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Paleofantasy and the State of Ancestral Science

NOTE:  PaleoFX is coming up quickly and my talk will be related to some of the issues discussed below. It’s going to be a fun meeting. If you’d like to attent, buy a ticket or try your luck in FastPaleo’s PaleoFX ticket giveaway.

Marlene Zuk is an evolutionary biologist at the University of Minnesota, and her Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live is an important milestone for the Paleo movement: professional evolutionary biologists and anthropologists are now responding to Paleo ideas.

I haven’t yet read Paleofantasy but I have read:

Of the reviews, John Hawks in Nature is the most useful. Most Paleo community members have taken the term “Paleofantasy” as an attack upon the Paleo diet and lifestyle – as an assertion that our views conflict with reality – but Hawks suggests another take:

Zuk’s use of the term ‘fantasy’ is just an emphatic way of describing the hypothesis-forming that is essential to evolutionary science. We play with hypotheses, explore their predictions and try very hard to falsify them. So it is, in a way, unremarkable that so many hypotheses proposed by anthropologists about ancient environments now seem to be wrong — and, in a few cases, even ridiculous. [1]

The title “Paleofantasy” may sell more books than “Paleohypothesis,” but the latter is undoubtedly more accurate. The Paleo movement is based on a scientific hypothesis, and exploring its validity is a very reasonable thing for an evolutionary biologist to do. The ancestral health community should be flattered, not offended, that its science is being engaged by other scholars.

The Paleo Hypothesis

What is the Paleo hypothesis? The original version was expounded by Melvin Konner, Boyd Eaton, and others in the 1980s and 1990s. Here is Melvin Konner’s (2001) summary:

One approach, applied by Eaton and colleagues since the mid-1980s, is to consider the environment of evolutionary adaptedness for our species and to view it as the shaper of the latest draft of our genome…. This approach leads us to the discordance hypothesis, which attempts to assess the disjunction between those environments and the ones we live in now … [S]everal important chronic degenerative diseases have been interpreted as “diseases of civilization” because they appear to result from this disjunction. [2]

I’ve bolded the key ideas: that humans have an “environment of evolutionary adaptedness” approximately represented by the Paleolithic, and that multiple diseases result from a discordance between the modern and Paleolithic environments.

To operationalize the Paleo hypothesis, one must identify a modern implementation of the Paleolithic diet and lifestyle – not necessarily a complete re-enactment, but mimickry in essential elements. The most influential operationalization was created by Loren Cordain in The Paleo Diet (2002) and subsequent popularizers such as Robb Wolf tracked his diet closely. Their advice can be found on Cordain’s “What to Eat” and Wolf’s “What is the Paleo Diet?” pages: eat meat, fish, eggs, nuts, fruit, and vegetables; eschew starches, dairy, and some other foods.

A Target-Rich Environment

Both the Paleo hypothesis and its popular operationalization are vulnerable to challenge.

Most vulnerable is the operationalization by Cordain. It consists of an odd mix of foods. The meats, in accordance with archaeological evidence, derive mostly from grassland herbivores, while the plant foods – nuts, fruits, and vegetables – come largely from forest plants – trees. It is almost as if the evolutionary picture was that humans are chimps who learned to hunt, and our ancestors would dwell in the forest like chimps when foraging for plants but commute to grasslands to hunt animals.

This view drives Paleo toward a low-carb diet, since modern domesticated fruits and vegetables generally have only 50 to 200 carb calories per pound, and Paleolithic fruits and vegetables had even less. It would not have been easy for Paleolithic hominids to gather and eat many pounds of forest plant foods per person per day – especially when bipeds are not suited for getting fruit and nuts out of trees, and much of the band would have been hunting animals in a sparsely-treed semi-open grassland!

Not surprisingly, anthropological evidence has found that Paleolithic diets were quite different from the meat, fruit, and vegetables diet. There is little doubt that in the Paleolithic, starchy plants were a more important source of carbohydrates than fruits, just as they are among modern hunter-gatherers.

What is interesting about Zuk’s work is that she takes on the theoretical part of Paleo – the hypothesis of modern discordance with an environment of evolutionary adaptedness. Many in the Paleo movement take this as foundational, so if it were rebutted then one might think it would call into question the whole ancestral health movement.

Zuk’s Critique of the Paleo Hypothesis

Zuk’s critique strikes me as sound but disappointingly unambitious.

The Chronicle excerpt focuses on the persistence of evolutionary change:

[I]t is easy to assume that evolution requires eons. That assumption makes us feel that humans, who have gone from savanna to asphalt in a mere few thousand years, must be caught out by the pace of modern life …

[D]iscoveries like [the timing of the development of lactase persistence] make it clear that we cannot assume that evolution has stopped for humans, or that it can take place only ploddingly, with tiny steps over hundreds of thousands of years. In just the last few years we have added the ability to function at high altitudes and resistance to malaria to the list of rapidly evolved human characteristics …

Gregory Cochran and Henry Harpending even suggest that human evolution as a whole has, on the contrary, accelerated over the last several thousand years …

In one way Zuk is understating her point. Human genetic change did accelerate significantly over the last 10,000 years, due to rising populations which introduce new mutations to the human genome more frequently [3], and due to changes in selection pressure resulting from the establishment of large-scale societies following the domestication of animals.

