Wednesday, January 18, 2012

What Causes Insulin Resistance? Part VI

In this post, I'll explore a few miscellaneous factors that can contribute to insulin resistance: smoking, glucocorticoids/stress, cooking temperature, age, genetics and low birth weight.

Smoking

Smoking tobacco acutely and chronically reduces insulin sensitivity (1, 2, 3), possibly via:
  1. Increased inflammation
  2. Increased circulating free fatty acids (4)
Paradoxically, since smoking also protects against fat gain, in the very long term it may not produce as much insulin resistance as one would otherwise expect.  Diabetes risk is greatly elevated in the three years following smoking cessation (5), and this is likely due to the fat gain that occurs.  This is not a good excuse to keep smoking, because smoking tobacco is one of the most unhealthy things you can possibly do.  But it is a good reason to tighten up your diet and lifestyle after quitting.

Glucocorticoids and stress

Glucocorticoids are "stress hormones" secreted by the adrenal gland, under the direction of the brain, that influence glucose metabolism among other things (hence the name).  The major glucocorticoid in humans is cortisol, while in rodents it is corticosterone.  A disorder called Cushing syndrome is caused by the oversecretion of cortisol in humans.  Cushing patients exhibit insulin resistance and an elevated risk of diabetes (6). 

Cortisol is part of the body's way of dealing constructively with stressful situations, so it is increased by both physical and mental stressors.  As with inflammation, it's helpful acutely, but may be damaging if overused.  It may be one link between excessive stress and insulin resistance. 

Cooking temperature

This is not a can of worms I've opened on WHS yet, but I think cooking temperature is a significant factor in health.  Gentle cooking methods preserve nutrients, form fewer potentially damaging compounds such as advanced glycation end-products, lipid peroxides and heterocyclic amines, and do not increase the energy density of foods.  In diabetics, a diet composed of gently cooked foods increases estimated insulin sensitivity, improves glucose control, and substantially decreases markers of inflammation, compared to one composed of similar foods cooked by higher-heat methods (7, 8).

One study showed that a gently cooked diet increases estimated insulin sensitivity in non-diabetics, relative to a high heat cooked diet, when eaten for one month (9).  Unfortunately, the result was confounded by a lower energy intake in the gently cooked food group.  Maillard reaction products (browning) are formed during high-heat cooking, and contribute substantially to the palatability of food.  Think grilled steak vs. steamed steak.  In addition, high heat (as opposed to wet heat) cooking increases the energy density of food by evaporating water.  Both of these factors promote increased food intake, which is what the study observed.  We can't know whether the difference in estimated insulin sensitivity was due to differences in energy intake, a direct effect of the high-heat cooked food, or both.  They didn't report changes in body weight.  Regardless, my opinion is that gentle cooking methods such as steaming, boiling and poaching are generally superior to frying, roasting and grilling for health.  Deep-fried food is poison.

Age

Age is a dominant risk factor for many health conditions, including obesity, cardiovascular disease and the most common metabolic disorders.  Insulin sensitivity generally declines with age, although not greatly (10).  However, most people in affluent countries become more sedentary and gain fat with age, so the change may not have anything to do with age per se.  Indeed, when investigators adjust for body composition, the effect of age on insulin sensitivity disappears (11).  Fitness, not age itself, seems to be the important factor.

Genetics

As with essentially all biological traits, insulin sensitivity is linked to your genetic inheritance (12), and the genetic contribution is likely substantial. 

Low birth weight

People who were born small and/or thin are at a higher risk of insulin resistance and diabetes later in life, and this is true even if researchers factor out differences in adult BMI (13, 14, 15). This suggests that the prenatal environment influences metabolic health throughout life.

OK, I'm done

I'm sure there are plenty of other factors that influence insulin sensitivity, but in this series I've covered the important ones I'm aware of.  In the next and final post in the series, I'll review the diet and lifestyle implications of all this. 

41 comments:

Bone Daddy Dawg said...

Any idea how much nicotine raises HGH when used in normal doses via gums/patches? Ditto leptin?

Murph said...

