Autism, Anorexia, and Metabolism

autism nutrition recovery
Autism, Anorexia, and Metabolism

Is metabolism a possible connector of autism and anorexia? To date, there is meager scientific evidence of the role that metabolism plays in neurodiversity and eating disorders separately, much less the role it plays when the conditions co-occur. In this post, you will learn two reasons why metabolism may be altered in autistic individuals and how this understanding can help us connect the seemingly invisible scientific dots to anorexia.

Having a fast metabolism as an autistic person: planting the seeds for anorexia?

I have always had a very fast metabolism. Even during my most restrictive years of anorexia, I ate an amount of food that would be considered “normal” for a majority of the population. Yet because it was a starvation diet for me, I suffered from severe malnutrition, which only amplified my anxious-natured thoughts.

When I finally decided to recover from anorexia once and for all, my body’s rapid energetic usage came to light with a vengeance. To gain weight, my body demanded caloric amounts that were upwards of five times the “recommended” 2,000 to 3,000 calories per day. When I went through extreme hunger, this nutritional need only increased. Even now, I patently eat much more than those around me, who are often flabbergasted as to how I can eat entire cakes, pies, and jars of nut butters on a daily basis while maintaining my weight.

While I, as well as my treatment providers, attributed my inflated energetic needs in recovery to a temporary requirement that would decrease as I came out of energy deficit and paid off energy debt (terms described in The Biological Importance of Honoring your Extreme Hunger), reflection of my childhood eating habits, combined with those I have now, beg the question of an intrinsic metabolic component independent of starvation’s effects.

Perhaps, this component may also underlie an autistic individual’s proneness to developing anorexia in the first place, for high energetic requirements – and a difficulty or inability to sense them – would increase the chances of falling into energy deficit in the first place.

#1 Brain Metabolism

The first component of hypermetabolism in autistic people has to do with brain metabolism specifically. While the brain makes up a mere 2% of our total body mass, it uses a whopping 20% of the body’s total energy! Of this, it is estimated that neurons consume 75%–80% of energy produced in the brain. Neurons, also called nerve cells, are the building blocks of the nervous system. Nerve cells are electrically excitable and communicate with each other through synapses, forming complex networks that enable all sorts of mental gymnastics, from thinking and feeling to moving and sensing. They're like the ultimate communication squad, passing messages in the form of electrical signals.

Intriguingly, several studies have found that autistic brains contain more neurons. One study indicated that autistic children had 67% more neurons in the prefrontal cortex, an area of the brain linked to social, emotional, and communication processing. This finding helps understand why autistic people may struggle in these areas, for the increased neuronal connections – that become activated in situations when social, emotional, and communication skills are necessary – may contribute to mental overwhelm. It’s like being at a really crowded concert where everyone's playing their own tune. Not only does it become impossible to hear each individual note, but the simultaneous melodies create a whirlwind of literal noise. Anyone would want to escape such a chaotic situation!

Bringing this back to metabolism: if up to 80% of the brain’s energy is consumed by neurons and autistic brains indeed have 67% more neurons, we don’t even need to do any math equations to conclude that the autistic brain requires much more energy to function than a neurotypical one. But because I love math, let’s calculate this – just for fun!

Let's a standard person requires 3000 calories.

20% of those calories are used by the brain: 20% of 3000 = 600 calories are used by the brain

80% of the brain's energy is used by neurons: 80% of 600 = 480 calories are consumed by neurons

Autistic people have 67% more neurons: 1.67 x 480 = 800 calories

In comparison to the 480 calories consumed by the neurons of a neurotypical brain, our final outcome of 800 calories indicates that the autistic brain – and keep in mind, we’re ignoring all other parts of the body right now – needs 320 more calories just to function.

But of course, the body needs much more energy than just to use as brain fuel! Think of digestion, a beating heart, breathing, and that’s not even considering all the energy it takes to get up in the morning, walk around, and deal with the challenges and stimulation of everyday life...which brings us to the next reason for why autistic people have a higher energy expenditure: the nervous system.

#2 The Nervous System

We’ve talked about nerve cells, which are the building blocks of the nervous system, the body's ultimate communication network. If neurons are like cars passing communication from one town to the next, the nervous system can be seen as all the roads through which the nerve cells travel to coordinate and regulate all of the body’s activities.

The nervous system can be divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS).

