Anorexia and bulimia usually begin with a resolve to lose weight fast. After a few days of severe dieting, thoughts focus almost exclusively on food. At some point, any food that comes within reach is consumed in a frenzy: a half gallon of ice cream or a whole loaf of bread. Have you ever tried to hold your breath as long as you can? A bulimic’s eating binge is as involuntary as the giant inhalation that ends an attempt to stop breathing.
When I was providing consultations on psychiatric patients on the medical and surgical wards, I would occasionally meet a surgeon who refused to operate on an obese patient, even for cancer, until the patient lost weight. Sometimes when a surgeon said, “Eating is voluntary; they just need to stop,” I would say, “Would you mind holding your breath for a minute while I explain the regulation of food intake?” Few played along, but I made my point—and a few enemies.
Imagine you are two days into a celery-and-water diet, and you have just polished off a half gallon of ice cream. How would you feel? Nauseated, of course. Making yourself vomit can relieve the nausea and prevent absorbing a few calories. But your emotions are shame, fear, and hopelessness. Your eating is out of control. If it continues like this, you really will become a blimp. What is the natural thing to do? Try harder. Resolve to eat nothing for the next three days. But on the evening of the second day, you suddenly find yourself holding an empty thirty-two-ounce jar of peanut butter. Now what? Laxatives? Vomiting after every meal? Starting an exercise regime that burns 4,000 calories a day?
Many studies have analyzed brain mechanisms or genes to explain why some individuals are more vulnerable to eating disorders than others. Our task is different; it is to figure out why we all have eating regulation mechanisms that are so vulnerable to dysregulation. The starting point is recognizing that selection has shaped powerful mechanisms to protect against starvation. During a famine, those mechanisms motivate animals to get food—any food—eat it quickly, and eat more than usual, because food supplies are obviously erratic. The system also adjusts the body weight set point upward because extra fat stores are valuable when food sources are unreliable. And, as noted already, weight loss slows down metabolism, which is appropriate when a person is starving but the opposite of what is needed when trying to lose weight. Also, intermittent access to food signals unreliable access to food supplies, so it increases food intake and bingeing, even in rats.17
Some peculiar behaviors of people with eating disorders fit this picture well. Our anorexic patients were caught stealing candy so often that we got to know the staff at the hospital gift shop all too well. More often, we discovered purloined sweets concealed in bedding or a closet corner. It’s terrible to imagine survival depending on stealing food, hiding it, and eating it rapidly in secret. However, concentration camp survivors reported stealing and hiding bits of food whenever they could.18 We don’t know about the behavior of those who didn’t survive. Patients with anorexia nervosa and bulimia are surrounded by excess food, but their bodies are aware only of starvation. Their behavior is appropriate for a situation in which getting just a few extra calories might make the difference between life and death.
The psychiatrist Hilde Bruch wrote thoughtfully about the hundreds of patients she treated with eating disorders.19 She observed that most disorders are initiated by intense efforts to lose weight but that patients’ motives are diverse. Some anorexics value appearance highly from their earliest years; others learn from parents that love is contingent on thinness. Some take inordinate pride in their superior ability to control themselves, often with contempt for others with less self-control. Sometimes a battle of wills with intrusive parents seems primary. A few cases are set off by unintentional weight loss due to medical causes.20 Sometimes an eating disorder begins with a traumatic experience, tragically often sexual abuse in childhood leading to using obesity to avoid sex as an adult. In rare cases, a brain tumor inhibits eating. Combinations of causes are often needed to explain why some individuals get sick and others do not. Overwhelmingly, however, eating disorders are preceded by a fear of obesity that initiates severe dietary restriction.21,22,23
Vulnerability to eating disorders is influenced by genetic factors. If one twin has anorexia nervosa, the other twin’s risk is much higher if they are identical twins with identical genes rather than fraternal twins from two different eggs. About half of individual differences in vulnerability can be attributed to genetic differences.24,25 This makes eating disorders seem like a genetic disease caused by abnormal genes, but it actually implicates rapidly changing environments;26 abnormal genes causing serious eating problems would have been selected out. The alleles that influence the risk for new disorders are mostly genetic quirks that cause problems only in novel environments. For instance, who gets nearsightedness depends overwhelmingly on genes, but the variations are not abnormalities, they are quirks that don’t cause the problem in cultures where children live outdoors and don’t learn to read.27 Like nearsightedness, smoking, substance abuse, and obesity, anorexia is a disorder of modern environments, and most alleles that influence it are harmless variations in the natural environment.
However, geneticists know how to look for genes, so they do. More than 100 researchers conducted a study of more than 5,000 people with anorexia and 21,000 controls. They surveyed the entire genome to find locations that increase the risk of anorexia. They did not find a single one.28 Another recently published study analyzed 10,641,224 genetic variations in 3,495 anorexia nervosa cases and 10,982 controls. It found one location in the entire genome that increases the risk of anorexia, but the finding is not exactly a smoking gun. The allele, on the 12th chromosome, is present in 48 percent of cases but also in 44 percent of controls, and it increases the risk of anorexia by only 20 percent.29 Eating disorders are not caused by abnormal genes; they are caused by normal genes interacting with abnormal environments.
