29 Discordance Hypothesis

Ms. Sangeeta Dey and Prof. A.K. Kapoor

Contents:

1. Introduction

2. Discordance Hypothesis

3. Nutritional comparisons and evolutionary pre-agricultural diets for health promotion

4. Implications of early hominin diets and discordance hypothesis 4.1 Total Fat Intake

4.2 Saturated Fat

4.3 Trans Fatty Acids

4.4 Polyunsaturated Fats

4.5 Dietary Cholesterol

4.6 Protein

4.7 Dietary Fiber

4.8 Energy

4.9 Acid-base Considerations

5. Reason for discordance hypothesis

6. Archaeological evidence of early dietary patterns

7. Discussion

8. Summary

Learning Objectives:

To describe Discordance hypothesis
To understand the nutritional imbalances between the past and the present
To describe reasons for the evolutionary discordance hypothesis
To know about factors that lead to discordance hypothesis
To understand impact of nutritional changes in the lifestyle of human kind
To describe the archaeological evidences to support primitive dietary evidences
To learn the importance of nutritional guidelines to promote health and livelihood

1. Introduction

During the past thirty years, health promotion advice, especially that involving nutrition, has been primarily on epidemiological research findings. Epidemiology has been by far the dominant force in the field of diseases prevention. Grant funding, academic publications, official recommendations, conferences and popular press accounts related to personal health all reflect an underlying faith that the epidemiological method will ultimately prevail. However, in terms of health promotion, ‘prevail’ means reducing the incidence or prevalence of targeted diseases conditions. However, epidemiological record when viewed from this bottom-line perspective has been unimpressive. Essential hypertension, obesity, diabetes mellitus, depression, age related fractures, melanoma, breast cancer, asthma all occur more frequently now than they did thirty years ago. It probably may be due to the paradigm shift.

Evolutionary health promotion of the ancestral human lifestyle offers a potential alternative that could make a vital contribution. This candidate paradigm arises from the discordance hypothesis that focuses on dissonance between our genetic heritage and our contemporary lifestyle (Eaton et al., 2002). The human genome was selected in adaptation to Stone Age living circumstances, culminating in the appearance of behaviourally modern humans between 100,000 and 50,000 years ago (kya). Before that time, human ancestors, like all other organisms adapted to changing environmental conditions mainly by genetic evolution. However, for humans during the past 50 kya, adaptation has increasingly involved cultural modification. Since the appearance of agriculture, about 10 kya, there have been few generally recognized genetic changes (e.g. hemoglobinopathies, adult lactose tolerance, etc.). To an overwhelming degree our genome and its epigenetic regulatory mechanisms remain adapted for a Paleolithic lifestyle. While our genes have been relatively constant, our culture has changed to an almost indescribable extent. This has produced discordance or mismatch between our genes and our lives, and this discordance promotes the chronic degenerative diseases that are responsible for most morbidity, mortality, and health expenditure in developed nations.

Differences in reproductive experience, physical activity, psychosocial factors, microbial infractions, and toxin-allergen exposure all play important role in evolutionary discordance theory.

2. Discordance Hypothesis

From an evolutionary point of view, most complex diseases appear as a result of imbalance or mismatch between our genetic makeup and the conditions of our westernized twenty – first century lifestyle. The basic contentions are that:

The contemporary human genome was selected over thousands of millennia during which our ancestral line existed as pre-human primates who became increasingly human like until during the period between 100 and 50 thousand years ago, they became behaviourally modern and lived as equivalent of hunter-gatherers which was studied during the last century.
The genetic makeup of human especially that concerns our core metabolic and physiologic characteristics has changed very little between the emergences of agriculture roughly 10,000 years ago, and the present.
On the other hand, cultural evolution during these past 10,000 years has progressed at an ever – accelerating rate. The resulting dissonance between what amount of Stone Age genes and Space Age lives fosters development of multiple health diseases or disorders ranging from the potentially life threatening (Cancer, pulmonary emphysema and heart attacks) to the more mundane, but still costly and uncomfortable conditions such as acne, high frequency hearing loss, high pressure, myopia (near sightedness) and dental caries.

