Fat storage and retrieval

Human beings are adapted to live on fat. This is self evident from the way we store energy. Any average human is probably carrying around 100-200g of glucose as glycogen, stored in their liver, plus a bit more in their muscles. Let's be over generous and say 400g of glucose in all, about 1600kcal. That's enough energy to last about a day if you sit still. Assuming that same person weighs 80kg and has a body composition including 25% fat, this spare energy store of adipose tissue weighs 20kg. Containing 20,000 X 9 kcal giving 180,000kcal. At 2000kcal per day this looks like a 90 day supply to me, and allows spare energy to run around after some food.

Does any one ever use this energy? Well anyone who has ever fasted will know that energy from fat is freely available. This is completely logical. When humans were hunting and gathering, living through hard times on the fat of your bum was essential for survival. Being rendered dysfunctional by 24 hours food deprivation was non survival. Maybe 90 days without food is a bit extreme, but functioning for a week or two without food seems quite safe and is a very useful attribute.

Given your fat and some oxygen, is much else needed to extract this stored energy? Well, probably not a lot. If you are a hunter in a bad patch you don't want to be having to stop to eat a few leaves to get vitamins in order to burn your body fat. The leaves, fruits and nuts may not be that available when they buried under 6 feet of snow, while you and your mates drive some poor herbivore over a cliff to extract its stored fat from last summer's grazing.

Logically fat as an energy store is designed to be oxidised with a minimum of input, using vitamins and minerals that are available from body reserves plus a little help from muscle breakdown (which is inevitable during full fasting). Being hungry should NEVER jeopardise your ability to catch your next meal.

If you live on sugar your need for vitamins becomes crucial. One of the most important is vitamin B1, which is water soluble and not stored in the body in any amount. Certain illnesses, especially chronic alcoholism or subsisting on white rice, result in very low B1 levels. What happens when a B1 deficient person collapses and they get hooked up to an iv glucose drip? The glucose requires B1 for its metabolism, grabs it and precipitates an acute neurological catastrophe.

Sugar needs B1.

Sugar also depletes vitamin E. Taking a 75g oral glucose tolerance test, and presumably drinking a Starbucks Mocha does the same, drops your vitamin E level and it is still down at 3 hours. I wonder when it gets back to normal?

Neither eating fat nor protein deplete vitamin E levels.

I've no data on other vitamins but these snippets fit the logic of fat burning vs sugar burning on an evolutionary basis.

Now, consider burning fat which is not on your posterior but on your dinner plate. Is there any huge difference in the metabolic process of extracting the energy from dietary fat compared to adipose stored fat? I doubt it. So no desperate grubbing around for tubers and leaves to go with your fat. Somewhere along the line some protein is essential, but extracting calories from dietary fat should as be easy as extracting calories from your own adipose tisue.

It would be very interesting to see the vitamin/mineral requirements of a substantial group of people who were long term adapted to obtaining the bulk of their calories from fat, preferably saturated fat. My guess is that vitamins B1 and E would not feature at the top of the list, but I doubt we will see such a study soon.

Frankly, I'm amazed that Dandona could get ethics committee approval for the 3 floz of cream that he gave to his volunteers.

Peter