How Malnourishment Affects the Brain: Research on Anorexia and Neurobiology

Humans are instilled with a survival instinct. Our bodies are made to survive — we instinctually breathe, blink, sneeze, and even jump from the path of moving vehicles. This fact makes anorexia perplexing to many. How can people starve themselves, sometimes to the point of death, while many, if not most, others struggle to stay on a small diet?

The answer is unknown, really. Research has honed in on several risk factors for anorexia, including genetics, environment, emotional stability, and perhaps most fascinating, the brain.

The brains of those with and recovered from anorexia have subtle but impactful differences from those who have never struggled with the disorder. The brains of people with anorexia have a different reward response, react differently to feedback, and have altered serotonin pathways.

puzzle that looks like a brain

Do Brain Changes Occur Before Physical Changes?

These differences are found not just in people who are actively anorexic but also in people long recovered from the disease. So nobody is certain if these neurobiological differences are present before someone becomes anorexic and are physical predictors of the illness or if these neurobiological differences are “scars” from prolonged starvation.

Clinically, individuals with anorexia have difficulty experiencing pleasure, but when compared to non-anorexics, they more easily abstain from pleasurable experiences — not only the after-dinner dessert but also most pleasures in life1.

Also, people with this eating disorder struggle to enjoy a reward because they’re too worried about the consequences, according to a paper by Walter Kaye, who has studied the neurobiological element of anorexia for some time2. This makes sense: the after-dinner dessert isn’t worth the anxiety it would cause.

Brains of Anorexics Respond Differently to Food Stimuli

In fact, the brains of people who have or had anorexia don’t even respond to food, or pictures of it, like control groups.

When given sugar, people who are recovered from anorexia show less brain activity than other people who like sugar and have never had an eating disorder, leading researchers to believe those with anorexia get less pleasure from food3.

The same researchers performed a well-known “guessing-game” protocol, where people can win or lose money, on people recovering from anorexia and on healthy controls.

The control group had very different neural brain activity for winning money than they did for losing money; but the group that recovered from anorexia had similar brain reactions to both winning and losing, the researchers found.

These results suggest people with anorexia may have trouble distinguishing between positive and negative feedback, the researchers wrote, which “could help explain why it is so tough to motivate them to go into treatment or appreciate the consequences of their behaviors.”


The Parts of the Brain that Are Affected By Eating Disorders

Kaye cites imaging data that show the brains of those with anorexia and those recovered from the illness have an under-active limbic circuity, which relates to feeling the reward, and an operatic executive neural circuity, which relates to inhibition. “That is,” Kaye writes, “ill persons with AN (anorexia nervosa) tend to perceive their actions as incorrect or flawed and are highly sensitive to criticism, rather than being able to appropriately proportion reward and punishment in order to learn from experience.”

The brains of people with this eating disorder also have a persistent disturbance of 5-HT (serotonin) neuronal systems that may be related to increased anxiety (Bailer, et al, 2005). Again, it’s unknown whether this defect was caused by or contributes to the disease.

If science can, in fact, delineate the neurobiological link to anorexia, then we may learn how to better treat the illness, which has the highest mortality rate of any mental illness. However, anorexia is a somewhat baffling condition in that it attacks both the mind and body.

Some neurological symptoms can be the result of self-starvation and low body-mass index indicative of an anorexic. For example, excessive weight loss can cause shrinkage of the brain’s gray matter4.

Also, people underweight due to this eating disorder scored higher for depression, anxiety, and obsessiveness than those with anorexia who had restored weight5. All of these symptoms, including loss of brain mass, improved with weight restoration.

Pain in Headaches

When Do Anorexia Symptoms Become Starvation Symptoms?

So where do symptoms of the disorder start and symptoms of starvation begin? Some insight is provided by a 65-year-old study of 36 young, healthy, and physiologically normal men, who were given the opportunity, instead of military service, to volunteer for a study on the effects of starvation6.

Researchers “semi-starved” (reduced their caloric intake by half) the young men for 6 months, and then monitored the young men for a 3-month-long refeeding period.

The men exhibited behaviors very similar to those who self-starve with an eating disorder. Not only were they preoccupied with food, but they also became more depressed and anxious. One subject of the study wrote: “I have never been more depressed in my life.”


  1. Bailer, U., Frank, G., Henry, S., et al. (2005). Altered brain serotonin 5-HT1A receptor binding after recovery from anorexia nervosa measured by positron emission tomography and [11C]raclopride. Archives of General Psychiatry, 62(9), 1032-1041.
  2. Kaye, W. (2014, May 6). Eating disorders: Understanding anorexia nervosa. Retrieved July 9, 2015.
  3. Kaye, W., Bailer, U., Klabunde, M., Brown, H. Is anorexia an eating disorder? How neurobiology can help us understand the puzzling eating symptoms of anorexia nervosa. University of California San Diego Medical Center, Department of Psychiatry.
  4. Bryner, J. (2010, May 26). Brain Shrinkage in Anorexia Is Reversible. Retrieved July 9, 2015.
  5. Pollice, C., Kaye, W., Greeno, C., Weltzin, T. (1997). Relationship of depression, anxiety, and obsessionality to state of illness in anorexia nervosa. International Journal of Eating Disorders 21, 367–376.
  6. Keys, A. Br’ozek, J, Henschel, A, et al. The biology of human starvation. Vols 1 and 2. Minneapolis: University of Minnesota Press, 1950.

About the Author:

Leigh Bell holds a Bachelor of Arts in English with minors in Creative Writing and French from Loyola Marymount University in Los Angeles. She is a published author, a journalist with 15 years of experience, and a recipient of the Rosalynn Carter Fellowship for Mental Health Journalism. Leigh is recovered from a near-fatal, decade-long battle with anorexia and is the mother of three young, rambunctious children.

Last Updated & Reviewed By: Jacquelyn Ekern, MS, LPC on February 18, 2020
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