The Paleo Diet for Athletes (25 page)

Just as in politics, there are smoking guns in the fossil record; these show beyond a shadow of a doubt what was going on. A few examples: In 1950, German anthropologists found an 8-foot thrusting spear, dated to 125,000 years ago, lodged between the ribs of an extinct straight-tusked elephant. How do you think that spear got there? A similar find was made in August 1951, when summer rains brought heavy flooding to the Greenbush Creek a mile northwest of Naco, Arizona. Erosion in the arroyo exposed part of a skull with teeth and the tusk of a large mammoth. Further excavation revealed eight razor-sharp stone spear points embedded between the animal’s ribs. Because there were no stone cut marks on any of the mammoth’s bones, anthropologists deduced that “this one got away.”

How incredible would it be if we could have just a single photograph of our Paleolithic relatives going about their hunting and food collecting activities? We do have the next best thing—a highly detailed drawing, “The Shaft of the Dead Man,” which you can see at the Web site
www.culture.gouv.fr/culture/arcnat/lascaux/en/
. This drawing, made 17,000 years ago in the famous Lascaux Cave in France, depicts a wounded European bison with its entrails spilling out and a spear stuck between its ribs. The enraged animal is in the process of goring a human armed with a spear-throwing device called an atlatl.

Now, why would our ancestors have risked life and limb to kill large, ferocious beasts to get meat? Couldn’t they have gone after much less dangerous small prey like rabbits, partridges, clams, and fish? Why would anyone in their right mind lunge a flimsy wooden spear between the ribs of a 6- to 8-ton elephant? They did it because they had to. At the time, they were aware of no other alternative solution to survive. Why is that?

Believe it or not, you can get too much of a good thing, and protein is good for you only up to a certain point. You can include as much
carbohydrate and fat in your diet as you like with no immediate ill effects, but the same can’t be said for protein. In the typical US diet, protein makes up about 15 percent of our daily calories, whereas in hunter-gatherer diets, it would have been considerably higher, ranging from 25 to 40 percent of the daily energy intake. Laboratory studies in humans show that the maximum amount of protein we can ingest on a regular basis is about 40 percent of our daily calories. Anything above this and we get sick—a lesson our hunter-gatherers knew quite well. Early frontiersmen and explorers also knew exactly what happened when they were forced to eat only the lean meat of fat-depleted animals. They called this sickness “rabbit starvation.” After eating enormous quantities of very lean meat, they would become nauseated and irritable, lose weight, develop diarrhea, and eventually die. They were better off starving than continuing to eat only lean meat. The only way around this situation: Get either fat or carbohydrate into the diet to dilute the protein level to below 40 percent.

In the modern world, it is easy to change the fat content of any food. Lobster is extremely lean (84 percent of its energy is protein) and would quickly cause protein poisoning if that’s all you ate. Most of us prefer to dip our lobster in melted butter, which allows us to eat all we want and never develop symptoms of protein excess. Hunter-gatherers weren’t so lucky. Fat and protein came in a single packet—the animal’s carcass. Either the animal had fat or it didn’t. There was no such thing as adding fat to a food. Similarly, if you were to eat a carbohydrate source such as brown rice or potatoes along with the lobster, you’d dilute the protein below the crucial 40 percent protein ceiling and have no problems whatsoever. However, until the development of agriculture and domestication of cereal grains, hunter-gatherers, particularly those living at higher latitudes, had no reliable year-round source of carbohydrate.

Now let’s answer the question of why Stone Age hunters risked life and limb on a regular basis to kill large, unruly beasts. Large animals are fat animals. The larger a species, the more body fat it has. The average body fat content of a small animal like a squirrel (1 pound) is 5.2 percent by weight, whereas a large animal such as a musk ox (900
pounds) has 20.5 percent body fat by weight. If we look at the squirrel’s body fat by total calories rather than weight, it’s clear why the sole consumption of squirrels would cause protein poisoning. A squirrel’s entire body is 35 percent fat by energy (calories) and 65 percent protein—way over the 40 percent ceiling. In contrast, the musk ox’s body is 73 percent fat and 27 percent protein. A carcass containing only 27 percent protein can easily be consumed in its entirety without even coming close to the protein ceiling.