These contentions make up the “discordance hypothesis” and its corollary is that the “afflictions of affluence” might best be prevented by reinforcing the essentials of our ancestral living pattern into our contemporary lives – ideally blending the best from the past with best from the present.

3. Nutritional comparisons and evolutionary pre-agricultural diets for health promotion

Assessing the nutrition of early behaviourally modern humans requires assessment of data from diverse anthropological and archaeological sources. Radio isotopic analysis of human skeletal remains and evaluation of archaeological finds that is bones of animals and fish consumed, botanical remains, implements, paintings etc are essential elements for the studies of recent hunter-gatherer subsistence patterns. Such ancestral human were the best, if imperfect, surrogates for Paleolithic foragers; therefore, proximate analysis of the game, aquatic resources and uncultivated plant foods they used have provided vital data.

Given the indirect, incomplete nature of the evidence has consistently revealed important differences between ancestral and contemporary human nutrition.

4. Implications of early hominin diets and discordance hypothesis 4.1. Total Fat Intake

Hunter-gatherers consume the total edible food available from game animals not just that in muscle meat, hence the estimate for total ancestral fat intake is about 35%. Fat intake for Paleolithic Hunter-gatherer varied drastically with latitude: the 35% estimate is for Stone Agers in northeast Africa, the region currently thought most pertinent to establishment of the contemporary human genome. A total fat intake of 35% is at the upper limit of the acceptable range proposed recently by the Institute of Medicine, 20% – 35% and above the 30% upper limit set by numerous other authoritative organizations.

4.2. Saturated Fats

Fat even though provided a substantial proportion of total energy for Stone Agers, the contribution of saturated fat was lower than in the average western diet. American adults obtain 11% – 12% of total dietary energy from saturated fat. Partially acculturated Greenland Eskimos obtain 8.4% and the estimate for Paleolithic humans is lower still, perhaps 7.5%. While its composition varies seasonally, the fat of game animals including that from muscle meat, brain, organs, bone marrow and storage depots tends to have more mono – and polyunsaturated fatty acid and less saturated fatty acid than is found in supermarket meal.

Early recommendations for saturated fat intake were less than 10% of total energy. It is now suggested that neither a specific recommended dietary allowance nor a tolerance upper intake level raises coronary heart diseases risk.

4.3. Trans Fatty Acids

Ancestral humans did obtain a minimal amount of trans fatty acids from mother’s milk during infancy and form the flesh of certain herbivores, but the total from these sources was a small fraction of American consumption, which approaches 2% of total caloric intake. In addition, most trans fatty acid from ruminants is converted after absorption into conjugated linoleic acid isomers which appear to have anti-neoplastic and anti-atherogenic properties.

4.4. Polyunsaturated Fats

In the United States, the total polyunsaturated acids consumption is estimated to average about 15 g/d with omega-6 polyunsaturated fatty acid intake about ten times that of omega-3 polyunsaturated fatty acids. The best available estimate of ancestral intake suggests that total PUFA intake was nearly twice present levels, due almost entirely to more omega-3 PUFA so that omega-6 : omega-3 ratio was closer to unity, perhaps 2 : 1. However, current recommendations are much different about 8 : 1.

Most contemporary omega-6 and omega-3 PUFA intake occurs as eighteen carbon omega-6 linoleic acid and eighteen carbon omega-3 a-linoleic acid. These can be converted slowly to longer chain derivatives: arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid. The latter appear to be more important structurally as membranous constituents and biochemically as eicosanoid precursors and biological response modifiers. It is likely that ancestral humans had much higher total intakes of these longer chain PUFA, and that the ratio of omega-3 forms to the chief 6 constituents was substantially greater than at present. This accord well with retrojected Stone Age experience but total ancestral intake would still have been much higher than at present because of higher total omega-3 PUFA intake.

