100 Million Years of Food (23 page)

Meanwhile, Shinichi Nakagawa and his colleagues at the University of Otago in New Zealand perused the results of more than a hundred calorie restriction experiments and noticed four surprising themes. The first is that the longevity benefit from reducing calorie consumption has been demonstrated mainly in animals that were bred for laboratory conditions: rats, mice, fruit flies, and yeast. Many wild animals have been tested, including fish, grasshoppers, and moths, but these don't show the same dramatic improvement in life span when their food portions are reduced. No one knows why this is the case, but lab animals live in a peculiar world where food is never scarce, and thus some important pathway in their physiology may have been altered or lost through generations of controlled breeding. A lab animal's appetite is uncoupled from the demands of life in a natural setting. By contrast, wild animals may be like Swiss timepieces, exquisitely honed by evolution to eat the right amount of food. It could be argued that humans in industrialized regions have also been exposed for many generations to conditions where food is in abundant supply, and therefore the calorie restriction effect might still apply to us—in other words, our genes may have more parallels to the genes of lab-bred rats and mice than to those of wild animals.
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The second wrinkle of the calorie restriction effect is that the life-lengthening result of calorie restriction is overshadowed by an even stronger impact from protein reduction. In other words, if you're looking to pump more days into your life, cutting back on calories while increasing your protein intake may end up accomplishing nothing, but keeping your calorie intake constant while reducing meat and other protein sources may be the clincher. Reducing protein intake causes a decline in IGF-1 circulating in the human bloodstream, which may turn out to be a good thing, because IGF-1 has been linked to increased risk of prostate and premenopausal breast cancer.
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A third recurrent theme is that a reduction in calories and protein brings benefits only up to a certain point; after that, if calories and protein continue to be eliminated, the organism will begin to suffer adverse health. There exists a sweet spot, an optimal intake level of calories and protein where life span is maximized. In studies, cutting calories to half of the organism's preferred intake and slashing protein by two-thirds yields longest life. Remember, these are estimates carried out across all species, including the laboratory animals that exhibit the strongest results from calorie reduction. For humans, the optimal levels of calories and protein may turn out to be different.
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The fourth issue to consider is that females tend to reap more benefit from calorie restriction than males. This amply documented sex difference has a worrisome implication: Cutting back on calories probably causes sexual desire to evaporate. Proponents of calorie restriction (they seem to be mostly men) are understandably less than eager to draw attention to this effect. The best argument thus far about why calorie restriction increases longevity is that extended hunger causes animals' bodies to switch priority from reproducing to prolonging life. It's analogous to a bear's instinct to hibernate through a long winter rather than waste energy by lumbering around a snowy forest searching for nonexistent food and mates. Many scientists believe that food deprivation similarly triggers a diversion of energy away from hopeless activities such as trying to conceive when a mother has barely enough food reserves to keep herself alive, instead channeling those scarce calories into repairing the body and conserving energy for a better opportunity down the road, when food finally comes hopping down the path or sprouts from a branch.
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For females, holding off on babies yields a jackpot of savings in energy. For males, on the other hand, having sex now or later does not entail a dramatic shift in physiological effort. The bodies of males may therefore be geared to smaller increases in longevity when food intake is reduced.

