The Paleo Diet for Athletes (24 page)

The study of human nutrition has no such guiding template or organizing paradigm. Except for a growing body of scientists and individuals who are privy to a new way of thinking about diet and nutrition, nutrition remains an immature discipline. Most of this field’s leading scientists and major players are mainly unaware of a very powerful idea that could bring order to the fog of disarray and chaos. So, you may ask, what is the larger and all-encompassing question that, when asked and answered correctly, can provide us with the template, the holy grail, the magical looking glass desperately needed to fill this void in nutritional theory?

The question is a very simple question—a child’s question: “Why?” That’s right; the “why” question. Why do we have nutritional requirements in the first place? Humans, most other primates, the guinea pig, and a few species of bats must obtain vitamin C from their diet, whereas all other mammals can synthesize vitamin C from glucose, a simple sugar found in the bloodstream of all mammals. Why in the world do humans have a dietary requirement for vitamin C when most other mammals do not?

For that matter, why do we have dietary requirements for any nutrient? What we are looking for here is not the proximate (nearby) answer but, rather, the ultimate answer. Every registered dietitian worth his or her degree knows that without vitamin C, we get scurvy. A dietitian who can remember the metabolic pathways well enough may even be able to tell you why scurvy causes all of its symptoms. But that is merely the proximate answer to “Why?” Do you know the ultimate answer to why we have a dietary vitamin C requirement? By answering correctly, you will be staring directly at the holy grail of nutritional science. The correct answer to this question represents the guiding template and the organizational paradigm that nutrition is so dearly missing.

THE GIFT FROM THE PAST

The selection of appropriate food for wild animals in zoos is no hit-or-miss business. Zookeepers at state-of-the-art facilities like the San Diego Zoo’s Wild Animal Park realized long ago that if they wanted animals to stay healthy and happy and even breed in captivity, they needed to replicate each animal’s natural environment as closely as possible. That meant duplicating diet as well. When lions or any other purely carnivorous cats were fed only raw muscle meat, their health rapidly deteriorated, and they developed vitamin A deficiency and bone loss (osteoporosis) and eventually died. Careful observations of wild lions in their natural habitat revealed that they ate their prey’s entire carcass, including the organs, liver (an excellent source of vitamin A), and calcium-rich ribs. Accordingly, both vitamin A deficiency and osteoporosis were averted when these wild animals ate the diet that they were genetically adapted to eat. Lions are not only endowed with sharp fangs and claws to take down their prey, but their digestive tracts are also much shorter than those of herbivores (plant eaters), which accommodates their calorically dense food. Additionally, lions’ livers and other metabolic machinery have become specifically modified to cope with an all-flesh diet. Pure carnivores like cats are literally genetically programmed to eat the flesh of other animals—it would make about as much sense to feed these animals cereal grains and berries as it would to feed them antelope meat.

All species of animals—whether cats, antelope, or tropical fish—occupy and exploit specific ecological niches and are well suited to their place in the environment. Their genetic makeup reflects their adaptation to their ecological niche, including not only their outward appearance but also the foods they are genetically programmed to eat. When new and different foods are fed to these animals, it almost invariably results in ill health or disease. Zookeepers know that exotic species of South American monkeys can be kept alive on cereal-based chow, but these animals don’t do well, are prone to disease, and will not reproduce under these conditions. Only when they are fed their normal diet of insects, leaves, and tropical fruit do they thrive and produce offspring
in captivity. Similarly, successful tropical fish hobbyists understand the superiority of live food over dry flaked fish food for getting certain exotic fish to breed in their aquariums.

Human nutritional requirements were determined in the exact same manner as those for lions, exotic monkeys, and tropical fish. As a species, we are genetically well adapted to the foods and food types that we typically encountered in our original and natural ecological niche. What, then, is the native human niche, and what foods and food types are typically encountered?

HOW WE KNOW WHAT PALEOLITHIC PEOPLE ATE

You likely realize by now that the original and natural human ecological niche was that of a hunter-gatherer, and you probably deduce that hunter-gatherers ate wild plant and animal foods. Well, right you are! However, the essence of the question—what did hunter-gatherers eat?—lies in the precise details. The Introduction discussed the foods and food types that couldn’t have been eaten by our Stone Age ancestors, but now let’s talk about what they ate—and how we know this.

Except for certain rare bits and pieces of tangible evidence, such as fossilized human feces (coprolites) and a few isolated cases of mummified bodies found with stomach contents intact, almost all estimates of Stone Age diets must be inferred from circumstantial evidence. The four main sources of circumstantial evidence are (1) studies of other primate diets; (2) studies of fossils and their isotopic element signatures; (3) anthropological accounts of modern-day hunter-gatherers, called ethnographic studies; and (4) examination of our own, present-day biochemical and metabolic pathways.

Before we look at these four lines of circumstantial evidence, it is important to make it clear from the outset that there was no single, standardized Stone Age diet. The Paleolithic Age (Old Stone Age) began with
the manufacture of the first crude stone tools, some 2.6 million years ago in Africa, and ended 10,000 years ago with the development of agriculture in the Middle East. The Stone Age ended a little later (5,000 to 8,000 years ago) for most Europeans and Asians, as agriculture spread from its origins in the Middle East. For some isolated hunter-gatherers, the Stone Age ended only within the last century. During the Paleolithic Age, perhaps as many as 20 distinctive species of the human tribe existed (see
Figure 8.1
). The best available information tells us that their diets were as varied as the environments they inhabited. However, of utmost importance to us are the universal dietary characteristics that transcend time, geographic locale, and even species. These worldwide dietary similarities established the range and limits of foods that shaped our modern genome and represent the range and limits of foods to which we are now genetically adapted.

