My name is Sydney Carroll and I am a dietitian in Seattle, WA. Welcome to Part Two in the Nutrition & Brain Health Series! In Part One, we covered nutrition and brain function. Today we will discuss the effects of restrictive eating on the brain. And in Part Three I will share nutrition tips to support brain health.

Ready to learn? Let’s dive in.

What Happens When You Under Eat

As we explored in Part One, our bodies and brains need a substantial amount of energy to run. Under-eating deprives the brain of the energy it needs to function properly. This is a huge reason why dieting and restrictive eating are so damaging. Both of these ways of eating involve intentionally restricting the type or amount of food eaten. The result of manipulating food intake in this way? Not eating enough to keep the body running smoothly.

Chronic undernourishment puts the body in a very hard position. The body experiences undereating as a state of famine or starvation. In this circumstance, the body must find a way to survive and keep all of our systems running smoothly. Given that the body cannot operate without the brain, it will go out of its way to prioritize brain function at all costs. 1

accessible energy is important

The brain needs a continuous supply of glucose to function. The food we eat is converted into blood glucose, aka blood sugar, for the body to use. Blood sugar is readily accessible and meant to provide in-the-moment energy to the body. 2

When all of the circulating blood sugar is used up, the body goes into a state called hypoglycemia (hypo- low, glycemia- sugar). When this happens, the body signals to us that more energy input is needed in the experience we know as hunger. Hunger communicates: “Energy supply is low! Please eat something”. We feel this communication in the form of grumbling tummy, hard to focus, “hangry”, headache, or fatigue. Hunger symptoms intensify the longer they are ignored. 3

In an ideal situation, we will respond to this hunger cue by eating food in order to replenish the body’s energy stores. But for people facing food insecurity, and for those engaging in restrictive eating, this response is interrupted. In both situations, the body is not receiving enough food input to produce enough energy to function properly.

Supporting the brain at all costs

On a physiological level, undereating goes like this: Once the body uses all available blood glucose, it will tap into stored glucose in the muscles and liver. The body is so intent upon having a continuous energy source for the brain to use that it will break down other systems and prioritize brain function. 4

During severe and long term food restriction, the body begins to eat away at muscle tissue and fat stores. Metabolic processes transform these molecules into usable energy for the brain. If food restriction continues and the body is not receiving enough external energy input, the body will eventually break down the muscle tissue of the heart. This can lead to heart failure and ultimately, death. 5

Restrictive Eating causes brain damage

We live in a world that promotes dieting and disordered eating so strongly that many people see restrictive eating as completely normal, harmless, or even ideal. But under eating is not innocuous- in other words, undereating is not harmless to the body. Undereating is harmful and damages the brain. Depriving the body of energy impacts day to day functioning and can cause long term damage. Below are some of the structural, functional, and long term impacts of undereating on the brain.

Your brain on Under Eating

Structural changes 6 7 8 9

Oxygen deprivation due to reduced heart rate
The brain shrinks in size including a reduction gray and white matter
Disrupted neurotransmitter behavior (a neurotransmitter is a kind of signaling chemical that is passes messages between nerves)
Alterations to the brain’s reward circuitry and a weaker response to this region firing
Alterations to the region of the brain that forms long term memories

Functional changes 10

Difficulty making decisions, thinking, and changing or prioritizing tasks
Impaired concentration and irrational thoughts
Obsessive thinking about food and weight
Reduced capacity for empathy, compassion and joy
Changes in the brain’s emotional centers which can lead to depression, irritability, and isolation
Increased prevalence of nerve related conditions including numbness in hands and feet and seizures
Loss of libido due to hormonal changes

Long term 11 12

Increased risk of dementia and cognitive decline
Heart failure and death. In a situation of severe restriction in which the body breaks down all other energy sources, the body will eventually break down heart tissue to keep the brain fueled.

I know this is a lot to take in

If you are currently undereating due to an eating disorder or disordered eating, I understand that this may be overwhelming to take in. I want to share with you that the body is incredibly resilient and doing its very best to keep you alive. And, restrictive eating does pose a significant risk to your health and wellbeing.

If you are struggling with your relationship to food and your body, I want to reassure you that healing your relationship to food and eating is possible. Not only this, but patient and consistent renourishment of the body over time can restore brain health and function in many ways.

If you or someone you know is engaging with restrictive eating and is ready to heal, reaching out for support is a great first step. If you are ready to begin nutrition therapy, I welcome you to reach out to begin on the path of healing today!

Thanks for being here and I hope this information empowers you! In Part 3 we will explore nutrition for brain health.

With Care & Solidarity,

Sydney