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Dr. Loren Cordain of the Paleo Diet discusses dietary protein intake with Dr. T. Colin Campbell of the China Study. The Paleo Diet is championed by Dr. Loren Cordain, professor of health and exercise science at Colorado State University. The China Study is a book by T. Colin Campbell, Jacob Gould Schurman Professor Emeritus of In a written debate with Campbell in , nutritionist Loren Cordain argued that “the fundamental logic underlying Campbell’s hypothesis (that.

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Introduction Protein plays a litany of roles in living systems: What, however, is the role of dietary protein in health and disease in humans? Is the source, type and quantity intimately and directly tied to optimal physical development and continued wellbeing? Is it causative or preventative of disease? How do we know, and how can we know? One would think this question should be straightforward and easily answered; as you will soon see the question is anything but simple!

In the pages that follow, two scientists at the top of their respective fields–Dr. D, Professor Department of Health and Exercise Science Colorado State University Introduction Although humanity has been interested in diet and health for thousands of years, the organized, scientific study of nutrition has a relatively recent past.

Other well known nutrition journals have a more recent history still: Nutritional science is not only a newly established discipline, but it is also a highly fractionated, contentious field with constantly changing viewpoints on both major and minor issues that impact public health.

These kinds of complete turnabouts and divergence of opinion regarding diet and health are commonplace in the scientific, governmental and medical communities. Surprisingly, the personnel makeup of both scientific advisory boards is almost identical.

At least 30 million Americans have followed Dr. Atkins advice to eat more fat and meat to lose weight 9. In utter contrast, Dean Ornish tells us fat and meat cause cancer, heart disease and obesity, and that we would all would be a lot healthier if we were strict vegetarians How in the world can anyone make any sense out of this apparent disarray of conflicting facts, opinions and ideas?

In mature and well-developed scientific disciplines there are universal paradigms that guide scientists to fruitful end points as they design their experiments and hypotheses. These central concepts are not theories for each discipline, but rather are indisputable facts that serve as orientation points for all other inquiry within each discipline.

Scientists do not know everything about the nature of the universe, but it is absolutely unquestionable that it has been and is expanding. This central knowledge then serves as a guiding template that allows scientists to make much more accurate and informed hypotheses about factors yet to be discovered.

The study of human nutrition remains an immature science because it lacks a universally acknowledged unifying paradigm Without an overarching and guiding template, it is not surprising that there is such seeming chaos, disagreement and confusion in the discipline. Indeed, nothing in nutrition seems to make sense because most nutritionists have little or no formal training in evolutionary theory, much less human evolution.

Nutritionists face the same problem as anyone who is not using an evolutionary model to evaluate biology: All human nutritional requirements like those of all living organisms are ultimately genetically determined. By carefully examining the ancient environment under which our genome arose, it is possible to gain insight into our present day nutritional requirements and the range of foods and diets to which we are genetically adapted via natural selection This insight can then be employed as a template to organize and make sense out of experimental and epidemiological studies of human biology and nutrition The Dietary Protein Conundrum: How Much is Enough?

An important dietary issue that has come under debate in recent years is the safety of high protein diets and their long term influence upon health and well being 17, In the current U. At this point, it should be noted that there is a physiological limit to the amount of protein that can be ingested before it becomes toxic 14, A byproduct of dietary protein metabolism is nitrogen, which in turn is converted into urea by the liver and then excreted by the kidneys into the urine.

When nitrogen intake from dietary protein exceeds the ability of the liver to synthesize urea, excessive nitrogen as ammonia spills into the bloodstream causing hyperammonemia and toxicity 14, Additionally excess amino acids from the metabolism of high amounts of dietary protein may become toxic by entering the circulation causing hyperaminoacidemia 14, The avoidance of the physiological effects of protein excess has been an important factor in shaping the subsistence strategies of hunter-gatherers Multiple historical and ethnographic accounts have documented the deleterious health effects that have occurred when humans were forced to rely solely upon the fat depleted, lean meat of wild animals Clinical documentation of this syndrome is virtually non-existent, except for a single case study The mean maximal protein intake for the average weight U.


