Kurt G. Harris MD

The PāNu approach to nutrition is grounded on clinical medicine and basic sciences disciplined by knowledge of evolutionary biology and paleoanthropology. The best evidence from multiple disciplines supports eating an animal-based diet high in fat, low in cereal grains and relatively low in carbohydrate.

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« Vitamin D | Main | Calorie Restricted Monkeys Part II »
Thursday
Jul162009

Calorie Restriction: partial restoration, not enhancement

Zen Teacher Shunryu Suzuki

My previous two posts, here and here, were a two-part explication of the recent paper in Science claiming life extension and mitigation of aging related diseases with calorie restriction (CR) in a rhesus monkey model.

Many commenters and bloggers have been critical of the suboptimal diets fed to the monkeys, and some have therefore questioned the relevance of this study. First let me defend the researchers a bit. The study was begun in 1989, and no doubt was conceived and planned some time before that. The late 1980's were almost a decade before most people had internet access, and it would be fair to say the reigning dietary paradigm, including Ancel Keyes' diet-heart hypothesis, was not being seriously challenged by many. I think a certain amount of cultural relativism is appropriate. I for one was only two years out of medical school. Expressing the idea that corn oil, wheat or sucrose could be poisons might well have threatened my nascent medical career, had I been smart enough to think such thoughts! So perhaps the Wisconsin team can be forgiven for using what was probably considered a very healthy monkey diet at the time. Once committed, they could not very well change it and start over with new monkeys after 18 years of effort because they just read Good Calories, Bad Calories.

That said, I do not disagree with the observation that the control diet was suboptimal. PaNu theory is that there is such a thing as an evolutionary metabolic milieu (EM2) that optimizes our phenotypic expression. That internal metabolic and hormonal milieu is probably quite similar for many mammalian species, but likely differs importantly in food inputs by species, depending on features of the original food econiche. I believe the EM2 of rhesus monkeys is not achieved by massive amounts of corn oil and excess and highly bioavailable sucrose, and many commenters have said the same.

With these flawed diets, is the study still relevant to whether life extension via CR is a real phenomenon?

I believe the answer is yes, but only because it allows us to re-frame the problem with a new question.

That question is: If CR works, what is CR?

This study speaks to the very concept of CR and its ontology as a phenomenon.

If we define CR as the phenomenon of improved lifespan or slower degeneration as a result of lower caloric intake, we can conceive of CR in one of two ways:

1) We have discovered a phenomenon that takes our natural aging phenotype and attenuates the aging process - an enhancement of our phenotypic potential

2) CR is a phenomenon that represents one of several ways that the damaging effects of our neolithic diets can be mitigated, and is likely mediated through lowering basal insulin levels. The CR effect is one among many changes to the neolithic diet that could be made, and which, if they work, are not enhancing our natural aging phenotype, but rather restoring it. Any such maneuvers will work only to the degree we were deviating from the EM2 for our species in the first place.

Listless and anorexic folks on plant-based diets, and those searching for profitable chemicals to sell us are promoting idea #1.

PaNu favors #2.

To the degree that CR or any dietary maneuver works, it is just getting us fractionally closer to the EM2 for our species. I believe the EM2 can be achieved or closely simulated with an ad libitum low carbohydrate diet relying on animal sources that minimizes fructose, gluten grains and linoleic acid. Accordingly, it is unlikely that any drug, intervention, or supplement can ever improve on what can be achieved with diet alone. From what I know so far, I believe the laboratory experiments with mammalian species to date can be interpreted this way. If the model animal lives longer, you are just mitigating the effects of an artificially unhealthy diet.

CR is therefore just a partial restoration of our optimal phenotypic expression, not an enhancement of some "natural" state.

I guess this is a little like the Soto Zen concept that you do not need to seek enlightenment because you are already enlightened. Enlightenment (Health) is not something outside yourself you can acquire from some special experience (medical science), but rather a potential you have always carried within you.

CR as practiced by Humans on plant-based diets is probably lowering basal insulin levels in the unhealthiest of several possible ways.

The healthiest and most sustainable way would be an animal-based low carbohydrate diet that minimizes wheat, fructose and linoleic acid.