Evolutionary Psychology and Eating Disorders
Evolutionary psychologists have proposed possible benefits from eating disorders. Michele Surbey noted that the cessation of menstrual cycling in anorexia nervosa could postpone reproduction when times are bad.30 Like many other species, humans have mechanisms that turn off reproduction when available calories are insufficient to support a successful pregnancy.31,32,33 The system monitors not only fat stores but changes of energy availability. When weight declines rapidly, or when exercise is as extreme as that by ballet dancers or marathon runners, the mechanism turns off fertility even if body weight is normal.34 The amenorrhea in anorexics is indeed a product of a useful system, but reproduction turns off all by itself when food is scarce; there is no need to stop eating.
Other evolutionary psychologists suggest that anorexia may be an extreme of a female strategy to compete for mates. If men want thin women, then women get thinner to be the winner.35,36 Men do generally prefer shapes typical of young, fertile women, but those shapes include substantial breast, thigh, and buttock fat, nothing like the skin and bones of anorexia.37 More damning for the hypothesis, most anorexics don’t seem to be on the hunt for a man, many are not interested in sex, and they don’t have very many children.
Those who view anorexia as a product of sexual competition do not all assume that anorexia itself is an adaptation; most note only that extreme competitive strategies to get mates often overshoot. This seems plausible: the rate of anorexia is ten times higher for women than for men. An alternative hypothesis is that women are competing for status, but a study of more than 200 young women found that disordered eating was much more common in those rated high on mate competition rather than on status competition.38 To those not in psychology it must seem blindingly obvious that women intent on getting the best men are especially concerned about their bodies.
It has even been suggested that restricting food intake is a strategy useful during famine. The “fleeing famine” theory tries to explain the failure to eat available food, and the excess exercise often observed in anorexics, as parts of a st
rategy to run away from an area where food sources are depleted into some other place.39 I can’t make sense of the idea or the other possibilities except as examples of the error of VDAA—Viewing Diseases as Adaptations. Anorexia nervosa and bulimia are disorders, new ones, without redeeming features.
New Problems
While examples of eating disorders can be found throughout history, they became much more common from the 1960s onward in technologically advanced countries, first in women from the upper classes, then spreading across the socioeconomic spectrum.40 What in modern environments explains the recent epidemic? Several possibilities are plausible. When humans lived in small bands of thirty to fifty foragers, only a few potential mates were available, and they likely looked rather similar. In modern societies, an individual’s appearance can be compared instantly to thousands of others’, including fantasies made real. The bodies we see on television are carefully selected one-in-a-thousand specimens that have been further augmented and sculpted by exercise and surgery. Then those rare sculpted shapes are airbrushed to create images as artificial, and as exquisitely tuned to what we want, as candy bars are to our appetites.
No real person can measure up. Some people manage to control their weight and get trim and toned. Most of us keep trying to keep eating under control. But the few unfortunate ones, often those driven the most to be thin, slip into a positive feedback spiral in which increased commitment to weight loss leads to out-of-control eating, more fear of gaining weight, more strenuous dieting, and an increased weight set point, in a spiral that can consume life itself.
When I asked one anorexic patient how many cans of diet soda she drank each day, I was dumbstruck by the reply. “About eighteen,” she said. The average number per week for patients who binge and purge is forty, along with one hundred packets of artificial sweetener.41 This should not be surprising; starving people crave sweets.
Sophisticated mechanisms prepare the body for a sugar load. Sweet tastes release insulin, which lowers blood glucose.42 If the sweetener is artificial and no real sugar comes in, the insulin surge could lower the blood sugar level and increase appetite, but studies of this phenomenon are tricky and results are inconsistent.43
There are taste receptors not just on the tongue but also in the stomach and small bowel,44 so testing the effects of an artificial sweetener by having people swish a sweet solution in the mouth is different from swallowing it. Also, the effects of artificial sweeteners may be different for obese versus lean subjects, and different artificial sweeteners have different effects.45
The increased use of artificial sweeteners by obese people could be a cause or a result or both. A study of 3,682 people in San Antonio, Texas, found that the risk of normal-weight people becoming obese over a six-year period was doubled for those who drank more than three cans of artificially sweetened beverages per day.46 Were people who worried about their weight especially likely to drink them? Or did they feel that the calorie-free drinks allowed them to eat more? Two review papers found no systematic evidence that the use of artificial sweeteners increases weight,47,48 while a more recent, larger study suggests that they probably do.49 The question is contentious, and the evidence is hard to interpret, because some research is supported by artificial sweetener manufacturers with billions of dollars at stake.
Thin Babies Become Heavy Adults
The British physician David Barker observed almost thirty years ago that babies born especially thin often developed obesity later in life.50 They were also especially prone to developing coronary artery disease and diabetes. These findings pose a classic evolutionary puzzle: Does limited nutrition in utero simply damage metabolic control mechanisms, or are the changes part of an adaptive response?