As you can see, the edifice of this theory is erected, so to speak, on the axiom that calorie restriction shifts priorities from reproducing now to reproducing later. Besides draining sexual urge, half-starving yourself will transform you into an ill-tempered ogre. Not surprisingly, taking food away from animals makes them aggressive. I remember an occasion when my family was tardy in feeding the house cat. When I finally brought out its plate, rather than being grateful, our normally placid cat leapt at me and scratched my leg. If people who are well fed view society on benevolent terms, as they are forced to forgo greater quantities of food, their circle of sympathy will steadily shrink, from society to friends to family to close family, and finally to the self alone.
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To rub barbecue salt into an open wound, the latest round of news for calorie restriction boosters is a tad gloomy. A second set of monkeys is currently being tracked by the National Institute on Aging (NIA) in the United States, and the results so far, released in the fall of 2012, indicate that shaving calories didn't help hungry monkeys gain extra years compared to well-fed monkeys. However, this most recent NIA experiment compared fit versus scrawny monkeys, while the previous Wisconsin study compared overweight versus scrawny monkeys. There may be only a slight difference in longevity between being fit and being scrawny (both are relatively healthy states), but a considerable difference between being fit and being overweight.
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Even if you'd rather eat ice cream while scientists quibble and the members of the Calorie Restriction Society practice dietary austerity, you may want to consider putting your dog on a diet. In a study of Labrador retrievers, half were allowed to eat until they were sufficiently (but not over-) fed, while the other half were allotted three-quarters this amount of food. By the time all the well-fed Labs had passed away (the last one survived to thirteen years, a ripe old age in dog time), nearly 40 percent of the underfed dogs were still alive (and irritably waiting, one presumes, to be fed).
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Although critics argue that the longevity benefits from calorie restriction are underwhelming, almost all scientists agree that the physiological effects are generally positive: These include reduced incidence of the most common human chronic diseases (diabetes, cardiovascular disease, and cancer), slowdown in cognitive decline, and lower levels of cholesterol, triglycerides, glucose, and insulin. The chief drawbacks are that a calorie-restricted animal stops growing, becomes less fertile, and is more vulnerable to cold and some infectious diseases. Taken to an extreme, calorie restriction imposes psychological and physiological side effects that few people would be willing to tolerate, but even a modest 10 percent reduction in calories—from buffet-style consumption to eating just enough to maintain constant body weight—is a supremely cost-effective ticket to a bonanza of health benefits.
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Although today the chief concern of many people in industrialized societies is reducing calorie consumption, for other places in the world the great struggle is avoiding starvation, and this was even more true in the past. This observation may seem banal, but an examination of the history of calorie consumption turns out to be fascinating. By examining this history, we can gain a better idea of why many people today struggle with health problems linked to calorie consumption, particularly obesity.

A few thousand years ago, if gamblers had wagered on which society would first beat the scourge of famine and rack up the caloric intake, the safe choice would have been the Chinese, based on their vast agricultural knowledge. The Chinese knew how to treat poor soil with organic wastes, ashes, manure, human waste, and river silt.
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By AD 0, they replaced slash-and-burn agriculture with complex crop rotations.
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They knew how to mix crops using plants like broad beans and ferns, and by the sixteenth century, they knew about the application of potash (minerals that contain potassium) and oil cake (the residue from seeds pressed for oil). Their authorities advocated plowing in the burned stubble from harvests. Through meticulous experimentation and refinement of farming practices, China was able to support a population of more than 100 million people in AD 1124; in comparison, the population of England, at under a million, was around the size of a large Chinese city.
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At first glance, the path of agriculture in the West seemed similar to China's, albeit slower. Through trial and error, and observation, the Romans learned to employ chalk, dung, and ash and to intercrop lupin (a kind of legume), beans, vetches, and clover. After the collapse of the Roman Empire, crops were changed from two-field rotation to three-field, then four-field rotations of corn, clovers, grasses, and fallow cropping. Inland oceans and rivers provided convenient highways for commerce, and the riches gained from trade propped up a social class that was interested in further profit and the technical means of increasing that profit. The decimation of the European population from the Black Death in the fourteenth century—likely introduced by rats from China, ironically—broke the static pattern of manorial serfdom and freed the gentry to exploit their lands for profit. The disparity in wealth also guaranteed that while some people worked continuously and lived in poverty, others had the time and means to engage in scientific inquiry.