I've been wanting to start gently cooking my food, but I'm having a hard time finding any good recipes. Anybody have any suggestions? It's seems like everything is fried or grilled these days.

I know it's not ideal but would roasting be better than grilling or frying?

Sara said...

@murph roasting while wrapped in foil seems to work quite well for avoiding browning and dehydration. I do a lamb roast this way with a mix of rosemary, garlic, salt and olive oil rubbed all over it (now you have my secret recipe..haha).

I also do quite a bit of what you might call 'poaching' but it's not really. For example, I put the meat in a frypan that is about half filled with water. In that water I add.. lots of different stuff. For example, if it's Moroccan inspired: dried apricots, cumin, cinnamon, thyme, salt and some white wine. Also butter. Cover and cook slowly for an hour or so. The liquid reduces and thickens up a bit and you can use that as a sauce. The meat gets really tender but doesn't brown (unless you go too hot and the liquid evaporates) or shrivel up.

Mmm.. should I get started on veges now?

The idea is to keep the water in and cook slow and low. I think anything done in a slow cooker (and both ideas above can be done in one - it just takes longer) or crockpot would count as gentle food.

Carlos Monteiro said...

Stephen,
Insulin resistance may contribute to enhanced sympathetic nervous system activity (1) and SNS activity may similarly increase insulin resistance (2).
Please see our article "Why atherosclerosis is milder or non-existent in individuals with Down syndrome?" - and others, at the blog www.aciditytheory.blogspot.com
In the acidity theory of atherosclerosis, developed by us in 2006, the sympathetic predominance is the primary step and shear stress is the last step in the cascade of events leading to the atherogenic process.
Carlos
1) Pikkujamsa SM, Huikuri HV, Airaksinen KE, Rantala AO, Kauma H, Lilja M, Savolainen MJ, Kesaniemi YA. Heart rate variability and baroreflex sensitivity in hypertensive subjects with and without metabolic features of insulin resistance syndrome. Am J Hypertens 1998;11:523–31
2) Moan A, Nordby G, Rostrup M, Eide I, Kjeldsen SE. Insulin sensitivity, sympathetic activity, and cardiovascular reactivity in young men. Am J Hypertens 1995;8:268–75

gunther gatherer said...

Thanks again Stephan. You are pumping out these posts faster than I can respond to your comments on the last one. I don't know how you do it all and keep a job too.

So in your comment on the last post, you mentioned how the ileum is involved in brain signalling for food reward purposes. Fiber and coarse foods are just about the only things that reach it, but this must take at least 12 hours or more to get there.

My question is: if it takes more than a day for the fiber you eat to reach the ileum where appetite and food reward are going to be (partially) controlled, doesn't this mean that there is about a 12-15 hour delay in the effects?

Is the fiber I ate YESTERDAY determining how much I eat today?

I did an experiment and ate two bowls of brown rice yesterday. Today it's 1pm and I can't get myself to eat so much as a banana.

gunther gatherer said...

Okay, I just checked and it seems transit time to the ileum-cecum is about 2 hours. Although the investigators did it with a barium solution, not with normal food. I suspect with a high fiber meal, it would take longer.

Even with the shorter transit time, we don't know how long the effects of ileum-brain signalling would have on food reward/appetite though. And I'm still not hungry.

Dennis said...

@ gunther gatherer

I am a radiologist and have performed many upper GI/ small bowel follow through studies.

The leading edge of the barium solution typically reaches the cecum by 30 minutes.

Alex said...

Damn, now we can't even cook our cardboard. :)

Joe said...

Hello Stephan,

Very interesting post!

I have a question about the importance you place on cooking temperature. The two studies cited here (7,8) are very interesting, but both seem to suggest that negative effects of exogenous AGE are much more significant in diabetic patients, who already have a pathological metabolism; the effect of high-temperature cooked foods on healthy people seem much more subtle. Multiple other dietary interventions seem to have had a much bigger influence on inflammation markers in healthy people than temperature, so while I can agree that cooking temperature may be important, I wonder how big of an impact it really has on an otherwise healthy diet.

