“Because starvation has been the main threat in evolution it is fitting to paraphrase Dobzhansky: ”Nothing in the biology of anorexia makes sense except in the light of evolution”. And 36 years ago, it was realized that the conspicuous high physical activity of anorexia is a normal, evolutionary conserved response, i.e., foraging for food when food is in short supply.“ 
According to Evolutionary Psychology EVERY human behavior (even the ones that appear today pathological and dysfunctional) is an evolutionary adaptation that once served survival and reproduction.
The following hypotheses concerning eating disorders are the most accepted in the scientific field and don't deserve a comment:
1. Unconscious attempt to compete with other females for male mates by self-starvation
(Dr Riadh Abed distinguishes that BN is all about mates and AN all about status.)
2. Adaptive attempt at reproductive suppression by the affected female because of environmental reasons
3. Manifestation of reproductive suppression of subordinates by dominant females
The following hypothesis by the psychologist Shan Guisinger ("Adapted to Flee Famine") I'd like to discuss in detail:
“Anorectic symptomology includes three distinct adaptations specifically relevant for surviving past famine conditions: ignoring food; hyperactivity; and denial of starvation, including distorted body image.”
Guisinger also writes
“History: Before the 1960s people with anorexia nervosa did not give fear of getting fat as their reason for eating little.”
You have to take into account that in prehistoric times "fat was beautiful". (see the image of Venus of Willendorf). But Guisinger "knows" that 100,000 years ago girls had a distorted body image, without mirrors, if there was any body-shaming, it would have been for being too skinny as in Mauritania today.
How being able to ignore food and deny starvation during food shortages is an advantage sounds paradoxically to me. Hunger pangs and food cravings are supposed to be an adaptation to prevent hunger. I know about the rat studies that should support an increased energy expenditure while starving, but the typical response is energy conservation. During the Minnesota Starvation Experiment, in a semi-starved state the men also performed less spontaneous physical activity.
“Normally, when a person or animal begins to lose weight, behavioral and neuroendocrine mechanisms conserve energy and increase desire for food. Metabolic rate declines as much as 40% and increasing hunger prompts food searches. If starvation continues, individuals become obsessed with eating, lethargic, and depressed.”
This was my personal experience, too, having had no drive for thinness (Guisinger admits many with AN are not hyperactive contradicting her hypothesis), so I suggest hyperactivity in AN can relate to the goal to lose weight (which definitely couldn't be an adaptation!), but not necessarily. Compulsively exercising can also be a trauma response. How a distorted body image is of advantage in a famine doesn't make sense to me either. What about the fear of calories and fat, picky eating, the disgust of food, the antisocial behavior, binge/purge cycles?
An Evolutionary psychologist makes the (unproven) assumption that even these behaviors MUST be adaptations, too. If Adaptationism was true, why did humans stop to adapt within the last 10,000 years, why do we still have the psychology of cavemen? For hundreds of generations the migration ability has turned into a disadvantage.
The very few cases of "holy anorexia" (Anorexia mirabilis) in medival times didn't reproduce. Yet Guisinger who idealizes AN, believes this trait is so advantageous that it became more and more prevalent, in particular in the last 100 years, even though she concurs it's deadly nowadays. Women do dieting these days but in the past people "dieted" involuntarily as well all the time, which should have triggered the migration "ability".
In this video a girl points out the paradox, she asks:
“If anorexia is a response to famine, why is it so hard to eat?”
Tabitha responds that in ancient times ED lasted only a few weeks. My comment is WHY? and that a few weeks of dieting is not yet an ED. There's a reason why you just can't stop by yourself after a few weeks, I don't see why it would have been different back then.
“The complex psychobiological changes of AN are difficult to explain except as the result of specific biochemical mechanisms resulting from natural selection.”
(translating to 'a highly complex behavior can only have very simple explanations' --- strongly disagreeing!)
In today's hunter/gatherer tribes you don't find AN, in regions where food is scarce, neither. Body obsessions you find only among wealthy people. If it's a genetic migration program that switches on when food becomes scarce, a bottle neck trait, all the normies die from lethargy, you should find it equally distributed, not only in teenage girls in industrialized countries.
Although body weight continues to rise until the early twenties, body weight relative to height is typically at it lowest point for females in early puberty.
“The hormonal changes associated with puberty might lead to intermittent with or without the psychosocial features of AN in genetically predisposed females during their puberty or adolescence.”
If inadequate body fat triggers the Adapted to Flee Famine response, what about normal or overweight sufferers?
In one interview she gives an explanation for the gender imbalance. Male anorexics were killed off by the tribe they came across during their migration. If this trigger is linked to (female) hormones, "real" men wouldn't get AN. Can I remind you of the male supermodel Jeremy Gillitzer, who died of anorexia, a prototype of masculinity?
