The Paleo diet — short for Paleolithic diet — undoubtedly is one of the most popular diets on the market today and is claimed to more effectively enhance weight loss, optimize athletic performance, promote health, and prevent disease than other dietary regimens (33). The underlying premise of the Paleo diet is that obesity and chronic disease are due, at least nutritionally, to a mismatch between what we as humans are genetically programmed to eat and what we currently are eating. The Agricultural Revolution (starting approximately 10,000 years ago) and the Industrial Revolution (occurring a couple centuries ago) have produced an environment and food supply vastly different from that of our Paleolithic ancestors, different from what Homo sapiens were thriving on for hundreds of thousands of years, and different from what is optimal for weight, health, and performance (33).
Although most popular among fitness enthusiasts, Paleo’s popularity also expands to the general public. In 2013, the term Paleo Diet was the most searched dietary topic on Google, and some estimates even put the number of American Paleo adherents between one and three million, or approximately 1% of the country’s population (1).
Popularity aside, is there any scientific substance to this dietary regimen or is it just a case of history repeating itself, literally, through diet? This article will provide a scientific evaluation of the Paleo diet including its origins, evolution, composition, and the available research examining its efficacy in terms of mitigating disease and promoting health and optimal athletic performance.
THE ORIGINS AND EVOLUTIONS OF PALEO
Although Dr. Loren Cordain credits himself as being the founder of the Paleo movement (33), the idea of eating like our Paleolithic ancestors to improve health and prevent disease likely originated some 25 years before Cordain’s popularization as a result of the academic musings of a gastroenterologist named Dr. Walter Voegtlin (39). In his book, The Stone Age Diet: Based On In-Depth Studies of Human Ecology and the Diet of Man, Voegtlin contended that humans are chiefly carnivores and, like other carnivorous animals (he uses dogs as an example), should consume a primarily animal-based diet (i.e., one rich in protein and fat) (39). Not surprisingly (given that he was a gastroenterologist), Dr. Voegtlin based his contention largely on gastrointestinal anatomy, claiming that man is more similar, anatomically speaking, to the carnivorous dog than the herbivorous sheep. These gross differences in anatomy render man unable to adapt successfully to a diet containing large amounts of plant foods, particularly carbohydrate-rich grains, as well as dairy products. He further claimed that the whole range of modern-day chronic diseases stemmed from modern man’s abandonment of the foods of his primitive ancestors (39).
A decade later, Dr. Stanly Eaton (12) (a physician and professor of Anthropology, Neuroscience, and Behavioral Biology at Emory University) and fellow physician Dr. Melvin Konner published a special article in the prestigious New England Journal of Medicine, echoing the sentiments of Dr. Voegtlin. The article, entitled “Paleolithic Nutrition: A Consideration of Its Nature and Current Implications,” provided data implying that differences between dietary patterns of our ancestors and those prevalent in modern, industrial societies have important implications for health and possible connections to what the authors referred to as “diseases of civilization” (e.g., heart disease, hypertension, diabetes, and cancer) (12). The data were derived largely from a dietary sample of approximately 50 hunter-gatherer populations that existed at the time and that varied both in their geographic locations and the amount of energy they obtained daily from animal foods. Because none of these groups used modern agriculture to acquire their food, Eaton and Konner (12) argued that their diets provided an estimate of what human beings are “genetically programmed to eat, digest, and metabolize.” Based on these data, Eaton and Konner (12) estimated that Paleolithic man derived approximately 50% to 80% of his food from plants, with the remaining 20%to 50% of his food coming from animal sources.
The concepts presented in that article were expanded on and published 4 years later in a book entitled, The Paleolithic Prescription: A Program of Diet and Exercise and a Design for Living (13). Authored by Drs. Eaton (13) and Konner along with Konner’s wife Marjorie Shostak (an anthropologist specializing in the female hunter-gatherer), the book went beyond simply implicating a connection between modern diets and chronic disease by providing a recommended dietary regimen (i.e., prescription) based on the macronutrient distribution consumed by Paleolithic man, that is, approximately 45% carbohydrate, 35% protein and 20% fat.
