Tag Archives: Rebuttal

USNWR Cherry Picks Diets | The Paleo Diet

Just as surely as the swallows make their annual return to Mission San Juan Capistrano, U.S. News and World Report (USNWR) embarrasses not only itself, but the scientific and nutritional communities via its annual (January) subjective ratings of various popular, not so popular, and virtually unknown diets. As I and others have previously pointed out in 2014’s Rebuttal and 2013’s Rebuttal, these listings have no basis in objective science, but simply represent tallied subjective ratings by a group of experts, cherry picked by an unknown process, presumably by non-scientists at USNWR. I recognize a number of colleagues and good scientist in the expert list and am dismayed that they would participate in such a baseless and non-scientific process. Surely they did not participate in analyzing the data, because it is statistically inappropriate.

Sound nutritional science should not be about people’s opinions, but rather should employ the scientific method in which hypotheses are tested and conclusions drawn using replicable data that is statistically analyzed. Clearly, these procedures were not even remotely followed for this report, consequently the data USNWR has compiled is virtually meaningless. A better use of resources would be for USNWR to actually experimentally test one or more diets against any other diet for the seven end points of concern in this report. Or, at the very least, the panel of experts should be required to read, tabulate and analyze peer review publications of the diets rated in this report. This objective undertaking would be virtually impossible as more than half of the diets have never been written up in peer review scientific journals, much less experimentally tested against one another.

Evidently, a non-scientist at USNWR, not versed in statistics, compiled these results. Let me explain. The panel of 22 experts were asked to give each diet a 1, 2, 3, 4 or 5 ranking for each of the seven categories of interest (short term weight loss, long term weight loss, easy to follow, nutrition, safety, diabetes, heart health). When data is correctly analyzed, one of the first decisions is to determine the level (nominal, ordinal, interval or ratio) of the data. The expert panel’s 1 to 5 rankings represents ordinal data and not higher level interval or ratio data.  Accordingly, it is statistically incorrect to calculate a mean score from ordinal data for each of the seven categories as USNWR has done. Rather a frequency distribution displaying the totals, for each of the 5 rankings, is required for all seven categories to more accurately display this data. But why even bother, as this subjective information, even if analyzed correctly, has zero objective merit when making any logical decisions about diet.


Loren Cordain, Ph.D., Professor Emeritus

U.S. News and World Reports | The Paleo Diet
As many of you are now aware, U.S. News and World Reports (USNWR) has just issued their annual ratings of Best Diets for 2014. As per their 2011, 2012 and 2013 evaluations, the DASH diet was rated number one by a panel of nutritional and health “experts,” and The Paleo Diet again emerged last out of 32 diets which were considered. We have previously addressed the USNWR report as it relates to the Paleo Diet in extensive detail in the Original Rebuttal to the USNWR. I have a few additional important points which follow:

I would like to point out a number of crucial flaws in logic along with a total breakdown of the scientific method in these types of artificial, media-generated reports that invalidate any wide sweeping conclusions about diet reached by the popular press, by individual member of the USNWR panel or by USNWR itself.

The 2014 USNWR diet ratings represent nothing more than the subjective rankings of 32 popular diets by a group of professionals, ultimately hand-picked by the editorial infrastructure at USNWR. Notably lacking in the makeup of this panel are academic and medical professionals with a background and publication record in human evolution, ancestral human diets and the application of this diet within a clinical setting.

The USNWR ratings represent a purely subjective appraisal of 32 popular diets and accordingly has little or no objective value from a scientific perspective because of numerous and glaring flaws in the research design of this report. Let me give you an example.

Say you would like to experimentally test three different diets (Diet A, Diet B and Diet C) on a single outcome variable (perhaps, blood pressure) to determine which diet was most effective in lowering blood pressure. Such an experiment would require that you test Diet A to Diet B, Diet A to Diet C and Diet B to Diet C. Scientists then run statistical tests on these three trials (A to B, A to C and B to C) to determine the effectiveness (or lack thereof) of all three diets and all three possible comparisons.

If we would like to test four different diets (Diets A, B, C and D) against one another for their specific effectiveness on blood pressure, it would require 6 individual experiments (A to B; A to C; A to D; B to C; B to D and C to D). As more and more diets are tested against one another, the number of experiments required to evaluate one diet against the next rises exponentially (actually factorially).

To test 32 diets against one another, would require 538 individual experiments and at least 538 statistical comparisons!

These 538 experiments have never been conducted. In fact, very few of the 32 popular diets evaluated by the USNWR panel have ever been examined in the scientific literature or tested against one another statistically. Without objective data, ratings of popular diets by this or any panel of “experts” represent nothing more than pure subjective speculation by the members of the panel. Clearly another “expert” panel with an entirely different makeup could be convened whose dietary ratings may vary entirely from the USNWR panel.

Like it or not this is how science works. Hypotheses must be formulated and statistically tested. If the USNWR panel believes the DASH diet is superior to The Paleo Diet, it must be experimentally tested. You cannot say that one diet is more effective than another diet without testing it statistically with either experimental or epidemiological (population) studies. So, to say that the DASH rates number #1 among all 32 diets for either a single outcome variable (say blood pressure) or multiple outcome variables (weight loss, blood pressure, blood cholesterol levels, ease to follow, satiety, etc. ) is absolute nonsense from a scientific perspective.