Sir Peter Gluckman, a physician-scientist who has been the chief science adviser to New Zealand’s prime minister, came up with a very interesting idea: he suggested that limited nutrition in utero could signal a harsh environment in which it would be wise to shift metabolism so it stores more calories.51 He calls this the predictive adaptive response. His idea inspired fascinating research showing that early exposure to caloric deprivation in utero adds tiny molecules to DNA that stop some genes from making proteins, a process called genomic imprinting.52 Those changes shift metabolism in ways that cause obesity and atherosclerosis. They can be transmitted to a future generation, so the obesity risk of a child may be influenced by a mother’s or grandmother’s diet.53 This finding may turn out to be an example of what are called epigenetic effects, but other mechanisms can also influence future generations, for instance, changes in the mother’s behavior.54
One enterprising primatologist, Jenny Tung, recognized an opportunity to test the predictive adaptive response theory. She studied baboons who were pregnant during a drought and kept track of their babies in future years. Another drought occurred. Were babies born during a drought better protected from the effects of the subsequent drought? No, they did worse than other baboons.55 This does not by itself shoot down the predictive adaptive response idea, but it’s a fine example of how creative scientists find ways to test hypotheses.
People sometimes think that an evolutionary view implies that everything is genetically determined. Quite the opposite: selection shapes systems that monitor the environment and adjust the body and behavior in useful ways. Sun exposure turns on the protective tanning response. Muscles that are used build up to do what needs to be done. The predictive adaptive response is another possible example. The Simon Fraser University evolutionary biologist Bernard Crespi and the leading British researchers Daniel Nettle and Melissa Bateson have shown why such self-adjusting systems are intrinsically vulnerable to going out of whack: they all require positive feedback to shift the system to a different mode, and controlling positive feedback is always a challenge.56,57
An evolutionary view offers no simple way to prevent or cure eating disorders, but it asks and answers new questions. It explains why dieting adjusts the weight set point higher: when food supplies are unreliable, extra stores are worthwhile. It explains how a useful response to famine, gorging, can spiral into bulimia and anorexia. It suggests that the brain mechanisms regulating weight will be hard to influence and that we should not expect to find specific defective genes for eating disorders. It encourages close attention to aspects of modern environments that could influence metabolism, such as artificial sweeteners and antibiotics. Most specific to our topic, an evolutionary perspective explains why severe dieting causes eating disorders and weight gain.
These principles may help to find ways to control the eating disorders epidemic. For those already in the clutches of anorexia or bulimia, recognizing how positive feedback maintains the disorder can be a revelation that changes behavior. For others, it can spur useful discussions with a therapist. Understanding why it is hard to control our eating encourages subtler and sometimes paradoxical strategies to control it. As Weight Watchers and other programs recognize, regular small meals work better than resolutions to not eat for days.
Tantalus in a Candy Store Watching Pornography and Tweeting on a Smartphone
Eating disorders are but one example of how modern environments set up our ancient minds for trouble. As resources of diverse kinds become more readily available, we all face multiple predicaments like that of Tantalus.
Social resources are now as abundant as food. Facebook, Twitter, and Snapchat create new kinds of social connections that are, to human relationships, what candy is to food. Watching others become Facebook royalty or Twitter stars boosts social desires more than it provides ways to satisfy them. Dissatisfaction grows from the gap.
Occupations that require boring, backbreaking labor are vanishing. Thousands of new kinds of jobs provide the satisfaction of using talents to accomplish meaningful work. However, satisfying work that pays well is available to only a few. Others watch with envy from factories, hotels, fast-food restaurants, and big-box stores. Seeing opportunities available only
to others arouses envy.
Material wealth beyond what previous kings and queens could imagine is now available to many. Possessions are so plentiful that some people make a living helping others to purchase, organize, and discard a surfeit of things. Our minds were not prepared for such material excess any more than they were prepared for social media or fast food. We can restrain clicking to order things from Amazon about as well as we can restrain taking one more bite of hot fudge sundae.
Attractiveness and abilities don’t come in the mail, but we can now compare ourselves to actors, models, musicians, artists, athletes, politicians and performers who are one in a million. We watch movies about aspiring, ambitious young men and women who overcome obstacles to succeed grandly; the 999,999 who fail get little attention.
Birth control and disease prevention have made sex more available to more people more often. However, ads, vibrators, and videos arouse desires that previously were at the edge of imagination. So there is more sex but also greater desire. Opportunities for romantic and sexual relationships are now a world marketplace of desire and deception, from Match.com to Tinder. We hardly know what we should do—except get our bodies in better shape and find someone to take attractive photographs of us.
Tantalus was chained, so he could never satisfy his desires. No such chains bind us, so we construct our own. Some people get their teeth wired shut to reduce eating. Some unplug the internet cable and mail it to themselves to get a few days free from distraction. Many join groups to help to control their desires. Psychotherapy and meditation help many more. There are so many solutions because desires will not be denied. Trying to satisfy desires leads to excess and more frustration. Trying to put a lid on them just increases the pressure in the pot.
Good Reasons for Bad Feelings Page 27