During the next several years, the Paleolithic diet was somewhat overshadowed by other low- and still lower carbohydrate eating programs, including Dr. Atkins’ New Diet Revolution, the South Beach diet®, The Zone Diet®, Protein Power diet, etc. But, in 2001, Paleo resurfaced when Dr. Loren Cordain published his book, The Paleo Diet. The self-proclaimed “world’s leading expert on Paleolithic diets,” Cordain (9) (a professor of Health and Exercise Science at Colorado State University) has authored or coauthored numerous articles (both peer-reviewed and nonpeer-reviewed) and four additional books on the topic, including one geared toward the athlete aptly entitled, The Paleo Diet for Athletes.
PALEO OR PALEOS?
Part of the difficulty in evaluating the nutritional adequacy, dietary efficacy, and scientific validity of the Paleo diet lies in the lack of agreement over what exactly constitutes The Paleo diet. Indeed, the evolutionary, anthropological, and nutritional assumptions behind Paleo have been the subject of widespread academic debate (16,21,35), which has led to varying interpretations of what foods should and should not be included as part of a Paleo dietary regimen. Based on their writings, it seems that Drs. Eaton and Konner (11–13) were more interested in a particular macronutrient distribution as opposed to the inclusion or exclusion of specific foods or food groups. They did not strictly prohibit foods that were absent before agriculture (e.g., whole-grain breads, pasta, legumes, and even some low-fat dairy products) as long as the 45/35/20 (carbohydrate/protein/fat) macronutrient ratio was approximately met (11–13). In contrast, the modern version of Paleo, as espoused by Cordain, is more rigid requiring that followers not only adhere to the precise macronutrient distribution of the preagricultural era but also consume the very foods that might have been available to Paleolithic humans themselves. The well-known Paleo motto, “if the cavemen didn’t eat it, you shouldn’t, either,” aptly sums up the modern Paleo mindset when it comes to choosing foods. A brief description of the components of the modern Paleo diet (and the rationale for their inclusion or exclusion) as advocated by Cordain (33) is presented in Table 1.
EVOLUTIONARY, REVOLUTIONARY, OR JUST ANOTHER FAD?
Because the premise on which the Paleo diet is based is rooted in evolutionary anthropology, it must be evaluated in the context of its historical accuracy as well as its nutritional validity. As previously described, the primary evolutionary assumption underlying the Paleo diet is that humans, genetically speaking, have been unable to adapt to the dramatic and rapid shift in the postagricultural food environment. The inability of modern man to adapt to a modern diet predisposes him to the myriad of modern chronic health conditions (e.g., obesity, cardiovascular disease, diabetes, and even cancer) (33). There are a number of fundamental flaws in this hypothesis, not the least of which is the assumption that diet alone is the cause of chronic disease. Although diet certainly plays a role in the pathogenesis of many chronic diseases, it is not the only (or even primary) causative factor (36,37). Other lifestyle factors play equal if not more important roles in the development of chronic disease. One that is conspicuously absent from most Paleo diet prescriptions is physical activity. Indeed, the very term hunter-gatherer implies that Paleolithic man engaged in significant amounts of physical activity: he had to hunt and forage for his food, build shelters, and defend his territories. Research clearly shows that physical activity is an independent predictor of health promotion and disease prevention and treatment (36).
The Paleo hypothesis also assumes that humans cannot adapt to changing environments; that they can only thrive in circumstances similar to the ones their predecessors lived in. If this were in fact true, human life would not have lasted very long (10,18). In the book, Paleofantasy: What Evolution Really Tells Us About Sex, Diet, and How We Live, evolutionary biologist Marlene Zuk (42) provides several examples of recent adaptations that show natural selection keeping pace with rapid environmental shifts. One of Zuk’s nutritional examples directly debunks the Paleo position on dairy products. According to Zuk, within a span of 7,000 years, people adapted to eating dairy products. Usually, the gene encoding the lactose-digesting enzyme lactase shuts down after infancy. However, when dairy became prevalent, many (although not all) people evolved a mutation that kept the gene turned on throughout life. The changing composition of our gut bacteria provides another poignant example of our physiological ability to adapt to the changing food environment (42).
