Paleolithic diet
The Paleolithic diet (abbreviated Paleo diet) is also known as the caveman diet, prehistoric diet, Stone Age diet, or hunter-gatherer diet. It is the diet of wild plants and animals that various human species (see Homo (genus)) habitually consumed during the Paleolithic period (the Old Stone Age), a period of about 2 million years duration, ending about 10,000 years ago, when Homo sapiens, invented agriculture.  The modern version of this diet uses domesticated sources in lieu of the wild sources of the original hunter-gatherer diet.
Those who advocate that contemporary humans should regularly consume a Paleolithic diet base their advocacy on the premise that natural selection had 2 million or more years to genetically adapt the metabolism and physiology of the various human species to such a diet, and that 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.  According to those advocates, physiological and metabolic maladaptations result from those suboptimal genetic adaptations, which in turn contribute to many of the so-called diseases of civilization.
Those considerations give rise to a simple theme for adhering to a Paleolithic-type diet in modern times:  if a food item resembles one that can be found in the wild, obtained with bare hands or simple tools, and ingested immediately without cooking, processing, and by simple preparation (i.e., peeling, cracking, washing, etc.), and cause the consumer no ill effects either during or after consumption, then it can be considered edible, and therefore permissible to eat.  Any food meeting this standard can then be cooked and prepared by the simplest means that are practical and consumed in modest quantities.  Food exclusions comprise those introduced in the human food supply late in the course of human evolution, in particular after the invention of agriculture about 10,000 years ago: cereal grains, legumes, dairy products, certain starchy root vegetables, yeast, salt, refined sugars, refined fats and alcoholic beverages (certain oils and wines have been allowed and sometimes cashews are excluded).

# Overview
According to S. Boyd Eaton, a medical anthropologist and "evolutionary nutrition" expert from Emory University: "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  some 20,000 years ago."
Supporters of this theory argue that human genetics have scarcely changed since the Stone Age, and therefore that an ideal diet would be a reconstructed prehistoric diet such as the one humans and proto-humans used before the Neolithic Revolution. Therefore through studying archeology and modern hunter-gatherers it could be determined what a healthy diet would comprise. Interest in Paleolithic nutrition has grown in recent years as low-carbohydrate diets have become more popular, as the two practices have certain similarities.
This dietary concept is concerned primarily with health issues, as opposed to ethical or economic concerns. Advocates of the Paleolithic diet believe that the best foods for the human body are those that humans are best adapted to eat, arguing that many modern  ailments are diet related and can be avoided using the Paleo diet approach.

# History of this theory
One of the first suggestions that following a diet similar to that of the late Paleolithic area would improve a person's health was made in the New England Journal of Medicine in 1985. This was followed up by a book, The Paleolithic Prescription, which focused on achieving the same proportions of nutrients (fat, protein, and carbohydrates, as well as vitamins and minerals) as were present in the diet of late Paleolithic people, not on excluding foods that were not available before the development of agriculture. As such, this early version of the Paleolithic diet recommended such foods as skimmed milk, whole grain bread, brown rice, and potatoes prepared without fat, on the argument that such foods have the same nutritional properties as Paleolithic foods.
More recent versions of the Paleolithic diet, such as Neanderthin : Eat Like a Caveman to Achieve a Lean, Strong, Healthy Body, and The Paleo Diet: Lose Weight and Get Healthy by Eating the Food You Were Designed to Eat, focus on eliminating all foods that were not available to human beings in Paleolithic times, such as milk, dairy products, and grains.

# Practices

## Foods in the diet
Foods which are included in the diet are ones that can be obtained by using Paleolithic tools and practices: meat (game and grass-fed animal meat are recommended), fish, and gathered or foraged fruits, leaves, and roots of plants, mushrooms, nuts, eggs, and honey.
Some practitioners allow the use of oils derived from those foods which can be obtained and produced through Paleolithic means and are edible in their natural, uncooked state. Examples could include sesame oil, olive oil, and safflower oil, but not oils derived from beans (for example, peanut oil) or grains (for example, corn oil). Others avoid the use of any oil, as it is a processed food.
The non-animal foods available in the diet are the same as those available in raw veganism. However, there are two fundamental differences between raw veganism and the Paleolithic diet: Firstly, practitioners consume meat and other animal products (in fact usually more is consumed than on a standard modern diet, in some cases substantially more). Secondly, any and all food may be cooked if desired.

