The dietary regimen known as the Paleolithic diet (abbreviated paleo diet or paleodiet), also popularly called the caveman diet, Stone Age diet and hunter-gatherer diet, is a modern nutritional approach which seeks to mimic the ancient diet of wild plants and animals that various human (Homo) species habitually consumed during the Paleolithic, a period of about 2.5 million years duration that ended around 10,000 years ago with the development of agriculture—this ancestral diet is also commonly referred to as the "Paleolithic diet". Based upon commonly available modern foods, the "contemporary" Paleolithic diet consists mainly of: lean meat, fish, vegetables, fruit, roots, and nuts; and excludes: grains, legumes, dairy products, salt, refined sugar, and processed oils.
First popularized in the mid 1970s by a gastroenterologist named Walter L. Voegtlin, this nutritional concept has been expounded and adapted by a number of authors and researchers in several books and academic journals. Building upon the principles of evolutionary medicine, it is based on the premise that modern humans are genetically adapted to the diet of their Paleolithic ancestors and that human genetics have scarcely changed since the dawn of agriculture, and therefore that an ideal diet for human health and well-being is one that resembles this ancestral diet.
This dietary approach is a controversial topic amongst nutritionists and anthropologists. Advocates argue that modern human populations subsisting on traditional diets similar to those of Paleolithic hunter-gatherers are largely free of diseases of affluence, and that such diets produce beneficial health outcomes in controlled medical studies. Supporters point to several potentially therapeutic nutritional characteristics of preagricultural diets. Critics of this nutritional approach have taken issue with its underlying evolutionary logic, and have disputed certain dietary prescriptions on the grounds that they pose health risks and may not reflect the features of ancient Paleolithic diets. It has also been argued that such diets are not a realistic alternative for everyone.
Gastroenterologist Walter L. Voegtlin was one of the first to suggest that following a diet similar to that of the Paleolithic era would improve a person's health. In 1975, he published a book in which he argued that humans are carnivorous animals and that the ancestral Paleolithic diet was that of a carnivore—chiefly fats and protein, with only small amounts of carbohydrates. His dietary prescriptions were based on his own medical treatments of various digestive problems, namely colitis, Crohn's disease, irritable bowel syndrome and indigestion.
In 1985, Melvin Konner and S. Boyd Eaton, an associate clinical professor of radiology and an adjunct associate professor of anthropology at Emory University, published a key paper on Paleolithic nutrition in the New England Journal of Medicine, which allowed the dietary concept to gain mainstream medical recognition. Three years later, S. Boyd Eaton, Marjorie Shostak and Melvin Konner published a book about this nutritional approach, which was based on achieving the same proportions of nutrients (fat, protein, and carbohydrates, as well as vitamins and minerals) as were present in the diets of late Paleolithic people, not on excluding foods that were not available before the development of agriculture. As such, this nutritional approach included skimmed milk, whole-grain bread, brown rice, and potatoes prepared without fat, on the premise that such foods have the same nutritional properties as Paleolithic foods. In 1989, these authors published a second book on Paleolithic nutrition.
Since the end of the 1990s, a number of medical doctors and nutritionists have advocated a return to a so-called Paleolithic (preagricultural) diet. Proponents of this nutritional approach have published books and created websites to promote their dietary prescriptions. They have synthesized diets from commonly available modern foods that would emulate the nutritional characteristics of the ancient Paleolithic diet, some allowing specific foods that would have been unavailable to preagricultural peoples, such as certain processed oils and beverages.
The Paleolithic diet is a modern dietary regimen that seeks to mimic the diet of preagricultural hunter-gatherers, one that corresponds to what was available in any of the ecological niches of Paleolithic humans. Based upon commonly available modern foods, it includes cultivated plants and domesticated animal meat as an alternative to the wild sources of the original preagricultural diet. The ancestral human diet is inferred from historical and ethnographic studies of modern-day hunter-gatherers as well as archaeological finds and anthropological evidence.
