100 Million Years of Food (24 page)

Nevertheless, since coal and natural gas deposits have been relatively plentiful, the process of fixing nitrogen using the Haber-Bosch method is feasible, for rich nations at any rate. Before 1840, no inorganic nitrogen had ever been applied to crops. A hundred years later, more than 3 million tons of nitrogen were being applied to farmlands every year, with more than three-quarters of this amount coming from industrial production. By 1988, production of nitrogen had increased nearly thirty-fold. This massive increase in synthetic nitrogen and the food it yielded meant more people coming into this world, surviving to older ages, and getting bigger in size. The use of nitrogen fertilizer around the world is greatly skewed, however; very little fertilizer, for example, is applied in Africa, while huge amounts are used in the developed countries to support the raising of livestock, which are notoriously inefficient at converting nitrogen into human food. This is one reason why daily calorie intake varies so widely around the world.

If the Europeans take credit for the discovery of nitrogen and the subsequent explosion in food availability, they also deserve credit (or blame) for another technological innovation that had a profound impact on calorie consumption. For millennia, humans had been trying to solve the inconvenience of walking. Wheeled sleds were employed in Sumeria in 3500 BC. The Egyptians had horse-drawn chariots by 1600 BC.
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The ancient Romans constructed an extensive network of roads for their chariots. By AD 1650, London suffered from traffic jams caused by horse carriages, despite the considerable discomfort of riding in these contraptions. Passengers paid by the mile; inside seats cost twice as much as outside seats. Horses were changed frequently on long trips.

The first self-propelled automobile was invented in the eighteenth century, and ever since people have been obsessed with cars. In the twentieth century the United States became a global leader in churning out cheap cars for the masses. City planners all over America adjusted for the influx of cars by building sprawling suburbs that catered to, and required, a car. Not only in the United States but all across the world, people were changing their habits to accommodate the vehicle that everyone wanted to own.

At this point, a reader might conclude that the root of modern food-related ailments like obesity and diabetes lies in people eating a lot more food, due to the miracle of nitrogen fixation, and doing a lot less physical activity, due to the miracle of combustion engines and private vehicles. However, it turns out that neither of these common beliefs is supported by the evidence.

First, the food intake myth. The daily energy consumed through food in contemporary industrialized nations runs from about 2,300 kcal (kilocalories) among Japanese men and 1,800 kcal among Japanese women to 2,600 kcal among American men and 1,900 kcal among American women.
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What is surprising is that the average daily caloric intake of these overweight industrialized societies is about the same as among hunter-gatherer groups, with some hunter-gatherer groups below and others above the calories consumed of industrialized nations.
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Although hunter-gatherers ate about as much as we do today, they faced much greater variability in their food supply. In northern Australia, among the Anbarra, the daily energy intake dropped to 1,600 kcal during the rainy season and peaked at 2,500 kcal during the dry season. The calorie consumption of the Hiwi in the rainforests of Venezuela bounced between 1,400 and 2,800 kilocalories, depending on the season (plant foods were most plentiful at the end of the wet season). Thus, if any major pattern emerges in terms of caloric intake, it is that our hunter-gatherer ancestors lived on a dramatically varying diet, which swung between feast and famine according to the season and other hazards of fortune.

Another surprising finding concerns physical activity. Although it is commonly believed that people in hunter-gatherer societies expended much more energy than people in industrialized societies today, the evidence so far does not support this assumption. One common measure of physical activity level (PAL) expresses the total energy used in one day as a multiple of a person's metabolic rate. For example, a PAL of 1 means that a person uses only his/her metabolic energy, i.e., the energy expended by breathing, thinking, digesting, etc. A PAL of 2 means that a person uses twice as much energy as his or her base metabolic rate. PAL allows us to adjust for the fact that people have varying levels of metabolism; a person who has a high metabolic rate can burn up a lot of energy by just sitting in one place compared to a person with low metabolism, so a good measure of physical activity needs to compensate for differences in metabolism. To determine the amount of energy used in a day, the best measure involves giving a person a drink of water that has been “tagged” with isotopes of hydrogen and oxygen. Measurement of these two tags in samples of saliva, urine, or blood allows measurement of exhaled carbon dioxide and hence the degree of respiration from metabolic processes.

