Science of Food Nutrition and Health

By Vinod Puri

Diet is one of the important facets of comprehensive approach to good health along with physical, social, emotional, and intellectual well-being. During the second half of the 20th century, we witnessed a dramatic change in our eating patterns and lifestyle aided by agricultural and industrial revolution, globalisation, and urbanisation and emergence of associated diet related chronic diseases such as obesity, coronary heart disease, hypertension, diabetes, some type of cancer, stroke, and degenerative arthritis.

The science of food and nutrition is very complex. Nutrition science like many other fields of science is evolutionary and there are always conflicting research outcomes that need to be carefully evaluated. We ingest hundreds of dietary components every day and understanding various metabolic pathways and the effect of interactions of various dietary components in vivo is rather challenging.

Recent advances in genetic research fostered the emergence of new disciplines such as nutrigenomics, proteomics, metabolomics, and transcriptomics which can shed light on the molecular level interaction between dietary nutrients and the genome. These technologies provide the vision for future nutrition research that may unravel how the diet/genome interactions modifies the phenotype.

Food may not be the overall cure for the treatment of every possible disease, but the importance of food in both causing and relieving certain problems cannot be neglected. This is one of the most researched topics and there is a lot written about it. However, this book is probably the only text that provides up to date information on the various interrelated topics on food and nutrition that would be of interest to wider community.

• Language: English
• Publisher: Austin Macauley Publishers
• Release date: Jul 21, 2023
• ISBN: 9781398454125

Vinod Puri

Professor Vinod Puri has over 40 years of research experience comprising both fundamental and applied research undertaken at CSIRO, Melbourne University, Defence Science & Technology Group and Deakin University. His work covering a range of disciplines related to carbohydrate chemistry, biotechnology, chemistry and technology of natural and synthetic polymers, cellulose chemistry and technology, pulp and paper science, power and energy, autonomous ground vehicle systems, artificial intelligence, robotics and military technologies has been widely reported in reputed scientific journals, conferences and as technical reports. As chief technology officer (retd.) at DST Group, Dr Puri was instrumental in developing and investigating concepts for the insertion of leading-edge emerging technologies with a view to enhance land force capability.

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About the Author

Professor Vinod Puri has over 40 years of research experience comprising both fundamental and applied research undertaken at CSIRO, Melbourne University, Defence Science & Technology Group and Deakin University. His work covering a range of disciplines related to carbohydrate chemistry, biotechnology, chemistry and technology of natural and synthetic polymers, cellulose chemistry and technology, pulp and paper science, power and energy, autonomous ground vehicle systems, artificial intelligence, robotics and military technologies has been widely reported in reputed scientific journals, conferences and as technical reports. As chief technology officer (retd.) at DST Group, Dr Puri was instrumental in developing and investigating concepts for the insertion of leading-edge emerging technologies with a view to enhance land force capability.

Dedication

This book is dedicated to my mother, Bimla Puri Khazanchi (late), who devoted her life to the education of children from remote rural areas in Panjab and Himachal Pradesh, India, at a time when there were no schooling facilities in 1950s after India’s independence.

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Acknowledgement

I would like to thank Professor Rishi Puri, Intervention Cardiologist and Researcher in Cardiology at Cleveland Clinic, Cleveland, OH, USA, for many discussions on the role of diet and the development of chronic cardiac diseases, which prompted me to look at the evolutionary aspects of development of human species and the contribution of foods over a period of millions of years.

I am also thankful to Prof (retd.) Valerie Krishna, who spent many hours in going through the manuscript and made many critical suggestions. Thanks are also due to Dr Despina Filippidis for her generosity to lend her time and effort in providing support in formatting of the manuscript and providing useful comments that helped in the improvement of the text. I am also indebted to many colleagues at Department of Defence, Deakin University, and CSIRO who have helped me through general discussions in the selection of topics that were of interest to many in understanding the fundamentals of food, nutrition and health. Finally, I would like to thank my partner, Veena Puri; and my daughter, Richa Puri, who have been a source of encouragement during the preparation of the manuscript.

Preface

Food is an essential and key component responsible for the survival and development of the human species. Food also plays an important role in the promotion of health and prevention of disease by furnishing essential macro nutrients in the form of carbohydrates, proteins and fats as well as micronutrients such as vitamins and minerals.

Human beings ingest a large variety of foods sourced from plants and animals consisting of many chemicals that on digestion and absorption are metabolised to deliver the energy to sustain life. It is a fact of life that ingestion of foods containing appropriate amounts of macro and micronutrients is critical for the maintenance of healthy life and deficiency of any of these nutrients results in the development of health disorders.

The diet of modern human has changed dramatically with industrial revolution, globalisation and urbanisation. We have seen enormous growth in commercially available foods that are now become a norm of our society because of easy accessibility and affordability. Food scientists have played a significant role in the development of a variety of foods that are highly palatable and are addictive. These foods are a rich source of sugar, saturates fats, and salt and contain various food additives added to ensure safety, shelf life, freshness, taste, texture, and appearance.

On weight per calorie basis, these foods are energy dense and consumption of these foods on everyday basis in large quantities leads to an imbalance between energy intake and expenditure. This change in our eating patterns is now associated with obesity and emergence of diet related chronic diseases such as coronary heart disease, hypertension, diabetes, some type of cancer, stroke and degenerative arthritis.

