As natural is a word with a vast definition, diet is one with almost unlimited scope. Hence, the exploration of a natural diet as the touchstone of optimal health is but a Grail quest.
The omnivorous diet of the San and Hadza interest us because modern hunter-gatherers are largely spared the common degenerative diseases afflicting West and East. They gather wild berries and nuts, hunt insects and small game, not the kind of fare that interests most of us, though nutritious. But do they represent a nutrition that molded our biology and genetics that we ought to imitate today?
Let’s look back in prehistory to when humans were evolving from apes, before they lived in degraded environments. We have lost an immensely rich megafauna that offered humans meaty meals. In a recent review, Tel Aviv researchers conclude that through most of the Stone Age we were apex predators and hypercarnivores (meaning >70% meat).
That we are flesh-eaters by nature (sic) can sound scandalous, implying we are not only responsible for the ongoing Sixth Extinction but a previous one in the Paleolithic era as well. Homo species probably carried as much responsibility for destroying biodiversity as climate change (perhaps more), causing mammoths, aurochs, saber-toothed tigers, cave bears, and other charismatic animals to vanish. I feel even more persuaded after my single experience of practical paleontology cleaning bones of a local Mastodon: our geologist, Jerre Johnson, declared it was killed by hunters.
The first hominids were primary vegetarians, like their ape antecedents. Before we emerged as a distinct species, our lineage was represented for a couple of million years by Homo erectus. By the Upper Paleolithic, a few tens of thousands of years ago, they helped to make large game scarce. We had to switch to a mixed diet of hunting and gathering, fishing and domesticating animals for meat and milk. The hunger for greater food security triggered the first Agricultural Revolution, and crop farming was so successful it created a population boom with social changes we still grapple with.
So, what is the evidence for carnivory? The authors reviewed 25 factors, including genetics and physiology, ecology and paleontology. Here are a few memorable examples, not just from gut and metabolism.
A highly acidic stomach adapted for killing bacteria in stale meat and carrion is absent in obligate plant eaters.
An adaptation for high fat consumption and insulin resistance
Micronutrients from animal sources (vitamin B-12 a top example)
Higher ratio of the length of small intestine to colon
Changes in masticatory apparatus and salivary enzyme genes for starch digestion
Endurance running and excess sweating for catching swift prey
Ability to throw weapons forcefully and accurately (chimps and gorillas can’t throw 100 mph fastballs)
Charles Darwin believed changes in diet shape evolution, famously illustrated by Galapagos finches. Maybe it’s hard for vegetarians and vegans to accept we are still adapted for a low-carb paleo diet, but our evolution creeps slowly because of long generation intervals. Eating mostly plants is no longer just a personal preference or from concern about animal welfare, but a virtue for lowering our impact on the environment. We never worried before about going against the grain by denying our nature of two feet on the ground when we wanted to launch into flight and space. Neither should we now.
Feeling carnivorous or vegetarian, or somewhere in-between?
Is it okay to be carnivorous? Is it natural (whatever that means)?
I asked these questions when I was a teenager, like many other people who love animals. For a while I half-heartedly courted vegetarianism as an ideal, but it would be hard for Mum to prepare separate meals for a lettuce-loafer. Grown-ups never replied to my questions, except with blank looks. I still think they are good questions. Had I asked Aristotle’s pupil, the Father of Botany Theophrastus, he would have declared that eating animals is immoral, but I can’t fully agree. There are health concerns and spiritual reasons for becoming vegetarian, but it is not for everyone.
Rich man, Poor man
Meat used to be a luxury only the rich and powerful could afford. Royalty and noblemen kept hunting preserves and woe betide the peasant who turned poacher to put venison or rabbit on his family table. The greater the amount and variety of meat consumed the higher the status of the eater. On April 4, 1662, the diarist Samuel Pepys proudly recorded: “We had a fricassee of rabbits and chickens, a leg of mutton boiled, three carps in a dish, a great dish of a side of lamb, a dish or roasted pigeons, a dish of four lobsters, three tarts, a lamprey pie (a most rare pie), a dish of anchovies … to my great content.” This was not a banquet but a feast shared with a few friends, and it took a massacre to prepare.
Meat is no longer the privilege of the few, but still a luxury in many places. In the New Guinea Highlands friends subsist on sweet potatoes and other vegetables while pigs, their most valuable possessions, are reserved for eating at weddings and other special occasions. But where animals and birds are now raised for food industrially and the fishing industry can efficiently hoover whole shoals of fish, flesh has become plentiful, cheap, and ordinary. Then it is undervalued.