Yet in another respect she is exaggerating it. The time required for favorable mutations to spread through the human population hasn’t shortened much since the Paleolithic. Even the most strongly selected recent mutations, such as that for lactase persistence, have spread only partially through the world’s peoples. There has certainly been insufficient time for the rest of the genome to evolve to an equilibrium with recently introduced mutations.

Yet, in the Paleolithic, the ancestral diet was probably similar in general outline for at least 2 million years: it consisted largely of meat, marrow, and plant foods collected from open woodlands and tree-spotted grasslands. There was sufficient time for new mutations to appear and rise to fixation, and then new mutations to appear and reach fixation against this new genetic background, and so on for many cycles. It is certainly possible that humanity became adapted to this (slowly changing) Paleolithic diet, and that the genetic variety introduced in the Holocene has been insufficient to destroy our fitness for a diet like that of the Paleolithic, and insufficient to make us well adapted to new Neolithic diets.

This point – that the relevant time-scale for assessing adaptedness may be the time for the genome to reach equilibrium, not merely the time for new point mutations to appear and grow to regional prominence – is an elementary one in evolutionary biology, one that is made in our book on pages 4-6, but from the Chronicle excerpt and various reviews (including this Amazon reader review), it appears that Zuk does not acknowledge this reason why treating the Paleolithic as an environment of evolutionary adaptedness may be a “Paleoinsight,” not a “Paleofantasy.”

Nor is it necessarily the case that adaptedness to the modern environment is assured by rapid recent evolution. To illustrate my point: a diet of Twinkies and Coca-Cola could never be healthful, and could never become our optimal diet, no matter how many billions of years we spent adapting to it. It simply lacks the nutrients needed to support sophisticated life.

So Zuk’s major points – that evolution has been a process of continuous change, never reaching a stable equilibrium; and that Paleolithic environments were diverse, making it difficult to specify an environment of evolutionary adaptedness or establish modern discordance with it – do establish that the Paleo hypothesis is not automatically trustworthy and needs to be supported in any given application by specific evidence. But she did not prove that it is never useful. It may guide us to a better diet and lifestyle.

Entertaining, But Unambitious

From reader reviews, the verdict emerges that Zuk wrote an entertaining book, using “Paleofantasies” as hooks on which to hang interesting facts, observations, and insights from evolutionary biology.

But most Paleo readers seem to have wanted a more ambitious undertaking. Most Paleo reviewers seem to agree with Theodore Roosevelt, who taught that in science

It is not the critic who counts … The credit belongs to the man who … strives valiantly, who errs and comes up short again and again, … who spends himself for a worthy cause; who, at the best, knows, in the end, the triumph of high achievement, and who, at the worst, if he fails, at least he fails while daring greatly … (“Citizenship in a Republic,” speech at the Sorbonne, Paris, April 23, 1910)

Evolutionary biology has much to teach us about how we should eat and live for best health. It would be good for evolutionary biologists to spend themselves for the worthy cause of identifying those truths.

What Does the Paleolithic Tell Us About Our Optimal Diet?

Coincidentally I came across a TEDx talk on Paleo diets by archaeologist Christina Warinner that makes a creditable effort at providing an alternative operationalization of a “Paleo diet.” Ignore the first three minutes in which she calls Paleo a fad diet based on meat; the latter part of the talk is excellent.

She makes the excellent point that domesticated plants have been bred for reduced toxicity. We may now be able to eat a much healthier diet than was possible during the Paleolithic, thanks to reduced-toxicity plant foods.

Warinner suggests the following modern operationalization of the “Paleolithic diet”:

  1. Eat a diet high in species diversity. Do not, as Americans do, concentrate plant consumption among a mere three species: corn, soy, and wheat.
  2. Eat fresh foods. Stored food loses nutrients and spoils; preservatives that inhibit microbial growth may disturb our gut microbiome.
  3. Eat whole natural foods; avoid refined processed foods. Natural foods have a full package of nutrition and healthful fiber. We should not indulge our new-found ability to consume sugar far more rapidly than would have been possible in the Paleolithic.

These are all points we make in Perfect Health Diet:

  • The benefits of diets high in species diversity are discussed in chapter 24 – because “the dose makes the poison,” diverse diets prevent toxins from becoming poisons.
  • The benefits of eating “recently living plants and animals” rather than processed foods constructed of purified nutrients are discussed in chapters 2, 8, and 23.

Warinner’s three recommendations are an excellent start toward a healthy diet. It’s good to see a scholar venturing to make prescriptive suggestions.