Another assumption of the Paleo diet is that Paleolithic man was free from the chronic diseases that plague modern man. In fact, there is some evidence to suggest that Paleolithic man was not free from the risk of chronic disease. Using computerized tomography scans, Thompson et al. (34) determined the prevalence of atherosclerosis in a sample of 137 mummies from 4 different geographical regions or populations spanning more than 4,000 years, including individuals from Egypt, Peru, the Ancestral Puebloans of Southwest America, and the Unangan of the Aleutian Islands. The researchers found evidence of probable or definite atherosclerosis in 34% of mummies and in all 4 geographical populations (34).
Finally, there currently is a paucity of valid, scientific evidence supporting the Paleo diet’s purported health benefits. To date, only four randomized controlled trials (RCTs) using human subjects (and one using piglets) have been published. A summary of the existing human RCTs is presented in Table 2. At first glance, it would seem that the existing research generally supports the efficacy of the Paleo diet to mitigate chronic disease (25). However, it should be noted that most of the studies suffer from one or more methodological weaknesses, including small and/or unrepresentative samples, inadequate dietary control and/or compliance to the diets, different definitions and compositions of the Paleo diet prescription, short study durations, and lack of blinding. Thus, the results from these studies should be interpreted with caution. Moreover, given the subject samples (i.e., older individuals with chronic diseases), there is low external validity and, thus, generalizability to an active or athletic population.
From a nutritional standpoint, foods are included or excluded from the modern Paleo dietary regimen based on 1) their purported prominence in the diets of our Paleolithic ancestors and/or 2) nutrient composition and unique nutrient contribution. The first criterion rests on the assumption that there was a single diet practiced by our Paleolithic ancestors and we know exactly what that diet was. In reality, we do not know exactly what people were consuming 2.5 million to 10,000 years ago (10,18). Moreover, as previously mentioned, it is quite likely that our Paleolithic predecessors consumed a variety of different diets that were influenced by geography, season, availability, and opportunity (10,18). According to anthropologist Dr. William Leonard (22), “Our species was not designed to subsist on a single, optimal diet. What is remarkable about human beings is the extraordinary variety of what we eat. We have been able to thrive in almost every ecosystem on the Earth, consuming diets ranging from almost all animal foods among populations of the Arctic to primarily tubers and cereal grains among populations in the high Andes.”
The other criteria for a food’s inclusion in or exclusion from the modern Paleo diet rests on the food’s nutrient composition and, thus, unique contributions to the diet. No one would argue that added sugars and highly processed foods should be limited in the diet because they generally are high in energy density and low in nutrient density. Moreover, there is ample scientific evidence linking these foods to obesity and chronic diseases (37). Similarly, there is some limited evidence suggesting a higher protein, lower carbohydrate diet (characteristic of the Paleo diet) may enhance satiety, promote weight reduction, and positively impact some markers of metabolic disease relative to a higher carbohydrate, lower protein diet (3,31,32). However, it should be noted that this is not universally true for all populations. There is no evidence to suggest that those who are not overweight or obese or suffering from metabolic diseases will benefit from a lower carbohydrate, higher protein diet. And, there is ample evidence to suggest that a lower carbohydrate diet can be detrimental to athletic performance, particularly for the endurance athlete (6). Other concerns with the exclusion of specific carbohydrate-rich foods from the Paleo eating plan, particularly for active individuals, are described as follows.
Grains: As described in Table 1, grains, whether whole or refined, are excluded from the Paleo diet on the grounds that they were not available or consumed during Paleolithic times, they contain no unique nutrients (i.e., unique from the foods allowed on the Paleo diet), and they contain antinutrients, most notably gluten, that can wreak havoc on the gastrointestinal tract and immune system (33). In fact, there is little scientific evidence to support Cordain’s claims that whole grains cause obesity, autoimmune disease, or chronic disease (33). In contrast, there is a significant body of evidence to suggest that whole grains not only provide beneficial health effects but may aid in weight loss (2,5). The recently published 2015 dietary guidelines reiterated the recommendation from both 2005 and 2010 that grain products are a key component of a healthy diet, and that at least half of an individual’s grain intake should consist of whole grains (37). Finally, a recent study examining gluten intakes and athletic performance found no beneficial effects of a short-term gluten-free diet on performance in nonceliac athletes (24). Given the concentration of complex carbohydrates in grains and the importance of adequate carbohydrates in the athlete’s diet, it makes little sense for active individuals to restrict grain products.