FIGURE 8.1

1. Other Primate Diets

By analyzing a special kind of DNA called mitochondrial DNA, found in all living primates, scientists have determined that our closest living relative is the chimpanzee. Even though our outward appearance is quite different from that of chimps, there actually is only about a 1.6 percent difference between our genome and theirs. A careful look at
Figure 8.1
reveals that the earliest member of our tribe (
Sahelanthropus tchadensis
) lived between 6 million and 7 million years ago in Africa. Scientists aren’t completely sure if this primate was an ape or a hominin (a primate that walks upright on two legs). Nevertheless, it was during this time or slightly later that the “last common ancestor” existed before the evolutionary split between chimps and hominins.

From field observations of chimpanzee eating habits and analysis of their feces, anthropologists have a pretty good handle on what they eat. In the wild, a chimp’s diet contains about 93 percent plant food, primarily ripe fruit. However, the wild fruit they eat would gag us. These fruits are tough, fibrous, and, by modern standards, definitely not sweet. Many contain substances that taste like turpentine. For wild chimps, a succulent apple or orange would be a candylike treat and voraciously gobbled up. You may be surprised to learn that wild chimps hunt, kill, and eat small monkeys and antelope. During the dry season in Africa, meat can account for almost 25 percent of a male chimp’s diet.

If you have seen pictures of wild chimps, you may have noticed their large, protruding guts. A chimp has a big gut not because it is fat (like the average American couch potato) but because it needs a large, metabolically active gut to handle all of that tough, fibrous fruit. Chimps are relative geniuses in the animal world; however, their average brain size (400 cubic centimeters) is about a third the size of ours.
The difference between their brains and guts and ours—and the reason for it—forms one of the most eloquent ideas in all of evolutionary anthropology. It also gives us a good clue to the kind of diets we modern humans are genetically programmed to eat. Let’s see how this works.

The brain is the most metabolically active organ in our bodies. In fact, at rest it uses nine times more energy than any other organ does. So, in order for us to have evolved a large brain, two possibilities exist: Either our overall metabolism increased, or the metabolism and size of another organ decreased. Think about it this way: If your entire body were made up of brains, it would have an overall metabolic rate nine times higher than it actually has. Of course, that’s not the case, but we do have a body that contains three times more brain relative to our body size than a chimp does. It seems reasonable to conclude that the evolution of our large brains caused our overall metabolic rate to increase. Right? Wrong! Our net metabolic rate at rest is exactly as predicted for our body size. So the first possibility is out, leaving the second—that another organ got smaller. And, indeed, a human’s gut is about half the size it should be, compared with a chimp’s.

Anthropologists call this concept the expensive tissue hypothesis. This evolutionary brain/gut energy trade-off could have occurred only when the demands placed upon the gut to digest a bulky, fibrous, plant-based diet were reduced by the consumption of more energetically dense foods. Slightly before the fossil record shows brain size increasing, hominins began to manufacture the first stone tools that were used to butcher and dismember animal carcasses. Taken together, these facts verify that starting about 2.6 million years ago, hominins began to eat more and more animal food. It was this energetically dense food (meat, marrow, and organs) that allowed natural selection to relax the former selective pressure that had required a large, metabolically active gut. Literally, without meat, marrow, and organs in the diets of our ancient ancestors, we would not be here now. And the take-home message for you, the athlete, is that animal food (meat and organs) has been part of our ancestral diet from the get-go.

2. The Fossil Record

One of the most important clues we have in trying to piece together what our Stone Age ancestors ate is the fossil record. These are the items our prehistoric relatives left behind: their garbage, possessions, tools, weapons, and, less frequently, bones and teeth. Unfortunately, the fossil record is biased and will never allow us to peer into archaic diets with exacting precision. You don’t have to be an archaeologist to figure this out. Animal remains such as hard teeth and bones resist decomposition in the soil and, thus, have a much greater chance of becoming fossilized than do soft plant remains. So when archaeologists dig up the remains of an ancient campsite, they rarely, if ever, find any evidence that plant foods were consumed. What they do find, typically, are bones of prey animals embellished with stone cut marks and sometimes the stone tools themselves. Does this mean that our Paleolithic relatives were total carnivores? Hardly. Our hunter-gatherer ancestors were opportunists: If it could be eaten, it probably was. But a few emerging themes play out in the fossil record, even with this preservation bias favoring animal remains.

The very earliest hominins who made stone tools were small (full-grown adults weighed 60 to 80 pounds and stood about 4½ feet tall) and probably not much more intelligent than chimps. Consequently, they probably weren’t very good hunters of large animals. Many anthropologists believe that stone tool marks found on bones of large animals such as the zebra, wildebeest, and hippo came about from scavenging rather than hunting.

By about 1.7 million to 2 million years ago, hominins had achieved modern-day body proportions from the neck down. A remarkable, nearly complete male skeleton found in Kenya and dated to 1.6 million years ago would have stood 6 feet tall as an adult, with a slender body and narrow hips similar to the bodies of modern-day champion runners from Kenya. Slightly later, toolmaking became a bit more sophisticated, and medium to large prey animals became the preferred target. At one particularly amazing archaeological site in Kenya, called Olorgesailie,
400 stone hand axes were found along with the butchered remains of 65 extinct gorilla-size baboons. At another site in Germany, dated to 400,000 years ago, seven wooden spears were discovered with the butchered bones of more than 10 horses.