Why We Get Fat: And What to Do About It (23 page)

This logic is implicit in virtually all public-health recommendations about chronic-disease prevention. It was set forth explicitly in the 1980s by Geoffrey Rose, a British epidemiologist, in a pair of articles—“Strategy of Prevention” and “Sick Individuals and Sick Populations”—that would take their place among the most influential articles in public health. The only measures that public-health officials can recommend as means of preventing chronic disease, Rose said, are those that remove “unnatural factors” and restore “ ‘biological normality’—that is … the conditions to which presumably we are genetically adapted.… Such normalizing measures may be presumed to be safe, and therefore we should be prepared to advocate them on the basis of a reasonable presumption of benefit.”

The obvious question is, what are the “conditions to which presumably we are genetically adapted”? As it turns out, what Donaldson assumed in 1919 is still the conventional wisdom today: our genes were effectively shaped by the two and a half million years during which our ancestors lived as hunters and gatherers prior to the introduction of agriculture twelve thousand years ago. This is a period of time known as the Paleolithic era or, less technically, as the Stone Age, because it begins with the development of the first stone tools. It constitutes more than 99.5 percent of human history—more than a hundred thousand generations of humanity living as hunter-gatherers, compared with the six hundred succeeding generations of farmers or the ten generations that have lived in the industrial age.

It’s not controversial to say that the agricultural period—the last .5 percent of the history of our species—has had little significant effect on our genetic makeup. What is significant is what we ate during the two and a half million years that preceded agriculture—the Paleolithic era. The question can never be answered
definitively, because this era, after all, preceded human record-keeping. The best we can do is what nutritional anthropologists began doing in the mid-1980s—use modern-day hunter-gatherer societies as surrogates for our Stone Age ancestors.

In 2000, researchers from the United States and Australia published an analysis of the diets of 229 hunter-gatherer populations that survived deep enough into the twentieth century to have their diets assessed by anthropologists.
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This analysis is still considered the most comprehensive ever done on the subject of modern-day hunter-gatherer diets and so, by implication, about the nature of the diets, as Rose would have said, “to which presumably we are genetically adapted.” Four of its conclusions are relevant to our question of whether a diet that makes us lean—one absent fattening carbohydrates—can be a healthy diet.

First, “whenever and wherever it was ecologically possible,” hunter-gatherers consumed “high amounts” of animal food. In fact, one in every five of these 229 populations subsisted almost entirely by hunting or fishing. These populations got more than 85 percent of their calories from meat or fish; some got 100 percent. This alone tells us that it’s possible to survive, if not thrive, on diets completely lacking fruits, vegetables, and grains. Only 14 percent of these hunter-gatherer populations got more than half their calories from plant foods. Not a single one of these populations was exclusively vegetarian. When averaged all together, these hunter-gatherer populations consumed about two-thirds of their total calories from animal foods and one third from plants.

The second lesson is about the fat-and-protein content of these diets. For the past fifty years, we’ve been told to eat low-fat diets—as the USDA Food Guide Pyramid counsels—and we certainly have made an attempt to do so. On average, we get 15 percent of our calories from protein, 33 percent from fat, and the remainder (more than 50 percent) from carbohydrates. But these modern hunter-gatherers ate quite differently, and so in all probability
did our Paleolithic ancestors. Their diets were high to very high in protein compared with today (19 to 35 percent of calories), and high to very high in fat (28 to 58 percent of calories). And some of these populations consumed as much as 80 percent of their calories from fat, as the Inuits did, for instance, before they traded with Europeans and added sugar and flour to their diets.