The science of food and nutrition is obviously very complex; however, there is tremendous interest globally in understanding and following guidelines that will help improve health. The internet generally is the first point of information for the general public which is flooded by conflicting messages about nutrition on popular social media sites by so-called experts, nutritionists, food bloggers, commercial food producers and other commercial organisations leading to public confusion.

Besides, media reports in the field of nutrition are often of tentative and speculative selected and constructed with an aim to cause sensation and enhance news value rather than representing true picture of established knowledge. Poignantly there are no filters on the accuracy of the information and many commercial organisations involved in the production of commercial foods and the ones involved in the nutrition and weight management use popular celebrities to endorse secondary food products leading to propagation of food trends, myths and fads.

Nutrition science like many other fields of science is evolutionary and there are always conflicting research outcomes that need to be carefully evaluated. We ingest hundreds of dietary components every day and understanding various metabolic pathways and the effect of interactions of various dietary components is rather challenging. Nutrition is one of the most researched disciplines; however, there are still many gaps in our understanding the interaction of many dietary components in vivo and their likely effect on overall health.

What food is healthy and what is not? It’s an incessant debate and the topic is extremely contentious. In general terms there could be many facets of healthy or non-healthy eating which may differ from culture to culture based on locally available foods, affordability and needs of the individual. There is no such thing as an ideal universal diet. Scientists now realise that diet guidelines should be based on food groups rather than singular food components, as well as energy intake vs energy expenditure with broader recommendations on the consumption of macronutrients and micronutrients, both essential and nonessential, to reduce the effect of diet related chronic diseases.

Also, the food-based dietary guidelines keep on changing with the advancement of our scientific and technical knowledge. In addition, contradictory information posted all over the popular websites cause confusion and backlash against nutritional advice in general. Initially food and nutrition research concentrated in alleviating nutritional deficiencies based on single nutrients, however, currently overeating energy dense foods is of primary concern and the scientists are looking at the effects of food groups on health, interaction with human microbiome, gene expression, energy metabolism and relationship between specific nutrients and chronic diseases.

In this context, the proposed book presents up-to-date information on the science of food nutrition and health by carefully synthesising the information from many peer reviewed published work till date. The chapters selected discuss the food and human evolution, followed by fundamentals of human digestive system, food metabolism and role of enzymes in the digestion of foods and in cellular metabolic processes. Further, the reader is introduced to science of phytonutrients and bioavailability and role of phytonutrients on human health, gut microbiota and health, food additives, food energy balance, obesity and weight management strategies and food induced allergies, intolerance and poisonings and the concept of superfoods.

The book also includes chapters on food habits of inhabitants of various countries and associated health aspects. There is a message that food may not be the overall cure for the treatment of every possible disease, but the importance of food in both causing and relieving certain problems, cannot be neglected. Chapter 1 presents the evolutionary journey of primates to humans and the role of foods in the development of human species and shaping our lives. Chapters 2-4 describe the fundamentals of human digestive system which is important in understanding basic principles of food digestion, absorption and metabolism to produce energy required for the conduct of all the body’s necessary functions.

We ingest a large variety of plant and animal derived foods and as such consume several bioactive compounds as part of our daily diet. Chapter 5 gives a detailed description of bioactive compounds and Chapter 6 provides our current understanding of the bioavailability and metabolism of these compounds and likely benefits/burden on human health.

In recent years, the role of human microbiome has been implicated in both health and disease based on the type of microorganism that flourish or erode during our life span. Chapter 7 provides an overview of the extant knowledge in Human Intestinal Microbiota and its relation to health and disease.

Genetics play an important role in human evolution. Nutrients in food has been the key components that interact with human genes resulting in the emergence of science of Nutrigenomics and other omics technologies that are believed to enhance our understanding of the role of food and nutrition in human health and disease. The concept of Nutrigenomics in human health is covered in Chapter 8.

Obesity/overweight is the modern disease and WHO, late in the 20th century, acknowledged that obesity or being overweight are potential health hazards and represent a rapidly growing threat to the health of world population. Obesity is now considered to be one of the major factors of chronic health disorders such as cardiovascular disease, hypertension and stroke, diabetes and some types of cancer. Chapters 9-10 provide detailed information on food energy balance and issues related to obesity and weight management and their relationship to trends in food consumption patterns of various communities all over the world.

In the 20th century, we witnessed the technology revolution in food industry with the development of commercial food processing technologies which generated demands for the assurance of food safety, physical characteristics and consumer appeal. This led to the development and use of many food additives either extracted from natural products or through chemical synthesis which have now become part of our daily diet. Chapter 11 covers the range of additives and preservatives currently in use in food processing, their regulation, benefits and implication on our health.

Humans have been using many naturally occurring plant-derived components such as herbs and spices as food additives over the years for flavouring or preservation purposes. Chapter 12 presents the chemistry and application of currently used culinary herbs and spices and their role in human health.

It has been reported that almost 20% of the world population show some adverse effects when ingest certain types of foods. Further Chapter 13 presents issues related to food intolerance, allergy and poisoning

Further, superfoods are the buzzword of this century and within the spate of few years we have seen an unprecedented growth in foods presented with the label as superfoods with unrealistic claims of their health benefits. Chapter 14 collates information with regards to chemical composition of various food groups and their likely health effects and the etymology of superfoods and comparative assessment and relationship to health.