I recognize a number of well-known and well published scientists on the USNWR panel. These scientists would be the first to tell you that the USNWR ratings are subjective in nature and not based upon factual comparisons found in the scientific literature testing each of the 32 diets against one another.

In contrast, The Paleo Diet has been frequently examined in the scientific literature and shown to be effective in facilitating weight loss, improving cardiovascular risk factors and satiety while being more nutrient dense for the 13 vitamins and minerals most lacking in the US diet when compared to the USDA Food Plate (formerly the Food Pyramid).


Loren Cordain, Ph.D., Professor Emeritus

Related Rebuttals

Robb Wolf’s US News Ranks The Paleo Diet: 2014. Deja Vu All Over Again!

Nell Stephenson’s The Paleo Diet on the ‘Worst Of’ List…

Mark Sisson’s Why Does the Paleo Diet Continue to Receive Low Points from “Established Authorities”?

Ben Balzer’s Paleo Diet Fights Back

Rebuttal | The Paleo Diet

A series of three scientific papers were published this this month in the early edition of the Proceedings of the National Academy of Sciences1-3 evaluating the diet of numerous species of fossilized hominins, bipedal or upright walking apes, who lived in Africa from 4.1 to 1.4 million years ago. The diet of a grass eating baboon was examined as well.4 Many of the authors of these papers are friends and colleagues whose data contribute to our understanding of our remote African ancestors’ diets. Collectively, the papers examined the following hominin genus’s and the time frame they lived: Australopithecus (circa 4 million years ago [MYA]), Kenyanthropus (circa 3-3.6 MYA), Paranthropus (circa 2.5-1.4 MYA), and early Homo (circa 2.3-1.5 MYA).

Before I get into the details of these studies, let me first openly reprimand some of the popular press who have incorrectly interpreted these studies by suggesting that our distant ancestors were regular consumers of grass and grass seeds (cereal grains). For instance, popular blogger Carrie Arnold, titles her write-up5 of these three scientific studies as, “Even Our Ancestors Never Really Ate the “Paleo Diet,” and goes on to say, “Researchers are just beginning to understand what ancient humans ate, and these recent studies show that grasses and grains have been part of the human diet for millions of years.” As I will shortly show you, this statement represents sensationalistic journalism and is patently false, as nowhere in any of these three papers1-3 is this conclusion reached by any of the authors.

Another piece of inaccurate and hyped journalism6 by author Chris Joyce at NPR labels his piece, “Grass: It’s What’s For Dinner (3.5 Million Years Ago).” Chris then tells us, “What the tale of the teeth reveals is this: About 3.5 million years ago, our ancestors started switching from the ape diet – leaves and fruit – to grasses and grass-like sedges.” This statement is false and again nowhere in any of these three papers1-3 is this assumption made by the scientists who wrote these manuscripts. Chris finally gets it right in his following statement, “Now, one thing this carbon isotope technique can’t tell is whether Australopithecus just grazed like a bunch of antelope, or whether they ate the antelope that did the grazing.” However, in his final paragraph his conclusion again is erroneous: “So, what to make of this? Well, for one, those who favor a “Paleo diet” that resembles what our early ancestors lived on might consider investing in a lawn mower. After all, lawn grass is probably American’s largest un-harvested crop – there’s plenty to go around. Why not go back to our roots?”

Catherine Griffin, a writer for Science World Reports obviously did not carefully read any of these three papers1-3 because of incorrect statements she has made in her brief article,7 “Human Ancestors’ Ape-like Diet Changed 3.5 Million Years Ago to Grass”. Catherine informs us, “Feel like eating some grass? Didn’t think so – but our ancient ancestors did. About 3.5 million years ago, our human forebears added tropical grasses and sedges to an ape—like diet of leaves and fruits from trees and shrubs.” She goes on to make other statements like, “In the end, the scientists found a surprising increase in the consumption of grasses and sedges” and “The earliest ancestors that consumed substantial amounts of grass foods . . .” which were never made in the original scientific papers.

In science, the devil is almost always in the details. Accordingly, all three of these popular science writers have done their readers a disservice by inaccurately reporting the details of these three studies1-3 and making assumptions about ancient hominin diets that the scientists themselves did not make.

In all three papers the measurement of two stable isotopes of carbon (13C and 12C) were made from samples of enamel in teeth of extinct hominins. From the ratio 13C/12C a difference (delta) (δ13C) is calculated relative to a standard value (8). δ13C values can then be used to determine if the carbon isotopes in the enamel ultimately originated from plants using either the C3 or C4 photosynthesis pathways.

In Africa and elsewhere, C4 plants include grasses and sedges and little else, whereas C3 plants include trees, shrubs, herbs and bushes. C4 plants incorporate relatively more 13C into their tissues during photosynthesis than do C3 plants. Hence, δ13C values extracted from enamel can reveal the dietary source of the isotopic signature, be it: 1) grasses and sedges, 2) trees, bushes, shrubs, herbs or 3) a combination of both categories of plants.

