The Paleo Diet
By Loren Cordain, Ph.D.
The government's position on healthy eating is exemplified by the Department of Agriculture's food pyramid, which exhorts us to eat between 6 and 11 servings of cereal grains daily and 2 to 3 servings of dairy foods, and to limit fats and sweets. Nutritional authorities such as Dr. Dean Ornish encourage us to lower dietary fat to less than 10% of calories and to eat plenty of whole grains and legumes. Noted alternative health physician Dr. Andrew Weil agrees with Ornish's advice on whole grains and legumes but takes issue with his fat recommendation, saying it is too low and deficient in omega-3 fatty acids. Still other nutritionists, such as Dr. Neal Barnard, president of the private nonprofit Physicians Committee for Responsible Medicine, caution us to eliminate from our diets all animal products, including meat, eggs, dairy and fish. In stark contrast, the Atkins Diet instructs us to reduce our carbohydrate content to less than 100 grams a day; and to eat all of the fatty, salty cheeses and meats we desire. Is there any way to make sense of this?
I'm sure you've struggled with the question I asked myself years ago: What is the best diet for improving health, losing weight and reducing the risk of chronic illness?
Horse sense for lions
Zookeepers learned long ago that in order for an animal not just to exist but to thrive, be healthy and reproduce in captivity, it was necessary to replicate as closely as possible in the zoo the animal's natural habitat. Part of that requirement was diet. Exotic lemurs from Madagascar or rare monkeys from the Brazilian rain forest could be kept alive in captivity when fed standard monkey chow, but they did not do well. They were prone to infections, developed chronic diseases and rarely, if ever, reproduced. However, when these animals were given a diet of insects, grabs, worms and fresh plants — foods they ate in their natural habitats — they became more active and healthy and began to produce offspring. Why?
Feeding a beefsteak to a horse makes about as much sense as feeding hay to a lion. Horses, like the big cats, are evolutionary specialists. In response to their particular ecological niche, horses have evolved with the physiology (such as grinding teeth) to prefer a vegetarian diet of grasses and shrubs. By contrast, lions are carnivores, and evolution has equipped these hunters with the tools (like fangs and claws) to handle a diet of meat, marrow, bones and organs. The genetic makeup of each of these animals has been shaped by the particular foods found in their environments. When an animal is fed foods with which it has little evolutionary experience (steak for a horse; hay for a lion), discordance occurs between the newly introduced foods and the animal's genetic profile. If the animal continues to eat unfamiliar foods, this discordance will ultimately result in disease and dysfunction.
Stone Agers living in the Space Age
Humans are no different from horses or lions in terms of occupying a specific ecological niche. The foods found in the diets of our hunter-gatherer ancestors are the foods to which we've genetically adapted during the past 100,000 years. And they are the foods that should serve as a starting point for optimal nutrition.
Although we live in a world of vast cities and complex technologies, each of us has a Stone Age genetic makeup. DNA studies from ethnic groups around the world confirm that the present-day human genome is virtually identical to that of humans living 40,000 years ago, a period well before the so-called Agricultural Revolution, which happened only about 10,000 years ago.
Farming began when people left behind the hunting and gathering way of life and began to sow the genetic forerunners of today's wheat and barley. Shortly thereafter, these early farmers domesticated farm animals (goats and sheep first, cows and pigs later). It took about 5,000 years for these practices to spread from their origins in the Middle East to the farthest reaches of Northern Europe and beyond.
The adoption of agriculture was necessitated by three factors: a rising human population, the extinction of large animals and the human physiologic protein ceiling.
The human physiologic protein ceiling is, in short, the upper limit of dietary protein that humans can digest. Small animals have less fat and more protein for their size than large animals do. The total protein content of a rabbit may be as high as 75%, with 25% fat, while a large animal may be only 35% protein and 65% fat. The maximum amount of protein humans can process at one time is about 35% to 40%. Therefore, using rabbits as a food source will rapidly exceed our protein ceiling, causing a syndrome referred to by early arctic explorers and frontiersmen as "rabbit starvation." Despite eating huge amounts of lean meat, men afflicted with rabbit starvation quickly became lethargic and developed diarrhea; death eventually followed.
When most of the large Pleistocene animals — bison, mammoth, large deer — became depleted or extinct, the fatter animals became scarcer, leaving primarily the leaner, smaller animals. Once this happened, human populations were threatened with decline. To survive, they needed a dietary source of carbohydrates or fats to dilute the excessive protein, particularly during winter months, when animals were at their leanest.