The average protein intake in the U. It should be pointed out that this categorization is completely arbitrary and based almost entirely upon comparisons to the U. However, in many non-westernized people these values would be higher than normal. Consider the data in Figure 1 below showing blood pressure in the Yanomamo Indians of Brazil, a non-salt consuming society. Not only is blood pressure lower than normal western values, but it stays uniform throughout life and does not rise with age Blood pressure in a group of Brazilian Indians In order to objectively answer the question whether or not high protein diets have detrimental or therapeutic health effects compared to the U.

The Evolutionary Evidence The Fossil Evidence A number of lines of evidence suggest that meat eating and high protein diets have been a component of human nutrition since the very origins of our genus Homo. A number of lines of evidence support this viewpoint. First, the very first stone tools Oldowan lithic technology appear in the fossil record 2.

Stone tool cut marks on the bones of prey animals and evidence for marrow extraction appear concurrently in the fossil record with the development of Oldowan lithic technology by at least 2. It is not entirely clear which specific early hominin species or group of species manufactured and used these earliest of stone tools; however, Australopithecus garhi is a likely candidate 30, The development of stone tools and the increased dietary reliance on animal foods allowed early African hominins to colonize northern latitudes outside of Africa where plant foods would have been seasonally restricted.

Both of these tool-producing hominins would likely have consumed considerably more animal food than pre-lithic hominins living in more temperate African climates, and it is likely the majority of their daily energy was obtained from animal foods during winter and early spring when plant food sources would have been scarce or unavailable. The earliest evidence for meat and marrow extraction dating to 2. Carnivorous diets reduce evolutionary selective pressures that act to maintain certain anatomical and physiological characteristics needed to process and metabolize high amounts of plant foods.

Why I Completely Agree w. Vegan Crusader T. Colin Campbell

In this regard, hominins, like felines, have experienced a reduction in gut size and metabolic activity along with a concurrent expansion of brain size and metabolic activity as they included more energetically dense animal food into their diets 16, 34, Further, similar to obligate carnivores 36humans maintain an inefficient ability to chain elongate and desaturate 18 carbon fatty acids to their product 20 and 22 carbon fatty acids Since 20 and 22 carbon fatty acids are essential cellular lipids, then evolutionary reductions in desaturase and elongase activity in hominins indicate that preformed dietary 20 and 22 carbon fatty acids found only in animal foods were increasingly incorporated in lieu of their endogenously synthesized counterparts derived from 18 carbon plant fatty acids.

Finally, our species has a limited ability to synthesize the biologically important amino acid, taurine, from precursor amino acids 38, 39and vegetarian diets in humans result in lowered plasma and urinary concentrations of taurine Like felines 41, 42 the need to endogenously synthesize taurine may have been evolutionarily reduced in humans because exogenous dietary sources of preformed taurine found only in animal food had relaxed the selective pressure formerly requiring the need to synthesize this conditionally essential amino acid.

Another genetic adaptation to a high meat diet involves the metabolism of purines. As DNA and RNA are broken down within cells, the purines then can be metabolized into uric acid by the liver and a few other tissues within the body. The liver cordaln purines from two sources: Although high protein, meat based diets contain high amounts of purines and would be expected to promote corfain symptoms, protein ingestion actually decreases blood uric acid levels by increasing uric acid excretion This seemingly paradoxical effect occurs because the kidney increases its excretion of uric acid when faced with elevated dietary purines But more importantly, over the course of evolution, humans have evolved a genetic mutation which tends to prevent uric acid synthesis in the liver.

Humans avoid the overproduction of uric acid in the face of increasing dietary purine intake from meats by decreasing campblel activity of an enzyme cordaim xanthine oxidoreductase 46a key catalyst in the final synthesis of uric acid. Compared to other animals, xanthine oxidase activity is almost times lower in humans This evolutionary adaptation has occurred because the gene coding for xanthine oxidoreductase has been repressed The final proof of the pudding has been borne out by dietary interventions showing that high protein, low glycemic load diets actually normalized serum uric acid concentrations in 7 of 12 gout patients and significantly decreased gout attacks The Isotopic Fossil Evidence Since the evolutionary xampbell between hominins and pongids apes approximately 7 million years ago, the available evidence shows that all species of hominins ate an omnivorous diet composed of minimally processed, wild-plant, and animal foods.