The Paleolithic diet consists of foods that can be hunted and fished, such as meat, offal and seafood, and that can be gathered, such as eggs, insects, fruit, nuts, seeds, vegetables, mushrooms, herbs and spices. Practitioners are advised to eat only the leanest cuts of meat, free of food additives, preferably wild game meats and grass-fed beef since they contain relatively high levels of omega-3 fats compared with grain-produced domestic meats. Food groups that were rarely or never consumed by humans before the Neolithic (agricultural) revolution are excluded from the diet, mainly grains, legumes (e.g. peanuts), dairy products, salt, refined sugar and processed oils, although some advocates consider the use of oils with low omega-6/omega-3 ratios, such as olive oil and canola oil, to be healthy and advisable. Practitioners are permitted to drink mainly water, and some advocates recommend tea as a healthful drink, but alcoholic and fermented beverages are restricted from the diet. Furthermore, eating a wide variety of plant foods is recommended to avoid high intakes of potentially harmful bioactive substances, such as goitrogens, which are present in certain roots, vegetables and seeds. Unlike raw food diets, the Paleolithic diet does not limit the consumption of cooked foods. Cooking is widely accepted to have been practised by at least 250,000 years ago, in the early Middle Paleolithic.
According to certain proponents of the Paleolithic diet, practitioners should derive about 56–65% of their food energy from animal foods and 36–45% from plant foods. They recommend a diet high in protein (19–35% energy) and relatively low in carbohydrates (22–40% energy), with a fat intake (28–58% energy) similar to or higher than that found in Western diets. Furthermore, some proponents exclude from the diet foods which exhibit high glycemic indices, such as potatoes. Staffan Lindeberg, an associate professor in the Department of Medicine at the University of Lund, advocates a Paleolithic diet, but does not recommend any particular proportions of plants versus meat or macronutrient ratios. According to Lindeberg, calcium supplementation may be considered when the intake of green leafy vegetables and other dietary sources of calcium is limited.
According to S. Boyd Eaton, "we are the heirs of inherited characteristics accrued over millions of years; the vast majority of our biochemistry and physiology are tuned to life conditions that existed prior to the advent of agriculture some 10,000 years ago. Genetically our bodies are virtually the same as they were at the end of the Paleolithic Era some 20,000 years ago."
Paleolithic nutrition has its roots in evolutionary biology and rests on the principles of evolutionary medicine. The reasoning underlying this nutritional approach is that natural selection had sufficient time to genetically adapt the metabolism and physiology of Paleolithic humans to the varying dietary conditions of that era. But in the 10,000 years since the invention of agriculture and its consequent major change in the human diet, natural selection has had too little time to make the optimal genetic adaptations to the new diet. Physiological and metabolic maladaptations result from the suboptimal genetic adaptations to the contemporary human diet, which in turn contribute to many of the so-called diseases of civilization.
Loren Cordain, a professor in the Department of Health and Exercise Science at Colorado State University, argues that "today more than 70% of our dietary calories come from foods that our Paleolithic (Stone Age) ancestors rarely, if ever, ate. The result is epidemic levels of cardiovascular disease, cancer, diabetes, osteoporosis, arthritis, gastrointestinal disease, acne, and more." According to Staffan Lindeberg, the Paleolithic diet, basically meat, fish, vegetables, fruit and nuts, prevents heart disease, stroke and some forms of cancers and it has a beneficial effect on overweight, digestive problems and more; it may have benefits even compared with prudent diets based on whole-grain cereals and low-fat milk.
Based on the subsistence patterns and biomarkers of hunter-gatherers studied in the last century, advocates argue that modern humans are well adapted to the diet of their Paleolithic ancestor. The diet of modern hunter-gatherer groups is believed to be representative of patterns for humans of 50 to 25 thousand years ago, and individuals from these and other technologically primitive societies, including those individuals who reach the age of 60 or beyond, seem to be largely free of the signs and symptoms of chronic disease (such as obesity, high blood pressure, nonobstructive coronary atherosclerosis, and insulin resistance) that universally afflict the elderly in western societies (with the exception of osteoarthritis, which afflicts both populations). Moreover, when these people adopt western diets, their health declines and they begin to exhibit signs and symptoms of "diseases of civilization". In one clinical study, stroke and ischaemic heart disease appeared to be absent in a population living on the island of Kitava, in Papua New Guinea, where a subsistence lifestyle, uninfluenced by western dietary habits, was still maintained.