Chapter 15 covers various cuisines that are popular, the foods that are staple to certain regions and the trends in eating patterns around the world. This chapter also explores the shift from traditional foods to popular commercial foods with the development of modern cuisines and its implication in human health. WHO/FAO has been instrumental in developing food based dietary guidelines for all its member countries with a view to promote healthy eating habits and combat some of the diet related chronic diseases. Even though the patterns of human diets are generally based on their origin, geography, culture, religion, social structure, politics, and environment, it is interesting to note that how globalisation has influenced the eating habits all over the world leading to the emergence of diet related diseases in the last 50 years. The good and bad of various diet patterns around the world and their likely health aspects are summarised in this chapter 16.

Chapter 17 is an Epilogue; summarising the fundamentals of the science of food nutrition and health.

The changes in food habits and genetic adaptations over the years have culminated in an intelligent species we call the modern humans. However, the agricultural and industrial revolution dramatically changed the lifestyle of the modern humans to its ancestors. The change in food habits and lifestyle was so vivid and intense that our genes could not evolve at the same rate resulting in the expression of many disorders that are prevalent all over the world. Hence the selection of chapters consolidating evidence-based information that are interlinked with human evolution, diet patterns and food component interaction in order to fully understand the science of food, nutrition and health.

Food is one of the most important facets of comprehensive approach to good health along with physical, social, emotional and intellectual well-being and the type of food that we consume daily can have a major impact on our health in the long term. Hence the topic is of immense interest to general public. Also, food science is multidisciplinary subject and encompasses many fields including biology, chemistry/biochemistry and engineering, computer science and informatics. This is one of the most researched topics and there is a lot written about it. However, this book is probably the only text that provides up to date information on the various interrelated topics on food and nutrition that would be of interest to wider community.

The topics covered in the book would appeal to professional people working in the fields of food and nutrition, weight management, health workers, research workers, policy makers, teachers, and as a reference for undergraduate students. The book is written at a level understandable to a person with some understanding of general science and an interest in food and nutrition.

Vinod Puri

Adelaide, SA, Australia

December 2020

Chapter 1

Food: Evolution

Introduction

There is considerable debate on the origin of life on earth. Scientific studies based on fossil records estimate that life originated sometimes between 4.5-3.5 billion years ago.

However, we will start our journey with the origin of primates. The scientific studies based on theories of evolution indicate that the primates emerged about 50 million years ago (mya) and human life appeared about 6 mya. The history of human evolution is reconstructed from evidence gathered by palaeontologists, anthropologists, anatomists and others from fossil records, behaviour, study of genetics and dating of fossils and artefacts. Fossils provide imprints of ancient living organisms that are found in layers of rocks.

It is important to note that food requirement for the sustenance of life is intricately linked with the evolution of both fauna and flora and it is critical that we understand the nutritional traits during the stages of evolution from primates to humans. A large body of literature indicates that food is a key factor in shaping human evolution as well as human variability. In this chapter, we will discuss the relevance of various studies on the evolution of diet which is central to the evolution of human species.

Before we explore the tenets of human dietary evolution, it is important to familiarise ourselves with human taxonomy which is involved in classifying the humans under hominid family or in animal kingdom in general.

International convention of classification uses the following rules:

Family name always ends in idae

Sub-family name ends in inae

Tribe name ends in ini

According to this convention, the humans are classified under superfamily Hominoidea as given in Fig 1.

Fig 1: Human classification system

It should be noted that ‘Hominid’ and ‘Hominin’ are the abbreviated form of ‘Huminidae’ and ‘Homininae’ respectively and have been used frequently in the human evolution studies.

In the current classification system ‘Hominid’ is the group consisting of all modern and extinct Great Apes including modern humans, chimpanzees and orangutans plus their immediate ancestors while ‘Hominin’ is the group consisting of modern humans, extinct human species and all our immediate ancestors; including members of genera Homo, Australopithecus, Paranthropus, and Ardipithecus.

The term ‘Hominid’ used to have the same meaning that ‘Hominin’ has now. ‘Hominid’ is assigned a broader meaning and now refers to all Great Apes and their ancestors. Currently the term ‘Hominid’ is used in the more restricted sense as ‘Hominins’ or humans and relatives of humans closer than chimpanzees

Similarly we have divided the different periods of evolution based on the environmental conditions that existed during that period (Figure 2). The following is the mostly agreed classification of different periods immediately after the conclusion of the Mesozoic Era. These names are commonly used during the discussion of human evolution.

Figure 2: Graphic representation of evolution through different periods

(Adapted from Early Primates Evolution: The First Primates. anthro.palomar.edu/early primates/early_2.htm)

Primate Evolution

Scientists believe that the beginning of the Eocene Epoch is marked by the appearance of two new groups of animals classified as Perissodactyl (odd toed) and Artiodactyl (even toed) mammals. The fossil records obtained from North America, Europe and Asia also indicate that the first true primates emerged around 55-50 mya during this era. (An Epoch can be defined as a particular period of time in history or person’s life or a point in time beginning a new or distinctive period or a long period of time marked by some predominant or typical characteristics).

Timeline for human evolution starting from the emergence of the first primates is tabulated in Table 1.