Despite the great effectiveness of Chinese agricultural techniques, Chinese knowledge had accumulated from trial and error and sharing of knowledge over the generations. There was no sustained effort in China—or anywhere else in the world, outside of Europe—to understand why these techniques worked, to discover what ashes, manure, broad beans, ferns, potash, and oil cake all had in common.
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Scholars were revered in China, but the scholarship concerned social relationships and was viewed as a means to gain access to prestigious mandarin employment, while commercial activities were disdained. Moreover, contact with other civilizations was relatively limited, due to barriers of mountains and long distances. Virtue, in the eyes of the Chinese, was found in honest rulers, stable societies, filial piety, hard work, and thrift. These were also the pillars of medieval Europe, but many of these lessons were forgotten as Europe turned toward capitalism and science.
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The key stumbling block to increasing agricultural yield was developing a proper scientific theory of the elements and of nitrogen in particular. One prominent step toward creating such a theory came from the Flemish scientist Jan Baptist van Helmont, who grew a willow tree from 5 pounds to 169 pounds in five years' time, with nothing but water added to the plant and soil. The soil decreased in weight by just two ounces, which he believed indicated that the tree had somehow transmuted water into tree material.
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An excellent experiment; the conclusion was wrong, but the method was precise, and other scientists would be able to make progress. A critical step was to understand what the substance was in air that helped plants grow and what this substance had in common with materials like beans and dung. Like a net around a fish, the scientific theories connecting plant-promoting substances were drawn together in a frenzy of collaboration and competition among European scientists. In 1772, the Scottish chemist Daniel Rutherford succeeded in isolating nitrogen gas. The English scientist Henry Cavendish applied an electric spark to a mixture of oxygen and nitrogen gases, which produced nitric acid; this was combined with sodium hydroxide to create a solution of potassium nitrate. The extraction of nitrogen from the atmosphere was one of the most important intellectual breakthroughs in the history of humankind; without this discovery, the population of the world today would have remained close to the 1800 level, around a billion people.
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Extraction of nitrogen in a laboratory was one thing; ramping up the conversion of nitrogen into various forms of ammonia as artificial fertilizer to help feed the hungry masses was another. At the opening of the nineteenth century, there was no practical way of achieving large-scale nitrogen fixation with the crude technology that was available. By 1913, two German chemists, Fritz Haber and Carl Bosch, and the industrial juggernaut BASF had surmounted the technical challenges. For Germany, the timing was auspicious, because the outbreak of World War I in 1914 led to the severing of the British-controlled guano-nitrate supply from Chile, which had been essential for the manufacture of explosives.

In complete contrast to the gargantuan supply of energy (from hydropower, coal, and, these days, “natural” or methane gas) and physical infrastructure required in industrial nitrogen fixation, there is another way to extract nitrogen from the atmosphere and convert it into usable form. Legumes like peas and beans maintain a form of bacteria in their root nodules. In soil, the rhizobia bacteria are free-living souls, like a crowd of laid-back hippies. When they get a chance to migrate into root nodules, however, they transform into bacteroid structures, roll up their little sleeves, and get to work. The legume plant protects its oxygen-sensitive bacteroid workers by removing oxygen and feeding the rhizobia bacteria meals of glucose. In exchange, the rhizobia release phosphate and energy; the energy is used by the bacteria to split the bond between the two atoms of nitrogen gas, freeing the nitrogen to combine with hydrogen and become available for the plant to use in the form of ammonia.
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What is most remarkable about the rhizobia is the extraordinarily scant energy required by the bacteria to split the powerful bond binding nitrogen molecules. Industrial furnaces used to fix nitrogen require temperatures well beyond the range produced in ordinary fires, and thus electric furnaces with special heat-resistant protection are essential to industrial nitrogen fixation. Modern science has not yet figured out how the rhizobia work their nitrogen-splitting magic with such energy thriftiness. Some twelve thousand species of
Leguminosae
perform nitrogen fixation, though fewer than fifty of these species are employed in agriculture. It is extremely humbling to think that a tiny bacterium can accomplish with ease what humans require massive inputs of energy and complex furnaces to do.