Should We Eat Meat?

Evolution and Consequences of Modern Carnivory

Vaclav Smil

• Publisher: Wiley-Blackwell
• Year: 2013
• ISBN:
  9781118278697
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Meat eating is often a contentious subject, whether considering the technical, ethical, environmental, political, or health-related aspects of production and consumption.

This book is a wide-ranging and interdisciplinary examination and critique of meat consumption by humans, throughout their evolution and around the world. Setting the scene with a chapter on meat's role in human evolution and its growing influence during the development of agricultural practices, the book goes on to examine modern production systems, their efficiencies, outputs, and impacts. The major global trends of meat consumption are described in order to find out what part its consumption plays in changing modern diets in countries around the world. The heart of the book addresses the consequences of the "massive carnivory" of western diets, looking at the inefficiencies of production and at the huge impacts on land, water, and the atmosphere. Health impacts are also covered, both positive and negative. In conclusion, the author looks forward at his vision of "rational meat eating", where environmental and health impacts are reduced, animals are treated more humanely, and alternative sources of protein make a higher contribution.

Should We Eat Meat? is not an ideological tract for or against carnivorousness but rather a careful evaluation of meat's roles in human diets and the environmental and health consequences of its production and consumption. It will be of interest to a wide readership including professionals and academics in food and agricultural production, human health and nutrition, environmental science, and regulatory and policy making bodies around the world.

Pork loin center chops. A close-up shows what most meat cuts are composed of:muscle fascicles, collagen sheaths, tendons, intra- and extramuscular fat, and bones.Photo by V. Smil.

1
Meat in Nutrition

First things first: no energy conversion is more fundamental for the ­survival of our species than photosynthesis (primary productivity), the source – directly in raw or processed plants and indirectly in (usually cooked or processed) animal tissues – of all of our food. Eating (setting aside food smells, taste, visual appeal and all those cultural and historical ­connotations subsumed in the act of ingestion) can be defined in the most reductionist biophysical fashion as a process that supplies macronutrients ­(carbohydrates, proteins, lipids) and micronutrients (vitamins and minerals) that are required to sustain our metabolism needed for growth, maintenance and activity and hence to perpetuate life of this most advanced of all heterotrophic organisms that cannot (as all autotrophs can) synthesize their own complex nutrients from simple inorganic inputs. Foodstuffs could be then seen as nothing but more or less complex assemblages of nutrients, and meat stands out among them for many reasons.

A small definitional detour is called for first because, as is often the case when dealing with seemingly straightforward subjects, everyday usage of the word “meat” does not coincide with biophysical realities. Meat, from a sensu stricto structural and functional point of view, refers only to the muscular tissue of animals, and the narrowest traditional definition would limit it to skeletal muscles of wild and domesticated mammals. Horowitz (2006) documents how even during the 1950s many American housewives did not consider chicken to be a meat and how the chicken industry was encouraged to run advertising campaigns that would confer on ­poultry a full meat status. There are also some national rules that make explicit definition. According to the Food Standards Code of Australia and New Zealand, meat is “the whole or part of the carcass of any buffalo, camel, cattle, deer, goat, hare, pig, poultry, rabbit or sheep, slaughtered other than in a wild state,” a definition that pointedly excludes all wild species, including kangaroos whose meat is now readily available in Australia (Williams 2007).

In contrast, a common, sensu lato, usage extends the noun’s coverage not only to muscles of all mammals and birds (much like the understanding of our pre-industrial ancestors for whom meat was everything from squirrels to bison and from thrushes to herons) but also to muscles of amphibians and reptiles (frogs, snakes, turtles) and to all other tissues that are often integrally or proximally associated with meat, above all to embedded or surrounding fat, sometimes also to skin and to internal organs (organ meats, innards, offal – abats in French, frattaglie in Italian, Innereien in German), most of which are not hard-working muscles. But even this liberal definition still leaves out all seafood although few skeletal muscles are as powerful and as efficient as those propelling fast cruising bluefin tunas that can (unlike all other ectothermic fish) raise their ­temperature above that of the surrounding water (Block 1994).

Nor is there any clear, universal divide between “red” and “white” meat. The distinction obviously owes to the amount of myoglobin in muscles (just 0.05% in chicken, up to 2% in beef), but because all mammalian meats have higher concentrations than poultry or fish, the USDA puts all large livestock meat into the red category. In contrast, the Australian ­definition of red meat refers to beef, veal, lamb, mutton and goat meat, but it excludes pork as well as all game meats, including buffalo whose meat is largely indistinguishable from beef. And then there is a common culinary usage that draws the line by age: veal, lamb and piglets are white; beef, mutton and pork are red, but so are duck and goose; and (to bring yet another color into the mix) in France, all game meat is labeled viandes noires. But lack of strict logic is common in classifying foodstuffs: tomato is, of course, a fruit that is always classified as a vegetable, to say nothing about counting tomato paste on pizzas as a vegetable.