Yet I think that evolutionary biology can tell us much more than this. To see what it teaches, we have to broaden our perspective beyond the Paleolithic and the original “Paleo hypothesis,” and venture into biology.

Maybe “Paleo” Should Stand For Paleozoic Diet

One of the novel insights of Perfect Health Diet is that the evolutionary roots of the optimal human diet are ancient – they extend back to the start of the Paleozoic Era 541 million years ago when a great flourishing of multicellular life took place.

The rise of multicellular life depended on the use of carbohydrates to glycosylate membrane proteins and to form a carbohydrate-rich extracellular matrix to support multicellular structures. This increased use of carbohydrate was the last major change in the macronutrient composition of life. As life feeds on life, it represented the last major change in food.

In Perfect Health Diet, we discuss a number of evolutionary patterns determined by evolutionary selection and indicative of our optimal diet:

  1. Until bodily protein is depleted, all animals tolerate fasting quite well. This is because the composition of the body closely resembles the composition of our optimal food, so that self-cannibalization is nourishing.
  2. Breast milk has a similar composition in all mammalian species. This is because all mammalian species – whether herbivore, carnivore, or omnivore – need the same nourishment.
  3. Evolution doesn’t modify the body’s composition in order to exploit a new environmental niche, but rather modifies the digestive tract’s ability to transform novel foods into the desired nutrient mix. Herbivores, carnivores, and omnivores have similar nutritional needs and similar bodies; only their digestive tracts differ. The digestive tract is evolutionarily “plastic” in a way the rest of the body is not.
  4. In humans, the brain’s food reward system is an important guide to our most healthful diet. As dominant hunters and skillful foragers, ancestral humans had their choice of foods. Mankind’s Paleolithic evolution developed a food reward system that helps us choose an optimal mix of foods, and that brought us a diet that required minimal transformation by the digestive tract, enabling digestive organs to shrink. This is Aiello and Wheeler’s “expensive tissue hypothesis” [4], re-interpreted.

From this perspective, the optimal human diet was determined 541 million years ago, at the start of the Paleozoic, when the composition of animal flesh was more or less fixed. From that point forward, it was evolutionarily inevitable that as soon as a creature became able to “rule over the fish in the sea and the birds in the sky, over the livestock and all the wild animals, and over all the creatures that move along the ground” (Genesis 1:26), so that the whole world became its buffet table, this creature would lose its expensive digestive tract and gain a brain capable of guiding it to a healthful pattern of eating.

Our optimal diet is deeply constrained by our biology; it does not vary in any environment. Environmental changes that bring a new dietary niche force evolutionary changes to our food reward system and our digestive tracts, but they do not change the optimal human diet – one that, like breast milk, is little altered by evolutionary change. Because our body composition is evolutionarily stable, the mechanisms by which we select our foods and transform imperfect diets into something better are changed; not the mix of nutrients we need.

I like the name “Ancestral health movement” better than “Paleo” because it is less specific about whether there was a specific time of evolutionary adaptedness, or when that was. In truth, different organs of the body reached evolutionary adaptedness at different times – some as far back as 541 million years ago.

But from another perspective, “Paleo” is quite fitting. The Perfect Health Diet is truly “Paleo” – in the sense of Paleozoic, not Paleolithic.


The Ancestral Health Society is forming a new scholarly journal, The Journal of Evolution and Health, to complement its annual Symposium.

It is coming at a good time: when scholars have begun to appreciate the significance of the Paleo/Primal/PHD/Ancestral movement, yet remain unfamiliar with its recent scientific and intellectual developments.

Yes, the scientific hypotheses on which “Paleo” began were flawed (though insightful and scientifically productive); but a newer and better scientific foundation has been developed.

The Ancestral health movement has become popular because it works: it truly does heal and prevent disease, and millions have experienced its benefits. So it is no fad diet, and will not fade away.

I hope that scholars like Zuk and Warinner will continue their engagement with the ancestral health movement, and help us refine the science still more.


[1] Hawks J. Evolutionary biology: Twisting the tale of human evolution. Nature. 2013;495(7440):172 – 172.

[2] Konner M. Evolution and our environment: will we adapt? West J Med. 2001 May;174(5):360-1.

[3] Hawks J, Wang ET, Cochran GM, Harpending HC, Moyzis RK. Recent acceleration of human adaptive evolution. Proc Natl Acad Sci U S A. 2007 Dec 26;104(52):20753-8.

[4] Aiello LC, Wheeler P. The expensive tissue hypothesis: the brain and the digestive system in human and primate evolution. Current Anthropology 1995 Apr;36(2):199–211.

Chicken, Why Art Thou So Mediocre?

Chicken is the most popular meat in the United States; in 2010, 8.6 billion chickens were killed to provide Americans with 37.2 billion pounds of chicken, compared to 26.4 billion pounds of beef, 22.5 billlion pounds of pork, 5.8 billion pounds of turkey, and only 0.3 billion pounds of veal, lamb, and mutton.