I ask about this for two reasons: first, you seem to feel very strongly (here and previously, such as your interview with Chris Kresser) that gentle cooking methods are much healthier and preferable. To go as far as calling fried foods "poison" you must feel strongly, since you usually seem reluctant to make strong such recommendations.

Second, you note that a high cooking temperature can substantially increase the palatability and reward value of food, which leads me to wonder: why is that? Our native food reward system seems to generally lead us to nutritious and healthy food, as Paul Jaminet has written about recently. While that can certainly lead to an unhealthy diet when in an environment of processed, toxin-filled industrially produced food, high-temperature cooking seems to be a very natural and traditional cooking method to me. Fire has been used by humans long enough to be evolutionarily relevant, and high-temperature cooking (especially of meat and animal products) seems to me much more practical than the alternative. If high-temperature cooking is so deleterious in a healthy person, why is a grilled steak so much more appetizing than one which was steamed? The higher energy density you mention may play some part in this, but every cook knows that the browning of the Maillard reaction has a unique and significant impact on taste, and is essential to many dishes.

I would love to hear your thoughts on the matter.

Thanks,
Joe

bentleyj74 said...

Are you primarily addressing meat prep re "gentle" or would tubers/veg be included as well?

Stephan Guyenet said...

Hi Bone,

I don't know.

Hi Carlos,

Thanks.

Hi Gunther,

Dennis has it right-- it doesn't take much time for the first food to hit the ileum. A meal spreads out through the GI tract as it's digested, such that the leading edge hits the cecum rapidly, but the last of it takes hours to get there.

Hi Joe,

You are correct that cooking temp seems to be more of a factor in diabetics than non-diabetics, and I would say the evidence is not definitive that high-heat cooking is detrimental to non-diabetics at this point. However, what I didn't mention in this post is that if you feed healthy rodents high-heat cooked food, they develop metabolic disease over time. Also, a shortened lifespan. So it seems likely that it takes a long time for the full effects to become apparent.

Regarding deep fried food, even if AGEs and other thermal products are irrelevant, it's still unhealthy. Deep fried foods are full of refined seed oils, often breaded with white flour, and are among the most hyperpalatable foods that promote overconsumption. Deep fried foods come out looking bad in virtually every study that examines them.

It is true that our reward and hedonic systems evolved to lead us to nourishing foods in the natural environment-- an environment in which the food was generally low in palatability/reward by today's standards. In general, hunter-gatherers and primitive agriculturalists use few if any flavorings, added fats, added sugars and added salt. Imagine the diet of an African hunter-gatherer such as an !Kung: plain baked roots, tough, gamey roasted meats, unsalted toasted nuts, assorted raw and cooked plant foods, raw fruit, raw grubs, sometimes plain honey. Most primitive agriculturalists eat plain porridges or plain starchy roots as the central food. For example, throughout W Africa, the center of every meal is a pile of bland starch made from corn, millet, cassava or some other root-- next to it are small portions of something more exciting like veg or meat that today may be spiced, but maybe 50 years ago, wasn't. These cultures have celebration foods that would be more complex, but these are the exception. You just can't get very gourmet if you don't even have a stove.

We certainly did evolve to enjoy Maillard product flavors, suggesting that we were selected to seek out cooked food and thus that cooking was advantageous for health. Think about it this way-- in an ancestral environment, the difference between raw and cooked meat is the difference between meat that contains parasites and meat that doesn't. Intestinal parasites are virtually universal in HG populations, and reducing the parasite load via cooking would have been a significant evolutionary advantage. This selective pressure would have overwhelmed any negative metabolic effects of cooking.

Hi Bentley,

Everything.

Stephan Guyenet said...

Another selective pressure to evolve a taste preference for Maillard products is that the digestive tract can extract more calories from cooked food than raw food, thus effectively increasing the caloric value of food, sometimes substantially. This, in conjunction with the parasite issue, would have overwhelmed any negative selective pressure from harmful metabolic effects of high-heat cooking.

Joe said...

Hello Stephan,

Thanks for the lengthy reply! The rodent studies sound very interesting.