Unfortunately, a number of fundamental limitations exist with δ13C analysis to evaluate diet. δ13C measurements cannot determine the exact species of either C3 or C4 plants that were consumed, but more importantly δ13C values cannot distinguish if the C3 or C4 signatures originated from the direct consumption of plants or from the indirect consumption of animals that consumed these plants. In all three studies,1-3 this crucial point was brought out again and again by the authors. Apparently, the popular science writers covering these papers missed it. The data from all three papers1-3 corroborates the increasing body of literature8 demonstrating an increased C4 signature in the enamel of African hominins starting about 3.5 MYA, but whether or not it resulted from increased consumption of animal or plant foods or both is unknown. The authors of one of these three scientific papers1 put it best, “The 13C-enriched resources that hominins ate remain unknown and must await additional integration of existing paleodietary proxy data and new research on the distribution, abundance, nutrition and mechanical properties of C4 (and CAM) plants.”

I would like to point out a number of logical shortcomings with any interpretation of the hominin C4 data suggesting that it originated primarily from increased consumption of either grass leaves, grass seeds (cereal grains) and sedges rather than from consumption of animals (grazers) that ate grasses and grains. The point in time (~3.5 MYA) at which the C4 signature begins to increase occurs simultaneously with the earliest known use (before 3.39 MYA) of stone tools to cut flesh from animal carcasses and to extract marrow from their bones.9 Such hominin dietary practices have also been documented by 2.5 MYA10 and appear to be widely employed by 2.0 MYA11 and by 1.5 MYA.12 Hence by triangulating these indisputable archaeological facts with stable carbon isotope data, it is virtually certain that δ13C values in hominin enamel were enriched partially or perhaps mainly from increasing consumption of animals that ate C4 plants.

Other lines of evidence indicate that early African hominins were increasingly consuming more animal foods during the same time interval (3.5 MYA to 1.5 MYA) that δ13C had become enriched. Aiello and Wheeler13 have shown that the mass of the human gastrointestinal tract is only about 60% of that expected for a similar-sized primate. Consequently, the increase in brain size that occurred in hominins starting ~2.5 MYA was balanced by an almost identical reduction in the size of the gastrointestinal tract.13 The selective pressures that simultaneously allowed for both a reduction in gut size and an increase in brain size are attributed to an improvement in dietary quality (DQ) that occurred largely as a result of increased consumption of animal foods by Australopithecine species prior to the emergence of the first members of Homo.13-15 Because a diet with an increased DQ contains less structural plant parts and more animal material,16 its nutrient and energy density is greater. Hence the greater DQ of animal foods permitted relaxation of the selective pressures in hominins that formerly selected for a large, metabolically active gut necessary to process low DQ foods, which in turn permitted the natural selection of a large metabolically active brain13, 14 Grass leaves and seeds maintain a low DQ,15 and are high in fiber and cellulose and are indigestible in their raw, unprocessed state in modern humans.17 Accordingly, the proposition that increased consumption of grass leaves and seeds were the C4 source in hominin enamel, is inconsistent with the evolutionary gut/brain metabolic tradeoff.13-15 Selective pressures that reduce the size and metabolic activity of the gut require more energetically dense foods like meat and marrow – not energy poor, high cellulose and high fiber foods like grasses and sedges.

In addition to their low DQ, grass leaves and seeds are devoid of long chain fatty acids of both the omega 6 family (arachidonic acid, 20:4n6) and omega 3 family (docosahexanoic acid, 22:6n3), as are all plant foods.15 These fatty acids are necessary structural elements required for the synthesis of brain and neural tissues and cannot be produced endogenously in sufficient quantities to relax the selective pressures normally constraining encephalization (brain volume expansion relative to body weight). Therefore, exogenous sources of these two fatty acids must be obtained through diet in hominins to permit the evolution of large metabolically active brains (15, 18-21). Likely candidate animal foods which simultaneously increased the DQ and provided arachidonic acid (AA) and docosahexanoic acid (DHA) were scavenged de-fleshed long bones (which contain marrow – a high fat food) and skulls (which contain brains – high in AA and DHA) from carnivore kills.15 These foods along with meats from grazing animals likely represent the dominant dietary source for the increasing C4 signature in our African ancestors.

Another nutritional point lends little support to the notion that the increasing C4 signature in hominins starting 3.5 MYA resulted from direct consumption of grass leaves or seeds. All great apes (chimps, gorillas, orangutans and gibbons) living in their native environment bear δ13C values indicative of near total reliance upon C3 plants. Only a single higher primate, a baboon species, Theropithecus gelada, consumes grass leaves and seeds as their primary dietary source. Accordingly, this baboon maintains a carbon isotopic signature that is nearly 100 % C4 derived.4

High reliance upon grass and grass seeds in Theropithecus gelada or in any hominin requires a number of evolutionary adaptations in the digestive tract to accommodate these low quality, high cellulose foods – none of which have been observed in contemporary humans. All vertebrates lack the enzyme cellulase which is required to breakdown cellulose and hemicellulose found in grass leaves and seeds into glucose. Mammals that rely heavily upon grass and grass seed consumption for their sustenance have evolved large hindguts (caecums) or a four compartment stomach (ruminants) containing enormous quantities of microflora which have the capacity to ferment and breakdown cellulose, hemicellulose, starches and proteins into simpler compounds which can then be assimilated and metabolized by the host animal. In the case of Theropithecus gelada (the grass eating baboon), it has evolved a large hindgut where microbial fermentation of grass takes place.22 In contemporary humans, and in the hominin line that led to Homo, there is no credible evidence that gut morphology became larger and more metabolically active to support fermentation of cellulose in the caecum, but rather the opposite.13, 14 Hence, without the evolution of hindgut fermentation, efficient consumption of grass and grass seeds would have been impossible in any hominin species.