## Foods not in the diet
Vegetable foods which are not edible raw and unprocessed are excluded from the diet. The foods falling into this category are grains (e.g. wheat, corn, rice), certain starchy vegetables (i.e. legumes including peanuts, beans, peas, soybeans, tofu, soy milk and flour, as well as starchy root vegetables including potatoes, yams, and sweet potatoes), refined sugars and yeast (e.g. baked goods, pickled foods, vinegar, fermented foods and fermented beverages, which all contain yeast). Alcoholic beverages are generally excluded because fermentation is also a form of processing, although some Paleolithic eaters allow certain exceptions (i.e., wine, since fermented (over-ripe) fruit can be found and consumed in small quantities with little ill effect). Dairy products are excluded despite being edible raw, since they cannot be found or consumed easily in nature, at least in any considerable quantity, and are consequently a post-agricultural food. Salt is also not recommended and some do not allow cashews.

## Intake
The generally prescribed proportions of protein, fat, and carbohydrate are approximately 20-35%, 30-60%, and 20-35% respectively by calories, with 35-65% of calories coming from animal foods and 35-65% from plant foods, although a version of the diet has also been advocated without any specifically prescribed ratios of animal to plant foods. Eating a wide variety of plant foods is also recommended.
Because of the large amount of water in fruits and vegetables, the diet is, by weight, roughly 2/3 plant products and 1/3 animal products. Consequently, because of the high water content of fruits and vegetables, it is generally accepted that slightly less non-food water is required for optimal health. This is also supported by the fact that fresh water is not always readily available in the wild and that humans must rely on other sources for their water needs. This is not a reduction in need for water, but a shift in where water can be obtained.
The vitamin and mineral content of the diet is very high compared to a standard diet, in many cases a multiple of the RDA.

# Food sources and preparation
For many practitioners of Paleolithic nutrition, the foods' source is just as important as the kind of foods being consumed. It is common practice to obtain Paleolithic foods from as natural a source as possible. Farmed meats, especially those organically farmed, are available from many natural sources, from free range poultry to grass fed beef, with many proponents preferring, though not as practical, wild game meats like quail, rabbit, and venison.
It is common practice among Paleolithic eaters that when cooking, unconventional cooking means should be avoided, such as the use of microwave ovens, and that foods are cooked just enough to kill any harmful bacteria that may be present.
Modern-day practitioners of the Paleolithic diet must be careful to get necessary nutrients found in foods that are not on the diet. For example, milk and other dairy products are a major source of calcium and vitamin D for most people following the conventional Western diet. Late Paleolithic people probably got sufficient calcium from wild vegetables and from gnawing the bones of animals they ate. Vitamin D can be synthesized by the body upon sufficient exposure to sunlight, and can be obtained from cod liver oil, and from oily fish such as salmon, mackerel, sardines, and tuna. Since cultivated vegetables have less calcium than their wild counterparts, since excessive exposure to sunlight has been linked to skin cancer, and since it can be expensive to eat fish several times a week, many followers of the diet may choose to take calcium and vitamin D supplements to be sure they get enough of these nutrients.

