistance, more food, more fat, less energy so more food etc. In humans, that process can advance slowly over years.
However, for bears it is a useful feature. When it starts getting cold they are somehow triggered to overeat and they pile on the pounds. I believe they can put on between ten and twenty pounds a day! The excess is stored as fat. When they start their hibernation, the body uses the fat as its energy source and that keeps them going until spring at which point they are no longer insulin resistant and they return to normal.
Maybe we should hibernate if we get fat!
The process which converts fat into glucose is called ketosis so while we think of a keto diet as a new dieting fad the bears have been doing it all along. Note, this is not medical advice because I am not qualified, but I am seriously looking into either a keto or carnivore diet to see if I can lose a few pounds in weight and inches off my waistline. I lost a couple of stones last time but I struggle to keep it going.
No, ketosis is breaking down fatty acids to make ketones. Creating glucose from fat (or protein) is gluconeogenesis. It's right in the names.
Thanks for the correction.
When I wrote this I had naively assumed that the mitochondria processed only glucose but now I realise that that is not the case. They can be dual-fueled!