Other comparative physiological data between modern humans and the grass eating baboon (Theropithecus gelada) support the notion that the increasing C4 signature in evolving African hominins was not a result of grass or sedge consumption. Dicots or C3 plants produce compounds called tannins which act as a chemical defense system that discourage animals from eating them. Monocots or C4 plants (such as grass and sedges) do not synthesize tannins.23 Over the course of evolution, mammals that consume tannin containing C3 plants have evolved measures to counter the adverse effects of tannins. The most important of these mechanisms are salivary proteins that act as a defense against dietary tannins.24 These proline rich salivary proteins (PRPs) bind tannins and form stable complexes which prevent tannins from producing adverse health effects.24-27

Species that usually ingest tannin containing foods as part of their natural diets produce high levels of PRPs, whereas species not exposed to tannins produce little or no PRPs.24 In this regard, the saliva of the grass (C4) eating baboon (Theropithecus gelada) produces a saliva devoid of PRPs23 In contrast, modern humans synthesize a saliva containing abundant concentrations of PRPs25-27 which have been suggested to result from the long evolutionary history of fruit and vegetable (C3 plants) consumption in human ancestors.25 If ancestral African hominins had intensely exploited C4 plants (grasses and sedges) for millions of years, then it might be expected that the line of hominins that led to Homo and modern humans would also maintain low concentrations of salivary PRPs similar to Theropithecus gelada. Data in contemporary Homo sapiens do not support this conclusion.

In summary, recent comprehensive analyses1-3 of δ13C values in the enamel of African hominins from 4.1 to 1.5 MYA support the conclusion that plants of C4 origin were ultimately responsible for this isotopic signature. Nevertheless, when the isotopic data is triangulated from archaeological, physiological and nutrition evidence, it is apparent that the C4 signature in ancestral African hominin enamel almost certainly is resultant from increased consumption of animals that consumed C4 plants.

I have written a formal letter to the Proceedings of the National Academy of Sciences to address shortcomings. I appreciate your willingness to help set the record straight by sharing this post and among others, Medical Meals’ Dr. Mark J. Smith’s Rebuttal to Christina Warinner’s TED talk “Debunking the Paleo Diet.”


Loren Cordain, Ph.D., Professor Emeritus


1. Matt Sponheimer, Zeresenay Alemseged, Thure E. Cerling, Frederick E. Grine, William H. Kimbel, Meave G. Leakey, Julia A. Lee-Thorp, Fredrick Kyalo Manthi, Kaye E. Reed, Bernard A. Wood, and Jonathan G. Wynn. Isotopic evidence of early hominin diets. PNAS 2013 : 1222579110v1-201222579.

2. Jonathan G. Wynn, Matt Sponheimer, William H. Kimbel, Zeresenay Alemseged, Kaye Reed, Zelalem K. Bedaso, and Jessica N. Wilson. Diet of Australopithecus afarensis from the Pliocene Hadar Formation, Ethiopia. PNAS 2013 : 1222559110v1-201222559.
3. Thure E. Cerling, Fredrick Kyalo Manthi, Emma N. Mbua, Louise N. Leakey, Meave G. Leakey, Richard E. Leakey, Francis H. Brown, Frederick E. Grine, John A. Hart, Prince Kaleme, Hélène Roche, Kevin T. Uno, and Bernard A. Wood. Stable isotope-based diet reconstructions of Turkana Basin hominins. PNAS 2013 : 1222568110v1-201222568

4. Thure E. Cerling, Kendra L. Chritz, Nina G. Jablonski, Meave G. Leakey, and Fredrick Kyalo Manthi. Diet of Theropithecus from 4 to 1 Ma in Kenya. PNAS 2013 : 1222571110v1-201222571

5. Arnold, Carrie. “Even Our Ancestors Never Really Ate the “Paleo Diet” – The Crux | Discovermagazine.com.” DISCOVER Magazine: The Crux. Kalmbach Publishing Co., 3 June 2013.

6. Joyce, Chris. “Grass: It’s What’s For Dinner (3.5 Million Years Ago).” NPR the Salt. NPR, 3 June 2013.

7. Griffin, Catherine. “Human Ancestors’ Ape-like Diet Changed 3.5 Million Years Ago to Grass.” Science World Report: Nature & Environment. Science World Report, 4 June 2013.

