Paleo Diet

modern caveman

The paleolithic diet (also popularly referred to as the caveman diet, Stone Age diet, and hunter-gatherer diet) is a modern nutritional plan based on the presumed ancient diet of wild plants and animals that various hominid species habitually consumed during the Paleolithic era—a period of about 2.5 million years which ended around 10,000 years ago with the development of agriculture and grain-based diets.

In common usage, such terms as the ‘Paleolithic diet’ also refer to the actual ancestral human diet. Centered on commonly available modern foods, the ‘contemporary’ Paleolithic diet consists mainly of fish, grass-fed pasture raised meats, eggs, vegetables, fruit, fungi, roots, and nuts, and excludes grains, legumes, dairy products, potatoes, refined salt, refined sugar, and processed oils.

 First popularized in the mid-1970s by gastroenterologist Walter L. Voegtlin, this nutritional concept has been promoted and adapted by a number of authors and researchers in several books and academic journals. A common theme in evolutionary medicine, Paleolithic nutrition 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.

Proponents argue that modern human populations subsisting on traditional diets allegedly similar to those of Paleolithic hunter-gatherers are largely free of diseases of affluence, and that multiple studies of the Paleolithic diet in humans have shown improved health outcomes relative to other widely recommended diets. However, it is a controversial topic among some dietitians and anthropologists, and an article on the National Health Service of the United Kingdom Choices website refers to it as a fad diet. Critics have argued that if hunter-gatherer societies fail to suffer from ‘diseases of civilization,’ it is likely due to reduced calories in their diet, shorter average lifespans, or a variety of other factors, rather than dietary composition.

Some researchers have also taken issue with the accuracy of the diet’s underlying evolutionary logic or suggested that the diet could potentially pose health risks. A 2011 ranking by ‘U.S. News & World Report,’ involving a panel of 22 experts, ranked the Paleo diet lowest of the 20 diets evaluated based on factors including health, weight-loss and ease of following. However, one expert involved in the ranking stated that a ‘true Paleo diet might be a great option: very lean, pure meats, lots of wild plants. The modern approximations… are far from it.’ He added that ‘duplicating such a regimen in modern times would be difficult.’

The ‘U.S. News’ ranking assumed a low-carb version of the paleo diet, specifically containing only 23% carbohydrates. Higher carbohydrate versions of the diet, which allow for significant consumption of root vegetables, were not a part of this ranking. Dr. Loren Cordain, a proponent of a low-carbohydrate Paleolithic diet, responded by stating that their ‘conclusions are erroneous and misleading’ and pointing out that ‘five studies, 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 editors of the ‘U.S. News’ ranking replied that they had reviewed the five studies and found them to be ‘small and short, making strong conclusions difficult.’

Dr. 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 self-published ‘The Stone Age Diet: Based on in-depth Studies of Human Ecology and the Diet of Man,’ 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, S. Boyd Eaton and Melvin Konner, both of Emory University, published a paper on Paleolithic nutrition in the ‘New England Journal of Medicine’ which increased mainstream medical attention to the concept. Three years later they 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 supported a diet with the same macronutrient composition as the Paleolithic diet.

Starting in 1989, Swedish medical doctor and scientist Staffan Lindeberg, now associate professor at Lund University, Sweden, led scientific surveys of the non-westernized population on Kitava, one of the Trobriand Islands of Papua New Guinea. These surveys, collectively referred to as the Kitava Study, found that this population apparently did not suffer from stroke, ischemic heart disease, diabetes, obesity or hypertension. Starting with the first publication in 1993, the Kitava Study has subsequently generated a number of scientific publications on the relationship between diet and western disease. In 2003, Lindeberg published a Swedish language medical textbook on the subject. In 2010, this book was wholly revised, updated and published for the first time in English.

