An elevator pitch on genetics: Thoughts on cause (part 2)

When I was first introduced to the idea that eating disorders are genetic, I was (to put it mildly) skeptical. It made no sense to me. I was somewhat knowledgeable about genetics, neurobiology, and mental illness, having read about it extensively in regards to my depression. And it made sense to me that an imbalance of neurotransmitters, incorrectly firing neural wiring, overactivity in some parts of the brain, and underactivity in others could lead to dramatic disturbances in mood. But that biological mechanisms could cause someone to engage in eating disorder behaviors and suffer from disordered cognitions seemed quite farfetched. And even after I came around to the idea that these are genetically based illnesses, I honestly still wasn’t clear on the mechanisms. [Which to be fair no one is completely, even 10 plus years later with much more research having been done.] So here’s the elevator pitch, the supremely overly-simplified nutshell version, of how genetics “cause” eating disorders:

People become undernourished (which I’m defining as their nutritional intake not meeting their body’s metabolic needs in total calories or in specific nutrients) for many reasons - intentional dieting, physical illness, depression, intense athletic training, following a restrictive diet for medical reasons, even having a growth spurt. Now for most people, their body takes note of this imbalance between energy needs and intake and does its best to remedy it. A cascade of biological processes kick off from slowing their metabolism to intensified hunger signals, to obsessively thinking about food. Bodies are wired to survive and this system usually works to get people to eat more and move back to a fully nourished state.

An entirely different cascade of biological processes is set into motion when a person with a genetic predisposition to an eating disorder enters a period of undernourishment. Rather than their body and brain working to drive them to correct the energy imbalance, the opposite happens. They may feel energized rather than sluggish, calm rather than anxious, less hungry rather than more. This seemingly bizarre and counter-intuitive neurobiological, hormonal, and metabolic response to undernourishment is encoded in their genetics, and once it’s been “triggered” it is self-perpetuating and incredibly difficult to reverse.

We have excellent research that clearly shows that there are markers on genes associated with other mental illnesses as well as metabolism that are significantly correlated to an eating disorder diagnosis. And the question remains - why? Why do people have this genetic trait? Why did it survive evolution and natural selection? Well, the theory goes, way back when, people had to migrate often to have consistent access to food and it was evolutionarily advantageous to have a part of the population who functioned at a high level when in a state of undernourishment. A famine hits and hundreds or even thousands of people have to migrate to where there is food. The people with this set of genes don’t feel as much agonizing hunger or debilitating anxiety or the need to rest - they are the ones who are planning the migration, scouting for danger and foraging for food to feed the others. Now obviously, eating disorders are not evolutionarily advantageous and our ancestors who carried these genes likely also had some innate biological process for “turning off” those genetically driven traits and returning to full nourishment. What happened to this “turning off” process? Why people with eating disorders fight so hard against returning to full nourishment, and why they often experience debilitating anxiety and depression when malnourished when that must not have been the case in our ancestors, remain huge question marks (at least for me). What we do know is the return to full nourishment is the required first step, the sine qua non (without which there is not), to the “turning off” process in eating disorders.

Frustrated by the lack of nuance in this post? Me too! Stay tuned for the rest of the “thoughts on cause” series addressing all that good stuff (well not all but a lot - people who know me will tell you that my brain lives for the nuance).