The Central Nervous System (CNS) can be seen as the body’s headquarters, consisting of the brain and spinal cord. The brain is the command center responsible for processing information, thinking, and coordinating responses. The spinal cord serves as a highway for signals between the brain and the rest of the body.

The Peripheral Nervous System (PNS) is the network that extends beyond the CNS. It includes nerves that branch out from the spinal cord to reach every part of the body. The PNS is further divided into the somatic nervous system (controlling voluntary movements and sensory information) and the autonomic nervous system (regulating involuntary functions like heartbeat and digestion).

The Autonomic Nervous System (ANS) can be divided even further. Historically, this has been done by splitting it into the sympathetic nervous system and the parasympathetic nervous system. However, according to the Polyvagal Theory invented by psychiatrist, neuroscientist, and author Stephen Porges, the autonomic nervous system can be subdivided into not two, but three distinct circuits: the Sympathetic Nervous System (SNS), the Dorsal Vagal Complex (DVC), and the Ventral Vagal Complex (VVC).

The Sympathetic Nervous System (SNS) can be seen as the body's escape-the-danger system. In the face of threat or stress, the SNS kicks in, preparing your body for action. It's responsible for the "fight or flight" response, increasing heart rate, dilating pupils, and redirecting blood flow to muscles. It's your body's way of saying, "We need to escape the danger – let's go!"

When the Sympathetic Nervous System fails to provide safety, the Dorsal Vagal Complex (DVC) kicks in. It’s part of the parasympathetic nervous system and can initiate the "freeze" response. It slows down heart rate, reduces energy expenditure, and can lead to a shutdown-like state. It's like playing possum in the face of danger.

The Ventral Vagal Complex (VVC), also known as the social engagement system, is also part of the parasympathetic nervous system along with the DVC, but plays a role in calming things down after a stressor. It's involved in social connection and relaxation. When activated, it can counteract the SNS's "fight or flight" response, promoting a sense of safety and connection.

Obviously, we want to spend most of our time in safety and connection mode, but the reality is that autistic people spend most of their time in fight or flight mode. Over time, this leads to burnout and other symptoms of shut-down because the body is just exhausted! Why? Because activation of your sympathetic nervous system is energetically draining.

Just think about it. If you’re in a threatening situation – which, if you’re living in a world that wasn’t built for you, you constantly are! – your body is going to initiate actions that will help you escape the danger. One of these actions is the release of stress hormones like adrenaline and cortisol, which mobilize energy stores in the body for quick use. In the short term, this survival mechanism is effective for dealing with acute stressors, but prolonged activation without adequate recovery can take a toll on the body's energy reserves. In a way, it's like sprinting – great for a short burst, but not sustainable for the long haul.

While this understanding of the nervous system shines light on why autistic people tend to become easily exhausted, it also explains why we tend to have higher metabolisms. For if your body is constantly saying “OMG! There’s danger! Let’s mobilize this stored energy so we can find safety!” you’re burning a lot of calories to fulfill this endeavor!

How understanding metabolism creates compassion in autistic eating disorder recovery

In conclusion, the exploration of the intricate relationship between autism, anorexia, and metabolism unveils a fascinating connection that extends beyond the conventional realms of neurodiversity and eating disorders. I hope that opening up about my own experience with metabolism as well as sharing the science on heightened brain activity and the state of the nervous system helps you to better understand yourself. Or if you’re a loved one or carer of individuals with co-occurring autism and anorexia, I truly hope this post has created a sense of increased compassion and empowerment on your journey.

I’ve said it before and I’ll say it again: recovering from an eating disorder and living a life of freedom as an autistic person in a neurotypical world all comes down to creating a sense of trust and safety. When we feel safe and trust our environment, there is simply no need to be in fight-or-flight mode all the time. Furthermore, when we take the time and space we need to process and recharge, we also protect our already hyperactive brains from becoming overwhelmed and increasing our anxiety. Yeah, autism is complex. Eating disorders are complex. But humans are complex and it’s our complexity that makes us rich and beautiful.

If you are looking for support on your autistically ED-free journey, schedule a consultation call for 1-1 coaching here!


  1. Cortical energy demands of signaling and nonsignaling components in brain are conserved across mammalian species and activity levels
  2. Neuron number and size in prefrontal cortex of children with autism
  3. The polyvagal theory: Neurophysiological foundations of emotions, attachment, communication, and self-regulation

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