Authors: Barbara Natterson-Horowitz
The similarities go beyond the physiological. In their article “Intriguing Links Between Animal Behavior and Anorexia Nervosa,” psychiatrist Janet Treasure and agriculture professor John Owen explain that while “
the affected animals restrict their intake of normal food … some consume large amounts of straw.” That’s similar to an old trick of human anorexics, too: eschewing food that’s dense in nutrition (and calories)
in favor of stomach-stuffing, “negative”-calorie fillers like lettuce and celery. Even more interesting is something Treasure and Owen learned from observing pigs on farms throughout Europe. Like food-deprived rats running nowhere on their wheels and human anorexics putting in yet another hour on the treadmill, pigs with thin sow syndrome are remarkably restless. As Treasure and Owen note, having observed the animals at Greece’s largest pig farm, where a full 30 percent of the females were affected, thin sows “
spend more time on nonnutritive hyperactive behavior … they move incessantly around their pen.”
Trying to figure out why and when certain pigs are at greater risk for developing thin sow syndrome has led to a hunt for the gene sequences that underlie it. And the search has turned up an intriguing culprit. In recent decades, consumer taste has veered away from fatty cuts of meat. Human pork eaters want their chops and loins lean. Even bacon has gotten skinnier. Livestock farmers have responded to the demand by breeding leaner pigs. And that’s where a problem seems to crop up. Treasure and Owen report that “
pigs, especially those that are bred for extreme leanness, can develop irreversible self-starving and emaciation.”
What’s happened is that selective breeding for leanness has “
led to the uncovering of recessive traits which produces extremes.” That these traits came to the fore in pigs in a matter of generations leads Treasure and Owen to suspect that anorexia nervosa has “
an analogous genetic basis”—in pigs and humans … and other animals, too.
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This indicates that gene sequences that code for thinness may exist in many animals, although they remain in the background, essentially unactivated, in wild populations, where breeding is not as controlled.
When we look at humans, we see something similar.
Studies of twins and generations of families show that heritability for anorexia nervosa is extremely high. Searching for an “anorexia gene” has led inevitably to questions about why it arises in the first place. Evolutionary psychologists have posited several varied theories to explain why anorexia nervosa may have been selected for in our human ancestors. Their hypotheses have included adaptation to famine, social hierarchy effects, and male preference for certain body types (both heavier and thinner).
What seems much more likely, says Michael Strober, a UCLA professor of psychiatry and biobehavioral sciences and the editor in chief of the
International Journal of Eating Disorders
, is that the gene sequences that anorexics are passing down the family tree are linked to anxiety. Anxiety, high stress, and fear responses are the main features Strober sees in human anorexics and other people with eating disorders every day in his office at UCLA. “
People with anorexia nervosa are nervous when they confront change or any novelty in their environment,” he told me.
And change is stressful for thin sows, as well. Even assuming an underlying genetic propensity, what’s remarkable is when and why the sows are most vulnerable to the syndrome.
It strikes most often during the socially and physically demanding weeks between giving birth and weaning their piglets, a period called farrowing. And it’s not just the new porcine moms who get so frightened and stressed that their diet is affected.
Weaning is a vulnerable and scary time for the piglets, too. In fact, that’s when the less gender-specific variant, wasting pig syndrome, can develop. Like females affected by thin sow syndrome, young pigs with wasting pig syndrome refuse food, become emaciated, and sometimes die. Young male pigs are just as susceptible as female piglets, and it strikes at that fraught yet crucial period when they’re moving out from under the protection of their mothers into the competitive world of the herd.
Your typical commercial swine operation is not the bucolic idyll you might imagine from fond rereadings of
Charlotte’s Web
. Strict, innate social hierarchies that serve pigs well in the wild lead to dominance displays in crowded conditions, especially around feeding. From their first day on the teat to their later days at the trough, pigs compete for food and may bite each other’s tails and ears to be first to chow time. The ones that prevail get fatter and healthier. The more timid ones miss out. In this environment, the pigs with genes that are overly expressed for anxiety, especially social unease, are vulnerable to a phenomenon that every middle school teacher and counselor of young adolescents will recognize: bullying.