The popularity of chicken has grown steadily over the last century. Here is a chart from the USDA Economic Research Service:

Increasing chicken consumption followed the development of cheaper chickens in the 1940s, which led to greater use of chicken into prepared and fast foods. It was further encouraged in the 1970s by the widely promulgated idea that red meat might be unhealthful and that chickens were comparatively healthful.

Yet in fact chicken may be the least healthful of the popular meats!

In our book (p 171) we give industrially raised chickens and their eggs a grade of C, eggs and meat from organically raised heritage chickens a B+/B. By comparison, beef gets an A. Why the difference?

Unhealthy Chickens

The methods that created cheaper chicken meat do not produce healthy chickens. Chickens were bred for rapid growth, but the modern Cornish Rock hens develop arthritis around age ten weeks, are often infertile, and prefer not to walk. (See “Local Farming and The Fight for Quality Food,” October 25, 2011.)

Factory farmed chickens are also fed arsenic, antibiotics, antihistamines, and, in China, antidepressants. [1] [2] (See Chapter 23 of the book.) It has recently been realized that these compounds may remain present at low levels in chicken meat. UPDATE: In the comments, Rachel Virden points out flaws in the studies cited above; chicken meat may be more healthful than these studies would suggest.

Omega-6 Fats and Obesity

Chicken have a moderately high omega-6 content; a whole chicken provides about 13% of all calories (about 20% of fat calories) as omega-6 fats. Because omega-6 toxicity begins at about 4% of energy (see chapter 11 of the book), replacing low-omega-6 foods like beef and seafood with chicken can help generate toxic levels of omega-6 in the body.

This has a variety of unfortunate consequences, including obesity. In my recent Q&A with Latest in Paleo readers, I gave six reasons why omega-6 fats promote weight gain. The last reason was that “omega-6 fats are precursors to endocannibinoids which increase appetite (see this article).”

The article in question shows an interesting figure which notes that chicken consumption is, after vegetable oils and with pork, the major contributor of omega-6 fats to the American diet, and is correlated with obesity prevalence (Figure 5):

Omega-6 Fats and Cancer

Omega-6 fats promote cancer growth and metastasis, and so we might expect that chicken consumption will also promote cancer.

It may. A study of men in remission from prostate cancer found that, “Intakes of processed and unprocessed red meat, fish, … and skinless poultry were not associated with prostate cancer recurrence or progression.” [3] However, the fatty parts of chickens – the skin and the eggs – were:

Greater consumption of eggs and poultry with skin was associated with 2-fold increases in risk in a comparison of extreme quantiles: eggs [hazard ratio (HR): 2.02; 95% CI: 1.10, 3.72; P for trend = 0.05] and poultry with skin (HR: 2.26; 95% CI: 1.36, 3.76; P for trend = 0.003)…. Men with high prognostic risk and a high poultry intake had a 4-fold increased risk of recurrence or progression compared with men with low/intermediate prognostic risk and a low poultry intake (P for interaction = 0.003).

Our results suggest that the postdiagnostic consumption of processed or unprocessed red meat, fish, or skinless poultry is not associated with prostate cancer recurrence or progression, whereas consumption of eggs and poultry with skin may increase the risk. [3]

We recommend three egg yolks per day for their nutrition, but the poor quality of industrial chickens is a real concern. If you can find a place in your budget for only one naturally raised food, make it your eggs.

Badly Cooked Chicken

Much chicken is bought in industrially produced forms or as fried chicken cooked in vegetable oils at high temperatures. High temperatures and peroxidizable vegetable oils are not a good way to treat any meat; as we note in the book (Chap 23), harsh cooking methods increase the toxicity of foods.

It seems to work that way with chicken. Another cancer study found that fried chicken consumption was associated with higher prostate cancer risk. They write:

Potential mechanisms include the formation of potentially carcinogenic agents such as aldehydes, acrolein, heterocyclic amines, polycyclic aromatic hydrocarbons, and acrylamide. [4]


I think most of the health problems with chicken are probably attributable to its omega-6 content, and in the context of a low omega-6 diet there is probably little harm to consuming gently cooked chicken or eggs. So I think most of the known concerns with chicken consumption should not frighten Perfect Health Dieters. Ironically, what makes chicken healthful is consuming red meat or seafood most of the week!

However, because eggs are such a significant part of our micronutrient recommendations, I think it is desirable to find an egg producer who lets the hens roam and eat insects and other natural chicken foods. Healthy chickens produce more healthful eggs; healthful eggs produce healthy people.


[1] Nachman KE et al. Arsenic species in poultry feather meal. Science of the Total Environment 2012 Feb 15;417–418:183–8,

[2] Love DC et al. Feather meal: a previously unrecognized route for reentry into the food supply of multiple pharmaceuticals and personal care products (PPCPs). Environmental Science & Technology 2012 Apr 3;46(7):3795–802,

[3] Richman EL et al. Intakes of meat, fish, poultry, and eggs and risk of prostate cancer progression. Am J Clin Nutr. 2010 Mar;91(3):712-21.