The fossil record unmistakably tells us that ancestral humans have always included meat and animal foods in their diets, but there is tantalizingly little evidence showing how much meat was eaten. And there is even less evidence to reveal how much plant food was typically consumed. Fortunately, anthropologists have developed a clever procedure that can give us a rough approximation of the dietary ratio of animal to plant by measuring stable isotopes in the fossilized bones and teeth of long-dead hominins. Stable isotopes are elements like carbon 13 and nitrogen 15 that vary slightly from the normal versions. Julia Lee-Thorp, PhD, and her colleagues from the University of Cape Town in South Africa have measured stable isotopes in many of the very first hominins who were living in Africa 1 million to 3 million years ago, and she concluded that all ate significant quantities of both animal and plant foods. Using stable isotopes to examine the diets of Neanderthals living in Europe 30,000 years ago, Mike Richards, PhD, of the University of British Columbia in Canada, concluded, “The isotope evidence overwhelmingly points to the Neanderthals behaving as top-level carnivores.” In a similar study of Stone Age people living in England 12,000 years ago, he summarized, “We were testing the hypothesis that these humans had a mainly hunting economy, and therefore a diet high in animal protein. We found this to be the case.”

Dr. Richards’s isotopic data are interesting but come from very specialized groups of our ancestors, whose diets may have significantly varied from the mainstream. The Neanderthals generally lived in Europe during the Ice Age, when very little plant food would have been available on a year-round basis. Consequently, they may have had no choice but to
eat animal food. Similarly, many anthropologists believe that modern humans living in Europe 12,000 to 40,000 years ago may have developed animal-based diet strategies because of the relative abundance of large game animals. There is another avenue available to us that can help to solve the riddle of how much plant and animal food was typically found in our ancestors’ diets.

3. Ethnographic Studies

Hundreds, if not thousands, of descriptions of hunter-gatherers and what they ate have been written throughout historical times. These accounts were penned by explorers, sailors, trappers, frontiersmen, physicians, anthropologists, and others who encountered native peoples during their travels. Fortunately, an industrious anthropologist, George Murdock, PhD, took it upon himself to compile and organize historical accounts not only of hunter-gatherers but also of all the world’s cultures and how they lived. His enormous database included more than 100 specific data points for each society. In 1967, Dr. Murdock completed his life’s work with the publication of a massive volume called the
Ethnographic Atlas,
a work that allows anybody to easily compare and contrast any society or culture on earth.

One year after the publication of Dr. Murdock’s massive volume, a young anthropologist at Harvard, Richard Lee, PhD, utilized some of the hunter-gatherer data from the
Ethnographic Atlas
to establish the plant-to-animal composition in the average hunter-gatherer diet. Dr. Lee concluded that hunted animal foods composed 35 percent of the energy in the average hunter-gatherer diet and that plant foods made up the balance (65 percent). For the next 3 decades, Dr. Lee’s conclusion became the unquestioned dogma in anthropological circles. Unfortunately, his analysis was flawed, and it wasn’t corrected until 32 years later with our publication of a reanalysis of the
Ethnographic Atlas
’s hunter-gatherer data. Let me show you how I came to this conclusion.

It’s pretty hard to overeat raw carrots and celery—in fact, most of us have had enough after one or two carrots or celery stalks. Can you imagine
eating 65 percent of your daily calories from celery? An active man who takes in 3,000 calories a day would have to eat 27 pounds of celery to obtain 65 percent of his daily calories from this plant food. Okay, perhaps celery is an extreme example. How about tomatoes? Try 20 pounds! Cantaloupe, maybe? Twelve pounds! Perhaps potatoes would work: To get 65 percent of 3,000 calories (1,950 calories), you would have to eat 4 pounds. This is a doable situation. But the problem is that most wild tubers and roots bear little resemblance to today’s thoroughly domesticated potatoes. Compared with their modern counterparts, wild tubers are smaller, usually more fibrous, less starchy, and, therefore, not nearly as calorically dense.