4.5. Dietary Cholesterol

The cholesterol level intake was generally greater among recent hunter and gatherer people than that of Americans because of high consumption of animal flesh whether from fat or lean animals, all cell membranes contain cholesterol. Nevertheless, mean total serum cholesterol levels for hunter and gatherer people averaged 123 mg% which was 200 – 210 mg% for Americans. The low density lipid to high density lipid fractionation of hunter and gatherer serum cholesterol has not been recorded but a total serum value of 123 mg% roughly corresponds to the recently suggested LDL target of 70mg% for high-risk coronary disease patients. Furthermore, the hunter and gatherer cholesterol value falls within the range found among free – living non human primates. That Hunter-gatherer cholesterol intake and serum levels seem inversely related to American experience adds to the growing evidence that dietary cholesterol is not a major independent driver of serum cholesterol.

4.6. Protein

Recently studies Hunter and gatherer protein consumption varies with latitude but in equatorial savanna populations, those most like the core group of ancestral humans, protein provides about 30% of daily energy intake. This corresponds to consumption of just over 3 g/kg/d for a person with 70 kg ad consuming about 3000 kcal/d. Such intake greatly exceeds the recommended daily requirement as 0.8 g/kg/d but is well within the range observed for free –living higher primates about 1.6 – 5.9 g/kg/d.

4.7. Dietary fiber

Dietary fiber is not digested by mammalian enzymes and passes relatively intact into the large intestine where a proportion is fermented by gut microflora. Fruits and vegetables contain fiber more completely fermentable than that found in cereals, a distinction which appears to influence the physiological and health effects related to fiber intake. The overall fermentability of ancestral dietary fiber would have much exceeded that typically found in today’s fiber containing foods.

4.8. Energy

Extrapolation from the estimated daily energy intake of foragers studied in the past century suggests that the taller and comparably active humans of 50,000 years ago probably consumed about 2,900 kcal/d averaged for men and women. However, it is suggested that the mean energy intake for Americans is much low about 2,093 kcal/d. Nevertheless, recently studies hunter and gatherers have body mass indices averaging 21.6 which is well within the accepted normal range (18.5 – 25 kg/m2). The American average is 26.5. Forager skin-fold thickness are typically half or less than those of age-matched contemporary North Americans.

Further, the skeletal remains showed that Paleolithic humans developed muscularity similar to that of today’s superior athletes, substantially greater than that of typical males and females. These findings suggest our ancestors existed within a high-energy throughput metabolic environment characterized by both greater caloric intake and greater caloric expenditure than is now the case.

Most contemporary recommendations for energy intake revolve around consumption commensurate with energy expenditure so as to achieve energy balance assuming pre-existing desirable body weight. That Americans are becoming ever more obese while consuming far less food energy than did ancestral humans is convincing evidence against the value of hypocaloric dieting and for increasing physical activity in our lives.

4.9. Acid-Base Considerations

Ancestral diets were net base yielding because of their vegetable and fruit content. They tended to drive systemic pH toward alkalinity. Conversely, the cereal grains and dairy foods that make up such a large proportion of contemporary diets are net acid yielding and tend to drive pH toward acidity. Homeostatic mechanisms ordinarily maintain pH at about 7.4, but over prolonged periods, the corrective metabolic measures necessary to offset persistent acid-yielding diets have deleterious effects, including urinary calcium loss to balance hydrogen ion excretion, accelerated skeletal calcium depletion, calcific urolithiasis, age-related muscle wasting, and progressive renal function deterioration.

5. Reasons for Discordance hypothesis

It is generally accepted that current humans differ little, genetically from ancestral Africans of 60,000 years ago but further evidence bearing on this relationship would be welcome. Individuals who have lived as hunter and gatherer are rapidly disappeared and thus we need to access diet and health related information as quickly as feasible from those who remain.

Paleolithic human’s dietary cholesterol intake would have exceeded present intake but their consumption of serum cholesterol – raising fat was lower, in line with or slightly less than current recommendations. Their low levels of serum cholesterol should be considered the intriguing result of a natural experiment.