Regarding deep fried foods, of course I definitely agree about seed oils, flour, etc.. I was actually thinking more about some "paleo" recipes – foods like sweet potatoes fried up in coconut oil or ghee, rather than boiled or baked. Would you consider this kind of fried food healthier than commercially-produced fried goods, but still not ideal?

Your thoughts on cooked food make a lot of sense – it is obviously advantageous to eat cooked food, and browned bits of food are a good signal that it is fully cooked. I still find it interesting, though, that it is the Maillard products – which can only be formed in high heat – that specifically influences food's palatability.

I guess I am still wondering whether the high-heat of cooking can be a significant factor in health on its own, or if it only becomes significant when the diet is otherwise poor or lacking (or if metabolism is already disturbed, such as in diabetes). If you were to discuss the rodent studies on this blog, I would be very interested in exactly what their diets consisted of, along with how they were cooked.

One more question: in your discussion on polyphenols, you talk about how polyphenol-rich foods can potentially prevent oxidation of fats during digestion. Do you think it is possible that foods high in polyphenols or antioxidants are to some degree protected from high-heat cooking and any resulting negative metabolic effects? In this case, something like sweet potatoes fried lightly in coconut oil would be orders of magnitude better than something breaded and submerged in seed oil.

In any case, I look forward to hearing more of your thoughts and discussion on the topic.

Thanks,
Joe

bentleyj74 said...

"Hi Bentley,

Everything."

No more nuked potatos then?

JBG said...

Here are some miscellaneous thoughts that the discussion bring to mind that may trigger useful comment from others.

* Once upon a time deep frying was done with animal fat. The fast food chains changed to "healthier" unsaturated seed oils as a result of vigorous arm-twisting.

* Baked goods haven't been mentioned, but they also are produced at high heat (ie, > 212) and generally have their taste enhanced by browning.

* At our house we've used low-temp cooking for a long time, but I've often wondered what the trade-offs might be for pressure-cooking -- where the temp is elevated but there is no browning.

* Then there is the real imponderable -- microwaving. A substantial fraction of what we eat is either cooked (eg, sweet potatoes, frozen foods) or re-heated (eg, refrigerated soups) in the microwave. I think the sensor keeps the temps reasonable, but I can't help reflecting that there is no evolutionary experience with microwaved food!

Perfect Parallel said...

Very interesting!

Do you know if the effect comes from actually inhaling smoke or just nicotine in the bloodstream?

JBG said...

Another miscellaneous thought:

* We really need an anthropologist or two to provide the straight skinny, but I'm guessing that in evolutionary time:
--frying was rare or absent
--deep-frying almost certainly absent
--roasting, grilling, and baking (as in hot coals) common
--cooking in water probably rare or absent

In spite of stereotypical cartoons showing savages cooking missionaries in big cauldrons, I'm guessing that nothing like a cauldron was available until neolithic times.

Stephan Guyenet said...

Hi Joe,

Yes, I would consider sweet potato fries made in coconut oil without deep frying less healthy than a baked sweet potato with coconut oil on it (when you bake a sweet potato, you remove the skin which is the main part that is subjected to high heat). But they're still healthier than if they were deep fried in seed oils and/or breaded IMO.

It is possible that cooking temp wouldn't matter much if other diet/lifestyle factors are in place; I don't know. I think some factors are dominant and others not. Cellular energy excess is probably dominant, cooking temp may not be.

Polyphenols and other antioxidants may protect food against oxidative damage, but it's complicated because they also lower the smoke point of oils, so in some contexts they increase susceptibility to thermal oxidation.

Here are the rodent studies I was referring to:

http://www.ncbi.nlm.nih.gov/pubmed/18599606
http://www.ncbi.nlm.nih.gov/pubmed/16046296

Humans have a fairly long evolutionary history with cooking, while rodents don't, so I don't place too much emphasis on the rodent studies, but they are interesting nevertheless.

Hi bentley,

Microwaving actually seems to be pretty gentle. It mostly excites water molecules, which means cooking temp doesn't much exceed the boiling point of water. That's why it's tough to brown foods in a microwave. I haven't seen any evidence that microwaving is any harsher than steaming or boiling.