Carnivores and calories
Average Americans eat a half-pound of meat per day. That represents a larger fraction of protein and calories than eaten by bears, badgers and raccoons, which are all members of the order Carnivora. Animal classification looks wonky when you consider that orders are defined by a trunk, hoof, blow-hole, egg-laying, brain size and opposable thumb. For carnivores, it’s the presence of butcher’s teeth that matters. Dracula apart, our dentition excludes us from the Carnivora, but neither is there an order called Vegetaria nor Omnivora which would fit us better. Taxonomy has no traction with the diet of our species.
Yards of gut
But you can tell if an animal is a true carnivore by looking in its mouth and along its gut. It will have:
long canines for grabbing prey and carnassial teeth for shearing meat
a gaping mouth and large throat for swallowing food unchewed
a large stomach with very acidic gastric juice for sterilizing raw meat
a relatively short small intestine
and a small colon
On the other hand, a strict herbivore will have:
small, stumpy canines and flattened, tightly-packed molars for chewing fiber
sideways movement of the jaws for chewing
an enzyme in saliva for starting to digest starch
a stomach of variable size with up to four chambers
less acidic gastric juice, especially in ungulates for allowing microbial fermentation
a long small intestine
a voluminous and baggy colon and cecum where cellulose is digested
The contrast is most obvious when guts are measured. The small intestine of carnivores is no more than three times as long as the body (head plus trunk), whereas in herbivores it is ten times the length. A short, simple tube is adequate for digesting meat, whereas cellulose takes much longer to break down to sugar available for absorption. Since the rabbit’s gut is not long enough for this process it swallows “soft pellets” as soon as they are evacuated from the rectum for a second pass through the system.
Our anatomy is closer to herbivores, though lacking the specialization in ungulates for a fiber-rich diet. We call ourselves omnivores because of a mixed diet, but frugivore is a more accurate rendering of our origin. Our early ancestors probably subsisted on tropical fruits and berries with some animal protein when available. Our primate cousins still enjoy the same. But when and how did we acquire a large appetite for flesh?
Fred Flintstone was more carnivore than trail-mix muncher, although the opposite may be closer to reality in the deep past. There was more big game in Paleolithic times, some now extinct, but hunting with spears was inefficient and dangerous before bows and arrows were invented (maybe 60k years ago). Our diet was then plant-based. The controlled use of fire goes back further (most authorities estimate since 500k years ago), and cooking followed. Red meat was probably a rare meal before cooking was discovered because we are poorly equipped for eating and digesting it raw.
Early humans were of course locavores. As they fanned across the world, they had to adapt to unfamiliar local foods in different climates and environments. As the plant foods changed so did the animal populations they supported. Animal protein and fat came from fish, shellfish, bird eggs, and insects (yes!), supplying essential fatty acids and vitamin B12 before serious hunting was able to garner more meat and offal. Animal domestication arrived only around 400 generations ago and changed everything.
It is surely one of the mysteries of human evolution how our species was pre-adapted to subsist on a wide variety of diets, for without that flexibility our story would be different.
It should be no surprise that that herbivore can manage a meat meal. Chimpanzees do; after inquiries into the cause of mad cow disease we know that cows can too. But carnivores don’t have the specialized gut needed for tackling plant fiber, except in the world imagined by Isaiah where: “The lion shall eat straw like the ox.”
Our physiology is flexible but urges modest amounts of meat, if any. Being designed for fruits and green leaves, our stomachs are not sufficiently acidic to kill Salmonella and other bugs in raw meat. And when the diet is rich in protein, and particularly purines, our lack of an active uricase gene can lead to painful joints if uric acid crystals accumulate. Carnivorous animals have active copies of the gene, so it is surprisingly that “Sue”, a T. rex from Cheyenne River Indian Reservation, had a touch of gout.
I guess that meat-eating was a necessary adjustment when people migrated to northern lands. Seasonally abundant vegetables disappeared in winter whereas most native wildlife remained, and some were good to eat. Much later, herds of sheep, goats and reindeer provided more food security than by hunting, although further north nomads depended on meat and blubber from marine mammals.
The modern paleo diet claims to bring food choices in line with our genes, which are assumed to have changed little since Paleolithic times. But there was no standard caveman diet across the world, and contemporary hunter-gatherers in Africa and South America eat only what they can catch, according to where they live. Besides, a standard can’t be offered without a matching lifestyle and age span. Early humans have to live strenuously to survive, and few lived to what we now call middle age. Backers of the paleo diet can’t insist on those changes. Some plants eaten in the past have come down to us as crops but they have been genetically altered by selective breeding or even genetic modification, and the microbes in our guts have probably changed too.
It’s a fallacy to believe we can copy the nutrition from bygone eras, but a more cogent reason for rejecting the paleo diet is that it aggravates the environment by reinforcing or even promoting more meat consumption.