In support of this view is the omnivorous nature of chimpanzees, the closest living pongid link to hominins. Although chimpanzees Pan paniscus and Pan troglodytesour genetically closest nonhuman relatives, primarily consume a frugivorous diet, they still eat a substantial amount of meat obtained throughout the year from hunting and scavenging Observational studies of wild chimpanzees demonstrate that during the dry season meat intake is about 65 g per day for adults Accordingly, it is likely that the very earliest hominins would have been capable of obtaining animal food through hunting and scavenging in a manner corrdain to chimpanzees.

Carbon isotope data also support the notion that early hominins were omnivorous. By about 3 million years ago MYA Australopithecus africanus obtained a significant portion of food from C4 sources grasses, particularly seeds and rhizomes; sedges; invertebrates, including locusts codain termites; grazing mammals; and perhaps even insectivores and carnivores Other fossils of early African hominins, including Australopithecus robustus and Homo ergaster, maintain carbon isotope signatures characteristic of omnivores 54, The finding of C4 in Australopithecus robustus fossils refutes the earlier view that this hominin was vegetarian There is little evidence to the contrary that animal xampbell have always ccordain a significant role in the diets corvain all hominin species.

Increased reliance on animal foods not only allowed for enhanced encephalization brain expansion relative to body weight and its concomitant behavioral sophistication 16, 34, 35but this campbeell practice also permitted colonization of the world outside of Africa.

An unresolved issue surrounding hominin diets is cirdain relative amounts of plant and animal foods that were typically consumed. Before the advent of Oldowan lithic technology about 2. Although all available data point to increasing animal food consumption following the arrival of stone tool technology, the precise contribution of either animal or plant food to energy is unclear. The analysis demonstrated that Neanderthals, similar to wolves and arctic foxes, behaved as top-level carnivores, obtaining all of their protein from animal sources Because Neanderthals were not direct predecessors of modern humans 60it may be more relevant to examine the isotopic data from fully modern humans living during the Cajpbell.

The Paleo Diet: What’s the Story? – Center for Nutrition Studies

The data indicated these hunter-gatherers were consuming animal protein year-round at a higher trophic level than the artic fox. All of these studies could be criticized as not being representative of typical hominin diets, as these two species lived in climates and ecosystems that fostered an abundance of large, huntable mammals, which were preyed upon preferentially.

Additional clues to the typical plant-to-animal subsistence ratio in Paleolithic hominin diets can be found capbell the foraging practices of historically studied hunter-gatherers. Campbeell Ethnographic Evidence Our analysis Figure 3 of the Ethnographic Atlas data 62 showed that the dominant foods in the majority of historically studied hunter-gatherer diets were derived capbell animal food sources For all hunter-gatherer societies, the median subsistence dependence on animal foods was 56 percent to 65 percent.

In contrast, the median subsistence dependence on gathered plant foods was 26 percent to 35 percent The major limitation of ethnographic data is that the preponderance of it is subjective in nature, campbsll the assigned scores for the five basic subsistence economies in the Ethnographic Atlas are not precise, but rather are approximations Table 1 lists these studies and shows the plant-to-animal subsistence ratios by energy.

The average score for animal food subsistence is 65 percent, while that for plant-food subsistence is 35 percent. When the two polar hunter-gatherer populations, who have no choice but to eat animal food because of the inaccessibility of plant foods, are excluded from Table 1 the mean score for animal subsistence is 59 percent and that for plant-food subsistence is 41 percent.

Consequently, there is remarkably close agreement between the quantitative data in Table 1 and the ethnographic data cordajn that animal food comprised more than half of the energy in historically studied hunter-gatherer diets. Based xordain hunter gatherer plant to animal subsistence ratios and the known macronutrient ccordain of wild plant and animal foods, it is possible to estimate the macronutrient content of these diets Consequently, when framed in an evolutionary context, current western dietary protein intakes fall outside the range of diets that would have conditioned the human genome for nearly 2 million years.