[4] Stott-Miller M et al. Consumption of deep-fried foods and risk of prostate cancer. Prostate. 2013 Jan 17. doi: 10.1002/pros.22643. [Epub ahead of print]


What’s New in the New Edition, 2: How to Lose Weight

NOTE: What’s New in the New Edition, 1 is here; and here is the Amazon book page.

Scribner wanted the new edition to show people how to lose weight. We were happy to do that. I’d been planning to devote 2012 to weight loss and obesity blog posts, and then to write an obesity and weight loss book in 2013. We just moved the schedule up and squeezed the ideas into Perfect Health Diet.

Our book offers a unique take on obesity and weight loss. Some of the science is original to us – the ideas do not appear in Pubmed – and the conclusions are unusual for diet books:

The best diet for weight loss is delicious and does not generate cravings or more than mild hunger. You can – and should! – lose weight with minimal suffering.

The popular diets that generate the quickest short-term weight loss are not optimal for long-term sustainable weight loss; they are prone to yo-yo weight regain.

Unlike those diets, the Perfect Health Diet offers a path to lasting weight less and permanent restoration of normal weight and normal body composition.

If we’re right about the science and these conclusions, then our book could be a game-changer for weight loss.

Filling in Some Missing Context

The major defect of squeezing our obesity & weight loss material into Perfect Health Diet, instead of distributing it over two books, is that we didn’t have space to provide a lot of context to the obesity material. Our stage-setting chapters were devoted to the general question of “what’s a healthy diet” and were framed with a discussion of Michael Pollan’s food rules, not with discussion of issues specific to obesity and weight loss.

So let me add some context here.

The Recipe for a Popular Weight Loss Book

The recipe for a popular weight loss book seems to be:

  • Declare that doltish mainstream authorities are stuck in some absurdly mistaken view, and their loyalty to this paradigm has led them to overlook the key to weight loss.
  • The key to weight loss is simple:  give up a single villainous food.

This formula has been followed to good effect by Dr. William Davis (Wheat Belly) who vilifies wheat, Gary Taubes (Good Calories, Bad Calories and Why We Get Fat) who vilifies carbs in general or sugar specifically, and Dr. Robert Lustig (Fat Chance) who vilifies sugar.

The view that authors attribute to mainstream authorities is, often, a straw man. Here is Gary Taubes in his Reddit “Ask Me Anything” describing the absurdly mistaken view that he calls “calories in, calories out”:

Imagine we have a pair of identical twins. Say 18-year-old boys. Every day we measure their energy expenditure and every day we feed them exactly how many calories they expend. So we match calories in to calories out. They get both the same diet with one exception: one gets 300 calories of sugar or HFCS where the other gets 300 calories of a different carbohydrate or of fat. Then we continue this feeding experiment for the next 20 years or so….

If you believe obesity is about calorie-in-calories-out and that’s the only thing that matters, then both twins are going to end up exactly the same weight with exactly same amount of fat on their body and they’re both going to end up expending the same amount of energy.

The view he is describing is that dietary quality doesn’t matter a whit, only quantity of calories matters: the only thing that affects body weight, fat mass, and energy expenditure is how many calories were consumed, and how many calories are consumed isn’t affected by dietary quality.

In other words, a diet of nothing but cotton candy, Twinkies, and Coca-Cola would generate after 20 years exactly the same body composition and health as a diet of fish, rice, and vegetables.

Is there a single person in the world who holds this view?

Here is a review of Dr. Lustig’s Fat Chance:

The book repeats and expands on the main point of contention in the sugar wars: whether our bodies treat all calories the same. The old guard says yes: A calorie is a calorie; steak or soda, doesn’t matter. Eat more calories than you burn, you’ll gain weight. Lustig believes that our bodies react to some types of calories differently than others. [PAJ: emphasis added]

The “old guard” does not always take kindly to the assertion that it never occurred to them that the body might react differently to different foods. The article notes:

[A] leading endocrinologist, who asked to go unnamed, called Lustig an “idiot.”

These are times when I wish our diet approved of popcorn!

Now, let me be clear: these authors are giving good advice. Indeed, we give the same advice. With Drs. Davis and Lustig, we recommend eliminating wheat and added sugar; with Taubes, we believe the average American should cut carb intake roughly in half. Taking these steps will help people lose weight.

But these books have significant flaws:

  • The advice is incomplete. There are many factors which promote obesity. Removal of a single factor will rarely normalize weight.
  • The scientific background is misleading. It often seems that the goal is not so much to provide insight, as to set up a compelling and entertaining narrative. The story reads like the script of a Hollywood action movie: a frightening and mysterious problem appears which befuddles everyone – a solution is proposed – a hero implements the solution.