Cereals were the perfect answer. They could be stored during winter without spoiling and allowed early farmers to eat blackbirds, rabbits, small fish, lizards — anything, as long as the cereal calories could dilute the excessive protein. Additionally, because cereals increased total edible yields per acre, human numbers could swell.
And that's just what happened. But there has been very little time, evolutionarily speaking, for our bodies to adapt to this new way of eating. Although 10,000 years sounds historically remote, it is evolutionarily quite recent — only 500 human generations have come and gone since agriculture began. And those of European descent have had even less evolutionary experience — about 250 human generations — with agriculture's "new" foods.
Cheeseburgers vs. barbecued buffalo
Cereal grains currently provide 50% of the protein consumed on the planet. Yet my research team has demonstrated that wild versions of this modern-day staple were rarely, if ever, consumed by hunter-gatherers and at best were considered starvation foods. Dairy products weren't part of humankind's original fare, either. (It's pretty difficult to catch a wild mammal, let alone milk one.) And except for rare treats of honey, excessive amounts of sugar were not on the Stone Age menu. (The typical American now consumes 149 pounds of refined sugar per year.) Other foods that were not regular components of the hunter-gatherer diet include fatty meats, salt, yeast-containing foods and legumes.
Of course, the highly processed foods that now dominate the American diet were not part of the Paleolithic meal plan, either. In fact, it's doubtful that hunter-gatherers would have recognized pizza, chips, ice cream, soda and the like as food at all.
In the United States, cereal foods supply 31% of daily calories, dairy products 14%, beverages 8%, oils and dressings 4%, and sugar and candy another 4%. Virtually none of these foods — which make up a grand total of 61% of our diet — would have been available to hunter-gatherers.
My research team recently analyzed the diets of 229 of the world's hunter-gatherer so-defies and published the results in the American Journal of Clinical Nutrition. Although there was no single typical "hunter-gatherer diet" — diets varied by locale, season and available resources — there were certain nutritional elements that characterized almost every one. Most of the 229 societies (73%) got at least 56% to 65% of their total daily calories from wild meat, whereas only 14% of these societies obtained more than 50% of their food from wild plants. Notably, not a single hunter-gatherer society survived solely on plant foods.
We analyzed the fat, carbohydrate and protein percentages of more than 800 wild plants known to be consumed by hunter-gatherers, as well as the content of wild game. We then determined the nutritional content for the average diet.
Lean game and fish were the staple foods in hunter-gatherer diets; consequently, the Paleolithic diet was much higher in protein than the typical U.S. diet. Because game is so lean on a calorie-by-calorie basis, it contains about two and a half times as much protein per serving as domestic meats. For instance, a 100-calorie serving of America's favorite meat — hamburger — contains a paltry 7.8 grams of protein. Compare that with 19.9 grams in an identical 100-calorie serving of roasted buffalo.
Game is also healthier. It contains two to three times more cholesterol-lowering polyunsaturated fats and almost five times more omega-3 fatty adds than meat from grain-fed domestic livestock.
The carbohydrate content in the average hunter-gatherer diet was considerably lower than in the typical American diet of today. More important, it was made up almost entirely of wild fruits and vegetables. The total fat content was similar to or slightly higher than in foods we eat today; however, the types of fats were vastly different. The dominant fats in hunter-gatherer diets were healthful forms of cholesterol-lowering monounsaturated fats, which comprised about 50% of total fats consumed. In contrast, the typical U.S. diet has less cholesterol-lowering mono- and polyunsaturated fats, more artery-clogging saturated fats and trans-fatty acids, and 7 to 10 times less heart-healthy omega-3 fatty acids than in hunter-gatherer diets.
The key to the optimal diet for modern humans lies in the evolutionary wisdom of our hunter-gatherer past. The best meat options are now fish (particularly fatty northern fish such as salmon, halibut, mackerel and herring), shellfish, grass-fed beef and pork (trimmed of visible fat), free-range chicken and turkey, and rabbit and any kind of game, either bought or hunted. The gastronomically adventurous can find buffalo, emu, kangaroo, ostrich and venison at many upscale supermarkets and health food stores.
The missing link between diet and disease
Dr. S. Boyd Eaton of Emory University has published numerous scientific papers showing that contemporary hunter-gatherers are almost completely free of the chronic diseases that plague Western civilization. Wild lean meats, organs and fish are the mainstays of hunter-gatherer diets. How can these hunters and foragers be free of heart disease, hypertension and the sorts of cancers associated time and again with meat-eating in epidemiological studies?