Since the end of the 1990s, a number of medical doctors and nutritionists have advocated a return to a so-called Paleolithic (preagricultural) diet. They have synthesized diets from modern foods that emulate nutritional characteristics of the ancient Paleolithic diet, some of which allow specific foods that would have been unavailable to pre-agricultural peoples, such as some animal products (i.e. dairy), processed oils, and beverages. The ancestral human diet is inferred from historical and ethnographic studies of modern-day hunter-gatherers as well as archaeological finds, anthropological evidence and application of optimal foraging theory (organisms behave in such a way as to find, capture and consume food containing the most calories while expending the least amount of time possible in doing so).

The Paleolithic diet consists of foods that can be hunted and fished, such as meat, offal and seafood, and can be gathered, such as eggs, insects, fruit, nuts, seeds, vegetables, mushrooms, herbs and spices. Some sources advise eating only lean cuts of meat, free of food additives, preferably wild game meats and grass-fed beef since they contain higher levels of omega-3 fats compared with grain-produced domestic meats. Food groups that advocates claim were rarely or never consumed by humans before the Neolithic (agricultural) revolution are excluded from the diet, mainly grains, legumes (e.g. beans and 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. More moderately, Kurt G. Harris recommends avoiding fructose, linoleic acid (a fatty acid found in many vegetable oils), and gluten grains (primarily wheat, barley, and rye) as the primary Neolithic agents responsible for modern diseases, and ‘the rest is just tinkering around the edges.’

On the Paleolithic diet, practitioners are permitted to drink mainly water, and some advocates recommend tea as a healthy 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 (substances which suppress the thyroid gland), which are present in some roots, vegetables and seeds. Unlike raw food diets, all foods may be cooked, without restrictions. However, raw Paleolithic dieters exist who believe that humans have not adapted to cooked foods, and so they eat only foods which are both raw and Paleolithic.

Paleo dieters eat 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. Some proponents exclude from the diet foods which exhibit high glycemic indices, such as potatoes. Dr. Lindeberg advocates a Paleolithic diet, but does not recommend any particular proportions of plants versus meat or macronutrient ratios, but cautions that calcium supplementation should 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 before 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.’ 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.’

More than 70% of the total daily energy consumed by all people in the United States comes from foods such as dairy products, cereals, refined sugars, refined vegetable oils and alcohol, that advocates of the Paleolithic diet assert contributed little or none of the energy in the typical preagricultural hominin diet. The consumption of these novel Neolithic and Industrial era foods is linked to the current epidemic levels of obesity, cardiovascular disease, high blood pressure, type 2 diabetes, osteoporosis and cancer in the US and other contemporary Western populations.

The evolutionary rationale has also been applied by researchers into the paleolithic lifestyle to argue for high levels of physical activity in addition to dietary practices. It has been proposed that human genes ‘evolved with the expectation of requiring a certain threshold of physical activity’ and that sedentary lifestyle results in abnormal gene expression. Compared to ancestral humans, modern humans often have increased body fat and substantially less lean muscle, which is a risk factor for insulin resistance. Human metabolic processes were evolved in the presence of physical activity-rest cycles, which regularly depleted skeletal muscles of their glycogen stores.

To date it is unclear whether these activity cycles universally included prolonged endurance activity (e.g. persistence hunting) and/or shorter, higher intensity activity. S. Boyd Eaton estimated that ancestral humans spent one-third of their caloric intake on physical activity (1000 kcal/day out of the total caloric intake of 3000 kcal/day), and that the paleolithic lifestyle was well approximated by the WHO recommendation of the physical activity level of 1.75, or 60 minutes/day of moderate-intensity exercise. L. Cordain estimated that the optimal level of physical activity is on the order of 90 kcal/kg/week (900 kcal/day for a 70 kg human.)