Reader Comments (27)

This is great stuff. The EMM is essentially what I believe to be ideal nutrition after reading and studying as much as I can get my hands on. The article by Dr. Rosedale http://drbass.com/rosedale.html is good at explaining why carb fuel is not optimal for the body in the long term. I do my best to eat meat, nuts, some veggies and some fruit. I cut out dairy and caffeine as part of an experiment in reseting my body. So for the next 30 days it's just pure Paleo. The only processed foods will be good quality sausage, almond or sunflower seed butter, coconut oil, coconut milk, fish oil, and olive oil. Spices and mustard will be in there too. http://www.byersgetsdiesel.com/2009/07/change-your-life-in-thirty-days.html

July 16, 2009 | Unregistered CommenterMark

Perhaps I missed this discussion, but can you discuss fructose in further detail?

I eat a small bowl of either blueberries, raspberries, and/or strawberries every day. Sometimes I'll throw in a kiwi or two. (if not a small bowl by itself, I usually mix half a small bowl of berries with fatty yogurt) That said, it's always a small bowl and not more than that. It's usually my first meal (whether it is at 830am or 3pm, depending on intermittent fasting or keeping it random). During that meal, I also have 3-4 hard-boiled eggs too. Are these fruits high in fructose? Is this choice, which in my own mind adds vitamins and other valuable nutrients to compliment the other aspects of the diet (coupled with my workouts), throwing it out of whack?

Thank again!

July 16, 2009 | Unregistered CommenterW.E.

W.E.

Large amounts of fructose (Fru) is one of the elements of our current (neolithic) diet that deviates substantially from the EM2 we evolved under. For a variety of reasons, Fru functions as a metabolic poison and is much worse than glucose.

Excess Fru raises your triglycerides, can cause inflammation in your liver, and causes insulin resistance independent of insulin levels. Big boluses of Fru are sometimes not digested completely. This can cause bacteria to grow in your upper bowel which is not good.

Look at Fru like cigarettes - if you smoke one cigarette a week it will probably not hurt you. The problem is not the one smoke, it is the reinforcement of the desire that leads you to smoke the whole pack.

If you can keep total carbs at 10% and some of that is sucrose, that may not be a problem. But, people like fruit because its sweet, and if you tell them fruit is healthy, they tend to eat a lot of it.

Fruit is not healthy, it is something that tastes good that you can tolerate in small amounts.

The vitamins in sweet fruits can't hold a candle to other foods. The "antioxidants" are probably more than balanced by Fru itself, which is actually an "oxidizing agent"!

As far as your breakfast, remember that anything that tastes sweet has fructose in it, unless it is artificially sweetened. Why not try a no-carb breakfast with cream in your coffee and a few eggs?

July 16, 2009 | Unregistered CommenterKGH

Thanks Kurt for these posts. The CR question is very interesting and is giving me much to ponder.

Your reply to the comment on fructose is also causing me to think. I eat fruit daily - apples, bananas, pears, kiwifruit. If I reduce these what do I eat?

I start the day with a 4 egg omlette with spinach, mushroom, pepper and tomato. I'll eat meat if we have some left overs or there is bacon.
Lunch is usually salad with meat. I would eat fruit here and again as an afternoon snack and also after tea.

Tea is meat, salad, sweet potato instead of potato, vegetables such as broccoli, carrot. Yoghurt and fruit.

I am a regular reader at Mark's daily apple and have read Taubes and Cordain so understand a little of the Low Carb concepts. Much of the advice is contradictory even though from the same basic ideas.

What I have not yet found is a clear guide to low carb food that is practical.

Any thoughts or suggestions would be helpful.

July 16, 2009 | Unregistered Commentertom

Kurt said,

CR is therefore just a partial restoration of our optimal phenotypic expression, not an enhancement of some "natural" state.

and
Health is not something outside yourself you can acquire from some special experience (medical science), but rather a potential you have always carried within you.

The Hebrews said:
Adam lived 930 years
Enoch lived 912 years
Methuselah lived 969 years

Myth telling or record keeping? It was Hebrew tradition to not begin the teaching of Kabbalah until the age of 40. If people then had a life expectancy of 36 years, as we've been told by scientists, that would make no sense. Why wait until a person is at death's door to begin to teach them high level knowledge that takes decades to acquire?

If the Torah is accurate record keeping, what did the anti-deluvian people know about living up to their optimal phenotypic expression that we haven't yet rediscovered? Are the ages of the patriarchs exaggerations? Or are they a dangling bit of information left behind by the ancients to get us to seek out our true genetic heritage?