Perhaps it is not possible to write books more popular than these, but I think it is possible to write books that provide more insight and have a better chance of delivering lasting weight loss to readers who are willing to invest effort.

Obesity is a complex disorder, and many factors contribute to it. I think we did a fairly good job of addressing many of those factors – enough to enable nearly all readers to lose weight effectively, but also to gain a deeper understanding of obesity and its causes.

The Puzzle of Fatty Acid Ratios

The focus on wheat, sugar, and carbs in the popular diet books ignores what may be the primary cause of the obesity epidemic. In my Q&A with Latest in Paleo readers, I gave six reasons why omega-6 fats promote obesity. Some of these are discussed in detail in the book.

Any explanation for the obesity epidemic should account for the accumulation of omega-6 fatty acids in the body that has coincided with the obesity epidemic:

This is a plot found on p 115 of the book; the data was compiled by Stephan Guyenet of Whole Health Source, the circles are the omega-6 fraction in adipose tissue, and the crosses are the obesity rate among 18-29 year olds. It is hard to make sense of this pattern if omega-6 fats are not causing the obesity epidemic. No carb-centric explanation for obesity will tend to make omega-6 fats accumulate this way. Unlike some of the other weight loss books, we make a good faith effort to explain data like this.

Why Do Low-Carb Diets Work?

The omega-6 accumulation is only one of a number of puzzles that a good theory of weight loss and weight gain should explain. Another is the efficacy of low-carb diets.

If carbs don’t cause obesity, why do low-carb diets promote weight loss?

This issue is explored in chapter 17, where we show reasons why reducing carbs to 30% of energy or less will be beneficial for weight loss, but also why there’s generally little long-term benefit from further reductions in carb intake. Low-carb is good, but very low-carb isn’t better for long-term weight loss.

The Problem of Yo-Yo Weight Loss

Another important puzzle: Why is yo-yo weight loss and regain so common?

Here is Jay Wright’s weight loss history, mentioned in the book at page 184:

Although he had successful short-term weight loss on a number of diets, including very low-carb Paleo, they always made him hungry and sooner or later the weight was regained.

On our diet, Jay reached his normal weight in October 2011. He emailed me a happy new year wish, and remains at his normal weight 15 months later – the first time since college he’s been able to maintain that weight.

Why did our diet normalize his weight permanently without hunger, when other weight loss diets led to hunger and weight regain? That is the primary subject of our chapter 17, and is one of our original contributions to the theory of obesity.

Malnutrition and Weight Gain

We argue that malnutrition is a potent cause of increased appetite and weight gain.

A theme of Weston A. Price’s Nutrition and Physical Degeneration is that pregnancy depletes nutrients in the mother, frequently leading (especially in closely spaced pregnancies) to malnutrition in both mother and child.

If we’re right, then this could be why pregnancies, especially closely spaced pregnancies, tend to produce maternal weight gain.

I got a New Year’s update from Jennifer Fulwiler, another source of a reader report in the book (on p 11). She’s now pregnant with her sixth child, and left a comment noting her much improved health this pregnancy:

I have been following the PHD for this pregnancy. The results have been amazing. In fact, with all five of my previous pregnancies I had debilitating, severe morning sickness. On the PHD, I had almost none!

In an email she gave further details:

My husband and I have a reality show that recently started airing [insert joke here about what we may have done to be deemed “reality show material”], and when the episodes air I’ve been engaging with fans on social media. One of the most common responses I get is that people are shocked that I look so healthy, since I’m pregnant with my sixth child in eight years. A lot of people just assume that women who have many and/or closely spaced pregnancies simply have to be overweight.

I used to assume that too. In fact, that had been my personal experience: I seemed to add a few pounds with each pregnancy, and after I had my fifth child I found myself tired, achy, and 35 pounds overweight. Thanks to the PHD I lost all the weight, and when the show was filmed, in my first trimester of pregnancy with my sixth child, I weighed the same as I did the day I got married, and felt better than I ever had in my life. A lot of people who watched the show asked me what my secret was, and of course I directed them to the PHD!

Here’s the first episode of Jennifer’s reality show:

She does indeed look healthy, energetic, and more than a match for a Texas scorpion!


I mentioned the other day that we got a 4* review at Amazon:

This diet has controlled my cravings. After almost 40 years of interest in and great benefits from proper nutrition, I believe this is as close to perfect eating as we can get…. I didn’t give it 5 stars for two reasons: 1. no recipes…but can get those online and 2. very technical, leaving more explanation or clarification.

That about covers the pros and cons of our book as a weight loss guide. Our story isn’t quite as simple as the other diet books. Perfect Health Diet doesn’t resemble a Hollywood action movie.

But if you want to understand the science and find a successful program for long-term weight loss, we’re the best choice on the market. Perfect Health Diet will eliminate cravings and hunger, get you close to perfect eating, and help you normalize weight for the rest of your life.