Meat Eating and Health: Benefits and Concerns

In this introductory chapter, I will deal first with the functional and ­structural properties and the basic composition of muscles and other ­animal tissues before I turn to specific surveys of meat as a source of energy that comes (given the virtual absence of carbohydrates in muscles) only from two macronutrients, lipids and high-quality proteins. Most societies could always secure abundant, or at least adequate, amounts of carbohydrates from plants, but lipids, and even more so high-quality proteins, were relatively scarce in all traditional agricultures, as well as in the early stages of post-1500 modernization. That is why the role of animal protein in early human growth deserves particular attention.

Eating relatively large amounts of meat must have a variety of health and longevity consequences, but, as with all long-term effects of specific components of human diet, it is not easy to tease them out in an ­unequivocal manner from often inadequate and sometimes questionable epidemiological evidence. There is no doubt about the benefits of high-quality protein for young children in general and for their growing brains in particular, and there is also a high degree of consensus regarding the undesirability of consuming large amounts of fatty meat (although even here there are some intriguing caveats). More recently, a consensus has been emerging about the undesirability of frequent ­consumption of processed meat ­products ranging from bacon to ­wieners.

In contrast, solid generalizations regarding the contribution made by low to moderate meat consumption to the prevalence of the two leading causes of death in modern societies, that is, to cardiovascular and cancer mortality, are much more elusive – and hence it is difficult to say what might be the exact role of meat consumption in extending or reducing average human life expectancy. And, finally, when looking at links between meat and health, it is unavoidable to address the concerns about diseased meat, about meat-borne pathogens whose effects can range from mild individual discomfort to viral pandemics.

These risks have always been present in terms of bacterial contamination arising during the growth, killing of animals and post-slaughter treatment of carcasses and retail cuts, and several animal diseases with potential for epizootic outbreaks have always made their episodic appearance. But there have been two new developments during the past two decades: the ­emergence of contagious avian viruses with a strong potential for viral pandemics, and beef infected with a variant Creutzfeld–Jacob disease (vCJD) (human form of bovine spongiform encelopathy [BSE], commonly known as mad cow disease). Individual risks of the latter infection have always been minimal, but the avian influenza is a cause for legitimate ­worries as its future virulent manifestation can cause large global death toll.

Meat and its nutrients

Evolution has left us with no shortage of specialized organs to admire because of their intricate structures and amazing functions: brains and eyes are commonly cited as the pinnacles of evolution, but such rankings are meaningless as in living organisms only the synergy of all organs matters, and hence skins or intestines or bones or muscles are no less important. Muscles – the prime movers of heterotrophic ­locomotion that make all walking, running, jumping, swimming and flying possible – look macroscopically fairly simple, but viewing their structure sequentially upward from molecular level is a different matter (Aberle et al. 2001; Lawrie and Ledward 2006; Myhrvold et al. 2011).

Molecules of specialized proteins, actin and myosin, are organized in myofilaments that form sarcomeres whose contraction and relaxation generates all muscle motion. In turn, sarcomeres are grouped into myofibrils that are bundled into muscle fibers sheathed by a collagen matrix (endomysium); muscle fibers are bundled into fascicles that are contained within another collagen mesh (perimysium), and the entire muscle is covered by yet another collagen sheath (epimysium, or silverskin). The ends of these connective tissues merge into tendons that are attached to bones (but there are also some muscles that are not attached to skeleton). Tenderness of meat is determined by the size of fascicles (muscle grain) and by the strength and thickness of collagen sheaths. Coarser grain of more ­powerful muscles covered with stronger collagen results in less tender meat.

The division between light and dark meat reflects the muscle functions: rapidly twitching muscles, reserved for sudden, fast movements and brief exertion at maximum power, are lighter-colored, while the muscles for continuous but relatively low power exertions (breathing, standing, ­masticating) are composed of darker, slow-twitching fibers – they have more myoglobin, another specialized protein that moves oxygen from the blood to muscle cells. But there is no stark color difference in muscle color among those domesticated animals whose ancestors had large home ­territories or migrated over long distances: intermediate fibers of muscles in cattle or aquatic birds are all colored by myoglobin which accounts for 0.5% of muscle mass in cattle but for less than 0.1% in pigs.

Actin, myosin, collagen and myoglobin are all proteins (collagen is the most abundant protein in animal bodies), and hence muscles can be best thought of as intricate assemblies of wet proteins: on the average, living muscles contain about 75% water (extremes range from 65% to 80%), and their protein content is, at nearly 19%, the least variable major component; embedded lipids average about 3%, non-protein nitrogen (including ­nitrogen in adenosine triphosphate) is less than 2% and the small remainder are traces of carbohydrates (mainly glycogen) and inorganic matter (particularly iron and zinc). Because of their higher fat content, there is less water in animal carcasses (about 55% in beef and just over 40% in pork), but the protein content of their separable lean meat varies within a very narrow range, from 19% to 23%.