# Health
The benefits of a Paleolithic diet are, as with most dietetic theories, widely debated. A systematic review of 4 randomized controlled trials (159 subjects) published through 2010 concluded "the Paleolithic diet resulted in greater short-term improvements in metabolic syndrome components than did guideline-based control diets".
It is generally argued that just because certain foods, quantities, and preparations eaten today were not available to humans during the Paleolithic period does not necessarily mean that they are actually harmful to humans. However, it has been pointed that while foods that are excluded from a paleolithic diet are not necessarily unhealthy, paleolithic foods may be essential for long-term health in the suggested proportions and quantities that we would have adapted to. When eaten, non-paleo foods necessarily replace (displace) paleo-foods and affect the diet.
There are however a number of medically diagnosed conditions whose sufferers have been shown to benefit directly from specific components of the diet. Some examples of this include:
- Coeliac disease, a gastrointestinal disorder whose sufferers are unable to digest the protein gluten, found in wheat.
- Dermatitis herpetiformis, a skin disorder linked also to digestibility issues related to gluten.
- Gluten ataxia, a common neurological manifestation of gluten sensitivity.
- Other conditions linked anecdotally, albeit unproven, to gluten and/or casein proteins include
Multiple sclerosis
Parkinson's disease
Rheumatoid arthritis
Schizophrenia
Tourette syndrome
Chronic fatigue syndrome
Attention deficit disorder
Autism
- Multiple sclerosis
- Parkinson's disease
- Rheumatoid arthritis
- Schizophrenia
- Tourette syndrome
- Chronic fatigue syndrome
- Attention deficit disorder
- Autism
Other key health benefits commonly associated with and supported by this theory include:
- Reduction or elimination of grains, dairy, and refined sugars in the human diet has shown to lower glycemic load. This is thought to lower risk of diabetes and other related syndrome X diseases by placing less stress on the pancreas to produce insulin, and preventing insulin insensitivity. A high consumption of cereal grains, even whole grains, is likely to result in a high glycemic load diet, which in turn increases the risk for Obesity, Diabetes and other diseases of the metabolic syndrome.
- Increasing intake of fruits and vegetables induces a net base load, as opposed to the net acidic load on the body when eating a grain based diet.  This is believed to prevent osteoporosis by passing less calcium salts through the kidneys. High reliance upon cereal grains is likely to yield a positive NEAP (Net Endogenous Acid Production) that in turn could increase the risk for osteoporosis, and other diseases of acid/base imbalance.
- Animals that have been fed a pastural diet (free-range beef and chicken) instead of grain fed animals tend to have higher ratios of omega-3 fatty acids and other nutrients.
- By reducing the intake of processed foods the sodium/potassium ratios in the body are more balanced.
- Phytic acid, a chemical present in grain, is a strong chelator of important minerals such as calcium, magnesium, iron, and zinc. It, in essence, 'binds up' these minerals, and since humans lack the digestive enzyme phytase required to break this bond, these important minerals are not bioavailable, contributing significantly to mineral deficiencies. This problem is increased when dietary mineral supplements are not available, such as in developing countries.
- Lectins present in cereal grains and legumes have the potential to cause auto-immune diseases, like rheumathoid arthritis, by a process called molecular mimicry (similarity of structure shared by products of dissimilar genes).
- Dairy products, especially those derived from cow's milk, are more or less correlated with a variety of health issues, including type 1 diabetes, prostate cancer, multiple sclerosis, and Crohns disease. They also don't always make life any easier for Type 2 diabetics: milk, yoghurt, and cottage cheese have low glycemic indices but are highly insulinotrophic, with an insulin index similar to that of white bread.

# Archeological and Anthropological Evidence
Milk and dairy products were not consumed prior to the agricultural revolution, i.e. prior to the domestication of milk-producing animals. Mature lactose tolerance is perhaps the most recent evolutionary change in humans, a phenomenon unique to humanity; it evolved independently in several regions (as noted above), but is not a universal trait in modern man -- although fermented dairy goods tend to be more readily digestible than unfermented. Dairy products have been very valuable historically (in post-Agricultural-Revolution times) as a cheap and reliable source of protein, particularly in Europe, the Middle East, and India.
It has been established that wild tubers would have been a common component in historically studied hunter-gatherer diets, comprising 23.6 % of all the plant food consumed by the average hunter-gatherer. High glycemic load tubers (such as potatoes, which were developed from intensive agricultural inbreeding of wild types), however, would not have been part of pre-agricultural diets. Most tubers, and many underground plant structures (corms, roots, etc) are inedible unless cooked.  Cooking serves to breakdown the cell walls and make the starch available for absorption and it also inactivates potentially toxic compounds.  Hence, until hominins could regularly control fire (~300,000 years ago), most roots were inedible.
Historical and ethnographic studies of hunter gatherers indicate that cereal grains were rarely consumed. However, there are some notable exceptions: Holocene hunter gatherers living in marginal areas such as desert ate grains seasonally such as the Great Basin Indians in the U.S. and Australian Aborigines. More importantly, for most of humanitys existence on the planet, up until the very end of the Paleolithic period grains were never consumed. Grains are virtually indigestible unless the cell walls are broken via (grinding or milling) and the starch is gelatinized by cooking. Hence the appearance of stone grinding tools (mortar and pestle, saddle stones etc) heralds the widespread use of grains in hunter-gatherer societies. The first documented record of stone grinding tools appearing in the fossil record occur 22,500  23,500 years ago in the near East, and the first hunter gatherer society known to have made wide scale use of grains were the Natufians who lived in the Levant ~13,000 years ago.  Hence, cereal grains have little or no evolutionary precedent in hominin diet.
There is evidence that legumes were not generally consumed before the agricultural revolution. However, recent archeological finds indicate that large seeded legumes were part of the human diet long before the neolithic agricultural revolution.