The results of initial prospective medical studies on the Paleolithic diet have shown positive health outcomes. The first animal experiment on a Paleolithic diet suggested that this diet, as compared with a cereal-based diet, conferred higher insulin sensitivity, lower C-reactive protein and lower blood pressure in domestic pigs. In the first controlled human trial on a Paleolithic diet, researchers found that the diet improved glucose tolerance more than a Mediterranean diet in individuals with ischaemic heart disease. Subsequently, a short-term intervention with the diet in healthy volunteers showed some favourable effects on cardiovascular risk factors. Regarding this medical trial, the NHS Knowledge Service states that there are several limitations to the study and that "readers should not draw too many conclusions from it." At least three clinical trials are currently underway to test various physiological effects of the Paleolithic diet.
Since the end of the Paleolithic period, several foods that humans would have rarely or never consumed during previous stages of their evolution have been introduced as staples in their diet. With the advent of agriculture and the beginning of animal domestication roughly 10,000 years ago, during the Neolithic Revolution, humans started consuming large amounts of dairy products, beans, cereals, alcohol, salt and fatty domestic meats. In the late 18th and early 19th centuries C.E., the Industrial revolution led to the large scale development of mechanized food processing techniques and intensive livestock farming methods, that enabled the production of refined cereals, refined sugars and refined vegetable oils, as well fattier domestic meats, which have become major components of Western diets. Such food staples have fundamentally altered several key nutritional characteristics of the human diet since the Paleolithic Era, and these dietary compositional changes have been implicated as risk factors in the pathogenesis of many of the so-called "diseases of civilization" and other chronic illnesses that are widely prevalent in Western societies, including obesity, cardiovascular disease, diabetes, osteoporosis, autoimmune-related diseases, certain cancers, myopia and acne, as well as many diseases related to vitamin and mineral deficiencies.
According to Cordain et al., the food staples and food-processing procedures introduced during the Neolithic and Industrial Eras have fundamentally altered seven crucial nutritional characteristics of the ancestral human diet, which serve to inhibit the development of the diseases of affluence in modern-day hunter-gatherers, namely glycemic load, fatty acid composition, macronutrient composition, micronutrient density, acid-base balance, sodium-potassium ratio, and fiber content.
Furthermore, cereal grains, legumes and milk contain bioactive substances, such as gluten and casein, which have been implicated in the development of various health problems. Consumption of gluten, a component of certain grains, such as wheat, rye and barley, is known to have adverse health effects in individuals suffering from a range of gluten sensitivities, including coeliac disease. Since the Paleolithic diet is devoid of cereal grains, it is free of gluten. The paleodiet is also casein-free. Casein is a protein found in milk and dairy products, which may impair glucose tolerance in humans.
Compared to Paleolithic food groups, cereal grains and legumes contain relatively high amounts of antinutrients, including alkylresorcinols, alpha-amylase inhibitors, protease inhibitors, lectins and phytates, substances known to interfere with the body's absorption of many key nutrients. Molecular-mimicking proteins, which are basically made up of strings of amino acids that closely resemble those of another totally different protein, are also found in grains and legumes, as well as milk and dairy products. Advocates of the Paleolithic diet have argued that these components of agrarian diets promote vitamin and mineral deficiencies and may explain the development of the "diseases of civilization" as well as a number of autoimmune-related diseases.
The therapeutic merits of the Paleolithic diet have been debated in numerous journals and edited volumes, covering such fields as nutrition, anthropology and medicine, and in various languages, including Swedish, and German. The controversy has focused on a number of key issues, including comparative life expectancy, the etiology of the diseases of affluence and the evolutionary assumptions underlying the Paleolithic diet.
One of the most frequent criticisms of the Paleolithic diet is that it is unlikely that preagricultural hunter-gatherers suffered from the diseases of modern civilization simply because they did not live long enough to develop these illnesses, which are typically associated with old age. In response to this argument, advocates of the paleodiet state that while Paleolithic hunter-gatherers did have a short average life expectancy, modern human populations with lifestyles resembling that of our preagricultural ancestors have little or no diseases of affluence, despite sufficient numbers of elderly.