And how likely is it that teenager cave girls would leave their tribe to migrate (especially if they were not concerned about the food situation), where their only prospect of survival was to find a new tribe whose language they wouldn't understand and where they would be "available" to any men? According to Evolutionary Psychology rape is an effective mating strategy. Under those circumstances recovery would have been easier than for anorexics today? No, teenage cave girls would have never left their band.
No good explanation is given why this genetic programming is malfunctioning in modern times having the opposite result. Because we don't match our environment anymore?
“When resources were depleted and the tribe despaired, an anorectic’s energy, optimism, and grandiosity could mobilize the other members to heroic marches, much as Joan of Arc, an apparently anorectic peasant girl, inspired soldiers to march with her.”
I think in most cases the illness rather suppresses a potential for grandiosity. Why would an anorectic mobilize tribe members if she is delusional about survival and starvation?
In our modern world those with ED are a $trillion burden to the economy but in cavemen days they were the heroes and saved humanity from extinction? I don't think so. These days the typical anorexic/bulimic is a social reject, suffering from depressions, OCD, self-inflicting injuries and other comorbidities, has a high likelihood to die from suicide or starvation prematurely. This is highly counterintuitive, yet Guisinger describes her hypothesis as "intuitive" in comparison with other approaches.
Here I agree with Guisinger, CBT is harmful:
“Treatments based on the conventional CBT assumptions have a dismal success rate. In fact McIntosh and colleagues (found that patients in what was supposed to be the control group, given only nutritional counseling and emotional support, did better than those given CBT that assumed anorexia is caused by overvaluing body size."
AN patients don't need experts (including Guisinger), high-tech medicine and therapy (at least not conventional therapy) for recovery but the support of loved ones.
“Virtually all diets are based on the “fact” that a “safe” 1–2 pounds (0.45– 0.91 kg) per week weight loss can be achieved by a daily intake reduction of 500 –1,000 Calories.1 This is false. It is impossible to lose only 1–2 pounds per week following this advice.”
Here Guisinger is very ignorant how hard weight loss can be for some. We know you can even gain weight while undereating. According to Guisinger you are cured once you have reached a healthy weight and eat enough, which is obviously not true either, weight restoration doesn't mean anything.
“Social pressure exerted by family and friends would in turn have helped anorexic member(s) to begin eating again.”
Seriously? Doesn't anyone have social pressure to eat and is it helpful to anyone?
“Anorexia has to make people feel special—even chosen, in order for its victims to tolerate the deprivation.”
I think most rather have a feeling of inferiority and low self-esteem. Who of the group members feels to be chosen like Joan of Arc? Might Guisinger be projecting her own feelings of grandiosity, being the one who figured out ED?
Conclusion: Guisinger has created a fantastic fairy tale that might be soothing to many of you, but which is very detached from reality. She cherry-picks every supporting evidence and ignores contradictory evidence like almost anyone of her peers. Because it's so radically different from all the other stigmatizing and humiliating theories and approaches to ED it is popular among those afflicted, whose critical thinking skills are impaired by their emotional investment.
You are neither a primitive migrating caveman nor a starving rat running in a wheel, but a spiritual being that is better in touch with its own emotions than others who don't have mental illness as a response to traumatic life events. ED is not a survival mechanism for the African savannah but for life after trauma. ED has a large spectrum of symptoms which overlap with other psychiatric conditions. It doesn't make sense to single out hyperactivity as a hallmark symptom. You might as well claim long-distance runners or boys with ADHD are trying to migrate.
There are contributing biological causal factors in ED, but you shouldn't focus too much on them (like all you have to do is rewiring your neural pathways) let alone reduce ED to biology. If you accept this hypermaterialistic and absurd paradigm, that you are nothing but a vessel for your genes and your sole purpose in life is to survive long enough to pass on your DNA to the next generation and that there cannot be underlying psychological issues, it's a tell-tale sign you have trauma you are pushing away.
We live in a cult of society ruled by experts where nobody would call her out for such lunacy.
“Research academics in the field, however, are more supportive. “It’s a plausible hypothesis,” says Janet Treasure, PhD, the director of the Eating Disorders Unit at London’s Maudsley Hospital. Evolutionary psychologist Debra Lieberman, PhD, of the University of Hawaii is skeptical but says, “It’s wonderful we’re starting to think about these disorders in an evolutionary light.”
Lieberman is skeptical as she has settled on the intrasexual competition hypothesis.
One afterthought: why not bring all chronic AN cases back to their natural habitat, leave them alone and let evolution run its course. They might stand a better chance of survival among lions and hyenas than in an ICU among doctors and psychologists.