Hunter-gatherers, as these researchers explained, preferentially ate the fattest animals they could hunt; they preferentially ate the fattest parts of the animal, including organs, tongue, and bone marrow, and they would eat “virtually all” of the fat on the animal. In other words, they preferred fatty meat and organs to the kind of lean muscle meat that we now buy at the supermarket or order in restaurants.
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Third, the diets were low in carbohydrates “by normal Western standards”—
averaging
from 22 to 40 percent of energy. One obvious reason for this is that these hunter-gatherers preferred meat if they could get it. Another is that wild plant foods have “relatively low carbohydrate content” compared with the floury foods and starches we eat today. All of the plant foods that these populations gathered (seeds, nuts, roots, tubers, bulbs, “miscellaneous plant parts,” and fruits) would have what nutritionists today call a low glycemic index: they would be very slow to raise blood sugar, which would dictate an equally slow and measured insulin response. Not only would these hunter-gatherers eat relatively few carbohydrates, but what digestible carbohydrates they did eat would be bound up tightly with indigestible fiber, making the great majority of these plant foods very difficult and slow to digest. (One argument seriously discussed today for the invention of cooking is that it was first used to render tubers and other plant foods edible. Only later was it used to roast meat.) Simply put, they wouldn’t be fattening.

The one thing we can say for sure, as this analysis did, is that
this hunter-gatherer diet is a far cry from the recommended diet today, which includes carbohydrate-rich, easily digestible starches and grains—including corn, potatoes, rice, wheat, and beans. In fact, all the carbohydrate-rich foods that Adiposity 101 (and anecdotal evidence, at least until the 1960s) tells us are fattening are very new additions to human diets. Indeed, many of these foods have been available for only the past few hundred years—the last thousandth of a percent of our two and a half million years on the planet. Corn and potatoes originated as New World vegetables and spread to Europe and then Asia only after Columbus; the machine refining of flour and sugar dates only to the late nineteenth century. Just two hundred years ago, we ate less than a fifth of the sugar we eat today.

Even the fruits we eat today are vastly different from the wild varieties consumed by hunter-gatherers, whether the modern versions or the Paleolithic ones. And they’re now available year-round, rather than for only a few months of the year—late summer and fall in temperate climates. Although nutritionists today consider copious fruit a necessary part of a healthy diet, and it has become popular to suggest that one problem with Western diets is the relative absence of fruit, it’s worth remembering that we’ve been cultivating fruit trees for only the past few thousand years, and that the kinds of fruit we eat today—Fuji apples, Bartlett pears, navel oranges—have been bred to be far juicier and sweeter than the wild varieties and so, in effect, to be far more fattening.

The essential point, as this 2000 analysis noted, is that the modern foods that today constitute more than 60 percent of all calories in the typical Western diet—including cereal grains, dairy products, beverages, vegetable oils and dressings, and sugar and candy—“would have contributed virtually none of the energy in the typical hunter-gatherer diet.” If we believe that our genetic makeup has a say in what constitutes a healthy diet, then the likely reason that easily digestible starches, refined carbohydrates (flour and white rice), and sugars are fattening is that we
didn’t evolve to eat them and certainly not in the quantities in which we eat them today. That a diet would be healthier without them seems manifestly obvious. As for meat, fish, and fowl, for protein and fat, these would be the staples of a healthy diet, as they apparently were for our ancestors for two and a half million years.

If we turn this evolutionary argument on its head, we come to the experience of isolated populations that go from eating their traditional diets to incorporating the kinds of foods that we eat daily in modern Westernized societies. Public-health experts call this a “nutrition transition,” and it’s invariably accompanied by a disease transition as well—the appearance of a collection of chronic diseases that are now known as Western diseases for just this reason. These diseases include obesity, diabetes, heart disease, hypertension and stroke, cancer, Alzheimer’s disease and other dementias, cavities, periodontal disease, appendicitis, ulcers, diverticulitis, gallstones, hemorrhoids, varicose veins, and constipation. These diseases and conditions are common in societies that eat Western diets and live modern lifestyles, and they’re uncommon, if not nonexistent, in societies that don’t. And when those traditional societies take up Western diets and lifestyles—through either trade or emigration (voluntary or forced, as in the slave trade)—these diseases will appear shortly after.

This association of chronic diseases with modern diets and lifestyle was first noted in the mid-nineteenth century, when a French physician named Stanislas Tanchou pointed out that “cancer, like insanity, seems to increase with the progress of civilization.” Now, as Michael Pollan points out, it’s one of the indisputable facts of diet and health. Eat Western diets, get Western diseases—notably obesity, diabetes, heart disease, and cancer.
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This is one of the primary reasons why public-health experts believe that there are dietary and lifestyle causes for all these diseases, even cancer—that they’re not just the result of bad luck or bad genes.