July 17, 2009 | Unregistered CommenterBen Fury

Ben

I think max age of 90 not 900.

Myth telling. I have some faith in science, but none at all in those old books.

July 17, 2009 | Registered CommenterKurt G. Harris MD

It certainly may just be myth telling. But those old books are part of some of the oldest written historical records left by a group of literate neolithic humans. I refer to them as an additional data source that may yield evidence for further thought. Skeletons and the remains of old campsite fires only tell us so much. These records give us an insight into the thinking patterns of these distant ancestors.

Did they merely boast of longevity? Or did they have something figured out? They were herders, mostly eating organic grass fed lamb, a high fat, moderate protein, very low carbohydrate diet. What else did they get right before the Egyptians taught them how to settle down and poison themselves with grain as the Egyptians did?

July 17, 2009 | Unregistered CommenterBen Fury

I just read your comment on keeping carbs to 10% and I find it interesting. As I am doing Orthodox Paleo for the next 30 days to reset my system, I am sticking with mostly meat and eggs, nuts and oils, some fruit and little veggies. I like veggies but I just don't usually think to make them a big part of my plate. Maybe I'm more so inclined to think of veggies as a complement like Peter at Hyperlipid. So when it comes to carbs and particularly fructose, would you say that it would be better to have a sweet potato with my meal than to have some berries at desert? This kind of runs in to a talk of fructose content vs glycemic index/load. I'm guessing you would naturally say to skip the berries and the potato and add more fat but if you were to choose, I'm interested in the basis of your decision. The main fruits I eat are: strawberries, blueberries, and clementines. Sometimes I'll have a LaraBar which uses dates predominantly. I train in Crossfit and being fat fueled predominantly will be an interesting experiment. Thanks for your blog and time.
-Mark

July 17, 2009 | Unregistered CommenterMark

Kurt,

I really like your expression:

"CR is therefore just a partial restoration of our optimal phenotypic expression, not an enhancement of some "natural" state."

I (as a physical therapist) often use similar words when talking about physical activity and its 'benefits'. Correct physical activity is not really improving health, it is suboptimal physical activity (too much, too less, too monotonous, ...) that is actually bad for your health...

Pieter

July 17, 2009 | Unregistered Commenterpieter d

Indeed Pieter!

My mentor, Aaron Mattes refers to ranges of motion in human movement as "normal" not "ideal". For "normal" he uses the ranges of motion of his son Troy. Troy has done Active Isolated Stretching since he was a toddler and thus his ranges of motion are so extreme that we fondly call him "Gumby."

Full and unfettered use of our bodies is "normal." All we do as physical trainers is remind the body to go back to its proper functioning.

Be well,
Ben Fury
Bettercise

July 17, 2009 | Unregistered CommenterBen Fury

Tom and Mark

If the fruit keeps you from eating bread it's more good than harm. I usually have a handful of blueberries or raspberries each evening covered in unsweetened whipped whole cream.

I think I read Peter at hyerlipid say " I eat some berries, I just don't think they are going to save my life." I have the same attitude to both fruit and veggies - if your carb level is kept low, eat what you want that is not wheat and not laden with excess fiber - 50 g of sweet potatoes vs 50 g of fruit per day - probably no difference once your metabolism is mostly fat burning.

If you are trying to lose weight or having other insulin resistance issues, I would favor veggies and stay away from fructose laden fruit for the carbs.

My heirarchy, I guess, is zero wheat is most important, minimize the 6's and then the Fructose. A little fructose is better than a little wheat.

I am not doing a controlled experiment to see which one kills me, though - I try to minimize all 3, but I am most strict about gluten.

There are lot of blogs out there about low carb - I read a lot of them - the fact that I don't link to them all is not a negative endorsement in any way, I just try to link to the ones that I agree with the most. If you buy what I am saying you won't be off track or confused if you visit, say, Peter or Stephan's blog.

I will tell you I am closer to Peter's (Hyperlipid) view on fruits and veggies, and Stephan is more Weston Price-like, very respectful of our years of neolithic tradition of food preparation. MDA seems more enthusiastic about fruits and veggies and nuts and frankly, if you were trying to convince a "significant other" to buy into paleonutrition, starting with the "Lifestyle" orientation and photogenic salads of Sisson may work better than some of the more carnivorous sites like mine!

