Good Calories, Bad Calories (47 page)

The world is ful of species that do fatten regularly, always to serve a purpose—long-distance migrations, reproduction, or survival during periods when food is either unavailable or too risky to procure. Hibernators seem to be an obvious choice to shed light on the assumptions underlying the thrifty-gene hypothesis. These animals accumulate enormous fat deposits in response to an environment that offers up periods of feast—spring, summer, and fal

—and famine in the winter. Yet this accumulation goes unaccompanied by the chronic il s, such as diabetes, that appear in obese humans. Hibernating ground squirrels, for instance, wil double their weight and body fat in a few weeks of late summer. Dissecting such squirrels at their peak weight is akin to

“opening a can of Crisco oil,” as the University of California biologist Irving Zucker, a pioneer of this research, has described it, “enormous gobs of fat, al over the place.”

Investigators who study hibernators, like Nicholas Mrosovsky, a University of Toronto zoologist, point out that weight gain, maintenance, and loss in these animals, and so perhaps in al species, is genetical y pre-programmed and particularly resilient to variations in food availability. This program is characterized by its ability to adjust readily to changing circumstances and the unpredictability of the environment. Ground squirrels wil gain weight through the summer at the same rate whether they’re in the wild or in the laboratory. They wil lose it at the same rate during the winter whether they are kept awake in a warm laboratory or are in ful hibernation, eating not a bite, and surviving solely off their fat supplies. “It is very hard to prevent them gaining and losing weight” on schedule, explains Mrosovsky, who did much of the original research in this area. When researchers surgical y remove a sizable portion of fat from experimental animals—a procedure known as a lipectomy—the animals wil restore the lost fat so that within months of the surgery they wil be just as fat as they would have been without the surgery.*74

Even the type of fat found in animals and humans is regulated in a way that accommodates differing internal and external environments. The fat in our limbs, for instance, is less saturated than the fat around our organs, and so is less likely to stiffen in cold weather. We wil also change the fatty-acid composition of our subcutaneous fat with temperature—the colder it gets, the more unsaturated the fats. This same phenomenon, independent of the type of fat consumed, has been observed in pigs, rats, and hibernators. Another example of the evolutionary specificity of fat deposits can be seen in those desert animals that do not store fat subcutaneously, as humans and most animals do, apparently because it would inhibit heat loss and cooling. So there are fat-rumped and fat-tailed sheep, and fat-tailed marsupial mice, al desert-dwel ers that carry their fat almost exclusively in the so-named locations.

The storage of fat, it seems clear, like al evolutionary adaptations, tends to be exquisitely wel suited to the environment—both internal and external—in a way that maximizes benefits while minimizing risks. This is why most investigators who considered these issues in the 1970s and 1980s assumed that a tendency to gain any excessive weight during periods of abundance would be the kind of obvious liability that evolution would work to select out of the species rather than select in. The thrifty-gene hypothesis does not hold up. But without a thrifty gene, rendered detrimental by the abundance of food in modern societies and the absence of physical labor needed to procure it, how do we explain why gaining weight in modern societies stil seems so much easier than losing it?

HUNGER

Khrushchev, too, looks like the kind of man his physicians must continual y try to diet, and historians wil some day correlate these sporadic deprivations, to which he submits “for his own good,” with his public tantrums. If there is to be a world cataclysm, it wil probably be set off by skim milk, Melba toast, and mineral oil on the salad.

A.J. LIEBLING, The Earl of Louisiana, 1961

IN OCTOBER 1917, FRANCIS BENEDICT, director of the Carnegie Institution of Washington’s Nutrition Laboratory (located, as it happens, in Boston), put twelve young men on diets of roughly fourteen hundred to twenty-one hundred calories a day with the intention of lowering their body weights by 10 percent in a month. Their diets would then be adjusted as necessary to maintain their reduced weights for another two months, while Benedict and his col eagues meticulously recorded their psychological and physiological responses. A second squad of twelve men was studied as a comparison and then they were put on similar calorie-restricted diets. The results were published a year later in a seven-hundred-page report entitled Human Vitality and Efficiency Under Prolonged Restricted Diet.