Farmers keep an eye out for bullying in their herds, knowing it can lead to thin sow syndrome. Psychiatrists, too, increasingly recognize eating disorders’ important associations with anxiety and dis-ease in addition to more traditional ways to explain why anorexia nervosa occurs: disordered psychosexual development, intrusive family dynamics, perfectionism, and body-image distortion.
Knowing this, then, could clues for treating human anorexia nervosa be found in a pigsty? Farmers, after all, take a financial hit if they just stand by while their sows and piglets starve themselves.
Connecting fearful states to eating behaviors, one study showed that piglets treated with anxiety-relieving drugs were indeed able to overcome their self-starving tendencies and resume eating and gaining normal amounts of weight. But pigs in general afflicted with thin sow and wasting pig syndromes don’t fare well. One veterinary website says flatly, “
There is no treatment.” Psychiatrists might agree: they have yet to find a consistently impressive pharmacological fix for anorexia nervosa once it’s fully taken root.
But there may be some preventative measures.
Farmers advise making sure the animals are warm. They suggest raising the heat in the animals’ pens and giving them more bedding material.
Similarly, rodent researchers found that warmer ambient temperatures significantly reduced wheel-running by food-deprived rats. In some cases it actually reversed weight loss. This is likely due to the effects of a tiny brain structure called the hypothalamus, located behind the pituitary gland and above the brainstem. Body temperature, food consumption, and metabolism are regulated by the hypothalamus, which also plays a critical role in stimulating and suppressing appetite. Indeed, early traumatic injury to the hypothalamus (and other brain structures) may lead to anorexia nervosa later in life. Conversely, anorexia nervosa itself can bring on hypothalamic dysfunction.
Pig farmers also recommend immediately increasing feed rations for the whole herd, not just the suffering pigs. Whether this reduces competition for food or catches at-risk sows before they tip into syndrome territory, it seems to improve the health of the entire group.
Could these measures help human anorexics? Although those with full-fledged anorexia nervosa would certainly need more comprehensive treatment,
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might people with early signs of this disorder benefit from something as simple as kicking up the thermostat a few degrees during stressful periods? Borrowing further wisdom from veterinarians and farmers, physicians and families might keep an eye out for bullies and
social competition during critical life transitions, such as adolescence and new motherhood, to stave off anorexia nervosa in at-risk individuals.
Some eating disorders, say psychiatrists, spread socially among susceptible individuals. It can take just a single “thought leader” to disseminate disordered eating behaviors to many others in a group.
Today’s aspiring bulimics and anorexics can learn tricks of the trade from anorexia-nervosa–promoting (a.k.a. “pro-ana”) websites.
Images of skeletal celebrities fill screen after screen, providing visitors with “thinspiration.” Comments and blogs give isolated anorexics and bulimics around the world a cyber support group in which to crow about their triumphs: a meal skipped, a parent tricked, chocolate bars and noodles regurgitated, an exercise goal exceeded. Online pals commiserate about laxative intolerance and family meals fake-eaten under the eagle eyes of parents or spouses. Helpful tips include how to mask your breath after a vomiting purge and how to smuggle heavy coins into your pockets to tip the scales at your yearly physical. An added thrill for devotees of these sites may come from a sense of persecution and secrecy. The sites are targeted by web managers and parents’ groups and are frequently pulled down, only to sprout up again on a different domain or server.
But what might surprise the aficionado-victims of “the ana lifestyle”—not to mention a bulimic men’s cross-country team or varsity cheer squad—is how much they have in common with the gorillas at their local zoo or belugas at their local aquarium. Because some of these animals have a nagging (and mostly secret) habit, too. Zoo vets call it R and R: regurgitation and reingestion.
The technical definition of R and R is “
the voluntary, retrograde movement of food or fluid from the esophagus or stomach into the mouth.”