July 18, 2009 | Unregistered CommenterKurt G. Harris Md

Thanks for the reply Kurt.
I have a question for you - when I go low carb I often feel lethargic and my head feels almost dizzy - kind of like I have been punched! This feeling lasts for a while and does lessen after a meal but if I avoid fruit and the meal is low carb then it will continue. For example I had the feeling today and it has abated this evening after I have eaten several biscuits and a little chocolate.

Any thoughts. I am a 46 year old male, very fit and healthy. 60kgs. 164 cms tall.

July 19, 2009 | Unregistered Commentertom

Hi Kurt,

Could you please comment on:http://cat.inist.fr/?aModele=afficheN&cpsidt=17028783

Although intermitent MG has been proposed as a benefit due to an hormetic effect, could cronic exposure be determintental?

Regards
Randy

July 19, 2009 | Unregistered CommenterRandy

Tom

Sounds like hypogylcemia. is your heart rate increased? How long have you been LC and how low? This usually goes away after a week or so of 50g/day carbs. Would be most common with a carb free meal in someone with zero ketoadaptation (carbs 100 -300 day). I assume you are otherwise healthy and drug-free.

July 19, 2009 | Registered CommenterKurt G. Harris MD

Randy

Here is the abstract so folks know what we are talking about:

Ketosis leads to increased methylglyoxal production on the atkins diet
Auteur(s) / Author(s)
BEISSWENGER Benjamin G. K. ; DELUCIA Elizabeth M. ; LAPOINT Nancy ; SANFORD Rebecca J. ; BEISSWENGER Paul J. ;
Résumé / Abstract
In the popular and widely used Atkins diet, the body burns fat as its main fuel. This process produces ketosis and hence increased levels of β-hydroxybutyrate (BOB) acetoacetate (AcAc) and its by-products acetone and acetol. These products are potential precursors of the glycotoxin methylglyoxal. Since methylglyoxal and its byproducts are recognized as a significant cause of blood vessel and tissue damage, we measured methylglyoxal, acetone, and acetol in subjects on the Atkins diet. We found that by 14-28 days, methylghy-oxal levels rose 1.67-fold (P = 0.039) and acetol and acetone levels increased 2.7-and 6.12-fold, respectively (P = 0.012 and 0.028). Samples from subjects with ketosis showed even greater increases in methylglyoxal (2.12-fold), as well as acetol and acetone, which increased 4.19- and 7.9-fold, respectively; while no changes were seen in samples from noncompliant, nonketotic subjects. The increase in methylglyoxal implies that potential tissue and vascular damage can occur on the Atkins diet and should be considered when choosing a weight-loss program.
Revue / Journal Title
Annals of the New York Academy of Sciences ISSN 0077-8923 CODEN ANYAA9
Source / Source
2005, vol. 1043, pp. 201-210 [10 page(s) (article)]

My comments:

methylglyoxal is an AGE or AGE intermediary and is usually cited as relating more to glycolysis (logically) than ketosis, which is more or less the polar opposite metabolically. As HBA1c is an index of tissue damage due to AGEs, and not just an intermediary compound, and we know that diabetes and other conditions with chronically high glu and insulin are associated with oxidatitve damage, the idea that long term ketosis in a non-diabetic is a cause of cellular ox damage is a bit counter-intuitive.

The low p value suggests the 95% CI is quite wide relative to the modest effect size for MG (1.67). The acetone and acetol levels per se should be of no concern, how else could it be ketosis?

I would like to see a paper showing evidence of actual oxidative damage to functional proteins or cellular apparatus with long term ketosis. 14- 28 days of Atkins, with positive urine ketones, tells me nothing about what methylglyoxal levels are 6 months later with full ketoadaptation. The elevated blood levels are even stated in the abstract to be higher in those with more ketosis (urine ketones?) Such levels may decline later the same way urine ketones decline after months of ketoadaptation and more efficient fatty acid metabolism. That is what I suspect is going on.

Find me an optimal diet practitioner, VLC like PaNu or even zero carber with rising HBA1c levels and I will start to worry.

I do not have academic access and would have to pay for the full text- the abstract does not look very convincing by itself - if you can send me the full text of the paper I will comment further.

For the record, I am also not a believer in consumption of AGEs or Maillard compounds in food as being an important mechanism of oxidative damage.

July 19, 2009 | Registered CommenterKurt G. Harris MD

Yes - thanks for the reply. I am drug free and have been going lLC since March this year. Have progressively moved into it and eliminating sugar/flour etc. I read some of your older posts and am grateful for your responses.

