Evolutionary Perspective of Eating Disorders
by Jordan Clement
The evolutionary instinct that told members of migrating populations not to stay in one place and keep moving when their food supply ran low and is thought to be a major contributor to modern anorexia nervosa (Kersting, 2004). Hunter-gatherers were familiar with how to handle famine, starvation was a reliable indicator that food sources were depleted, and it was time to move. A starving hunter-gatherer had two choices when this occurred: conserve energy and wait out the famine or utilize their last bit of energy and mobilize in search of a new area with more resources (Hazzard et al., 2020). This is the adapted-to-flee-famine hypothesis, proposing that ancient adaptations encouraging migration as the solution to famine contribute to the development of Anorexia Nervosa. These individuals' “high level of self-control, energy, optimism and perseverance created a selective advantage” for survival (Hazzard et al., 2020). All of the features of modern day anorexia would have allowed for a successful migration. Having a fear of eating would keep the migrator on their path to new land without being distracted by a limited amount of food that would not sustain them for long. A distorted self image, by viewing themselves as having ample amounts of fat stores would assist emaciated migrators to push themselves to keep moving.
The continuous restriction of food, something that used to be essential in human survival, sends signals to the brain that food is limited, making automatic adjustments to hunger and satiety signalers (Kersting, 2004). Today, having food unavailable is not often the reality, there may be plenty of food available, however, the brain does not know this and reacts to the data it is being given. The data is that the individual is not taking in enough calories to cover their daily needs, and thus, this must be because there is not enough food available in the environment. The brain responds accordingly, sending signals to restrict food even more and move a lot, which may push individuals to get an excessive amount of movement each day in the form of getting a set number of steps each day or working out. This hyperactivity was brought to attention in the 1800’s when Frances Gull wrote, “the patient complained of no pain, but was restless and active…it seemed hardly possible that a body so wasted could undergo the exercise which seemed agreeable” (Hazzard et al., 2020). He noted that, although his patients were weak and in no condition to be up and moving, this did not stop their desire for movement, and he attempted to get them to abstain from movement. This abstinence led to an increase in their aptitude for movement. Gull described them as seemingly never tired. Hyperactivity and the drive for movement would aid an individual well during the time of famine and migration. The increased levels of energy that were greater than normal is present in all patients at one point within the illness.
When the moral protest of self starvation is agonizing and the drive to eat is typically too strong to be denied, how do individuals develop an eating disorder? Supporters of the adapted-to-flee-famine hypothesis believe weight loss is the trigger for anorexia in the genetically susceptible, not the decision to engage in restrictive eating (Hazzard et al., 2020). Weight loss and restrictive eating go hand-in-hand, creating the appearance that the restriction is the trigger, however Anorexia Nervosa symptoms have been found to be initiated by inadvertent weight loss. There are biological changes or “features” arising from natural selection in these select individuals including: extraordinary self-control over hunger, increased pain tolerance, athletic ability and endurance (Papežová et al., 2005). These features make it easier to ignore the symptoms of malnutrition as the individual continues to engage in their eating disorder.
Operating out of the evolutionary perspective, the solution remains to get the individual with Anorexia Nervosa out of an energy deficit by increasing their caloric intake and decreasing their activity levels. These individuals are often resistant to treatment as eating–something that is a requirement to live–fills them with feelings (fear, panic, dread, regret, and shame), they may not be aware of their body’s hunger cues, and cannot see how thin they are, making balancing their input and output an extremely difficult task. As with many other mental health disorders, they must do the opposite of what their brain is telling them. Reducing exercise and increasing food when it feels like everything within them is screaming to not eat and move their body to burn more calories. The evolutionary neurobiological explanation can be a tool to motivate individuals in their recovery journey. Preliminary data indicate an improvement in recovery by explaining that their compulsions to move and fear of feeding are evolutionary adaptations that would have saved their life helps the individual resist them (Carter, 2011). Having this explanation reframes their situation that their body was looking out for them, increasing motivation and belief that they can recover.
References
F. A. Carter, The long‐term efficacy of three psychotherapies for anorexia nervosa: A randomized, controlled trial. Int J Eat Disord 44, 647-654 (2011).
Hazzard, V. M., Loth, K. A., Hooper, L., & Becker, C. B. (2020). Food Insecurity and Eating Disorders: a Review of Emerging Evidence. Current psychiatry reports, 22(12), 74. https://doi.org/10.1007/s11920-020-01200-
H. Papežová, A. Yamamotova, R. Uher, Elevated pain threshold in eating disorders: Physiological and psychological factors. Journal of psychiatric research 39, 431-438 (2005).
Kersting, K. (2004, April). An evolutionary explanation for anorexia? American Psychological Association. https://www.apa.org/monitor/apr04/anorexia
