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  • Helly Barnes

Linking The Evolutionary Theory & Addiction Model for Eating Disorders

Restrictive eating disorders and the ability of the brain to develop an addiction to energy deficit has a very compelling evolutionary explanation. For our hunter-gatherer ancestors, a high reward response to restricting their food intake and constantly being on the go, to avoid energy surplus, would have better enabled them to migrate when food resources were in short supply. And in fact, many of today's 'mental illnesses' can be explained in evolutionary survival-based and advantageous terms. Of course, in our modern world, where there aren't the same threats to our safety and we have everything available at the touch of an app, these evolutionary brain changes can be unhelpful and problematic. This post explores the evolutionary theory of restrictive eating disorders, including how and why, once upon a time, the typical addictive drive to pursue energy deficit seen in people with restrictive eating disorders would have been a beneficial survival response.

Evolutionary Explanation for Addictions

Any addiction can develop when someone engages in a 'drug' that creates a high reward response through the brain's reward pathways with the release of dopamine and natural opiates, making them feel incredible and highly motivated to repeat the experience for the same rewarding effects. These brain-based reward systems evolved so that we find pleasure in the things in life that are essential for the survival of not just ourselves as individuals but also our species. Therefore, food, shelter, sex and safety are all things that would trigger the reward system, ensuring that we feel motivated to seek more of the same to stay safe and procreate! In our ancestors' times when life was pretty basic compared to now, this survival-based reward system was really quite a good thing, ensuring they stayed alive long enough to procreate and eventually lead to the birth of each of us! But although times have moved on since our ancestor's day and we now live in an age full of highly-rewarding substances and activities available to us at the touch of a button, our brains haven't evolved to catch up. The reward systems we have in our brains that were built to find the motivation to pursue the good things in life are now finding pleasure in highly-rewarding things that are so rewarding that our brains will then pursue more of them above and beyond other, less rewarding things in life.. and this is a key reason for why addictions today are much more prevalent.

But why doesn't everyone develop an addiction if we all have brains that have evolved to find rewards in these highly rewarding and freely available 'drugs' that our modern world is littered with? After all, some people can have a drink socially, while others become addicted; some people can engage in video games here and there and others develop a drive to keep playing video games to the point they lose their careers and relationships.

The answer to this is that each person's brain is wired to find pleasure in different pursuits, which through evolution helped to ensure the survival of the whole tribe. It was beneficial at a tribal level if one member found hunting much more rewarding than another tribe member who might have found building shelter a highly rewarding pursuit. Today, our brains are still wired to find pleasure in different rewards.

Of course, there are additional factors that make some people more susceptible to developing addictions than others. These include sociocultural factors, availability of their 'drug' and ease of access to it, stress or trauma history, as well as factors like a person’s age when they first engage with the drug.

Evolutionary Theory to an Addiction to Energy Deficit AKA Restrictive Eating Disorders

When you understand that our brains evolved to find pleasure and reward in finding food and eating for the sake of our survival, it makes restrictive eating disorders, where a person develops a high reward response to the state of energy deficit seem even more illogical.

A 'normal' brain finds pleasure in food, triggering dopamine release, and motivating a person to continue eating because food is essential for survival. Most people who attempt diets will find that at some point their brain and body take over and drive them to eat so that they stay sufficiently nourished. So, what has happened in the brain of someone with an eating disorder in which there is the opposite response? Was there a time in evolution that these seeming deliberate self-starvation behaviours were ever helpful?

Many of you will already be familiar with the flee-from-famine evolutionary theory of eating disorders which explains why some brains have evolved to pursue food restriction and high levels of movement when it perceives food scarcity in the immediate environment.

The flee-from-famine theory hypothesises that the typical symptoms of a restrictive eating disorder—particularly restricted food intake, excessive movement and denial of a problem—evolved as it enabled our ancestors who were nomadic foragers to leave depleted environments and move to find a new foraging ground. A normal physiological response to low food intake is to preserve energy by reducing urges to move and increasing hunger. However, this response is not beneficial to someone if they need to migrate and find somewhere with dense food availability for survival. In this situation, it’s beneficial for a starving forager to be able to stop foraging and eating the depleted resources locally and to feel restless and energetic so they can move to find food. As well as this, there is an additional benefit to them not being able to recognise how dangerously malnourished they are. Therefore, the flee-from-famine theory highlights three key adaptations to someone with a restrictive eating disorder: the ability to ignore food immediately available, hyperactivity and denial of starvation symptoms with distorted body image. And it would naturally have been essential for survival if these compulsions to move and find food while avoiding intake in the here and now, were more urgent than other human needs.