July 19, 2009 | Unregistered Commentertom

Kurt,

If I had the full paper I'd gladly send it.

Here's a cross over study (PMID:http://www.ncbi.nlm.nih.gov/pubmed/19328268) comparing a high carb, moderate carb and ~ketogentic (supposively mantaince Atkins) at iso and eu caloric levels (no weight loss) that indicated impaired endothelial functioning only on the Atkins diets.

I just wish we had more data if the kind of diets are really healthy.


Comparative effects of three popular diets on lipids, endothelial function, and C-reactive protein during weight maintenance.Miller M, Beach V, Sorkin JD, Mangano C, Dobmeier C, Novacic D, Rhyne J, Vogel RA.
Divisionof Cardiology, University of Maryland Hospital, Room S3B06, 22 S. Greene St, Baltimore, MD 21201, USA. mmiller@medicine.umaryland.edu

July 19, 2009 | Unregistered CommenterRandy

Randy
I think the fact that this is all you can find that questions low carb is pretty good evidence that low carb is healthy - have you even read any of the other resources here?

The first study you quoted is not at all convincing for the reasons I gave.

This second abstract is even more meaningless than the first, as crossover studies of such short duration make it impossible to tell which diet you are really evaluating - this is a terrible study design.

Brachial artery reactivity is quoted as being made worse by carbs, saturated fat, low fat and high fat, depending on the study - BAR is not atherosclerosis, period. It is operator dependent as well,

LDL without particle size is meaningless, as I am sure you already know.

Making the diets isocaloric also completely defeats the purpose. If Atkins works by lowering caloric intake, what is the point?

July 20, 2009 | Unregistered CommenterKurt G. Harris MD

Dr. Harris,

I have been following the journal postings of Lex Rooker regarding his Paleo diet, zero carbs, grass fed raw meat diet with either 68% or 80% fat and the remainder protein. He has been on this program since mid 2006. He has been dutifully testing himself for ketosis, blood glucose levels, etc attempting to understand how his body works. His own body experiments indicate that his body converts about 58% of the protein he consumes converts to glucose.
I do not recall if he ever had his HBA1c tested. Lex is truly an optimal primal diet practioner

His family doctor is aware of his raw meat diet and was warned about all the conventional dangers associated with eating a raw meat high fat, high protein, zero carb diet.

And his doctor is always amazed at how good his lipid panel is. This year he will have a DEXA bone scan
in August to see if he has had any degradation in his bone density. His dentist tells him his jaw bone structure is very dense when compared to previous years examinations.

Lex's journal at http://www.rawpaleoforum.com/journals/lex's-journal/

July 22, 2009 | Unregistered CommenterDexter

Dexter

I can think of no advantage to eating the meat raw - hominids are adapted over at least 500 k to 2 M years to eating cooked food.

Eating meat raw exposes you to risk of infection from e.coli, etc. - it may be less risk if truly grass fed, but sometimes grass fed is processed with the same gear as feces- stained factory beef.

Rare for steaks, medium for hamburger is fine.

Eating vegetables raw is even more pointless nutritionally than cooked, IMO. More fiber to feed the bacteria in your gut.

July 26, 2009 | Registered CommenterKurt G. Harris MD

Dr. Harris,

Lex eats raw because he says no other animal eats their meat cooked. He will eat the occasional steak rare when out on social occasions.

But if he has to travel to conventions for a few days, he only eats breakfast foods consisting of eggs, bacon, sausages....avoiding all the high carb foods. The result is usually a severe case of painful edema in legs, ankles and feet and it takes a couple of weeks for the swelling to go down.

For him raw grass fed beef from Slankers in Texas is unadulterated food and he has never in the years he has been eating raw experienced any gastric problems.

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August 18, 2009 | Unregistered Commenterniccisweden

I'm going to disagree here and suggest that the interpretation that CR is simply a return to the natural, healthy state our ancestors lived in.

There is little evidence that the paleolithic man was chronically on a calorie-deficient diet. Something like intermittent fasting, probably, but calorie restriction? I highly doubt it.

If CR was the natural way of life, how come putting animals (basically any animal) on CR extends their lifespan? I mean, being animals in the wild, they are already in their natural environment? Therefore, CR in animals is an artificial state, not a natural state.