Benedict hoped to establish whether humans could adjust to this lower nutritional level and thrive. His subjects lost the expected weight, but they complained constantly of hunger—“a continuous gnawing sensation in the stomach,” as described by the Carnegie report—and of being cold to the extent that several found it “almost impossible to keep warm, even with an excessive amount of clothing.” They also experienced a 30-percent decrease in metabolism. Indeed, Benedict’s subjects reduced their energy expenditure so dramatical y that if they consumed more than twenty-one hundred calories a day—a third to a half less than they had been eating prior to the experiment—they would begin to regain the weight they had lost. The men also experienced significant decreases in blood pressure and pulse rate; they suffered from anemia, the inability to concentrate, and marked weakness during physical activity. They also experienced “a decrease in sexual interest and expression, which, according to some of the men, reached the point of obliteration.” That these phenomena were caused by the diet itself rather than the subsequent weight loss was demonstrated by the experience of the second squad of men, who manifested, according to the Carnegie report, “the whole picture…with striking clearness” after only a few days of dieting.

“One general feature of the post-experimental history,” the Carnegie researchers reported, “is the excess eating immediately indulged in by the men.”

Despite repeated cautions about the dangers of overindulgence after such a strict diet, the men “almost invariably over-ate.” As the Carnegie report put it,

“the circumstances militated against” any acquisition of “new dietetic habits.” In particular, the cravings for “sweets and accessory foods of al kinds,”

—i.e., snacks—were now free to be indulged, and so they were. Perhaps for this reason, Benedict’s young subjects managed to regain al the lost weight and body fat in less than two weeks. Within another three weeks, they had gained, on average, eight pounds more, and came out of this exercise in calorie restriction considerably heavier than they went in. “In practical y every instance the weight prior to the beginning of the experiment was reached almost immediately and was usual y material y exceeded,” Benedict and his col agues wrote.

In 1944, Ancel Keys and his col eagues at the University of Minnesota set out to replicate Benedict’s experiment, although with more restrictive diets and for a greater duration. Their goal was to reproduce and then study the physiological and psychological effects of starvation of the kind that Al ied troops would likely confront throughout Europe as the continent was liberated. Thirty-two young male conscientious objectors would serve as “guinea pigs,” the phrase Keys used in this context. These volunteers would eventual y spend twenty-four weeks on a “semi-starvation diet,” fol owed by another twelve to twenty weeks of rehabilitation.

The subjects consumed an average of 1,570 calories each day, split between two meals designed to represent the daily fare of European famine areas. “The major food items served,” the researchers noted, “were whole-wheat bread, potatoes, cereals, and considerable amounts of turnips and cabbage. Only token amounts of meats and dairy products were provided.”*75 This diet provided roughly half the calories that the subjects had been consuming to maintain their weight. It was expected to induce an average weight loss of 20 percent—or forty pounds in a two-hundred-pounder—aided by a routine that required the subjects to walk five to six miles each day, which would burn off another two to three hundred calories.

Keys’s conscientious objectors lost, on average, a dozen pounds of fat in the first twelve weeks of semi-starvation, which constituted more than half of their original fat tissue, and they lost three more pounds of body fat by the end of twenty-four weeks. But weight loss, once again, was not the only physiological response to the diet. Nails grew slowly, and hair fel out. If the men cut themselves shaving, they would bleed less than expected, and take longer to heal. Pulse rates were markedly reduced, as was the resting or basal metabolism, which is the energy expended by the body at rest, twelve to eighteen hours after the last meal. Reflexes slowed, as did most voluntary movements: “As starvation progressed, fewer and fewer things could stimulate the men to overt action. They described their increasing weakness, loss of ambition, narrowing of interests, depression, irritability, and loss of libido as a pattern characteristic of ‘growing old.’” And, like Benedict’s subjects, the young men of the Minnesota experiment complained persistently of being cold.

Keys’s conscientious objectors reduced their total energy expenditure by over half in response to a diet that gave them only half as many calories as they would have preferred. This was a reasonable response to calorie deprivation, as Keys and his col eagues explained, “in the sense that a wise man reduces his expenditure when his income is cut.”