Critics further contend that food energy excess, rather than the consumption of specific novel foods, such as grains and dairy products, underlies the diseases of affluence. According to Geoffrey Cannon, science and health policy advisor to the World Cancer Research Fund, humans are designed to work physically hard to produce food for subsistence and to survive periods of acute food shortage, and are not adapted to a diet rich in energy-dense foods. Similarly, William R. Leonard, a professor of anthropology at Northwestern University, states that the health problems facing industrial societies stem not from deviations from a specific ancestral diet but from an imbalance between calories consumed and calories burned, a state of energy excess uncharacteristic of ancestral lifestyles.
The evolutionary assumptions underlying the Paleolithic diet have also been disputed. According to Alexander Ströhle, Maike Wolters and Andreas Hahn, with the Department of Food Science at the University of Hannover, the statement that the human genome evolved during the Pleistocene (a period from 1,808,000 to 11,550 years ago) is resting on an inadequate, but popular gene-centered view of evolution. They rely on Russell (2001) to argue that evolution of organisms cannot be reduced to the genetic level with reference to mutation and that there is no one to one relationship between genotype and phenotype.
They further question the notion that 10,000 years since the dawn of agriculture is a period not nearly sufficient to ensure an adequate adaptation to agrarian diets. Referring to Wilson (1994), Ströhle et al. argue that "the number of generations that a species existed in the old environment was irrelevant, and that the response to the change of the environment of a species would depend on the hereditability of the traits, the intensity of selection and the number of generations that selection acts." They state that if the diet of Neolithic agriculturalists had been in discordance with their physiology, then this would have created a selection pressure for evolutionary change and modern humans, such as Europeans, whose ancestors have subsisted on agrarian diets for 400–500 generations should be somehow adequately adapted to it. In response to this argument, Wolfgang Kopp states that "we have to take into account that death from atherosclerosis and cardiovascular disease (CVD) occurs later during life, as a rule after the reproduction phase. Even a high mortality from CVD after the reproduction phase will create little selection pressure. Thus, it seems that a diet can be functional (it keeps us going) and dysfunctional (it causes health problems) at the same time." Moreover, S. Boyd Eaton and colleagues have indicated that "comparative genetic data provide compelling evidence against the contention that long exposure to agricultural and industrial circumstances has distanced us, genetically, from our Stone Age ancestors." According to Kopp, the implementation of high-glycemic and high-insulinogenic food, like refined cereals and sugars, into human nutrition only about 200 years, or 10 generations, ago, occurred too recently on an evolutionary time scale for the human genome to adjust.
Referencing Mahner et al. (2001) and Ströhle et al. (2006), Ströhle et al. state that "whatever is the fact, to think that a dietary factor is valuable (functional) to the organism only when there was ‘genetical adaptation’ and hence a new dietary factor is dysfunctional per se because there was no evolutionary adaptation to it, such a panselectionist misreading of biological evolution seems to be inspired by a naive adaptationistic view of life."
Katharine Milton, a professor of physical anthropology at the University of California, has also disputed the evolutionary logic upon which the Paleolithic diet is based. She questions the premise that the metabolism of modern humans must be genetically adapted to the dietary conditions of the Paleolithic. Relying on several of her previous publications, Milton states that "there is little evidence to suggest that human nutritional requirements or human digestive physiology were significantly affected by such diets at any point in human evolution."
The high protein and low-carbohydrate diet recommended by Loren Cordain and colleagues—i.e. about 56–65% of food energy coming from animal foods and 36–45% from plant foods, with 19–35% of energy derived from protein, 22–40% from carbohydrates and 28–58% from fat—based on the dietary patterns of worldwide modern-day hunter-gatherers has attracted a number of criticisms, including the following:
It has been argued that relative freedom from degenerative diseases was, and still is, characteristic of all hunter-gatherer societies irrespective of the macronutrient characteristics of their diets. Katharine Milton states that "hunter-gatherer societies, both recent and ancestral, displayed a wide variety of plant-animal subsistence ratios, illustrating the adaptability of human metabolism to a broad range of energy substrates. Because all hunter-gatherer societies are largely free of chronic degenerative disease, there seems little justification for advocating the therapeutic merits of one type of hunter-gatherer diet over another."