Potatoes: On his Web site, Cordain provides an exposé on Are Potatoes Paleo? (7). His antipotato stance is because of their supposed high glycemic index (GI) and theoretically high content of saponins (a class of “soap-like” antinutrients), most notably glycoalkaloids (7). With respect to the GI, research indicates that potatoes actually vary considerably in terms of their GI depending on variety, origin, processing, and preparation (potatoes rarely are consumed plain; thus, the GI numbers posted in popular GI tables are moot) (14,27). The glycoalkaloids in potatoes serve the important function of protecting the potato’s outer layer from microbial and insect attack. But, according to Cordain, when consumed by humans, they can adversely affect the intestinal lining and aggravate symptoms of inflammatory bowel disease (7). Cordain even provides a table showing various potato products along with shockingly high values of glycoalkaloids (7). What he does not clarify for his readers (and what is obvious just by looking at the title of the table) is that the values are given in milligrams of glycoalkaloids per kilogram of potato food. Moreover, the data are taken from an article examining the interaction of Solanum tuberosum agglutinin with human platelets (17). In fact, actual levels of glycoalkaloids in potatoes as typically consumed are significantly lower (and of far less concern) than Cordain presents (41). It is interesting that the only vegetable Cordain chooses to malign is the potato, a nutrient-dense vegetable that has been a dietary staple throughout history. Like grain products, potatoes provide a nutrient-dense source of complex carbohydrates for the active individual.
Legumes: Like potatoes, Cordain blacklists legumes, claiming that they contain large amounts of saponin antinutrients, most notably lectins and protease inhibitors, that theoretically contribute to gut irritation, reduced nutrient absorption, and gastrointestinal distress (8). And, if they are eaten undercooked or entirely raw, Cordain asserts, “They can be downright toxic” (8). According to Cordain, red kidney beans, for example, can cause nausea, vomiting, abdominal pain, diarrhea, muscle weakness, heart inflammation, and even death without proper preparation (8). It should be noted that this information is based on a single study published in 1980 documenting food poisoning from the consumption of large amounts of raw red kidney beans (30). In fact, beans are a rich source of a number of important micronutrients including potassium, magnesium, folate, iron, and zinc and are a key protein source in vegetarian diets, particularly because they are among the only plant foods that provide a significant amount of the indispensable amino acid lysine. Commonly consumed dried beans also are rich in total and soluble fiber as well as in resistant starch. They also provide ample amounts of polyphenols, many of which are potent antioxidants. Intervention and prospective research suggests that diets that include beans reduce low-density lipoprotein cholesterol, favorably affect risk factors for metabolic syndrome, and reduce risk of ischemic heart disease and diabetes (29,38).
There is no doubt that the foods available to and consumed by our Paleolithic ancestors were vastly different from those consumed today. However, the notion that these dietary differences are solely responsible for the chronic diseases that plague modern man is an evolutionary oversimplification and lacks academic support. Similarly, with a few exceptions, the rationale for including or excluding certain foods from the modern Paleo diet is nutritionally and scientifically invalid. Thus, individuals seeking to improve health, minimize disease risk, and optimize athletic performance should focus on consuming a diet that provides a variety of nutrient-dense foods from within and among the different food groups while meeting individual calorie needs.
BRIDGING THE GAP
The Paleo diet is one of the most popular diets on the market today and has a particularly strong following among fitness enthusiasts. Although interesting from a historical perspective, the nutritional and health claims being made by proponents of the modern Paleo diet lack evolutionary and scientific support. Individuals seeking to improve health, minimize disease risk, and optimize athletic performance should focus on consuming a diet that provides a variety of nutrient-dense foods, from within and among the different food groups, while meeting individual calorie needs.
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