8. Lee-Thorp JA, Sponheimer M, Passey BH, de Ruiter DJ, Cerling TE. Stable isotopes in fossil hominin tooth enamel suggest a fundamental dietary shift in the Pliocene. Phil. Trans. R. Soc. B (2010) 365, 3389–3396.

9. McPherron SP, Alemseged Z, Marean CW, Wynn JG, Reed D, Geraads D, Bobe R, Béarat HA. Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia. Nature. 2010 Aug 12;466(7308):857-60

10. de Heinzelin J, Clark JD, White T, Hart W, Renne P, WoldeGabriel G, Beyene Y, Vrba E. Environment and behavior of 2.5-million-year-old Bouri hominids. Science. 1999 Apr 23;284(5414):625-9.

11. Ferraro JV, Plummer TW, Pobiner BL, Oliver JS, Bishop LC, Braun DR, Ditchfield PW, Seaman JW 3rd, Binetti KM, Seaman JW Jr, Hertel F, Potts R. Earliest archaeological evidence of persistent hominin carnivory. PLoS One. 2013 Apr 25;8(4):e62174.

12. Pobiner BL, Rogers MJ, Monahan CM, Harris JW. New evidence for hominin carcass processing strategies at 1.5 Ma, Koobi Fora, Kenya. J Hum Evol. 2008 Jul;55(1):103-30.

13. Aiello L, Wheeler P. The expensive tissue hypothesis. Curr Anthropol 1995;36:199-221.

14. Leonard WR, Robertson ML: Evolutionary perspectives on human nutrition: the influence of brain and body size on diet and metabolism. Am J Hum Biol 1994;6:77–88.

15. Cordain L, Watkins BA, Mann NJ. Fatty acid composition and energy density of foods available to African hominids: evolutionary implications for human brain development. World Review of Nutrition and Dietetics, 2001, 90:144-161.
16. Sailer LD, Gaulin SC, Boster JS, Kurland JA: Measuring the relationship between dietary quality and body size in primates. Primates 1985;26:14–27.

17. Cordain L, (1999). Cereal grains: humanity’s double edged sword. World Review of Nutrition and Dietetics, 84: 19-73.

18. Broadhurst CL, Cunnane SC, Crawford MA: Rift valley lake fish and shellfish provided brainspecific nutrition for early Homo. B J Nutr 1998;79:3–21.

19. Crawford MA, Sinclair AJ: The long chain metabolites of linoleic and linolenic acids in liver and brains of herbivores and carnivores. Comp Biochem Physiol 1976;54B:395–401.

20. Crawford MA, Bloom M, Broadhurst CL, Schmidt WF, Cunnane SC, Galli C, Gehbremeskel K, Linseisen F, Lloyd-Smith J, Parkington J: Evidence for the unique function of docosahexaenoic acid during the evolution of the modern hominid brain. Lipids 1999;34:s39–s47.

21. Crawford MA: The role of dietary fatty acids in biology: Their place in the evolution of the human brain. Nutr Rev 1992;50:3–11.

22. Mau M, Johann A, Sliwa A, Hummel J, Südekum KH. Morphological and physiological aspects of digestive processes in the graminivorous primate Theropithecus gelada-a preliminary study. Am J Primatol. 2011 May;73(5):449-57

23. Mau M, Südekum KH, Johann A, Sliwa A, Kaiser TM. Saliva of the graminivorous Theropithecus gelada lacks proline-rich proteins and tannin-binding capacity.Am J Primatol. 2009 Aug;71(8):663-9

24. Shimada T. Salivary proteins as a defense against dietary tannins. J Chem Ecol. 2006 Jun;32(6):1149-63

25. Bennick A. Interaction of plant polyphenols with salivary proteins. Crit Rev Oral Biol Med. 2002;13(2):184-96

26. Bacon JR, Rhodes MJ. Binding affinity of hydrolyzable tannins to parotid saliva and to proline-rich proteins derived from it. J Agric Food Chem. 2000 Mar;48(3):838-43.

27. Yan Q, Bennick A. Identification of histatins as tannin-binding proteins in human saliva. Biochem J. 1995 Oct 1;311 ( Pt 1):341-7

Dr. Cordain's Rebuttal to U.S. News and World Report Top 20 Diets | The Paleo Diet

U.S. News & World Report ranked Paleo last of 32 diets claiming a lack of scientific evidence and no-long term weight maintenance guidelines. Are you interested in defending it or willing to provide specific refutations of their claims?

U.S. News & World Report – Health & Wellness Profile – The Paleo Diet

U.S. New & World Report – Top-Rated Diets Overall


Seth Stern

Dr. Cordain’s Response:

Hi Seth,

Good to hear from you and many thanks for your continued support of The Paleo Diet. It is obvious that whoever wrote this piece did not do their homework and has not read the peer review scientific papers which have examined contemporary diets based upon the Paleolithic food groups which shaped the genomes of our ancestors.  Accordingly the conclusions are erroneous and misleading.  I feel strongly that it is necessary to point out these errors and make this information known to a much wider audience than those reached by the readers of the U.S. News and World Report.

You have my permission to syndicate my response to any of the major news services including AP and UPI. Colleagues and scientists worldwide will receive this response to ensure that it will be widely circulated across the web and on blogs.