According to Marion Nestle, a professor in the Department of Nutrition and Food Studies at New York University, judging from research relating nutritional factors to chronic disease risks and to observations of exceptionally low chronic disease rates among people eating vegetarian, Mediterranean and Asian diets, it seems clear that plant-based diets are most associated with health and longevity.
Ströhle, Wolters and Hahn rely on Bjerregaard et al. (2003) to argue that hunters like the Inuit, who traditionally obtain most of their dietary energy from wild animals and therefore eat a low-carbohydrate diet, seem to have a high mortality from coronary heart disease, and they further indicate, based on previous observational studies, that many populations of horticulturists, pastoralists and simple agriculturists living today are ingesting a high-carbohydrate diet without having signs and symptoms of CHD.
Wolfgang Kopp states that "carbohydrate food, consumed by hunter-gatherers, is high in fiber and low-glycemic in effect, eliciting small amounts of insulin only. [...] Are high-carbohydrate diets atherogenic per se? Not if they have a low glycemic load. In this point, Stroehle et al. are right. However, it is the question, whether diets high in low-glycemic plant food (which is relatively high in indigestible fiber and relatively low in carbohydrate) should be labeled as “high-carbohydrate” diets." Kopp also says that it is very likely that diets with only a moderately increased glycemic load are atherogenic to some degree, referencing Coutinho et al. (1999) and Kopp (2006).
According to Erica Frank, professor of health care at the University of British Columbia, eating an animal also involves absorbing the toxins stored in its body fat. She quotes the EPA: "The average American intake is between 300 and 500 times the safe daily dose of dioxin." She argues that dioxin, which is stored in animal fat, is a cancer-causing substance and disrupts hormones and the immune system. "People would be in error if they think they're doing themselves a service by eating bison."
Critics have questionned the notion that preagricultural hunter-gatherers would have generally consumed a low-carbohydrate and high-protein diet. They argue that there is insufficient data to determine the average daily intake of animal and plant foods by Paleolithic humans, and stress the inherent variability of ancient and modern hunter-gatherer diets. According to Katharine Milton, "data from ethnographic studies of nineteenth and twentieth century hunter-gatherers, as well as historical accounts and the archeological record, suggest that ancestral hunter-gatherers enjoyed a rich variety of different diets. Thus estimates of nutrient proportions for "the Paleolithic diet" are hypothetical, at best." Echoing Milton's criticism, Ströhle et al. rely on Lindeberg (2005), Jenike (2001) and Conklin-Brittain et al. (2002). to argue that it is questionable if all hunter-gatherers living between 150,000 and 10,000 years ago in different geographical regions ate a low-carbohydrate diet. Based on Marlowe (2005), Ströhle et al. (2006) and Jenike (2001), they indicate that, because the plant–animal subsistence ratios of contemporary hunter-gatherers vary in a remarkable manner (0–90% food from gathering; 10–100% food from hunting and fishing), it is likely that the macronutrient intake of preagricultural humans varied enormously.
Skeptics, such as Sara Elton and Ströhle et al., have also drawn attention to anthropological research indicating that preagricultural hunter-gatherers may have consumed large quantities of carbohydrates in general. This includes hypotheses which suggest that carbohydrate tubers (plant underground storage organs) were eaten in high amounts by preagricultural humans, and models of the subsistence strategies of early hunter-gatherers that emphasize the limited role of meat as an energy source in ancestral forager diets. According to Staffan Lindeberg, an advocate of the Paleolithic diet, a plant-based diet rich in carbohydrates is consistent with the evolutionary past of humans.
The Paleolithic diet has been criticized on the grounds that it cannot be implemented on a worldwide scale. According to Loren Cordain, if such a diet was widely adopted, it would compromise the food security of populations dependent on cereal grains for their subsistence. However, he says that where cereals are not a necessity, as in most western countries, reverting to a grain-free diet can be highly practical in terms of cutting long-term healthcare costs. Barry Bogin, a professor of anthropology at the University of Michigan, states that less intensive farming techniques, such as pasture-grazed cattle, will not produce sufficient meat to feed the world’s population. On another level, critics have argued that exclusion diets such as the Stone Age diet "can be highly restrictive, socially disruptive, and expensive."