I think chronic CR exploits a mechanism hard-coded into most (if not all) species. When resources are scarce, reproductive processes grind to a halt and maintenance processes take priority. 50 years of CR is not something nature designed us for (and I'm using a metaphor here), but apparently it still works through that same mechanism and extends lifespan.

Furthermore, if you compare the reconstructions of what the paleolithic man looked like, it's not consistent with how a person on lifelong CR would look. Heck, it's not even consistent with people who begin CR in their adulthood.

If your theory is true, then going on a low-carb paleolithic diet should extend maximum lifespan the same way CR does. But there are no studies showing that it does. In fact, we have evidence that it doesn't. Living a paleolithic life is about maximizing mean lifespan but it does very little to increase maximal lifespan. I.e. you have a better chance of making it to a 100 years old, but not to 120 -- which is what CR is about.

Besides, since evolution aims at reproduction, "natural" is not always compatible with "longevity". I, for one, choose the latter.

You also write that there will never be a supplement or intervention that will be better than the natural way of life. Yet, the world is full of examples that this is not true. Take medicine, for instance. Without it, mean lifespan would be dramatically lower. More importantly, to say that we won't have the technology to radically increase lifespan seems terribly short-sighted to me. Does anyone really believe we'll still be dying of cancer in 500 years?

August 19, 2009 | Unregistered CommenterJLL

Oops, there's a typo in the first sentence:

"I'm going to disagree here and suggest that the interpretation that CR is simply a return to the natural, healthy state our ancestors lived in."

Should read:

"I'm going to disagree here and suggest that the interpretation that CR is simply a return to the natural, healthy state our ancestors lived in is incorrect."

August 19, 2009 | Unregistered CommenterJLL

JLL

"I'm going to disagree here and suggest that the interpretation that CR is simply a return to the natural, healthy state our ancestors lived in."

That is not at all what the essay says. It says that to the degree there are benefits to artificial CR, they arise from insulin levels that are close to the EM2.

"There is little evidence that the paleolithic man was chronically on a calorie-deficient diet. Something like intermittent fasting, probably, but calorie restriction? I highly doubt it."

My point is that relative to the SAD, the natural diet has less calories in it, that is why VLC diets spontaneously reduce caloric intake. IF is short term starvation, actually. If you starve one day a week, that is relative CR in the context of that week.Think insulin

"If CR was the natural way of life, how come putting animals (basically any animal) on CR extends their lifespan?'

This (any animal) is simply not true. CR works in artificial laboratory situations. You can't really do it with a wild diet because they are too ad lib and highly variable to control.
Also, I definitely did not say artificial CR is natural. I said that to the degree it works in experiments it is because it is restoring a more evolutionary hormonal milieu. Very different claim.

"I mean, being animals in the wild, they are already in their natural environment? Therefore, CR in animals is an artificial state, not a natural state."

RE-read the essays. CR is an artificial modification to an already artificial diet (especially this monkey study)


"I think chronic CR exploits a mechanism hard-coded into most (if not all) species. When resources are scarce, reproductive processes grind to a halt and maintenance processes take priority. 50 years of CR is not something nature designed us for (and I'm using a metaphor here), but apparently it still works through that same mechanism and extends lifespan."

I am indeed arguing the exact opposite. CR works only if you had an abnormally deviant diet in the first place. I predict it would not work at all if you started with a healthy wild diet. I am saying you will not benefit from correcting your insulin levels if they are already correct. RE-read all three essays, perhaps.

"Furthermore, if you compare the reconstructions of what the paleolithic man looked like, it's not consistent with how a person on lifelong CR would look. Heck, it's not even consistent with people who begin CR in their adulthood."

Once again you are misqouting. The very title of the essay is partial restoration. I explicitly say that it is improving insulin levels but PaNu is what is healthiest over all. I do not recommend artificial CR and I definitely never said paleo man practiced it. So what does paleo man's appearance compared to misguided humans that practice CR have to do with anything

"If your theory is true, then going on a low-carb paleolithic diet should extend maximum lifespan the same way CR does. But there are no studies showing that it does."

"In fact, we have evidence that it doesn't. Living a paleolithic life is about maximizing mean lifespan but it does very little to increase maximal lifespan. I.e. you have a better chance of making it to a 100 years old, but not to 120 -- which is what CR is about."