The writer of this article suggests that the Paleo Diet has only been scientifically tested in “one tiny study.”  This quote is incorrect as five studies (1-7); four since 2007, have experimentally tested contemporary versions of ancestral human diets and have found them to be superior to Mediterranean diets, diabetic diets and typical western diets in regards to weight loss, cardiovascular disease risk factors and risk factors for type 2 diabetes.

The first study to experimentally test diets devoid of grains, dairy and processed foods was performed by Dr. Kerin O’Dea at the University of Melbourne and published in the Journal, Diabetes in 1984 (6).  In this study Dr. O’Dea gathered together 10 middle aged Australian Aborigines who had been born in the “Outback”.  They had lived their early days primarily as hunter gatherers until they had no choice but to finally settle into a rural community with access to western goods.  Predictably, all ten subjects eventually became overweight and developed type 2 diabetes as they adopted western sedentary lifestyles in the community of Mowwanjum in the northern Kimberley region of Western Australia.  However, inherent in their upbringing was the knowledge to live and survive in this seemingly desolate land without any of the trappings of the modern world.

Dr. O’Dea requested these 10 middle aged subjects to revert to their former lives as hunter gatherers for a seven week period.  All agreed and traveled back into the isolated land from which they originated.  Their daily sustenance came only from native foods that could be foraged, hunted or gathered.  Instead of white bread, corn, sugar, powdered milk and canned foods, they began to eat the traditional fresh foods of their ancestral past: kangaroos, birds, crocodiles, turtles, shellfish, yams, figs, yabbies (freshwater crayfish), freshwater bream and bush honey.   At the experiment’s conclusion, the results were spectacular, but not altogether unexpected given what known about Paleo diets, even then.  The average weight loss in the group was 16.5 lbs; blood cholesterol dropped by 12 % and triglycerides were reduced by a whopping 72 %.  Insulin and glucose metabolism became normal, and their diabetes effectively disappeared.

The first recent study to experimentally test contemporary Paleo diets was published in 2007 (5). Dr. Lindeberg and associates placed 29 patients with type 2 diabetes and heart disease on either a Paleo diet or a Mediterranean diet based upon whole grains, low-fat dairy products, vegetables, fruits, fish, oils, and margarines.  Note that the Paleo diet excludes grains, dairy products and margarines while encouraging greater consumption of meat and fish.  After 12 weeks on either diet blood glucose tolerance (a risk factor for heart disease) improved in both groups, but was better in the Paleo dieters.  In a  2010 follow-up publication, of this same experiment the Paleo diet was shown to be more satiating on a calorie by calorie basis than the Mediterranean diet because it caused greater changes in leptin, a hormone which regulates appetite and body weight.

In the second modern study (2008) of Paleo Diets, Dr. Osterdahl and co-workers (7) put 14 healthy subjects on a Paleo diet.  After only three weeks the subjects lost weight, reduced their waist size and experienced significant reductions in blood pressure, and plasminogen activator inhibitor (a substance in blood which promotes clotting and accelerates artery clogging).  Because no control group was employed in this study, some scientists would argue that the beneficial changes might not necessarily be due to the Paleo diet.  However, a better controlled more recent experiments showed similar results.

In 2009, Dr. Frasetto and co-workers (1) put nine inactive subjects on a Paleo diet for just 10 days.  In this experiment, the Paleo diet was exactly matched in calories with the subjects’ usual diet.  Anytime people eat diets that are calorically reduced, no matter what foods are involved, they exhibit beneficial health effects.  So the beauty of this experiment was that any therapeutic changes in the subjects’ health could not be credited to reductions in calories, but rather to changes in the types of food eaten.  While on the Paleo diet either eight or all nine participants  experienced improvements in blood pressure, arterial function, insulin, total cholesterol, LDL cholesterol and triglycerides.  What is striking about this experiment is how rapidly so many markers of health improved, and that they occurred in every single patient.

In an even more convincing recent (2009) experiment, Dr. Lindeberg and colleagues (2) compared the effects of a Paleo diet to a diabetes diet generally recommended for patients with type 2 diabetes.  The diabetes diet was intended to reduce total fat by increasing whole grain bread and cereals, low fat dairy products, fruits and vegetables while restricting animal foods.   In contrast, the Paleo diet was lower in cereals, dairy products, potatoes, beans, and bakery foods but higher in fruits, vegetables, meat, and eggs compared to the diabetes diet.  The strength of this experiment was its cross over design in which all 13 diabetes patients first ate one diet for three months and then crossed over and ate the other diet for three months.  Compared to the diabetes diet, the Paleo diet resulted in improved weight loss, waist size, blood pressure, HDL cholesterol, triglycerides, blood glucose and hemoglobin A1c (a marker for long term blood glucose control).    This experiment represents the most powerful example to date of the Paleo diet’s effectiveness in treating people with serious health problems.

So, now that I have summarized the experimental evidence supporting the health and weight loss benefits of Paleo Diets, I would like to directly respond to the errors in the U.S. News and World Report article.

1. “Will you lose weight? No way to tell.”