# Sustainability
Environmental sustainability
It has been estimated that, worldwide, agricultural activity, especially livestock production accounts for about a fifth of total greenhouse-gas emissions. Accordingly, the reduction of the average worldwide consumption level of animal products to 90g per day has been proposed as a means to fight global warming. In addition to its role in climate change, the current production of livestock has been claimed to increase land degradation, air pollution, water depletion and pollution, and loss of biodiversity. Whether the paleolithic diet can currently be environmentally sustainable depends on the ratio of plant to animal foods consumed. In that regard, it is worthy to note that a version of the paleolithic diet without any specifically prescribed ratios of animal to plant foods has been advocated.  Furthermore, policies have been proposed to address livestock's impact on the environment and alternatives to large-scale industry agriculture have been suggested for sustainable animal and plant-food production. There are also concerns that a widely adopted paleolithic diet including fish would destroy the world's fisheries. However, informed consumers can buy fish produce that comes from well managed fisheries and has not contributed to the environmental problem of overfishing.
Economic sustainability
If the paleolithic diet was widely adopted, there are concerns that not enough food could be produced to feed the world population and that, when produced, this food would be unaffordable. Providing fresh food free of preservatives on a large scale could introduce logistical challenges that would increase costs to producers and retailers. The advantages gained by using foods that are designed for longevity (e.g. cereal grains, legumes, salted foods) in storage would be lost. These additional costs could make food less affordable. That being said, the economic cost of sustaining the world-wide consumption of a paleolithic diet must be evaluated in light of the possible savings resulting from the health-promoting benefits that such a diet may have. Moreover, the gathering of wild food plants appears to be an efficient method of subsistence that could prove instrumental in preventing malnutrition if the paleolithic diet was widely adopted.

# Cautions about poisoning
As the consumption of raw foods gains popularity, some unsafe foods have occasionally entered the human diet. It should be pointed out that it is generally accepted among the supporters of Paleolithic nutrition that while it is necessary to eat only those things that can be consumed raw, it is not necessary or advisable to eat those foods raw. Many foods can harbor dangerous pathogens, including, among other things, salmonella, norovirus, and Trichinella spiralis, many of which can have serious health consequences if not first killed by means of heating, i.e., cooking. For this reason, cooking is allowed of things that, under normal healthy circumstances, would not require cooking to be consumed (grains still being discounted).
The heating to an adequately high temperature of meat, poultry, and fish will normally destroy harmful bacteria and in worse cases parasite eggs (such as tapeworm). Raw eggs can also contain many harmful substances, most commonly salmonella. However, recent studies have shown that the level of salmonella infection found in commercial eggs is negligible.

# Paleolithic diet for animals
Pet food diets such as the BARF Diet (Bones and Raw food) (Biologically Appropriate Raw Food) for dogs and Prey Model Diet for cats are directly analogous to the Paleolithic diet for humans.  Proponents of raw feeding note that cats and dogs are carnivores that have evolved to survive on raw meats, bones, offal, and small amounts of leafy plants, and are concerned that modern commercial pet foods contain a high proportion of health compromising grains, salt and sugars.