Table 1: Estimated timeline of human Evolution (Pickrell)

(mya=million years ago. kya= thousand years ago)

The high temperature at the beginning of Eocene favoured the existence of smaller animals as they were better able to manage the heat. They appeared to have hands and feet suitable to manipulate objects and to climb trees and weighed under 10kg. In parallel, the high temperatures created a moist and temperate environment favouring the spread of forests throughout the planet earth. Many flowering plants and abundance of grasses encouraged the evolution of grazing animals. However, during late Eocene the temperature started to drop significantly causing seasonal variation and resulting in the thinning of the forests with a shift towards increasingly open savannah like vegetation. Accordingly, the size of the mammals changed with the emergence of large body sized mammals including bats, elephants, rodents, and marsupials as well as primates. These mammals had tough hoofs, specialised teeth for grinding and digestive systems capable of processing grass, leaves and other plant materials.

Many new primate species emerged during this era that resembled modern prosimians (a primitive primate of a group that includes lemurs, lorises, bush babies and tarsiers). There was probably maximum prosimian adaptive radiation (that is rapid expansion and diversification because of adaptation to new ecological niches) during this Epoch. The prosimian species evolved into many other species as a result of different populations becoming reproductively isolated from each other while trying to adapt to different environment. The diversification in prosimians species resulted in major evolutionary changes in some providing an insight into the type of species that would emerge in the future. Because of food abundance their brain sizes started to become larger with snouts becoming smaller.

Similarly, marked changes were observed in the spinal column where foramen magnum (an opening in the base of skull through which the spinal cord passes) in some primate species moved from back of the skull towards the centre; a condition that supported the primates to hold their bodies erect while hopping or sitting. With the cooling of the environment during the end of Eocene, most of the prosimian species became extinct.

Eocene transitioned into Oligocene (33.9-23.0 mya) with a major drop in global temperature and sea levels and extinction of many Eocene primates (17-generic extinction) from North America and Europe. The climate favoured the emergence of open grasslands and appearance of new primate taxa in Asia, Africa, and South America. Oligocene primates have been classified under three taxonomic groups:

Parapithecidae: These primates appeared in late Eocene to early Oligocene containing about 8-10 species ranging in body mass from 300-3000g. Examination of their dental features indicate that these primates were mostly diurnal (active during the day), frugivorous and excellent leapers.

Propliopithecidae: These primates appeared early in Oligocene and were similar to Parapithecidae except they were larger in size with a body mass ranging from 900-6700g. Simmons reported that the brain size of these primate was similar to extant lemurs and there were considerable differences in size or appearance between the sexes in addition to the sexual organs themselves (sexual dimorphism). The morphological examination of post cranium and cranium indicates that these primates were arboreal quadruped, diurnal, and had frugivorous and folivorous diet.

Platyrrhines: The fossil data from these primates that originated in South America indicate that these were small primates with a body mass between 500-1000g and were frugivorous.

The Oligocene was followed by the Miocene (23.0mya-5.3 mya). The climate during the beginning of Miocene was moderately warmer and during the later stages of this Epoch the climate became cooler and drier, leading to Pleistocene glaciation. Considered to be one of the longest Epochs of the Cenozoic era, it is noted for the formation of open grasslands and emergence of new forms of mammals. During early Miocene, ape-like primates appeared in Africa which are classified under the family Proconsulidae.

As these primates exhibited both ape-like and monkey like characteristics, some paleoanthropologists tentatively placed them under the superfamily Hominoidea while others placing Proconsul outside it. These apes-like primates weighed between 17-50 kg; however, their brain sizes were similar to the monkeys of the Miocene. These primates had sexually dimorphic canines and they were frugivorous. Most of the Preconsul were quadrupeds, while some species were arboreal.

During the mid-Miocene period, the most notable apes, Dryopithecus and Sivapithecus, appeared in Europe and Asia respectively. These primates with body sizes ranging from 20-90 kg had teeth suited for masticating fruit pulp. Their brains were similar in size and proportions to modern chimpanzees. Most of the ape species of the Miocene period went extinct. One of the notable features of this epoch was a mass land migration from Africa to Eurasia. This movement resulted in adaptive radiation with the evolution of many different forms which laid the groundwork for the emergence of great apes and humans.

The late Miocene experienced reduced rainfall and a gradual decline in global temperature, resulting in the extinction of many ape species. Some of the species of late Miocene include Oreopithecus, Ouranopithecus, Lufengpithecus, and Ankarapithecus. Oreopithecus was one of the large numbers of European immigrants settled in the Tusco Sardininan area. These apes were estimated to weigh between 30-35 kg and were folivorous, as evidenced by the presence of shearing crests on its molars. This is in contrast to the diet of present-day apes that are generally frugivorous. Ouranopithecus on the other hand were large body primates estimated to weigh between 70-110 kg.

In-depth analysis of their teeth revealed that they had a diet heavy in hard foods such as nuts and tubers. Like most primates, their teeth exhibit sexual dimorphism with males having much larger teeth than females. Another late Miocene ape Lufengpithecus, which is now extinct and is regarded a very close relative of the orangutan like Sivapithecus, had low crowns and thick enamel suggesting a diet of tough vegetation and gritty food.

The Miocene was followed by the Pliocene (5.3-1.8 mya) which had a cool and dry climate that further favoured the expansion of grasslands and reduction in tropical forests. The vast majority of the Miocene Apes became extinct with the beginning of the Pliocene and fossil evidence supported the emergence of monkeys and early hominins. Because of the formation of land bridges between North and South America, there was a massive migration of plants and animals to new habitats. Many fossil specimens of Pliocene monkeys have been recovered from Africa, Asia and Europe. These primates showed marked resemblance to extant primates such as cercopithecines and colobines.