Using tagged water, the average PAL among foragers was found to be 1.78 for men and 1.72 for women. Among industrialized contemporary societies with a high human development index (which measures income, literacy, and so on), the PAL of men was 1.79 for men and 1.71 for women.
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In other words, the energy expenditure of overweight contemporary industrialized societies is roughly the same as that of lean hunter-gatherer societies once metabolism is taken into account; or to put it another way, the cause of obesity is unlikely to be lack of exercise, because people in industrialized societies today use about the same amount of energy as people in hunter-gatherer societies.
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This finding has important implications for understanding obesity. All of us living in industrialized societies are aware of the stigma associated with obesity, and perhaps the longer-term health consequences of diabetes, high blood pressure, gout, and cancers associated with being overweight. Since food intake and energy expenditure levels today are roughly the same as during ancestral times (using the lifestyles of modern hunter-gatherers as a reasonable model for our ancestors' lifestyles), why are obesity and diabetes so prevalent among industrialized societies and virtually nonexistent among our ancestors?

The first argument might be an objection that obesity has in fact been with us since the days of our earliest ancestors, so nothing has changed. It has been suggested that figurines of markedly obese women, found in Europe and dating to thirty thousand years ago, are proof that obesity existed at that time. However, no hunter-gatherer or small-scale horticultural group has ever manifested signs of obesity, despite having caloric intake and energy expenditure (adjusted for metabolism) within the range of contemporary industrialized populations. Thus the prehistoric statuettes may be representative of idealized feminine beauty, just as Barbie dolls and Japanese anime characters with huge eyes and exaggerated busts are fantasies more revealing of their creators than of real women.

Among the plumpest nonindustrial populations were the Inuit (the past tense is used in this paragraph because weight is changing dramatically among virtually all populations around the world). A male Inuit of Foxe Basin in eastern Canada measured on average 5'5" and 146 pounds, for a body mass index (BMI) of 25; women in the same group averaged 5' and 123 pounds, for a BMI of 24.
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By comparison, the average BMI in the United States is around 29 for both men and women; obese is defined as a BMI 30 or over.
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At the other end of the scale, Dobe!Kung males in Western Africa were a bit shorter (5'3") and a lot leaner (108 pounds), for a BMI of 19, while women were on average 4'11" and 90 pounds, for a BMI of 18. Since heat loss is reduced in bigger animals—bigger animals have more surface area to radiate heat, but their greater mass more than compensates for this loss—it makes sense that the Inuit and the!Kung, dwelling in the Arctic and sub-Saharan Africa, respectively, are at opposite ends of the BMI spectrum.

On the other hand, fat was likely considered desirable and sexually attractive in ancestral populations. In recent times, some groups in Africa and Oceania went to great lengths to fatten young people through force-feeding in preparation for marriage. However, the process was difficult, uncomfortable, and reserved for children of rich families who could afford fattening food and could do without the labor services of the participants. In societies where food was typically scarce, obesity was a sign of wealth, privilege, strength, and fertility rather than shame. To take one example, among the Massa of northern Cameroon and Chad, the lucky lad who was chosen for fattening went through a two-week gorging ritual. To make room in his stomach for the onslaught of food (twenty-nine pounds, in one observed case), he ate bitter roots that caused him to vomit and drank sour milk or other liquids that triggered diarrhea. He was then fed eleven meals a day of sorghum, milk, meat, and fat from six in the morning to four the next morning. The ordeal, marked by frequent vomiting, farting, pooping, and peeing, was considered painful and potentially hazardous. On the other hand, the fattened few were safe during the periods when most Massa suffered from greatly decreased food intake; the chosen were also considered the most sexually attractive.
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Despite this grueling ritual, the young men typically lost their weight once the force-feeding ended. (However, they were believed to gain weight thereafter more readily than others.)