Obviously, the author of this article did not read either the study by O’Dea (6) or the more powerful three month crossover experiment by Jonsson and colleagues (9) which demonstrated the superior weight loss potential of high protein, low glycemic load Paleo diets.  Similar results of high protein, low glycemic load diets have recently been reported in the largest randomized controlled trials ever undertaken in both adults and children.

A 2010 randomized trial involving 773 subjects and published in the New England Journal of Medicine (8) confirmed that high protein, low glycemic index diets were the most effective strategy to keep weight off.   The same beneficial effects of high protein, low glycemic index diets were dramatically demonstrated in largest nutritional trial, The DiOGenes Study (9), ever conducted in a sample of 827 children. Children assigned to low protein, high glycemic diets became significantly fatter over the 6 month experiment, whereas those overweight and obese children assigned to the high protein, low glycemic nutritional plan lost significant weight.

2. “Does it have cardiovascular benefits? Unknown.”

This comment shows just how uninformed this writer really is.  Clearly, this person hasn’t read the following papers (1 – 6) which unequivocally show the therapeutic effects of Paleo Diets upon cardiovascular risk factors.

“And all that fat would worry most experts.”

This statement represents a “scare tactic” unsubstantiated by the data.  As I, and almost the entire nutritional community,  have previously pointed out, it is not the quantity of fat which increases the risk for cardiovascular disease or cancer, or any other health problem, but rather the quality.  Contemporary Paleo Diets contain high concentrations of healthful omega 3 fatty acids, monounsaturated fatty acids and long chain polyunsaturated fatty acids that actually reduce the risk for chronic disease (10-18).

3. “Can it prevent or control diabetes? Unknown.”

Here is another example of irresponsible and biased journalism which doesn’t let the facts speak for themselves.  Obviously, the author did not read the study by O’dea (6) or Jonsson et al. (2) which showed dramatic improvements in type 2 diabetics consuming Paleo diets.

“but most diabetes experts recommend a diet that includes whole grains and dairy products.”

If the truth be known, in a randomized controlled trial, 24 8-y-old boys were asked to take 53 g of protein as milk or meat daily (19).  After only 7 days on the high milk diet, the boys became insulin resistant.  This is a condition that precedes the development of type 2 diabetes.  In contrast, In the meat-group, there was no increase in insulin and insulin resistance.  Further, in the Jonsson et al. study (2) milk and grain free diets were shown to have superior results in improving disease symptoms in type 2 diabetics.

4. “Are there health risks? Possibly. By shunning dairy and grains, you’re at risk of missing out on a lot of nutrients.”

Once again, this statement shows the writer’s ignorance and blatant disregard for the facts.  Because contemporary ancestral diets exclude processed foods, dairy and grains, they are actually more nutrient (vitamins, minerals and phytochemicals) dense than government recommended diets such as the food pyramid.    I have pointed out these facts in a paper I published in the American Journal of Nutrition in 2005 (13) along with another paper in which I analyzed the nutrient content of modern day Paleo diets (12 ).  Most nutritionists are aware that processed foods made with refined grains, sugars and vegetable oils have low concentrations of vitamins and minerals, but few realized that dairy products and whole grains contain significantly lower concentrations of the 13 vitamins and minerals most lacking in the U.S. diet compared to grass produced or free ranging meats, fish and fresh fruit and vegetables (12, 13).

“Also, if you’re not careful about making lean meat choices, you’ll quickly ratchet up your risk for heart problems.”

Actually, the most recent comprehensive meta analyses do not show fresh meat consumption whether fat or lean to be a significant risk factor for cardiovascular disease (20-25), only processed meats such as salami, bologna, bacon and sausages (20).


Loren Cordain, Ph.D., Emirates


1. Frassetto LA, Schloetter M, Mietus-Synder M, Morris RC, Jr., Sebastian A: Metabolic and physiologic improvements from consuming a paleolithic, hunter-gatherer type diet. Eur J Clin Nutr 2009.

2. Jönsson T, Granfeldt Y, Ahrén B, Branell UC, Pålsson G, Hansson A, Söderström M, Lindeberg S. Beneficial effects of a Paleolithic diet on cardiovascular risk factors in type 2 diabetes: a randomized cross-over pilot study. Cardiovasc Diabetol. 2009;8:35

3. Jonsson T, Granfeldt Y, Erlanson-Albertsson C, Ahren B, Lindeberg S. A Paleolithic diet is more satiating per calorie than a Mediterranean-like diet in individuals with ischemic heart disease. Nutr Metab (Lond). 2010 Nov 30;7(1):85

4. Jonsson T, Ahren B, Pacini G, Sundler F, Wierup N, Steen S, Sjoberg T, Ugander M, Frostegard J, Goransson Lindeberg S: A Paleolithic diet confers higher insulin sensitivity, lower C-reactive protein and lower blood pressure than a cereal-based diet in domestic pigs. Nutr Metab (Lond) 2006, 3:39.

5. Lindeberg S, Jonsson T, Granfeldt Y, Borgstrand E, Soffman J, Sjostrom K, Ahren B: A Palaeolithic diet improves glucose tolerance more than a Mediterranean-like diet in individuals with ischaemic heart disease. Diabetologia 2007, 50(9):1795-1807.