An affected gorilla causes himself to vomit a bolus of food into his mouth or hand, or sometimes onto the ground. Just before he does it, he goes through some preliminary behavior. Gorillas have been seen poking and massaging their stomachs. Others prepare a special place on the ground. Some hunch over or rock back and forth and shake their heads. After the mouthful comes up—onto the floor or into a hand or mouth—the gorilla reconsumes it. They use their fingers, or lick it up directly, or simply rechew and swallow what’s already in their mouths.
Sometimes the process is repeated, with the same material going up and down numerous times.
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Just as with human bulimia nervosa, once R and R behaviors start in one member of a group, they can spread. For example, when the elder gorillas of a troop engage in it, infants and adolescents become fascinated, sneaking up behind silverbacks and females to steal slurps of regurgitant. In one group of gorillas, the young literally aped the adults’ stooped body postures after watching them go through their R and R routines. The youngsters spit and reswallowed their own saliva, leading researchers to remark that the behavior “
might be socially enhanced, if not learned.”
R and R is widely believed not to occur in the wild, or at least not that researchers have reported. But it is common in captive settings in both terrestrial and aquatic mammals. Chimpanzees, dolphins, and beluga whales—all animals said to share our so-called higher cognition—have been seen engaging in R and R outside wild environments. One marine mammal specialist described to me a time she saw a beluga whale gag up a swirling ribbon of white liquid and then balletically, deliberately, reingest it while on display in its underwater tank—in full view of a group of disgusted aquarium visitors.
When veterinarians notice R and R, the first thing they do is take stock of the individual’s social environment. Like the pig farmers, they carefully monitor group interactions to see where stressors and fear might be coming from and to minimize opportunities for R and R to be learned by others.
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Veterinarians are careful to point out that R and R differs in some ways from human bulimia. In fact, R and R bears similarities to another human condition called rumination disorder. It’s diagnosed in humans who bring up food from their stomachs into their mouths, chew, and then spit out or reswallow repeatedly. One veterinary theory is that R and R behaviors are an animal’s way of self-soothing or prolonging feeding pleasure. This may be true, but many human sufferers of rumination disorder also have mental disorders driving the behavior.
Given the relationship between R and R and stress, does this vomiting behavior also connect to the ecology of fear? I believe it does, though it’s not predatory fear that underlies R and R but, rather, the dangerous and oppressive anxiety of social stress.
For a scared animal, an emotionally activated digestive tract can be a powerful weapon in its defensive arsenal.
The black vultures in McKinney Falls State Park, in central Texas, are notorious regurgitators able to “vomit with a vengeance” when threatened by humans or other animals.
Some caterpillars, too, according to lepidopterists, are well-known regurgitators. Some upchuck reflexively at the slightest provocation, while others stoically withstand stressor after stressor until finally they blow. Looking at the opposite end of the digestive tract,
some animals defecate as an offensive strategy to drive predators away and to facilitate escape. Others, including many mammals, defecate in response to fear or threat. Perhaps you yourself have felt a stomach-emptying urge—from either end—before a major presentation or during a stressful social encounter.
I found no corresponding term in the human literature to describe it, but wildlife biologists have a great one. They call throwing up when threatened “defensive regurgitation.” Although the psychology is vastly different, the effect of stress hormones on the gut may be very similar. Thinking of bulimia nervosa as “defensive regurgitation” may help physicians
reconsider how they approach and treat this disease. And it may help patients reframe it as well.
I never did get to the bottom of all of Amber’s fears. But after a few weeks she left the unit, carrying a few more pounds on her small body and a little less anxiety in her mind. From time to time in the years after, I would see her on campus, home from college. She was recovered and appeared healthy.
But if I could go back to that moment in the dining room when she was scared of a sandwich and change one thing, it would be this. While sorting through her fears—of getting fat, of food, of change—I would help her understand her fear of feeding as a protective physiology gone astray. I would tell her about the ecology of fear and share the story of the Yellowstone elk. How severely they restricted their eating when wolves abounded. And how their eating expanded when the predators went away. We would work together to help her identify the wolves in her life and uncouple her fear from her feeding. Because Amber was a lot like other vulnerable animals venturing out of nests, caves, and burrows. Threat comes not from the food they might eat, but rather from the uncertain and dangerous world in which they must consume it.