Hi Perfect Parallel,

I would guess both. Nicotine stimulates the sympathetic nervous system which releases FFA. But smoke contains substances besides nicotine that trigger inflammation.

Sara said...

Sweet potatoes fried in coconut oil? This I have to try...

bentleyj74 said...

"Hi bentley,

Microwaving actually seems to be pretty gentle. It mostly excites water molecules, which means cooking temp doesn't much exceed the boiling point of water."

In case you couldn't see the choir of angels positioned over my house singing...yay!

Razwell said...

I always try to NOT heat oils when possible.


Deep fried fat, especially unsaturated fat , is VERY damaged fat. These very damaged fats damage the endothelium and are pro - inflammatory in a significant way . These type sof things are the most atherogenic substances you could eat.

Dr. Steven Nissen gave the exmaple of a deep fried candy bar as being SUPER atherogeneic in his lecture.

(I believe that is one of thre things that contributed to Bill Clinton's CAD. His love of southern deep fried foods etc., plus stress of being president,plus the Monica Leweniski thing.)

Poached eggs are FANTASTIC by the way.

I can appreciate the fact that Stephan is a young scientist working hard on specific components of obesity, while other scientists work on other parts. Science is a group effort. And all scientists build upon the work from others that came before them - even Newton and Einstein did.

David Pier said...

Have you found any reliable lists of AGE contents of various foods?
I know cheese as a food category, especially pastured dairy cheese, is good for me, but maybe my 3-year old Gouda and Gjetost are not. I would like to know how they compare to deep fried foods.
All I can find is that flawed immunoassay study that claims raw butter is the worst offender.

Dr. K@ said...

Hey S, great post!
Anything that has to deal with educating people about the horrors of insulin resistance is gold in my world!! Would you argue that anything that increases insulin leads to resistance, and therefore anything that either causes a stress response, or an inflammatory response will lead to IR, if even for a short while?

Also, with regard to heating and cooking food, I was wondering how much you know about acrylamide and it's effects? I know that any starches cooked above a certain temp end up having high levels of it, and it has a link to cancer in animal (?) studies. Anyways, pardon the pun, but food for thought :)
Keep the awesome posts coming!

gallier2 said...

@JBG you should visit Africa or Asia/Pacific some time. There, you could learn that slow cooking of food is widespread and doesn't need more than big sturdy leaves, a shovel and a fire. Take your bushmeat or your fish, wrap it in banana leaves with spices and salt, add a taro root, or an pieces of ignam (not to be confused with yams) to it, take your shovel and bury it under your fire, i.e. make a hole in the sand, put a little sand to insulate and add hot embers on top. Wait an hour or two, dig up and enjoy your "monkey sous-vide" ;-)

To be a bit more serious, this kind of cooking is so widespread that I am surprised that people even can assert that potery is required for slow cooked food.

Stephen said...

Ok, but the last thing I'm going to do is steam a steak! The French blood running through my veins won't allow me to do such a thing.

Don't be a killjoy ;-)

Nyx said...

I think it's interesting that oversecretion of cortisol increases insulin resistance, since exercise increases cortisol but also improves insulin resistance. or so I thought. It's all so complicated ....

Dr. K@ said...

I agree Nyx, seems weird doesn't it, but with exercise it's the other 3 powerful hormones (Adrenalin, GH, Glucagon) that are released that actually hyper-sensitize us to insulin, and make it such that even the tiniest amount is extremely efficient. On top of that, exercise, when done in moderation, doesn't increase cortisol in large enough amounts, or for long enough to actually cause insulin resistance like it might in someone taking steroids like prednisone, or in someone who is chronically under severe stress. Amazing how timing, amount, and synergism with other chemicals all work to give different results!! Get exercising I say :)

JBG said...

gallier2, you may have read too quickly. I explicitly mentioned cooking in hot coals, and I didn't say anything questioning availability of slow cooking in general. All I questioned was cooking in water, given the likely absence of pots.