Because adult Stone Agers are only high fiber uncultivated fruits and vegetables and high protein wild game, their fiber and protein intake would necessarily have far exceeded current consumption. Reconstructions of ancestral nutrition indicate a micronutrient intake much above contemporary recommendations. This fuels the argument that optimum levels of dietary vitamins and minerals exceed currently accepted minimum requirements. We suspect that ancestral intake of phyto chemicals and antioxidant, like that of micronutrients in general, was greater in the Paleolithic than at present. Sodium intake now exceeds that of potassium, a sticking reversal of prior human experience. The physiological effects of this electrolyte inversion deserve scrutiny.

A potentially similar importance concerns the impact of diet on the body’s acid base balance. That contemporary foods tend to drive systemic pH toward acidity whereas those of Paleolithic humans had alkalinizing properties is a fundamental difference with potentially major implications.

The foraging existence necessitated high – energy throughput. Hunter and gatherers body composition and mass indices were almost always in the highly desirable range despite caloric intake well above the American average. Their example suggests that effective prevention of obesity involves increasing physical activity more than decreasing caloric intake.

6. Archaeological Evidence of early dietary patterns

Early hominins began eating things in a manner that leaves durable traces about 2.5 Mya. Bones preserve cutmarks that, by their frequencies and locations, tell us something about how hominins processed animals for food. Bone fractures patterns and elements found at archaeological sites can also provide clues to the diets and subsistence practices of early hominins. Despite debates about methods of acquisition, processing, and transport of carcasses, it is clear that by 2.5 Mya, hominins at least occasionally consumed meat, marrow, and perhaps other tissues from a variety of animals. We can even begin to put together a species list of animals eaten by early hominins, which included mammals ranging from 10 kg to 2500 kg. Larger concentrations of archaeological remains are known, beginning around the Plio-Pleistocene boundary, perhaps suggesting an increased reliance on such foods by some hominins.

The association of Oldowan stone tools with large mammal bones bearing cut marks and percussion fractures confirm the acquisition and almost certain consumption of animal products. Studies of non-human primate diets likewise provide potential insights into the diets of our ancestors. For example, African apes today have a penchant for easy to digest, sugar-rich fruits. It is mostly at times of resource stress that gorillas “fall back” on tougher, lower – quality food resources. Early hominins, too, then may have preferred higher quality food sources such as fruits except at “crunch times”. Some author develops this idea further distinguishing different types of fall back foods. Her comparisons of chimpanzees and bonobos suggest possible links between biome variability, diet and tool use by hominins.

7. Discussion

Thoughtful people interested in their own health typically pay careful attention to research findings and official recommendations about diseases prevention. A the New York Times observed, not surprisingly, inconsistency has been coupled with ineffectiveness: many targeted conditions, including, for instance, breast cancer, type 2 diabetes, depression and hypertension occur more frequently now than they did twenty years ago.

The lifestyle of ancestral humans, that for which our genome was originally selected, could be considered a paradigmatic baseline. Deviation from the essentials of that experience appears to underlie the patho physiology of chronic diseases propagation and, conversely, behaviour, which tends to match the Stone Age lifestyle model, is likely to forestall development of chronic illness while positively enhancing health.

The nutritional considerations presented an approach to diseases prevention based on the evolutionary-discordance paradigm might operate. The first requirement would be to determine as accurately as possible the pertinent lifestyle characteristics of ancestral humans. Next the health effects of deviation from, and reversion toward these original bio-behavioural parameters would require meticulous scientific investigation. Thereafter. those factors whose importance is supported by careful research would be promulgated as recommendations for healthy living. Finally, the fundamental rationale, research findings, and actual recommendations would be integrated into an understandable, persuasive framework – that the essentials of our ancestral lifestyle constitute a guide for healthy living in the present.

The theoretical benefits of disease prevention are great but to date, this potential has been unrealized and the health-conscious public deserves a fresh approach. A program of research and recommendations based on the evolutionary discordance paradigm might be a logical way to address this need.

8. Summary

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