To get a feel for the kind of modern evidence supporting this idea, consider breast cancer. In Japan, this disease is relatively rare, certainly not the scourge it is for American women. But when Japanese women emigrate to the United States, it takes only two generations for their descendants to experience the same breast-cancer rates as any other local ethnic group. This tells us that something about the American lifestyle or diet is causing breast cancer. The question is what. We could say that something about the Japanese diet or lifestyle protects against breast cancer, but similar trends have been seen among the Inuits, in whom breast cancer was virtually nonexistent until the 1960s; the Pima; and a host of other populations as well. In all these populations, the frequency of breast cancer is low to very low on traditional diets, and it goes up significantly, if not dramatically, when they become Westernized.

There’s little controversy about this. It appears again and again in virtually all the studies of Western diseases. Colon cancer is ten times more common in rural Connecticut than in Nigeria. Alzheimer’s disease is far more common among Japanese Americans than among Japanese living in Japan; it’s twice as common among African Americans as among rural Africans. Pick a disease from the list of Western diseases, and a pair of locations—one urban, say, and one rural, or one Westernized and one not—compare people in the same age groups, and the disease will be more
common in the urban and Westernized locations and less common outside them.

Mainstream nutritionists and public-health authorities have responded to these observations by indicting all aspects of what they believe is the prevailing modern Western diet and lifestyle. They define the Western diet as copious meat, processed food, sugar, and total calories, with few vegetables, fruits, or whole grains. They define the Western lifestyle as sedentary. If we stay away from meat, they tell us, avoid processed foods and sugars, eat less or at least not too much, eat mostly plants and more fruit, and exercise, we’ll prevent these diseases and live longer.

The problem with this approach is the basic assumption that everything about the Western diet is bad, and so they can incriminate all of it and feel they’ve done their job. (This approach reminds me of the story of the thirteenth-century Inquisitors who set out to sack a city of heretics—Béziers, in southwestern France—only to realize that they couldn’t tell the heretics from the good Catholics. “Kill them all,” they were instructed, “and let God sort them out,” and so they did.) What if only some aspects of the Western diet are deleterious to our health and the rest are perfectly benign or even beneficial? After all, lung cancer is also a Western disease, but we don’t blame that on the Western diet and sedentary lives, only on cigarettes. And the reason we know cigarettes are responsible is that we know that nonsmokers are relatively free from lung cancer whereas smokers get it frequently.

It’s useful (as it is when any crime is committed) to narrow down the list of suspects. First of all, among the non-Westernized populations that have been well studied, quite a few that were exclusively meat eaters, or meat and fish eaters, and so ate no fruits and vegetables at all—the Inuits, again, are an example, as are the Maasai—suffered little or no cancer (or heart disease, diabetes, or obesity). This suggests that meat eating is not a cause of these diseases, and it suggests that copious fruits and vegetables are not necessary to prevent them. In fact, when the disparity in cancer rates between Western and non-Westernized societies was
first actively studied a century ago, the idea that meat eating caused cancer, and that isolated populations were protected against it by eating mostly plants, was raised. It was dismissed for the same reason it should be dismissed now: it failed to explain why cancer was prevalent among vegetarian societies—the Hindus in India, for instance, “to whom the fleshpot is an abomination,” as one British physician described it in 1899—and rare to absent among the Inuits, Maasai, Native Americans of the Great Plains, and other decidedly carnivorous populations.
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Clearly, as Pollan points out, humans can adapt to a wide range of non-Western diets, from those exclusively animal-based to those mostly, if not exclusively, vegetarian. If all of those populations were relatively free from Western diseases, as they apparently were, the more logical question to ask is what is it that distinguishes Western diets from the diets of
all
these populations, not just some of them (the ones that eat copious vegetables and fruits, for instance, and little meat). The answer, it turns out, is the same foods that were absent entirely among the hunter-gatherer populations (in which Western diseases were also mostly absent): “cereal grains, dairy products, beverages, vegetable oils and dressings, and sugar and candy.”