Not every member of the tribe would have needed this adaptive response to a famine situation. Those who did were the minority in their groups, but they were the individuals who would have had the drive and stamina to migrate even though malnourished. They will have had a powerful aversion to any behaviours that could lead to energy surplus because this would have switched off the migratory response and not been helpful for survival. At the end of the day, it was these individuals and their optimism and energy who inspired the others in their tribe who were feeling the effects of energy deprivation to continue migrating so they could all reach a new hunting and gathering ground.

Today, some of us still carry the genetic blueprint for this adaptation response to famine and so we can then trigger our brain into these behaviours if we lose too much weight and enter a state of sufficient energy deficit. What was a means to survival for our ancestors can be an invisible, life-limiting prison to those affected today.

The need to inspire others in the tribe is another characteristic from the evolutionary theory that also links to a key feature many with restrictive eating disorders experience, which is 'Martyr Complex'. Martyr Complex is important to be aware of with restrictive eating disorders and is covered in depth in my book, Addicted to Energy Deficit.

A question you might now how have is, what then happened to our ancestors who were lucky or unlucky enough (depending on how you view it) to have this predisposition to this flee-from-famine response? How did they start eating again when they did migrate and find food if they had such a strong aversion to eating in the same way people with eating disorders do?

For our ancestors, the migratory response and ability to motivate the tribe to follow would have been switched on just until an abundant environment was found. Once they had lots of yummy foods to eat again, the social pressure and support from family would have encouraged them to start eating. This in turn reversed their energy deficit state switching off the migratory response. Because the migratory behaviours had been short-lived, there was minimal risk of our ancestors developing deeply entrenched brain circuitry that was then highly resistant to change. Instead, support to eat again would have reactivated the circuits in their brain driving normal eating, causing the migratory response to subside.

Linking the Flee-from-Famine Evolutionary Theory & the Addiction Model for Restrictive Eating Disorders

For those with the genetic blueprint to flee-from-famine or, as we know it today, develop a restrictive eating disorder, the brain is primed to make key changes if they enter a state of energy deficit. When body fat and lean tissue stores fall below a certain point, the brain will switch on the adaptive migratory famine response. This involves a high reward response to food avoidance behaviours, movement and exercise and other behaviours that sustain energy deficit. The brain will also promote and reward thoughts that prevent the person from recognising their hunger or how malnourished they are and stimulate an avoidant response to weight gain. The brain achieves this with the same processes as other forms of addiction—through the release of natural opiates and dopamine to reward and drive the behaviours.

In someone with an eating disorder today, these behaviours last much longer than they would have done in our ancestors' time, possibly years or decades. This creates deeply wired-in brain circuitry that then causes these behaviours to become embedded habits and to the significant dopamine deficit people also develop. In addition, the numbing effects of the addictive nature of the eating disorder become a strong maintaining factor, making it even more painful and difficult to stop. All this combined leads to the entrenched addiction to energy deficit that people with eating disorders experience today.

The other factor that makes overcoming this evolutionary phenomenon more complicated today relates to the beliefs that underlie the behaviours. Our ancestors would have understood why they needed to keep moving without stopping to eat in the scarce environment they were in. The compulsion to migrate and lead others to do the same made sense to them and their tribe. When they found a dense foraging ground, stopping to eat again would have been logical and hence easier to pursue. Today, people believe that they are engaging in compelling energy-deficit-creating behaviours because they have a 'fear of weight gain' or want to fit a societal norm. Perhaps they fear being 'unhealthy' or becoming 'obese' due to public health messages that often do more harm than good. Therefore, in people with eating disorders today, not only have their behaviours lasted longer and become more embedded than in our ancestors' time, but they also are maintained by powerful, ongoing beliefs.

In Conclusion

Understanding the evolutionary theories to addictions and eating disorders can help you make sense of behaviours or 'illnesses' that in today’s world seem inexplicable, adding to the self-perception that too many people have of being a bit 'crazy'. At one time, these brain changes served a real purpose for survival. Today they form addictions that ruin lives.

To me, the evolutionary theory of eating disorders makes so much sense and takes the concept of 'mental illness' or a 'diseased brain' to what is a very clever brain believing it's fighting for survival.

Perhaps your understanding of this evolutionary theory and why your brain developed this addiction to the pursuit of energy deficit can simultaneously give you better reasoning for why it makes sense to eat large amounts of food so that your brain can trust that it’s now in an environment that is a dense foraging ground and start to switch off the migratory response.

Guisinger, S. (2003). Adapted to flee famine: Adding an evolutionary perspective on anorexia nervosa. Psychological Review, 110(4), 745–761.

**The information here is taken from my newly available book,

'Addicted to Energy Deficit - A Neuroscience Based Guide to Restrictive Eating Disorders'

which you can buy now ...

And my second book is also now available and it is called,

'Aiming for Overshoot'

available if you click here

If you like to listen, as well as (or instead of read!) then this blog post is the transcript of a podcast episode which you will find on my podcast series,

available on this website, all mainstream podcast platforms and on YouTube.


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