6. O’Dea K: Marked improvement in carbohydrate and lipid metabolism in diabetic Australian aborigines after temporary reversion to traditional lifestyle. Diabetes 1984, 33(6):596-603.

7. Osterdahl M, Kocturk T, Koochek A, Wandell PE: Effects of a short-term intervention with a paleolithic diet in healthy volunteers. Eur J Clin Nutr 2008, 62(5):682-685.

8. Larsen TM, Dalskov SM, van Baak M, Jebb SA, Papadaki A, Pfeiffer AF, Martinez JA, Handjieva-Darlenska T, Kunešová M, Pihlsgård M, Stender S, Holst C, Saris WH, Astrup A; Diet, Obesity, and Genes (Diogenes) Project. Diets with high or low protein content and glycemic index for weight-loss maintenance. N Engl J Med. 2010 Nov 25;363(22):2102-13

9. Papadaki A, Linardakis M, Larsen TM, van Baak MA, Lindroos AK, Pfeiffer AF, Martinez JA, Handjieva-Darlenska T, Kunesová M, Holst C, Astrup A, Saris WH, Kafatos A; DiOGenes Study Group. The effect of protein and glycemic index on children’s body composition: the DiOGenes randomized study. Pediatrics. 2010 Nov;126(5):e1143-52

10. Cordain L. Saturated fat consumption in ancestral human diets: implications for contemporary intakes.  In: Phytochemicals, Nutrient-Gene Interactions, Meskin MS, Bidlack WR, Randolph RK (Eds.), CRC Press (Taylor & Francis Group), 2006, pp. 115-126.

11. Cordain L, Miller JB, Eaton SB, Mann N, Holt SH, Speth JD. Plant-animal subsistence ratios and macronutrient energy estimations in worldwide hunter-gatherer diets.Am J Clin Nutr. 2000 Mar;71(3):682-92.

12. Cordain L. The nutritional characteristics of a contemporary diet based upon Paleolithic food groups. J Am Nutraceut Assoc 2002; 5:15-24.

13. Cordain L, Eaton SB, Sebastian A, Mann N, Lindeberg S, Watkins BA, O’Keefe JH, Brand-Miller J. Origins and evolution of the Western diet: health implications for the 21st century. Am J Clin Nutr. 2005 Feb;81(2):341-54.

14. Kuipers RS, Luxwolda MF, Dijck-Brouwer DA, Eaton SB, Crawford MA, Cordain L, Muskiet FA. Estimated macronutrient and fatty acid intakes from an East African Paleolithic diet. Br J Nutr. 2010 Dec;104(11):1666-87.

15. Ramsden CE, Faurot KR, Carrera-Bastos P, Cordain L, De Lorgeril M, Sperling LS.Dietary fat quality and coronary heart disease prevention: a unified theory based on evolutionary, historical, global, and modern perspectives. Curr Treat Options Cardiovasc Med. 2009 Aug;11(4):289-301.

16. Cordain L, Eaton SB, Miller JB, Mann N, Hill K. The paradoxical nature of hunter-gatherer diets: meat-based, yet non-atherogenic. Eur J Clin Nutr. 2002 Mar;56 Suppl 1:S42-52

17. Cordain L, Watkins BA, Florant GL, Kelher M, Rogers L, Li Y. Fatty acid analysis of wild ruminant tissues: evolutionary implications for reducing diet-related chronic disease. Eur J Clin Nutr. 2002 Mar;56(3):181-91

18. Carrera-Bastos P, Fontes Villalba M, O’Keefe JH, Lindeberg S, Cordain L. The western diet and lifestyle and diseases of civilization. Res Rep Clin Cardiol 2011; 2: 215-235.

19. Hoppe C, Mølgaard C, Vaag A, Barkholt V, Michaelsen KF. High intakes of milk, but not meat, increase s-insulin and insulin resistance in 8-year-old boys. Eur J Clin Nutr. 2005 Mar;59(3):393-8.

20. Micha R, Wallace SK, Mozaffarian D. Red and processed meat consumption and risk of incident coronary heart disease, stroke, and diabetes mellitus: a systematic review and meta-analysis. Circulation. 2010 Jun 1;121(21):2271-83

21. Micha R, Mozaffarian D. Saturated fat and cardiometabolic risk factors, coronary heart disease, stroke, and diabetes: a fresh look at the evidence. Lipids. 2010 Oct;45(10):893-905. Epub 2010 Mar 31.

22. Mozaffarian D, Micha R, Wallace S. Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLoS Med. 2010 Mar 23;7(3):e1000252.

23. Siri-Tarino PW, Sun Q, Hu FB, Krauss RM. Saturated fatty acids and risk of coronary heart disease: modulation by replacement nutrients. Curr Atheroscler Rep. 2010 Nov;12(6):384-90.

24. Siri-Tarino PW, Sun Q, Hu FB, Krauss RM. Saturated fat, carbohydrate, and cardiovascular disease. Am J Clin Nutr. 2010 Mar;91(3):502-9

25. Siri-Tarino PW, Sun Q, Hu FB, Krauss RM. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. Am J Clin Nutr. 2010 Mar;91(3):535-46

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