The evolutionary assumptions underlying the Paleolithic diet have been disputed. According to the Department of Food Science at the University of Hanover, the statement that the human genome evolved during the Pleistocene (a period from 1,808,000 to 11,550 years ago) rests on the gene-centered view of evolution, which they believe to be controversial. They rely on Gray (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 is an insufficient period of time to ensure an adequate adaptation to agrarian diets. For example, alleles conferring lactose tolerance increased to high frequencies in Europe just a few thousand years after animal husbandry was invented, and recent increases in the number of copies of the gene for salivary amylase, which digests starch, appear to be related to agriculture. 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 heritability 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’; however, they mention exceptions such as increased lactose and gluten tolerance, which improve ability to digest dairy and grains, while other studies indicate that human adaptive evolution has accelerated since the Paleolithic.

However, 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 UC Berkeley, 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. 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 specific plant to animal food ratio in the Paleolithic diet is also a matter of some dispute. The average diet among modern hunter-gatherer societies is estimated to consist of 64–68% of animal calories and 32–36% of plant calories, with animal calories further divided between fished and hunted animals in varying proportions (most typically, with hunted animal food comprising 26–35% of the overall diet). As part of the ‘Man the Hunter’ paradigm, this ratio was used as the basis of the earliest forms of the Paleolithic diet by Voegtlin, Eaton and others. To this day, many advocates of the Paleolithic diet consider high percentage of animal flesh to be one of the key features of the diet.

However, great disparities do exist, even between different modern hunter-gatherer societies. The animal-derived calorie percentage ranges from 25% in the Gwi people of southern Africa, to 99% in Alaskan Nunamiut. The animal-derived percentage value is skewed upwards by polar hunter-gatherer societies, who have no choice but to eat animal food because of the inaccessibility of plant foods. Since those environments were only populated relatively recently (for example, Paleo-Indian ancestors of Nunamiut are thought to have arrived in Alaska no earlier than 30,000 years ago), such diets represent recent adaptations rather than conditions that shaped human evolution during much of the Paleolithic. More generally, hunting and fishing tend to provide a higher percentage of energy in forager societies living at higher latitudes. Excluding cold-climate and equestrian foragers results in a diet structure of 52% plant calories, 26% hunting calories, and 22% fishing calories. Furthermore, those numbers may still not be representative of a typical Stone Age diet, since fishing did not become common in many parts of the world until the Upper Paleolithic period 35-40 thousand years ago.

Another view is that, up until the Upper Paleolithic, humans were frugivores (fruit eaters), who supplemented their meals with carrion, eggs, and small prey such as baby birds and mussels, and, only on rare occasions, managed to kill and consume big game such as antelopes. This view is supported by the studies of higher apes, particularly chimpanzees. Chimpanzees are closest to humans genetically, sharing more than 98% of their DNA code with humans, and their digestive tract is functionally very similar to that of humans. Chimpanzees are primarily frugivores, but they could and would consume and digest animal flesh, given the opportunity. However, their actual diet in the wild is about 95% plant-based, with the remaining 5% filled with insects, eggs, and baby animals. Some comparative studies of human and higher primate digestive tracts do suggest that humans have evolved to obtain greater amounts of calories from sources such as animal foods, allowing them to shrink the size of the gastrointestinal tract, relative to body mass, and to increase the brain mass instead.

A difficulty with this point of view is that humans are established to conditionally require certain long-chain polyunsaturated fatty acids (LC-PUFAs), such as AA and DHA, from the diet. Human LC-PUFA requirements are much greater than chimpanzees’ because of humans’ larger brain mass, and humans’ abilities to synthesize them from other nutrients are poor, suggesting readily available external sources. Pregnant and lactating females require 100 mg of DHA per day. But LC-PUFAs are almost nonexistent in plants and in most tissues of warm-climate animals. The main sources of DHA in the modern human diet are fish and the fatty organs of animals, such as brains, eyes and viscera; microalgae is a plant-based source. Despite the general shortage of evidence for extensive fishing, thought to require relatively sophisticated tools which have become available only in the last 30–50 thousand years, it has been argued that exploitation of coastal fauna somehow provided hominids with abundant LC-PUFAs. Alternatively, it has been proposed that early hominids frequently scavenged predators’ kills and consumed parts which were left untouched by predators, most commonly the brain, which is very high in AA and DHA.