There is no evidence for any of these assertions you just made. There is no evidence that CR in humans would increase maximum lifespan beyond what good nutrition would do. That is my assertion and you may disagree but there is no evidence yet that I am wrong.

"Besides, since evolution aims at reproduction, "natural" is not always compatible with "longevity". I, for one, choose the latter."

You can choose what you like, but just because you think you will get that does not mean you will.

"You also write that there will never be a supplement or intervention that will be better than the natural way of life."

That is my prediction

"Yet, the world is full of examples that this is not true. Take medicine, for instance. Without it, mean lifespan would be dramatically lower."

You are confusing maximum lifespan with average lifespan.

"More importantly, to say that we won't have the technology to radically increase lifespan seems terribly short-sighted to me. Does anyone really believe we'll still be dying of cancer in 500 years?"

We will all die of something. We don't have the technology. Let me know when you find it, though.

August 19, 2009 | Registered CommenterKurt G. Harris MD

Kurt,

Thanks for replying to my comment and sorry for misquoting/misinterpreting your original essay. I have now re-read them, as you suggested.

"My point is that relative to the SAD, the natural diet has less calories in it, that is why VLC diets spontaneously reduce caloric intake. IF is short term starvation, actually. If you starve one day a week, that is relative CR in the context of that week."

Not sure what your definition of VLC is, but I find that at least on an LC diet, my total calorie intake is not necessarily reduced. I eat about 2,000 kcal per day, and when I'm fasting, I make up for it the next day by eating more. So the weekly calorie intake is not changed (not sure if this is what you meant by relative CR, though).

But yes, I do agree that most studies show a voluntary decrease in calorie intake when subjects change from their normal diet to a VLC diet. But what about the hunter-gatherers who eat a low-carb diet naturally (the Inuit, for example)? I'm not aware that their calorie intake is any lower than average -- at least not to the degree that it would count as CR.

"I am indeed arguing the exact opposite. CR works only if you had an abnormally deviant diet in the first place. I predict it would not work at all if you started with a healthy wild diet. I am saying you will not benefit from correcting your insulin levels if they are already correct."

I see. How would you test this hypothesis then? By feeding mice in group A their natural wild diet and restricting group B to 50% of their natural wild diet? Clearly, we can't use humans, because we'd outlive the scientists doing the study.

The fact remains that we can make mice live extraordinarily long when their calorie intake is restricted artificially. Yes, that's compared to the mice who were fed an ad libitum artificial diet, but where is the mouse that was fed a wild diet and that lived as long as the artificial CR mouse?

"There is no evidence for any of these assertions you just made. There is no evidence that CR in humans would increase maximum lifespan beyond what good nutrition would do. That is my assertion and you may disagree but there is no evidence yet that I am wrong."

I agree. It wasn't meant as scientific evidence, I was just underlining what the aim of CR is -- which is extending maximum lifespan.

Having said that, what is your opinion on the Okinawans? They're the closest data we have on CR in humans. Plus, their diet is not a paleolithic diet.

There's also no evidence of a paleolithic diet extending lifespan -- it's all speculation based on biomarkers, really. I personally follow a diet that is very much like what you recommend on your blog, but that's because there is data on disease prevention from following a paleo diet. What we don't have is life extension (beyond, say, 100 years) from following a paleo diet.

"You can choose what you like, but just because you think you will get that does not mean you will."

Of course not, I'm not saying it does. That was simply a reference to the naturalistic fallacy. There's a lot of things that are both bad and natural. And if the choice is between "good" and "natural", I will opt for the former.

"--You also write that there will never be a supplement or intervention that will be better than the natural way of life.--

That is my prediction."

That is a strange prediction. What is the natural way of life anyway? Living in a cave, hunting bisons and dying of an infection in your early 30's? Or is it the combination of a paleo diet and modern medicine (in which case I wouldn't call it 'the natural way of life')?

"We will all die of something. We don't have the technology. Let me know when you find it, though."

We are all dying of something, yes. And we don't have the technology yet. But science is progressing and maximum lifespan is increasing, slowly but surely. Once we learn how to really take advantage of things like nanotechnology to repair the damage in our bodies, the sky is the limit. Solving aging is really a matter of "when", not "if".

We can already do some pretty amazing stuff, like grow new body parts and

So yes, I will let you know when we find it ;) Until then, stay healthy and strong!

- JLL

August 20, 2009 | Unregistered CommenterJLL
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