Though fattening among the Massa was reserved for privileged boys, the typical rule across most societies was that fattening for marriage was for daughters—and what glories their corpulence commanded! In recent decades, among the Annang of Nigeria, privileged adolescent girls entered a fattening room and were fed copious quantities of food while refraining from any work. They slept on beds that were deliberately uncomfortable, to keep the girls rolling about and thereby softening their muscles, according to the belief. When the seclusion period concluded sometime between June and August, the girls emerged to dance in front of the villagers on two occasions, once in the village square and once in the market, naked save for bells about the waist, blue beads in the hair, and heavy brass bracelets around the legs, to show off their privileged rolls of fat. Among the neighboring Efik in Old Calabar Province, the daughters of rich families were fattened on a deluge of food and freed from physical labor, after which they were adorned with beads and bracelets and danced naked before family and townspeople “with an air at once arrogant and querulous.”
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As with the privileged young Massa men, gaining weight was not easy; despite all the force-feeding, some young Annang women were unable to gain much weight and remained moderately proportioned.

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In view of the difficulty in traditional societies of attaining substantial weight, and the apparent similarities in terms of caloric intake and physical activity levels between nonindustrial and industrialized populations, why has obesity risen so dramatically in industrialized populations? One possibility is that the pattern of eating has changed drastically, with adverse consequences for health. In nonindustrial societies, as we discussed earlier, the number of calories people consumed varied over the seasons from feast to famine, while in industrialized societies, people's caloric intakes are close to constant. There has been an explosion of interest in intermittent fasting diets, like the 5:2 diet (five days of regular eating and two days of fasting), because they seem easier to comply with than regular diets, but scientific studies on the effects of such diets are just starting to be undertaken. Small-scale studies following rats and humans for weeks or months of alternate-day fasting or intermittent fasting a few times per week seem mostly promising so far, with modest improvements in weight, body fat, and heart and brain functioning, as well as improved risk factors for diabetes and heart and brain diseases.
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(However, one study on rats found that the diabetes risk factors of abdominal fat and glucose intolerance worsened on an intermittent fasting diet compared to rats that ate freely or that were on a calorie-restricted diet.
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Religious fasts provide an opportunity to assess the health consequences of seasonal fasting. Greek Orthodox observe three major fasting periods, during the Nativity, Lent, and Assumption. Fasters avoid eating dairy products, eggs, and meat, as well as fish and olive oil. Outside of the three major fasting periods, followers abstain on every Wednesday and Friday, except during the weeks of Christmas, Easter, and Pentecost. All told, 180 to 200 days have dietary restrictions. (Nowadays, apps on iTunes are available to help Greek Orthodox followers remember the injunctions.) Studies on the effects of these fasts show modest health benefits, including lowered levels of LDL cholesterol.
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During Ramadan, the ninth lunar month of the Islamic Hijri calendar, healthy males are expected to abstain from food and drink from dawn to dusk.
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Typically, one large meal is consumed after sunset, and a smaller meal is taken before sunrise, though some Muslims also eat again before sleeping. Studies of the health effects of the Ramadan fast show mixed results, which is not surprising considering the extensive geographical and cultural range of the more than one billion Ramadan followers.

Obesity, then, can be linked to changes in eating patterns, but the evidence for this is not very strong, so far. What about physical activity? As we noted previously, energy expenditure levels in industrialized societies are not that different from those in hunter-gatherer societies; moreover, since the 1980s, energy expenditure increased in the United States and Europe, just as obesity surged.
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Critics of the link between physical activity and obesity have pointed out that exercise just makes people feel hungrier and eat more, and the body compensates by lowering metabolism, obliterating any gains from working out.
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