Since the end of the Paleolithic period, several foods that humans 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 and salt. In the late 18th and early 19th centuries, 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 as 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, including glycemic load, fatty acid composition, macronutrient composition, micronutrient density, acid-base balance, sodium-potassium ratio, and fiber content. These dietary compositional changes have been theorized 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, high blood pressure, type 2 diabetes, osteoporosis, autoimmune diseases, colorectal cancer, myopia, acne, depression, and diseases related to vitamin and mineral deficiencies.

The Paleolithic diet has lower energy density than the typical diet consumed by modern humans. This is especially true in primarily plant-based/vegetarian versions of the diet, but it still holds if substantial amounts of lean meat are included in calculations. For example, most fruits and berries contain 0.4 to 0.8 calories per gram, vegetables can be even lower than that (cucumbers contain only 0.16 calories per gram). Lean game meat, such as cooked wild rabbit, is more energy-dense (up to 1.7 calories per gram), but it does not constitute the bulk of the diet by mass/volume at the recommended plant/animal ratios, and it does not reach the densities of many processed foods commonly consumed by modern humans: most McDonalds sandwiches such as the Big Mac average 2.4 to 2.8 calories/gram, and sweets such as cookies and chocolate bars commonly exceed 4 calories/gram.

Fruits, vegetables, meat and organ meats, and seafood, which are staples of the hunter-gatherer diet, are more micronutrient-dense than refined sugars, grains, vegetable oils, and dairy products in relation to digestible energy. Consequently, the vitamin and mineral content of the diet is very high compared with a standard diet, in many cases a multiple of the RDA. Fish and seafood represent a particularly rich source of omega-3 fatty acids and other micronutrients, such as iodine, iron, zinc, copper, and selenium, that are crucial for proper brain function and development. Terrestrial animal foods, such as muscle, brain, bone marrow, thyroid gland, and other organs, also represent a primary source of these nutrients. Calcium-poor grains and legumes are excluded from the diet. Although, leafy greens like Kale and dandelion greens as well as nuts such as Almond are very high sources of calcium. Also, components in plants make their low calcium amounts much more easily absorbed, unlike items with high calcium resources such as dairy. However, modern humans require much more vitamin D than hunter-gatherers, because they do not get the same amount of exposure to sun. This need is commonly satisfied in developed countries by artificially fortifying dairy products with the vitamin. To avoid deficiency, a modern human on a hunter-gatherer diet would have to take artificial supplements of the vitamin, ensure adequate intake of some fatty fish, or increase the amount of exposure to sunlight (it has been estimated that 30 minutes of exposure to mid-day sun twice a week is adequate for most people).

Diets containing high amounts of animal products, animal protein, processed foods, and other foods that induce and sustain increased acidity of body fluid may contribute to the development of osteoporosis and renal stones, loss of muscle mass, and age-related renal insufficiency due to the body’s use of calcium to buffer pH. The paleo diet may not contain the high levels of calcium recommended in the U.S. to prevent these effects.

Compared to Paleolithic food groups, cereal grains and legumes contain 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.

One line of evidence used to support the Stone Age diet is the decline in human health and body mass that occurred with the adoption of agriculture, at the end of the Paleolithic era. Associated with the introduction of domesticated and processed plant foods, such as cereal grains, in the human diet, there was, in many areas, a general decrease in body stature and dentition size, and an increase in dental decay prevalence. There is evidence of a general decline in health in some areas; whether the decline was caused by dietary change is debated academically.

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 fifty to twenty-five 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.

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. According to S. Jay Olshansky and Bruce Carnes, ‘there is neither convincing evidence nor scientific logic to support the claim that adherence to a Paleolithic diet provides a longevity benefit.’ 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. In hunter-gatherer societies where demographic data is available, the elderly are present, but they tend to have high mortality rates and rarely survive past the age of 80, with causes of death (when known) ranging from injuries to measles and tuberculosis.

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 hard physically 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.

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