It became increasingly clear to me that only a very few wild plant foods could be consumed at quantities approaching 65 percent of the daily caloric intake. These were oily nuts and seeds, tubers, and cereal grains. Grains were out of the equation because they were rarely, if ever, consumed by hunter-gatherers, as explained in the Introduction. Also, when hunter-gatherers forage for food, they need to make some critical decisions. First, they must get more energy from the food they are hunting or gathering than the energy they expend to obtain it. It would be a losing proposition to run around all day using up 800 calories, only to bring back 500 calories. Second, hunter-gatherers prioritize food choices relative to their energy return rate. These are the foods that give them the most “bang for their foraging buck”—large animals are preferred over small, and animal foods are almost always preferred over plant foods. Anthropologists have dubbed these hunter-gatherer decisions “optimal foraging theory.”

At any rate, all of this information made me suspicious. It seemed unlikely that plant foods could have made up the majority of daily calories in the typical hunter-gatherer diet. So I went back to the original
Ethnographic Atlas,
plugged all the data points for the 229 hunter-gatherer societies into a spreadsheet, and reanalyzed the whole kit and caboodle. I completed my analysis on Christmas Day 1997 and could not believe my eyes. Not only were the results different from Richard Lee’s analysis; they were exactly reversed. Plant foods represented about 35 percent of the total calories, while animal foods stood out at 65
percent! How could this be? I carefully checked all of the more than nearly 23,000 data points—no errors there. Hmm! What was going on?

At last I saw it. Dr. Lee had failed to include fished animal foods along with hunted animal foods in determining the overall animal-to-plant subsistence ratio.

One of the huge problems with ethnographic studies is that they are almost entirely subjective. We went back to some of the original studies that Dr. Murdock had used to estimate the subsistence ratios and were dumbfounded at how he did it. There were absolutely no concrete data in many of these accounts of hunter-gatherers to show how much meat or plant food was consumed. Using some of the accounts as a starting point, my research team and I rooted out each and every quantitative study in which the foods were weighed and the caloric content known. It turned out that 13 reports could be used. Two of them involved Eskimos, who have no choice but to eat animal food, so we were down to 11 reports. These more robust, quantitative studies were in agreement with our earlier analysis and once again demonstrated that animal foods made up two-thirds of the average energy intake in hunter-gatherer diets.

So, three separate lines of evidence (other primate diets, the fossil record, and ethnographic studies) now independently point to the notion that meat, organs, and animal foods have always been a significant part of the diet to which we are genetically adapted. But, as you’ll see in
Chapter 9
, wild animals and domesticated, feedlot-produced animals are worlds apart nutritionally. A modern diet with 65 percent of its energy coming from processed fatty meats (bologna, salami, hot dogs, sausages, bacon, etc.) produced from grain-fed animals bears little resemblance to our ancestral diet.

Let’s take a brief look at another piece of the puzzle that shows the types of foods Mother Nature intended for us.

4. Biochemical and Metabolic Pathways

Within our own body’s biochemical machinery lie clues to the way in which diet has changed in the 5 million to 7 million years since our evolutionary
split from the apes. It may come as a surprise to you, but we humans have evolved a number of biochemical adaptations that are parallel to those found in pure carnivores. Obviously, we are not pure carnivores. We are omnivores who are genetically adapted to eating a mixed diet of both plant and animal foods. However, substantial biochemical evidence suggests that, during the past 2.6 million years, we have made a significant evolutionary shift that has brought us closer to a meat-based diet than to a plant-based diet.

Pure carnivores, such as cats, must obtain all of their nutrients from the flesh of other animals. Because of this requirement they have evolved certain biochemical adaptations that demonstrate their total dietary dependence upon animal-based foods. Most of these adaptations involve either the loss or reduced activity of certain enzymes required to build essential nutrients. These losses occurred because the evolutionary selection pressure to maintain these enzymes and metabolic pathways was no longer needed. Let me give you a few examples and show you how humans have moved down a similar evolutionary pathway.

Taurine is an amino acid that is not found in any plant food and is an essential nutrient in all cells of the body. Herbivores, such as cows, are able to synthesize taurine from precursor amino acids found in plants, whereas cats have completely lost that ability. Since all animal foods (except cow’s milk) are rich sources of taurine, cats have been able to relax the evolutionary selective pressure required for taurine synthesis because they obtain all they need from their exclusive meat-based diet.