Tuesday, December 04, 2007

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

14 comments:

Bruce said...

"Neither eating fat nor protein deplete vitamin E levels."

Peter, this study compared cream to casein. Polyunsaturated fats, OTOH, do deplete vitamin E. The more PUFA there is in a fat, the more it will tend to deplete Vitamin E. Corn and soybean oil, safflower and flaxseed oil, and canola oil are probably by far the worst. Eating a lot of fish oil or fatty fish will also deplete Vitamin E levels. Saturated fats do not do this. The best fats are ones with very low PUFAs: red meat, palm oil, coconut oil, cocoa butter, mac nut oil, foie gras, etc.

Peter said...

Yes, seems to be the case...

Peter

Bruce said...

I agree with you that the needs for vitamins and minerals seems to vary widely depending on diet. JK's diet probably reduces nutritional needs, while also providing nutrient dense foods. Where we both seem to oppose him is in the emphasis on pork. Red meat and dairy are better. Coconut, macadamia, and cocoa butter are the safest vegetable oils. I guess I am combining Jan Kwasniewski and Bear, with Ray Peat and others.

Peter said...

Everyone must make their own decisions. There are very intelligent people out there, but ultimately our responsibility for ourselves rests with us. I think each person must make up their own minds. No gurus.

Peter

Bruce said...

Right, we should read as much as we can, and take what makes sense from various gurus. And, of course, rely on our own experience and intuitive wisdom. I don't agree 100% with any guru. I take what works and discard the rest. Kwasniewski's idea that a high-fat adequate-protein diet will cure diseases makes a lot of sense. But I think Bear's food choices are more appropriate to our biochemical and evolutionary needs.

I eat more carbs than you, based on Ray Peat's theories. Maybe 150-200 grams. I'm also using Art De Vany's Evolutionary Fitness principles for exercise and intermittent fasting. Also using some raw dairy and other foods like that. I don't think any guru has all the answers.

GK said...

Hi Peter,

Your example scenario of survival during harsh times in winter makes the point of having evolved an efficient storage system: large enough to last, small enough not to be a burden.

The natural human diet is what was eaten while our species evolved. All species thrive eating what they are adapted to eat; speculating what exactly that is for our ancestors (and us) will have to be based on some guesswork.

During discussions on this, I notice a lot of people like to invoke the feast/famine principle as you mentioned. I would argue that this has no place in our evolution.

Since the split from chimp ancestors about six million years ago, to genetically modern humans about two hundred thousand years ago, our guts evolved to be what they are today. During that entire time, our hominid ancestors never left Africa. They would have subsisted as hunter-gatherers in savannah and forest. Winter would not have existed, so it played no part in our evolutionary diet.

Seasons did exist, though. There might have been droughts, but even then, we would have had plenty of game down at the old watering hole from which to choose. There is no reason to believe that in our evolutionary history there were times of famine. Those only happened after agriculture, ten thousand years ago, too little to effect genetic selection.

GK

Peter said...

Hi GK,

An interesting comment. I like to think in terms of any given population expanding to the limits of its food supply. If there is food in excess of the needs of the group it will be used to increase the size of the group, unless there is another limitation placed on population size. I think water supply has been cited for the Kalahari. Unless food availability is constant then there must be fluctuation in availability, some times better than others.

I agree that I found the roll of seasonality in hunger came from temperate climates, particularly dental enamel defects in Neanderthals and from arctic climates where Stefansson's accounts included fairly common periods of hunger during poor hunting times with the Eskimo. With a dry/wet pattern there seems to be a similar possibility for periods hunger in tropical Africa. If food congregated at limited water holes, so too would hunters. If drought was bad enough for shrinkage of prey pools then some hunters would need to go hungry... assuming that population size was set by the normal level of relative plenty. The other option for tropical hunger would be immediately following drought when the depleted number of herbivores would disperse, becoming thin on the ground and making hunting much more difficult with a lower yield per unit effort...

The concept of severe and frequent famine does seem to be fully agricultural or political in origin. The Harper's article by Richard Manning covers this nicely.