The Price of Meat
In a world of soaring population where 30 % of usable land is already devoted either directly or indirectly to raising livestock the meat industry is on an unsustainable trajectory. Our appetite for red meat impacts virgin rainforests which are converted to ranches, production of greenhouse gases, vast subsidized cornfields, water consumption and pollution, and antibiotic abuse for animals confined to feedlots. Cattle are not the only species to beef about, but the growing middle class in Asia has a greater appetite for white meat which is produced more efficiently. Fish farming helps to relieve pressure from ocean harvests, although not without its own problems.
Our ability to produce ever larger quantities of animal protein will finally be capped by the carrying capacity of the environment and the unchallengeable Laws of Thermodynamics. The problem is illustrated by a pyramid representing an ecosystem where energy is transferred from bottom to top by a thermodynamic “hand-shake:”
At the base plants absorb solar energy for growing
Herbivores occupy an intermediate level where they gain energy from plants
Carnivores on top of the pyramid dine on herbivores below
The biomass diminishes sharply higher up because energy is transferred between levels with only 10% efficiency. Sometimes, there is a fourth level of super-carnivores (sharks, tuna, and T. rex) feeding on lower carnivores, but there can be no more because less than 0.01% of the original energy remains.
We don’t eat carnivores because they are relatively rare and considered unpalatable. But herbivores taste good to us, and we eat lots of them. There are perhaps 1.5 billion cattle in the world today, and countless other beasts and birds farmed for meat. But if crops grown to feed animals were switched for direct human consumption much larger numbers of people could receive their daily ration of 2,000 Calories.
For example, the 10% rule-of-thumb predicts that 20,000 Calories of corn has a net yield of only 2,000 Calories of cow because most energy is lost. The same amount of corn could support several people, though perhaps not quite as many as ten. Beef has higher quality protein than in corn, but the example stands an argument for swaying food choices and policy. One government actually took a swipe at national food consumption.
Less is More
In World War Two, German U-boats blockaded shipments of food from North America to British ports triggering a fear of hunger because the country was not self-sufficient in food. The British Government secretly commissioned two Cambridge nutritionists to find out how many home-grown Brussel sprouts and sausages the public needed to keep in good health (no Bratwurst, only patriotic British sausages.)
Elsie Widdowson and Robert McCance fed subjects in their clinical trial 1 lb of meat, 1 egg, and 4 oz of fish per week, plus 5 fluid oz of milk a day, and unlimited amounts of vegetables and wholemeal bread, which together would meet dietary requirements. After the subjects w remained in excellent health months later, the meager rations were rolled out as government policy with only a fraction of the meat consumed in Britain today. Family health was said never to be better; infant mortality fell and life expectancy rose (discounting deaths from hostilities), and the only downside was a “remarkable” increase in flatulence.
Since then, Britons have been eating more and more meat, following the prosperous example of America. There are plenty of sound reasons for cutting back on meat consumption, and some people are, but short of a national catastrophe or an environmental calamity policy-makers won’t go further than offering bland health advisories. The only other potential check on growth is the market, and producers won’t forgo sales while demand exists. So it remains for individuals to make up their own minds and hope to make a difference.
Cutting back may be the first step to cutting out, but often the hardest to make. A trade-off can make a step easier, and there is none better than trading quantity for quality. They generally pull in opposite directions. Forcing the productivity of farm animals, like the breeding of high-yielding fruit and vegetables, pleases shoppers by lowering prices but comes at a cost. The cost is mainly elsewhere and unseen (on land and water), but we notice differences in flavor, and wonder if the host of biochemical differences have consequences for our health.
Away then with factory farming, away with corn feedlots. Bring back more grass-fed beef; bring back pastured chickens and eggs from happier animals; bring back flavors that old-timers still remember.
It would help if instead of casually tossing packs of steak, pork or chicken in our trolley as mundane shopping, we remember that meat is special. It costs the earth more, and it demands the sacrifice of animal lives. Eating less but better seems an excellent exchange for the half-pound steak that never inspired any note in a diary. Samuel Pepys was inspired to celebrate tasty food, but he might have curbed the temptation to eat to excess had he known it contributed to his gout.
But cutting back seems to run counter to the America tradition as a land of plenty where self-denial can appear eccentric. A 16 oz steak, or even a Flintstone-sized 32 oz, is emblematic of that life, but maybe carnivores can be satisfied with less. I dream of a new Marlboro ad on a billboard showing a man standing beside a barbecue grill, beckoning to us, “Come to Where the Flavor Is.” Outsized steaks have been vaped. He turns over with his fork a smoking nugget of grass-fed beef.