The old-world monkeys mainly were frugivores and folivores. However chimp’s diet includes fruit, termites and ants and even smaller species of monkeys, antelope pigs, and anything young and catchable. The first hominids including Australopithecines and Kenyanthopines appeared in this Epoch in Africa around 4.2 mya. The fossil evidence supports at least the existence of 12 species of early hominin dating from 4- 1.5mya. The prominent species included:

Australopithecus anamnesis: lived around 4.4-3.9mya in East Africa. These were efficient tree climbers and bipedal, with large canine teeth in comparison with later Australopithecines and humans. They were largely vegetarian relying mainly on fruits and nuts.

Australopithecus afarensis: lived around 3.7-3mya, had slender curved fingers for efficient tree climbing. The researchers report a considerable variation within afarensis species and recent fossil discovery of Kenyanthropus platyops was considered to be one variant. However, this is disputed by Leakey who believes this to be a separate species of Australopithecus.

Australopithecus africanus: lived around 3.3-2.3 mya had a small and light frame with teeth more like humans. The microscopic wear patterns of teeth suggest a largely plant-based diet with a possibility of some meat obtained either from scavenging or hunting smaller animals in a way similar to modern chimps, as well as insects and eggs.

Paranthropus aethiopicus: lived around 2.5 mya, was one of the robust species mainly found in East Africa. It had a smaller brain, with a larger sagittal crest than others. This was considered as a transitional species from one of the earlier Australopithecus species.

Paranthropus robusts: lived around 2-1.4 mya and had strong jaws and large molar and premolar teeth with thick enamel.

Paranthropus boisei: a super robust species that lived around 2-1.4 mya, was muscular with a large sagittal crest and large grinding teeth with thick enamel. The microscopic evidence of dental wear pattern and carbon-isotope analysis indicate that this species predominantly ate grasses, leaves, roots and possibly meat.

Homo habilis, the likely first human ancestor, appeared in the Epoch in Africa around 2.0mya. Stone tools were also discovered from around this time and possibly Homo habilis used these tools for hunting. The Homo line evolved through Homo ergaster and Homo erectus an extinct species of Homo that lived in eastern and southern Africa between 1.8-1.3 mya. The species later expanded to Eurasia, China and Java. Members of the Homo genus are distinguished by an erect posture, robust cranial features, two-footed gait, fully opposable thumbs and well-developed tool making ability.

The Pleistocene epoch began about 1.8mya and lasted until about 11,700 ya and is considered the last ice age, the glaciers covering a large part of the Earth. The global temperature ranged between 5-10°C. Many vertebrates became extinct during this period but many survived, including apes, bears and members of canine and feline families. This epoch is defined with the marked changes in ocean current, composition of the atmosphere and changes in the position of the Earth in relation to the sun. The fauna and flora differed from the modern era of Holocene as changes in climate caused large-scale migration of both plants and animals.

Homo sapiens emerged during this period (0.2mya) and covered nearly every part of the planet. This is the only surviving species in this genus. The now extinct species of Homo genus Homo heidelbergensis, Neanderthals, inhabited Europe and parts of western Asia in the middle and late Pleistocene. DNA sequencing has revealed that Neanderthals, modern humans and another hominid known as Denisovans descended from a common ancestor around 500-350kya.

Diet Evolution of Primates

Our main source of evidence of diet patterns comes from the study of fossil records. The food habits of our ancestors starting from the first hominids is largely determined by examining morphological changes, archaeological material evidence and direct measurement of chemicals extracted from bones. Additionally, studies of diet patterns of living primates provide us with information on many aspects of their lives. The diet patterns of early primates can be deduced from fossil and archaeological records by comparing the primate dentition and skeletal morphology with that of extant primates.

It has been clearly demonstrated that all primates have diphyodonty that is all primates have two sets of teeth—baby or deciduous teeth during early development which are then replaced by adult teeth. In addition all the primates are characterised by heterodonty i.e., they have different kinds of teeth. Most primates have four kinds of teeth namely incisors, canines, premolars and molars. Food being the key aspect of any living organism, it similarly must have dominated the biology of extinct primates similar to the living primates.

A comparison of food habits of living primates with the data obtained from fossil records may help us in unravelling some aspects of the food habits of our ancestors.

The craniodental morphology data obtained from fossil records of Australopithecines, Paranthropus and kenyanthopines indicate that these primates had relatively large, flat and thick enamelled cheek, teeth with massive mandibles, and significant muscle attachments. These features are similar to gorillas and are linked to mostly vegetarian plant-based diets that are hard and abrasive such as nuts, fruits with hard shells, skin and stones.

Even though these early hominins share common cranio-dental characteristics, there are some remarkable differences in their morphology indicating that there must have been differences in their diet. This is expected as Paranthropus appeared in late Plio-Pleiostsocene epoch when the environments were open, and they had to adapt to a more flexible diet than Australopithecus who lived in a wooded environment. The stable isotope studies suggest that the diet of an africanus mostly consisted of C3 foods such as fruits, leaves, bushes and shrubs or animals which consumed them while P boise consumed C4 rich foods such as grasses and sedges indicating that their robust cranio-dental adaptation helped in the processing of large quantities of low-quality foods. (C3 foods are derived from plants that convert carbon to a compound containing three carbon atoms.