But most muscles also contain fat that is embedded in the sheathing collagen in order to supply long-acting aerobic fibers with a readily ­available and highly dense source of energy. This embedded fat also plays an essential role in meat’s gustatory quality as it weakens collagen structures and makes meat more succulent, particularly once it degrades to gelatin during moist heat cooking once meat reaches 65°C. In ­contrast, no external application of fat can make a very lean meat as ­succulent as a more fatty cut, a reality that engendered a partial help through an ancient practice of larding lean cuts of meat. In some mammalian and avian species (particularly in such highly mobile wild animals as hares, deer or pheasants), there is only a small quantity of fat beyond the limited amount that is present in embedded stores, while in others there are substantial subcutaneous fat deposits as well as rich deposits surrounding internal organs.

Shares of separable lean and separable fat range widely among both beef and pork cuts. The extreme for beef are top round steak with almost 90% separable lean, just 8% of separable fat and about 2% of refuse when all fat is trimmed away, and short ribs with only about 40% of separable lean, 32% of separable fat and 27% of refuse (USDA 1992). Depending on taste preferences and health concerns, separable fat may be almost completely removed during butchering, preparation of retail cuts or final trimming before cooking, or it may be left in copious amounts on retail meat cuts and eaten as part of stews, roasts, barbecues or processed meats.

The heart is, of course, the only constantly working muscle in the human body, but among all other organ meats only tongue and gizzard are peculiar muscles (in the first instance, a complex network of muscles of great agility and omnidirectional mobility, in the second case an ­involuntary smooth muscle), while liver and sweetbreads (thymus) are enzyme-rich glands, tripe is a lining of ruminant stomach, and brain and kidneys are each sui generis organs. The composition of raw mammalian livers is very similar to that of skeletal muscles (about 70% moisture and 20–21% of protein), and tripe has about 19% of protein, but other innards are slightly to substantially less proteinaceous: kidneys and tongues have about 16% protein, hearts between 15% and 17%, sweetbreads 15% and brains only about 10% (and 80% moisture). Skin, contrary to common perception, has very high moisture content, and in some species (including pigs, chicken, ducks and geese), it is eaten as a part of broadly defined meat, either as crisply cooked part of meat in roasts or as a separate preparation.

Finally, all meat eaters also ingest some blood. Between 40% and 60% of all blood is lost by exsanguination and all but a small share of the rest is retained in viscera; as a result, the residual blood content amounts only to 2–9 mL/kg of muscle, and this minuscule rate does not appear to be affected by different ways of slaughter (Warriss 1984). When assuming mean blood content of 5 mL/kg, an annual consumption of 80 kg of boneless meat (recent US average) would imply annual intake of some 400 mL of residual blood. For comparison, the pastoral Maasai tribe in Kenya, who used to tap regularly the jugular veins of their cattle to drink blood or to collect it for mixing with milk, would draw at a time 4–5 L from a steer or a bull and half that volume from a cow or a heifer and ­consume several liters in a single month (Århem 1989). Maasai blood drinking has been in decline for decades, but in many societies blood is still consumed (albeit irregularly and in small amounts) in traditional dishes ranging from soups and stews to stir-fries and sausages. But a habit from the late 19th century is no longer with us: young Parisian women do not visit slaughterhouses to drink the blood of freshly killed animals in order to redden their cheeks (Gratzer 2005).

Although meat has been an important component of food energy ­supply during the long period of hominin evolution and a major contributor to energy intake in Paleolithic and Neolithic societies, its prime role was qualitative rather than quantitative: foods that are equally, or much more, energy-dense could be secured by gathering, but before animals were domesticated, and in societies that had limited access to aquatic foods, meat was the only source of the highest-quality protein. And while most wild animals have low, or even very low, deposits of fat, high energy ­density made animal lipids much sought-after, and only modern nutritional ­science discovered meat’s value as an outstanding source of a key vitamin and of several essential minerals.

The physical and chemical properties of meat obviously determine its taste, ease of cooking, flexibility of preparation and hence the popularity of individual species or specific meat cuts. Nutritional composition is a ­different matter as the tissues and cuts that may rank low in terms of ­culinary preference may contain virtually identical shares of essential nutrients. Three kinds of preformed organic macromolecules present in plant and animal foodstuffs – carbohydrates, proteins and lipids – must be digested in relatively large quantities to serve as source of food energy, as well as sources of proteins and fatty acids that are indispensable for the growth and maintenance of human bodies. In modern diets, typical consumption rates of these macronutrients range from 10¹ g/day for proteins and lipids to 10² g/day for carbohydrates. In contrast, compounds and elements belonging to two distinct classes of micronutrients – vitamins and minerals – are ingested at low to very low rates, ranging from just a few grams per day for sodium and potassium to just a few micrograms per day for vitamin B11.

Meat contains virtually no carbohydrates, but it is an excellent source of high-quality proteins and fats. In those prehistoric societies that had no milking animals and no, or limited, access to aquatic species, meat was the only source of proteins needed for normal childhood and adolescent growth and adult body maintenance. The importance of meat in diets of hunters and gatherers encountered by the European expansion in the Americas, Africa, Asia and Australia has b...

Table of contents

• Cover
• Table of Contents
• Preface
• 1 Meat in Nutrition
• 2 Meat in Human Evolution
• 3 Meat in Modern Societies
• 4 What It Takes to Produce Meat
• 5 Possible Futures
• References
• Index
• End User License Agreement