Peter

GK said...

You wrote: "If there is food in excess of the needs of the group it will be used to increase the size of the group..."

Yeah, true, this reminds me of one of my favourite lines from Good Calories, Bad Calories [if memory serves]: "in times of plenty, species thrive and multiply, they don't become obese and diabetic."

Peter said...

Have you read Daniel Quinn?

Important thinker, that's where I pinched the idea!

Peter

Elton said...

As far as a paleo-diet, I am confused on where Dairy would fit in?

Ed said...

"Is there any huge difference in the metabolic process of extracting the energy from dietary fat compared to adipose stored fat? I doubt it."

Well... Aren't there a dozen or so fatty acid lengths, plus minor variations in saturation (ie quantity and location)

Perhaps the metabolism of the fats is relatively common, but I think there might be more variation in hormonal effects. I curious to find a catalog of these. For example, I think I recently heard that palmitic acid can cross the blood brain barrier and cause short term leptin resistance in the hypothalamus. But what about stearic acid? Etc etc. There might be important differences between the various fatty acids that would be important. Polyunsaturated fats ate clearly an important sub class.

I guess your point in this post is more about vitamin utilization than other impacts, and my guess is you're right in that all saturated fatty acids are probably burned the same way, using the same co-factors (although of course I don't know this to be a fact). So my query is really tangential. But anyway, I remain curious for a catalog of interactions of the various fatty acids.

Peter said...

Hi Ed, the fatty acids all do very different things and are handled in different ways. Certainly the omega 3 fatty acids are PPAR gamma agonists and will turn on a whole cassette of fat burning genes and I believe palmitic is the same. Very LCFAs are shortened in peroxisomes before beta oxidation in mitochondria. We have techniques for dealing with odd carbon chain fatty acids and trans fatty acids too. The business about palmitic crossing the blood brain barrier and causing hunger (the presumed end result of leptin resistance) is so bizarre that I wrote the post on doner kebabs about it. In truth I CAN manage two doner kebabs, large ones at that, but 20 is beyond even my best efforts. Next week's house keeping money is safe in the doner den. Doners are a cheap meal, now banned due to gluten inclusion as a poison along side the healthy saturated fats.

Peter

Vanessa said...

Hi Peter, this is very interesting and the real need for vitamins and minerals from plants is something I've been questioning recently.

Going off topic... I don't understand, clicking on the 'fat nor protein' link to the PubMed study and reading through it seems to show, on a different note, that:

'Both fat and protein intakes stimulate ROS generation. The increase in ROS generation lasted 3 h after cream intake and 1 h after protein intake. Cream intake also caused a significant and prolonged increase in lipid peroxidation. These data are important because increased ROS generation and lipid peroxidation are key events in atherogenesis.'

Is this supposed to be bad?

I came to your site today to see how you manage to get most of your daily calories from fat, as this is what I'm trying to achieve. I would love to start eating more cream again (I've been avoiding dairy and grains for a while to clear up eczema) but I still have a question mark about dairy since going primal (only from an allergenic point of view and not because of the fat contant) and this pubmed article is confusing me!

Can you shed any light?

Vanessa said...

Hi Peter, this is very interesting and the real need for vitamins and minerals from plants is something I've been questioning recently.

Going off topic... I don't understand, clicking on the 'fat nor protein' link to the PubMed study and reading through it seems to show, on a different note, that:

'Both fat and protein intakes stimulate ROS generation. The increase in ROS generation lasted 3 h after cream intake and 1 h after protein intake. Cream intake also caused a significant and prolonged increase in lipid peroxidation. These data are important because increased ROS generation and lipid peroxidation are key events in atherogenesis.'

Is this supposed to be bad?

I came to your site today to see how you manage to get most of your daily calories from fat, as this is what I'm trying to achieve. I would love to start eating more cream again (I've been avoiding dairy and grains for a while to clear up eczema) but I still have a question mark about dairy since going primal (only from an allergenic point of view and not because of the fat contant) and this pubmed article is confusing me!

Can you shed any light?