About 95% of all plants on earth use C3 photosynthesis. C3 plants include rice, wheat, rye, barley, cassava, potatoes, algae, spinach, and yams. C3 plants are slower to take in ¹³C so their total biomass ranges from -22 to -35 % with a mean of -26.5%. C4 plants convert carbon to a compound containing 4 Carbon atoms and absorb ¹³C faster than Carbon 12 and their total biomass ranges from-9-16.5. They are better adapted to dry climates. C4 plants of special interest include maize, sorghum, sugarcane, millet, fonio, teff and papyrus. It is believed that a diet of C4 plants indicates grazing mostly grasses and the diet of C3 plants indicates browsing from higher foliage (shrubs and trees).

Stable isotope analysis can distinguish between C3 and C4 vegetation from a tissue sample from an animal (blood to bone) and from the ratios of different C-isotopes can be determined the relative rates and degrees to which different species adapted to the food sources that become available due to environmental changes.

Subsequent species such as Australopithecus africanus and Homo habilis that appeared around 2.5-1.8 mya were relatively gracile and their cranio-dental morphology was similar to chimps rather than gorillas. Researchers believe that increased body size was the single most important adaptation to diet in gorillas (average body mass male/female: 169/80 kg) and orangutans (average body mass male/female: 78/35 Kg) and was associated with the consumption of low-quality foods that were available in abundance. Chimpanzees, who have low body mass and size (male/female: 50/41 Kg as compared to gorillas and orangutans), are omnivores and consume both vegetarian foods as well as animals. Most of the chimpanzees’ diet is based on ripe fruits, leaves, seeds, nuts, and flowers; however they also consume small amounts of insects and meat from larger animals. Chimpanzees rely mostly on high quality and high energy foods and coupled with their smaller body size these primates have higher mobility and sociality.

Scientists also looked at the gut morphology of extant primates and humans to understand the diet patterns of primates. Milton compared the relative volume of the different parts of the gut for selected hominid species. Even though the basic gut anatomy of all extant apes and humans is similar, in humans 56-67% of total gut volume is found in the small intestine compared with 23-28% for apes. However the apes’ exhibit total gut volume in the range of 52-54% in the colon compared with 17-23% for the humans. Based on gut morphology, Chivers and Hladik suggest three basic dietary patterns:

Animal source foods (faunivory) including invertebrates and vertebrates, which are easily digested and are suitable for short and simple gut.

Fruits (frugivory) including reproductive parts of plants, seeds and tubers, which are high sugar foods also readily digested and absorbed in the intestines.

Leaves (folivory) including the structural parts of plants i.e., grasses, stems, bark and gums, which require a large stomach or the large intestine/colon to effect fermentation.

According to Milton, large gut volume of the colon in apes indicates adaptation to a lower quality diet based on hard to digest considerably bulky plant materials while the large gut volume of the intestine in humans suggests adaptation to high quality diets based on nutritionally dense and highly digestible foods.

Another factor that is considered important in affecting food choices by different species is gut kinetics. Gut kinetics is the study of the food passage through the digestive tract and can be used to understand the effects of various foods that influence its passage through the digestive tract. Various studies undertaken on humans and apes suggest that higher quality diet pass through the digestive tract more slowly in comparison with lower quality diets. In humans the average time taken for food to pass through the digestive tract is estimated to be around 36 hours. The feeding trials conducted on chimpanzees also reveal that the food transit time in the digestive tract was very similar to humans even though chimpanzees have considerably larger total as well as hindgut.

On the other hand, gut kinetics in carnivores reveal that food transit time is quite rapid i.e., 2.4h (range 1.03-3.6) for minks and for polar bears showing bimodal modes of defecation occurring 17-18 h and again 23-26h. It should, however, be noted that the gut anatomy of carnivores though similar to omni and herbivores is rather very simple having a simple stomach and short total gastrointestinal tract.

Large body primates such as gorillas (body mass ranging from 99.5-211kg) and orangutans (body mass ranging from 38-86 kg) evolved to survive on a low-quality plant-based diet in the absence of higher quality foods. This is true when the primate numbers increased and there was a considerable competition for food sources. Plant based foods are also seasonal and the environmental conditions can be detrimental for their growth. It is obvious that there were probably times when high quality foods were in short supply and the primates had to eat whatever was available.

Based on the available data, the researchers conclude that extant hominoids come from a strongly plant eating ancestry; however, it may have been possible that some of the species were able to maintain a diet of high-quality foods. This is true for extant chimpanzees and bonobos as they normally seek a diet of ripe fruits, protein rich young leaves, buds, flowers and also animal matter. However they also have a capacity to consume other plant-based foods such as seeds, cellulosic materials and pectic substances.

Their gut anatomy therefore differed slightly from humans as the large colon size in chimpanzees helps retain plant materials for sufficient times to extract nutrients. It is reasonably well established that these primates preferred animal-based diet but such foods are difficult to procure in large quantities. Hence animal-based food constitutes small proportion of their daily diet.

As chimpanzees have been shown to consume animal source foods, it is believed that early Homo species may have relied on animal source food in addition to plant-based food. Scientists also observed increased racialisation of the mandible as well as increase in cranial capacity. Further it has been suggested that consumption of high-quality plant based or animal source food resulted in an increase in brain size through time hence greater intelligence. The brain size as well as the intelligence of Human species growth with evolution is highlighted in the Table 2 below:

Table 2: Height and brain size of Homo species

Also, a larger brain demands more energy that could only be met by high-quality energy-rich foods. It is believed that the animal source food is more energy efficient as compared with plant foods inferring that it is likely that our ancestors probably started to consume more animal source food to satisfy the body energy demands. Increased intelligence also contributed to manipulation of the foods in a way that it can be digested easily. Our digestive system evolved accordingly with the reduction in gut size.