What’s New in the New Edition, I: Evolutionary Dieting

UPDATE: The new edition has launched! Books are in stock and shipping. Here is the Amazon page.

Readers of our first edition, like Steven, are naturally wondering what’s new in the Scribner edition.

There’s a lot that’s new. The Scribner edition is 50% longer; almost half of the material is new. Original material is revised and updated.

In a series of posts this week, I’m going to walk through the book and discuss what’s new and original. This post is about Part I, “An Evolutionary Guide to Healthful Eating.” (You can see a Table of Contents for the whole book on our Notes page, or in the Scribd excerpt below.)

Paleolithic Diets: An Evolutionary Story

Loren Cordain uses a striking analogy: he compares the length of the Paleolithic, 2.6 million years, to the length of a football field, 100 yards. By that scale, the Neolithic – the period when grains and farmed foods became a major part of our diet – is about a foot long. The point is that, in evolutionary terms, our relationship with agriculturally mass-produced cereal grains has been relatively short (to say nothing of our relationship with high-fructose corn syrup and soybean oil!). It stands to reason that we’d be adapted to the diet and lifestyle of the Paleolithic, and we agree, for reasons discussed in Chapter 1.

But what was the composition of Paleolithic diets? The Paleolithic was the era of stone tool use, and one of the primary purposes of stone tools was butchering animals, so the Paleolithic roughly corresponds to the period when meat was a significant part of our diet. But plants were also a major part.

The popular Paleo movement presents a fairly consistent view of what a “Paleo diet” is: meat and fish, fruits and vegetables, nuts and seeds. But how close is this “Paleo diet” to actual Paleolithic diets? Did Paleolithic peoples forgo starches? Did they eat almond meal waffles, muffins, and cookies? Looking into the actual Paleolithic diet is the subject of Chapter 2.

Unfortunately, the standard Paleo “evolutionary” argument doesn’t get us very far toward finding the optimal human diet. First, there was no one Paleolithic diet: it varied considerably by time and place. Second, the contention that our hunter-gatherer ancestors “adapted” to the diet they were eating and were optimized for it is open to question. Our biology is not infinitely malleable, capable of adapting to any diet. We could subsist on Twinkies for 2.6 million years, and Twinkies would never become the optimal human diet. How can we know that plants and animal foods gathered and hunted in the Paleolithic were then, or are now, our optimal diet?

Fortunately evolutionary evidence tells us much more about what is healthful for us, and what it tells us is supportive of the Paleolithic diet story.

A Richer Evolutionary Story

Evolution selects every aspect of our biology – how cells work, how organs work, how our brain works.

In the first edition, we gave a few very brief summaries of some alternative evolutionary arguments for the optimal human diet. We found that even very smart readers often misunderstood or didn’t appreciate the strength of these arguments, so we elaborated on them in the new edition.

These arguments are spelled out in Chapters 3-6: The “Cannibal Diet” of Fasting, What Breast Milk Teaches Us About Human Diets, What Mammalian Diets Teach Us About Human Diets, and The “Tastes Great!” Diet.

Why does fasting tell us about the optimal diet? Think about how food is handled. Our food doesn’t go straight from our digestive tract to our mitochondria to be turned immediately into energy. Instead, nutrients from food are incorporated into tissue within a few hours after a meal, and then that tissue is cannibalized to supply energy needs over the following 24 hours.

As a rule, tissues won’t accept just any macronutrients. Cells have a very specific structure, with fatty membranes and protein-rich cytosols; and they have very specific fatty acid profiles in their membranes, and amino acid ratios in their proteins. Cells specifically take up nutrients in the proportions they need, and refuse to incorporate nutrients they don’t need.

So if we evolved to be nourished by self-cannibalization of tissue, then the nutrient composition of our tissues must be close to our optimal diet.

What about breast milk? Most people will agree that this is the optimal food for infants. But many have thought there must be so many differences between infants and adults that breast milk will tell us little about the adult diet.

Not so. We can quantify the differences between infants and adults – they have mainly to do with the large and fast-growing infant brain – and can see which parts of the breast milk are designed to support that brain. We can adjust for those differences, and estimate the optimal adult diet from the composition of breast milk.

What about mammalian diets? I think this is one of the most interesting parts of our book and will be of great interest to pet owners, farmers, veterinarians, zookeepers, and anyone who has to feed animals.

The reality is that evolutionary selection has been operating for far longer than the Paleolithic, and it settled on certain solutions quite early. Multicellular life was common by 500 million years ago, and the basic composition of cells and their extracellular matrix scaffolding hasn’t changed much in that time.

So if our cellular biology hasn’t changed much in 500 million years, then the nutrients needed by cells hasn’t changed much either. That means the optimal diet hasn’t changed much. Yet there is a diversity of animals that occupies every possible ecological niche and type of food. How can a common biology be fed by a diversity of diets? Why are there herbivores, omnivores, and carnivores?