RLL said...

Wasn't putting hot rocks in a tightly woven basket filled with water used by a number of North American natives?

EB Hansen said...

I have seen demonstrations of cooking in water using animal hide containers over hot coals/very low fire. IIRC it was a portrayal of Native American hunter/gatherer culture.

I don't know if this was an accurate depiction of actual practice (or how ancient of a practice it may be). But boiling without pots seems possible.

Marwan Daar said...

A lot of my dishes begin with sauteing onions and garlic (I use coconut oil on medium heat). I've only done this because the recipes and passed down wisdom recommend this. I'm not sure what exactly it accomplishes.

Are there any alternatives to sauteing these ingredients that don't rely on high heat, yet still allow for tasty results?

Nyx said...

I see several articles here and there that suggest that we have found pottery dating from the late Paleolithic .... (e.g., http://www.mendeley.com/research/on-the-origins-of-pottery/).

@Murph, I find that anything cooked in a crockpot is delicious (as well incredibly easy!!). Two days ago I put in a chicken carcass, 2 onions, 2 carrots and a handful of greens and nothing else, and it was the best soup ever. I even slow-cooked my thanksgiving turkey (in the oven), and it was incredibly delicious!

JBG said...

Thanks to several folks for comments on the possibility of paleolithic water cooking.

And second on Nyx's endorsement of slow cooking. As Nyx says, it is super easy and can produce delicious results. We do a major part of our cooking that way, and we haven't fried ANYthing in a very long time.

Nyx said...

@murph, I just realized I fibbed about my crockpot soup. I also put in at least one stalk of celery. possibly 2?:)

Galina L. said...

@Murph,
I was fed with boiled or steamed food most of my childhood, because I had an eczima, and in Russia such diet is a standard treatment for such condition. I like to eat boiled chicken and meat even since. It is important to keep boiled chicken or meat in a broth after it is done. You can also always flavor to it if you want to by quickly worming up cut meat with sour cream and garlic, for example, or onion powder and a little bit of milk, or put it in a reduced vine.

Logan said...

I read somewhere (I don't have a link) that a Kansas City University study showed that doing an herb rub before grilling meats reduced production of HCAs from forming-- up to a 100% in the case of rosemary (Ithink?). This was attributed to the herbs high antioxidant properties. I think there are studies showing wine marinades provide similar protection, how would this read into the high heat cooking methods? Anyone have any insight into those studies?

eg said...

As somebody referenced in an earlier comment, the gentlest cooking method is probably "sous vide".

Jenny said...

I just had a look at the full text of the Diabetes Care study about the lower AGE diet in people with Diabetes.

What's striking is that despite the lowered HOMA measures of blood sugar were worse in the low AGE group. The FBG didn't vary enough to be significant but the A1c went up substantially in the low AGE group.

HOMA is a very poor measure of insulin resistance--as proven by studies that compared the calculated value to the value determined with insulin infusion. So I wonder if this diet really lowered IR given those higher blood sugars.

They probably replaced fast food with pasta, which might help explain the worsening blood sugar. But if the point of lowering IR is to improve health, a diet that raises A1c and has no significant impact on fbg is not compelling.

fg said...

Hello Stephan,

Regarding microwaving food, I found this paper cited in _The Great Cholesterol Con_ by Anthony Colpo, a book which you recommend:

http://onlinelibrary.wiley.com/doi/10.1002/jsfa.1585/abstract

Abstract:

Total flavonoid and individual hydroxycinnamoyl derivative (sinapic and caffeoyl-quinic acid derivative) contents were evaluated in the edible portions of freshly harvested broccoli (cv Marathon inflorescences) before and after cooking and in the cooking water. High-pressure boiling, low-pressure boiling (conventional), steaming and microwaving were the four domestic cooking processes used in this work. The predominant sinapic acid derivatives were identified as 1,2,2′-trisinapoylgentiobiose and 1,2′-disinapoyl-2-feruloylgentiobiose. In addition 1,2-diferuloylgentiobiose and 1-sinapoyl-2,2′-diferuloylgentiobiose were also identified in broccoli inflorescences. The results showed large differences among the four treatments in their influence on flavonoid and hydroxycinnamoyl derivative contents in broccoli. Clear disadvantages were detected when broccoli was microwaved, namely high losses of flavonoids (97%), sinapic acid derivatives (74%) and caffeoyl-quinic acid derivatives (87%). Conventional boiling led to a significant loss of flavonoids (66%) from fresh raw broccoli, while high-pressure boiling caused considerable leaching (47%) of caffeoyl-quinic acid derivatives into the cooking water. On the other hand, steaming had minimal effects, in terms of loss, on both flavonoid and hydroxycinnamoyl derivative contents. Therefore we can conclude that a greater quantity of phenolic compounds will be provided by consumption of steamed broccoli as compared with broccoli prepared by other cooking processes. Copyright © 2003 Society of Chemical Industry

What do you think? Honestly I was disappointed to read this since the microwave is such a time-saver... :)

turkeysong said...

Native people in various places boiled in bark, pottery, soapstone, basketry, wood and skin containers. Some flammable containers were used by placing very hot stones into the liquid, which is fuel inefficient, but remarkably effective. Steatite (soapstone) and pottery can be placed directly on flame and so can bark sometimes as long as it is full of water. If you put a green leaf or other very thin cellulose container full of water on a fire it will not burn. The area above the water level will dry out and burn, but only down to the water level. Maple sugar is traditionally boiled this way in birch bark containers over low heat. Another slow cooking method is the earth oven which was common world wide. A pit in the ground, often stone lined, is heated with a fire. Often most of the coals are removed and then the food is placed inside. The food is either wrapped in green vegetation, or a layer of wet green vegetation is placed in the oven before and after the food to protect it from the heat of the stones and from dirt. I usually toss in a small amount of water before covering the pit, but not everyone does and it is not always necessary depending on what is being cooked. A fire is sometimes built on top. This was the primary long cooking method worldwide. It is very convenient since it does not require significant tending. Underground ovens made possible the use of foods which are otherwise toxic unless exposed to very long cooking.

Another very common method among primitives is to throw the meat right on the fire. Generally the skin is left on, but I sometimes quick cook smaller pieces of meat by laying them directly on the coals... yummy! This is very simple and doesn't require tools of any kind. By the time the meat is done the skin is blackened, but I don't believe anyone probably relished eating that... but I don't know that. If the carcass is whole, a hot stone may also be put into the body cavity to cook the carcass more quickly. Examples of this can be seen in the movies Walkabout and The Great Dance

Personally I have a hard time working up a sweat worrying about some carbonization or browning on the outside of my meat. Generally we are talking about the outside of surface area only which does not amount to much of the total mass of a steak or whatever. What I do personally have a problem with actually is very long cooked meat. Sometimes pit very long cooked meat as described above which is basically steamed, or very long boiled meats reach a point where my body just does not like the smell or taste any more. I'm not talking about something that is stewed for two to four hours at very low heat, but getting too far beyond that, something changes. I have to trust my body on this one, and I'm not saying it's right, but I'm still just saying... I feel that its important to enjoy our food and that should also be taken into consideration. Making food primarily about what is and isn't going to kill us can make for some neurotic food relationships. I think that in all aspects of our lives (and in the health, diet, personal growth and environmental movements etc) we would do well to embrace a certain level of sustainable hedonism in order to stay sane, healthy and sustainable.

Think 360x365 said...

Came across this research regarding microwaving & AGEs.

http://missclasses.com/mp3s/Prize%20CD%202010/Cooking/fulltext.pdf

"Researchers at the Department of Geriatrics, Mount Sinai School of Medicine have determined that AGEs are mostly found in foods cooked at
very high temperatures (Uribarri and others 2007). This includes
foods that have been fried, barbecued, broiled, or cooked in the microwave." ...

In all categories, exposure to high temperatures raised the AGE level for equal foodweights. The temperature level appeared to be more critical than the duration. Furthermore, microwaving increased AGE content more rapidly compared to conventional cooking methods
(Parliment 1993)."