Milton theorised that as the angiosperm forests flourished during the late Cretaceous (94-64 mya), it is likely a small, insect eating mammal, which may have resembled a tree shrew, existed scaling the trees in search of pollen distributing insects. However, its descendants moved on to derive nutrition substantially from edible parts of the plants. Milton further concludes that this change set the stage for the emergence of the primate order.

Based on the theory of natural selection, proposed by Darwin that Variation is a feature of natural populations and every populations produces more progeny than its environment can manage. The consequence of this overproduction is that those individuals with the best genetic fitness for the environment will produce offspring that can more successfully compete in that environment. Thus the subsequent generation will have a higher representation of these offspring and the population will have evolved, the traits that enhanced the efficiency of foraging were favoured resulting in development of a suite of traits characteristic of primates.

A recent study also provided an insight into the likely eating habits of primates. If we assume that a species with characteristics of modern primates existed 50 mya and is the ancestor of apes, it is then reasonable to presume that a major portion of their food (about 95%) may have been derived from plants such as fruits, nuts, leaves, gums, and stalks. It is also reasonable to assume that as much as 5% of their dietary intake was derived from insects, small animals, and eggs.

Hawes and Peres based on data collected from 290 primate dietary studies spanning 42 years revealed the amount and diversity of fruit consumed by primates in neo-tropical forests of South and Central America. They also revealed that primate body mass and the amount of fruit eaten are linked-with smaller primates such as marmosets and tamarins, which have high metabolic rates, eating more insects and less fruit. Meanwhile medium sized primates such as the saki monkey consumed more fruit while larger primates such as howler and woolly spider monkeys, eat a lot more foliage because their guts can tolerate high levels of cellulose and toxins.

Further, Eaton and Eaton proposed that considering the early primates were similar to current chimpanzees and bonobos the general patterns of their diet parameters could be estimated with modest confidence. They assumed that:

Proteins derived largely from vegetable sources would have contributed to a greater proportion of total energy as compared with modern humans.

Simple carbohydrates would have provided moderate levels of starch and total complex carbohydrates providing dietary energy somewhat less than the typical contemporary human diet.

Dietary fibre intake would have far exceeded the current levels; a figure quoted being 200g vs 20g a day highlighting that for some ancestral hominoids, colonic fermentation would have provided over 50% of total dietary energy.

Daily intake of vitamins and minerals would have far exceeded that of humans with the exception of Iodine which would have been based on the geographic location such as proximity to ocean or volcanic activity.

Sodium intake would have been very limited compared with the current consumption by humans and substantially lower than potassium intake.

Total fat intake would have been reasonably lower (18-20%) than current recommendations (30%).

The predominant fatty acids available in the wild foods generally contain palmitic acid (approx.30%), linoleic acid (approx. 23%) and alpha linolenic acid (approx. 16%). Fatty acids with less than 16 and more than 18 C-atoms are uncommon in the wild. The wild foods are also rich in ω- 3 and ω-6 fatty acids. In comparison the dietary fats consumed by humans is either from animal fat or oil extracted from seeds. Most oil seeds are high in ω-6 but low in ω-3 fatty acids as compared with the diet of ancestral humans which was rich in ω-3 and ω-6 fatty acids.

Based on this data, it can be estimated that howler monkeys eating a typical leaf and fruit diet show a polyunsaturated to saturated fat ratio (P/S ratio) of 0.85 while human consumption of fats gives a P/S ratio in the range of 0.4-0.5. Also it is estimated that fat contributes about 18% of dietary calories of monkeys in comparison with 30% suggested intake for humans. It should be noted that the dietary intake of longer chain C20 and C22 polyunsaturated fatty acids (PUFAs) such as arachidonic (AA, C20, ω-6) and docosahexaenoic acid (DHA, C22:6, ω-3) by primates was limited between the range of 0-7%.

The existence of materials/artefacts that can be directly linked to dietary changes through time provide additional evidence on the diet patterns of Homo lineage. First stone tools, known as Oldowan tools (an archaeological term used to refer to the earliest stone tools industry), appeared in Africa around 2.5-1.8 mya are associated with Homo species which were supposed to be used for hunting or scavenging inferring that animal source food was an integral part of the Homo species.

Later development of Acheulean industry dated to 1.6 mya revolutionised the stone tool technology. These stone tools are considered to be the products of Homo erectus, a closer ancestor to humans. Acheulean tools included stone hand axes of different shapes and studies of surface wear patterns reveal that these tools were used for butchering and skinning the game, digging soil and cutting plant materials. Fossil evidence also shows signs of embedded animal bones in these tools linking the use of these tools for animal butchering.

Acheulean lithic technology later evolved into Mousterian industry in Europe with the production of smaller and sharper knife-like tools as well as scrapers. The development of this lithic technology has been credited to Neanderthals which were native to Europe and Middle East. Neanderthals developed Levallois flake making technique (a distinctive technique of stone knapping) for making a variety of scraping, cutting and puncturing tools. Also around 400-380 kya Homo heidelbergensis has been associated with wooden spears used for hunting.

All these evidences support that Neanderthals and other homo species relied for subsistence on plant as well as animal-based foods. The Neanderthals living near coastal areas also consumed marine food sources such as molluscs, seals, dolphins and fish. Chemical analysis of Neanderthal skeletons indicates that meat was a major part of their diet. It is however not very clear whether these Homo species were hunters, scavengers or both. However scientists believe these species lived in subarctic environment in Europe and had limited access to fruits and vegetables so hunting for meat was a necessity.