The resolution of this seeming paradox lies in the digestive tract and how it transforms food into nutrients. This allows us to infer from the digestive tract what an animal’s optimal diet is. We can do that for humans, too.

Those three evolutionary arguments were present in capsule form in the first edition, but the next one is entirely new to this edition: a discussion of the food reward system of the brain. Food reward evolved to motivate us to go seek out healthy, nourishing foods. If it evolved in the Paleolithic environment, then it tells us what foods were hard to get in the Paleolithic, but still necessary for health – these were the foods that Paleolithic foragers had to be motivated to work for.

But in our modern world, all foods are easy to obtain; they are on the shelves of supermarkets. So those foods that were hard to get in the Paleolithic are going to be precisely the ones that we overeat today.

The presence of an innate food reward system explains why peoples around the world eat very similar diets – almost always 50% carb, 15% protein, 35% fat, or close to it. If this food reward system evolved for the Paleolithic food environment, which was radically different from the modern agricultural and industrial global food production system, then we can’t trust our unconscious food buying impulses. If we just go to the supermarket and put whatever seems desirable into our cart, we will overeat all the things that our Paleolithic ancestors tended to undereat.

Worse, we will be tempted to eat junk foods designed to appeal to the tastes that signal healthfulness to the food reward system, without supplying the nutrients that actually deliver healthfulness.

On the other hand, this evolutionary argument is encouraging. It tells us that, if we eat Paleolithic foods and if we educate ourselves to select healthy foods in the optimal proportions, then we can be confident that our brains will find our meals to be delicious and satisfying.

A healthy diet is also a delicious and satisfying diet! There is no need to suffer to be healthy. There is no need to suffer to lose weight. If you are suffering on a diet, you are doing something wrong.

Part I ends by circling back to a recurring topic: animal diets. Our pets, zoo animals, and even feral rats living in urban areas and eating our trash are partaking of our ill health. They are becoming obese in parallel with us, and develop cardiovascular disease at similar rates; their wild counterparts do not have these problems. Yet returning zoo animals to their natural diets returns them to good health. Adopting our natural diet works for humans too. Our Perfect Health Diet reader success stories support this claim.

Evolutionary Fine-Turning

The rest of the book also puts some weight on evolutionary arguments. When we look at individual nutrients, we find that the body has evolved mechanisms to bring them close to an optimal level:

  • The body adjusts toward an optimal carb intake. When carb intake is too high, glucose is converted to fat. When carb intake is too low, glucose is manufactured from protein. The Goldilocks level, at which the body neither manufactures nor disposes of glucose, is an indicator of the optimal carb intake.
  • The body adjusts toward optimal fatty acid proportions. In Americans today, omega-6 fats are more than three times more likely to be burned for energy than saturated fats. Yet on omega-6 deficient diets, omega-6 fats are less likely to be burned for energy than saturated fats. This evolved system for regulating the body’s fatty acid composition is clear evidence that Americans eat too many omega-6 fats and too few saturated fats.

Similar arguments from evolutionary biology guide us toward optimal intake of micronutrients, which have degradation or excretion pathways turned on when they are present in excess, and conservation pathways turned on when they are scarce.

Cooperating with Our Bodies to Build Health

The earliest human temptation, if we are to believe the story of the Garden of Eden, was to “be as gods” and define good and evil — healthful and unhealthful — for ourselves. There is an undoubted attraction, we have felt it ourselves, to masterminding our diet and nutrition. We like to think that evolution got it wrong, or optimized for the wrong thing, and that an extreme diet or unnatural intervention can improve our health.

It’s not just extreme dieters who think this way. What is the pharmaceutical model of medicine, but the idea that we can alter the natural functioning of our bodies in ways that will make us healthier?

Sometimes this can work, but usually wisdom and deeper knowledge show us that evolution got it right, that our innate biology works to maintain our health rather than harm it, and that interventions which subvert natural functions tend to do more harm than good.

A more promising approach, we think, is to cooperate with our bodies. This leaves plenty of room for medicine to help – through diagnosis and testing, through antimicrobial treatments, through integrated dietary and lifestyle advice, and through interventions that support natural bodily functions (as, for instance, thyroid hormone replacement in hypothyroidism, or insulin therapy in type 1 diabetes).

It’s this cooperative approach, integrating the best of medicine with the best ancestral health practices, that we think will be most effective at generating good health and long life. We hope our book will illuminate what those “best ancestral health practices” are, and help build a cooperative effort between the natural health movement and the medical community.

Concluding Thoughts & a Book Excerpt

It could be said that our book is an “owner’s manual” for the human body, helping our readers know how to best support their own health by living in accord with our evolved biology.

The great thing is, the way to do this is by eating delicious, satisfying food!

If you’d like to get a feel for the book, check out this excerpt, which Scribner has put on Scribd:
PERFECT HEALTH DIET: How anyone can regain health and lose weight by optimizing nutrition, detoxifying the…