More than fifty pages of the two-volume final report by Keys and his col eagues, The Biology of Human Starvation, document the “behavior and complaints” induced by the constant and ravenous hunger that obsessed the subjects. Food quickly became the subject of conversations and daydreams.

The men compulsively col ected recipes and studied cookbooks. They chewed gum and drank coffee and water to excess; they watered down their soups to make them last. The anticipation of being fed made the hunger worse. The subjects came to dread waiting in line for their meals and threw tantrums when the cafeteria staff seemed slow. Two months into the semi-starvation period, a buddy system was initiated, because the subjects could no longer be trusted to leave the laboratory without breaking their diets.

Eventual y, five of the subjects succumbed to what Keys and his col eagues cal ed “character neurosis,” to be distinguished from the “semi-starvation neurosis” that al the subjects experienced; in two cases, it “bordered on a psychosis.” One subject failed to lose weight at the expected rate, and by week neurosis” that al the subjects experienced; in two cases, it “bordered on a psychosis.” One subject failed to lose weight at the expected rate, and by week three was suspected of cheating on the diet. In week eight, he binged on sundaes, milk shakes, and penny candies, broke down “weeping, [with] talk of suicide and threats of violence,” and was committed to the psychiatric ward at the University Hospital. Another subject lasted until week seven, when “he suffered a sudden ‘complete loss of wil power’ and ate several cookies, a bag of popcorn, and two overripe bananas before he could ‘regain control’ of himself.” A third subject took to chewing forty packs of gum a day. Since his weight failed to drop significantly “in spite of drastic cuts in his diet,” he was dropped from the study. For months afterward, “his neurotic manifestations continued in ful force.” A fifth subject also failed to lose weight, was suspected of cheating, and was dropped from the study.

With the relaxation of dietary restriction, Keys avoided the dietary overindulgence problem that had beset Benedict’s subjects by restricting the rehabilitation diets to less than three thousand calories. Hunger remained unappeased, however. For many of the subjects, the depression deepened during this rehabilitation period. It was in the very first week of rehabilitation, for instance, that yet another subject cracked—his “personality deterioration culminated in two attempts at self-mutilation.”

Even during the last weeks of the Minnesota experiment, when the subjects were final y al owed to eat to their hearts’ content, they remained perversely unsatisfied. Their food intake rose to “the prodigious level of 8,000 calories a day.” But many subjects insisted that they were stil hungry, “though incapable of ingesting more food.” And, once again, the men regained weight and body fat with remarkable rapidity. By the end of the rehabilitation period, the subjects had added an average of ten pounds of fat to their pre-experiment levels. They weighed 5 percent more than they had when they arrived in Minneapolis the year before; they had 50 percent more body fat.

These two experiments were the most meticulous ever performed on the effects on body and mind of long-term low-calorie diets and weight reduction.

The subjects were selected to represent a range of physiological types from lean to overweight (albeit al young, male, and Caucasian). They were also chosen for a certain strength of character, suggesting they could be trusted to fol ow the diets and remain dedicated to the scientific goals at hand.

The diets may seem severe in the retel ing, but, in fact, fourteen to sixteen hundred calories a day for weight loss could be considered generous compared with the eight-to-twelve-hundred-calorie diets that are now commonly prescribed, what the 1998 Handbook of Obesity refers to as

“conventional reducing diets.” Nonetheless, such diets were traditional y known as semi-starvation diets, a term that has fal en out of use, perhaps because it implies an unnatural and uncomfortable condition that few individuals could be expected to endure for long.

In both experiments, even after the subjects lost weight and were merely trying to maintain that loss, they were stil required to eat considerably fewer calories than they would have preferred, and were stil beset by what Keys and his col eagues had cal ed the “persistent clamor of hunger.” Of equal importance, simply restraining their appetites, independent of weight loss, resulted in a dramatic reduction in energy expenditure. This could be reversed by adding calories back into the diet, but then any weight or fat lost returned as wel . One lesson learned was that, for the weight reduction to be permanent, some degree of semi-starvation has to be permanent. These experiments indicated that would never be easy.