In the 1950s, when scientists were first unraveling the link between heart disease and diet, they found that saturated fat raised blood cholesterol levels and increased the risk for coronary heart disease. Dietary sources of saturated fat such as fatty, grain-fed domestic meat were deemed unhealthful, and rightly so. Unfortunately, the message the public and many nutrition professionals got was that meat was unhealthful and promoted heart disease and cancer. This notion was further ingrained by popular books written in the '60s and '70s promoting vegetarian and vegan diets.
But it turns out that high amounts of animal protein, as predicted by evolutionary medicine, are quite healthful for the human species. It's the saturated fat that can accompany that protein that causes the problems. The grams fed to many domesticated animals turn healthful lean protein with a proper balance of fatty acids into a nutritional nightmare that promotes coronary heart disease and various types of cancer.
Andrew Sinclair and Kevin O'Dea at the Royal Melbourne Institute of Technology demonstrated in a 1990 study of 10 subjects that consumption of lean meat trimmed of any fat actually lowers blood cholesterol levels. Dr. Bernard Wolfe from the Department of Medicine at the University of Western Ontario replicated Sinclair and O'Dea's experiments in 1999 and further showed that diets emphasizing lean meat are more effective than low-fat, high-carbohydrate diets in their effects upon blood lipid profiles. Dr. Wolfe's experiments indicated that high levels of lean protein elevate HDL cholesterol (the "good" cholesterol) while reducing triglycerides, LDL cholesterol (the "bad" cholesterol) and total cholesterol. In contrast, low-fat, high-carbohydrate diets tend to elevate triglycerides and lower HDL cholesterol, thereby likely increasing the risk of Coronary heart disease. High-carbohydrate diets also raise small dense LDL cholesterol — one of the most potent predictors for atherosclerosis and heart disease.
Furthermore, in another 1999 study — this one with a group of 50,000 subjects — researchers at the Harvard School of Public Health showed that increased dietary protein reduces the risk for coronary heart disease. Other population studies indicate that elevated protein reduces the risk of stroke and hypertension and helps boost survival time for women with breast cancer. A high-protein diet also improves or normalizes insulin metabolism in Type II diabetics.
In other words, lean animal protein is good for us and an excessive amount of saturated fat is not — exactly as predicated by our evolutionary template.
Despite all the ruckus created by advocates of low-fat, high-carbohydrate, cereal- and legume-based vegetarian diets, there is strong evidence that lean animal protein is effective for weight loss. All foods require a certain amount of the body's own energy for digestion and assimilation. This is called dietary-induced thermogenesis, or DIT. Dietary carbohydrates and fats have about the same DIT rate, whereas the assimilation of dietary protein raises the body's metabolism two to three times more — meaning that protein facilitates weight loss better than either carbohydrates or fats.
Meat makes us feel full, too. In 1997, a study at the University of Milan found high-protein meals to be more effective than high-fat ones in satisfying appetites. High-protein meats also do a much better job of reducing hunger between meals than do high-carbohydrate vegetarian meals.
In one study, researchers at the Karolinska Hospital in Stockholm, Sweden, served 20 healthy women one of two lunches — either a high-protein meat casserole or a high-carbohydrate vegetarian casserole — of identical caloric value. The researchers then measured how much food the women ate at dinner. The women who ate the meat consumed 12% fewer calories during their evening meal than the women who had a vegetarian lunch.
A nutritional research group at the Royal Veterinary and Agricultural University in Copenhagen, Denmark, recently studied weight loss in 65 people placed on either high-protein or high-carbohydrate diets. After six months, those in the high-protein group had lost an average of 19.6 pounds — and 35% of the participants had lost more than 22 pounds. People in the high-carbohydrate group, however, lost an average of 11.2 pounds, and only 9% lost 22 pounds or more.
Putting it all together
Readers of this
magazine might consider it heretical that lean meat is healthful while whole
grains and dairy products are not necessarily so. But the basis for this
conclusion is overwhelming evolutionary evidence, increasingly being
corroborated by epidemiological, tissue, animal and human studies. We all remain
hunter-gatherers, displaced in time, still genetically adapted to a diet
dominated by lean meats and low-sugar fruits and veggies.
Professor Cordain is a faculty member in the Department of Health and Exercise Science at Colorado State University. The author of more than I00 scientific articles and abstracts, he has focused his research for the past 10 years on the new scientific discipline of evolutionary medicine. His book, The Paleo Diet, detailing the health and weight-loss benefits of hunter-gatherer diets, was published by John Wiley & Sons this month.
Copyright Alternative Medicine Magazine, March 2002