Further, with the advent of fire and in particular controlled fire by humans, led to improve nutrition from cooked carbohydrates and proteins. Cooking made the food more digestible and able to release energy quickly as compared with uncooked food. A large body of researchers believe that cooking of food started around 780-400 kya. However recent investigations by researchers at Harvard University reveal that cooking was prevalent among Homo erectus that appeared in Africa around 1.9 mya and that the homo species evolved biologically to adapt to cooked food. Also, the changes in tooth size and feeding times further lend support to this concept.

Homo erectus and Neanderthals spent 6-7% of their time every day eating while Homo habilis and Homo rudolfensis in comparison spent 7.2-9.5 % of their time eating indicating that they were less accomplished cooks than erectus. Humans in comparison spend about 5% of their time for eating. These studies lend support to the argument that control of fire for cooking by Homo species was instrumental in the rise of modern human as cooking increase the value of the food. Cooking meat and or plant source foods would have helped in the use of less energy for digestion allowing more energy to be directed for the maintenance of growing brain. There is some evidence that human ancestors may have used fire 1 mya. However the current fossil evidence does not support the existence of controlled fire beyond 780-400 kya.

Stable isotope analysis of bone collagen and tooth enamel of preserved hominin fossils has also been used to shed some light on early hominin diets. Stable isotopes of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N) can be extracted from bones and tooth enamels even after millions of years and analysed to determine ratios of stable carbon and nitrogen isotopes. The carbon in nature is fixed by the process of photosynthesis. Differential fractionation of stable isotopes of carbon during photosynthesis causes C4, C3 or marine C3 plants to have a distinct C-isotope signature.

In some cases, plants use Crassulacean Acid Metabolic (CAM) photosynthetic pathway. Variation in isotopic ratios from isotope fractionation can be measured using Mass Spectroscopy, which separates the different isotopes of an element on the basis of mass to charge ratio. The stable isotope ratios (δ¹³C) for various categories are listed in Table 3.

Table 3: Stable isotope ratios for carbon ((¹³C/¹²C) fixed by C3 and C4 plants (Kelly)

It can be seen that δ¹³C for C3 plants is lower with an average value of -27 %0 while C4 plants have values averaging about -12.5 %0.

The stable isotope analysis conducted from samples obtained from Australopithecus africanus and Paranthropus robustus reveal that they predominantly consumed C3 derived foods but also ate significant quantities of C4 and CAM foods. It can also be interpreted that in addition to C3 and C4 foods australopiths could have consumed animals that had eaten these plants.

In comparison, chimpanzees’ diet is dominated by C3 foods. The stable isotope studies reveal that in Pliocene and Pleistocene South African hominids on average consumed about 25% of carbon from C4 plants. This trend continued even with the severe changes in environmental conditions from closed wooded environment to more open habitats dominated by grasslands.

The application of stable isotope analysis to Neanderthals from Marillac Cave in France (40- 45ky old), Scaldinia Cave in Belgium (80-130 ky old) and from Vindija Cave in Croatia (28 ky old) revealed that in all cases the Neanderthals, based on values obtained for ¹³C and ¹⁵N, were similar to top level carnivores deriving the majority of their proteins from animal sources that are likely to be herbivores. Further studies on Upper Palaeolithic modern humans (13 ky old) from Gough’s and Sun Hole Cave in Southern England confirm that the main source of their dietary protein was derived from animals that were likely to be herbivores. Another study on isotope values from modern humans (30-20 ky old) indicates animal proteins derived from marine sources. Isotopic study of Mesolithic humans from Europe further confirms that the consumption of marine based food was the major source of animal proteins.

Holocene Epoch, the period starting around 12000 ago after the end of the Palaeolithic ice age, witnessed the rapid evolution and development of Homo sapiens (the modern human). The mean global temperatures increased and many scholars believe that the human population increased substantially and their activities and exploitation of the environment is the main cause for this change. However, we have seen pronounced development of human knowledge and technology leading to understanding of the world around us. This era also brought great changes in our living conditions, sources of food and diet patterns. Table 4 below lists the likely dietary changes that occurred in the evolution of humans.

Table 4: Stages of evolution of humans and likely dietary changes

Archaeological evidence obtained from the residues of plants, animals and other food types; inferences drawn from artefacts; signatures of diet in the bone chemistry of skeletons; pictorial representation of subsistence activities; and DNA and genetic diversity in modern population of humans, animals and plants and DNA in ancient bones supports the start of farming earth around 12 kya at the end of Pleistocene when the global temperatures began to rise and transitioned to Holocene.

Human population began to increase and many mammals that were used for food became extinct. Humans once dependent upon these animals switched to smaller animals and plant source foods to supplement their diet. With further increase in population hunting and gathering could not support human life. This led to domestication of grasses and cereals which became a fundamental source of subsistence.

Similarly, sheep, goats, pigs and cattle were domesticated in the near east along with wheat, barley, legumes and many fruits and nuts. By 5 kya the agriculture has spread widely all over the world and plant source foods became the major component of the human diet.

The modern era adopted the stationary farming over hunting and gathering and the humans moved on to a diet of cultivated foods. The Neolithic revolution changed the way the humans lived in towns and villages in an arable farmland fully embracing agriculture