Unit 12. Food and Nutrition Issues

12.5 Malnutrition and Underweight

For many, the word “malnutrition” produces an image of a child in a third-world country with a bloated belly, and skinny arms and legs. However, this image alone is not an accurate representation of the state of malnutrition. For example, someone who is 150 pounds overweight can also be malnourished.

Malnutrition refers to one not receiving proper nutrition and does not distinguish between the consequences of too many nutrients or the lack of nutrients, both of which impair overall health.

There are two basic types of malnutrition. The first is macronutrient deficiency and relates to the lack of adequate protein, which is required for cell growth, maintenance, and repair. The second type of malnutrition is micronutrient deficiency and relates to inadequate vitamin and mineral intake.[1] Even people who are overweight or obese can suffer from this kind of malnutrition if they eat foods that do not meet all of their nutritional needs.dernutrition is characterized by a lack of nutrients and insufficient energy supply, whereas overnutrition is characterized by excessive nutrient and energy intake. Overnutrition can result in obesity, a growing global health threat. Obesity is defined as a metabolic disorder that leads to an overaccumulation of fat tissue.

Although not as prevalent in America as it is in developing countries, undernutrition is not uncommon and affects many subpopulations, including the elderly, those with certain diseases, and those in poverty. Many people who live with diseases either have no appetite or may not be able to digest food properly. Some medical causes of malnutrition include cancer, inflammatory bowel syndrome, AIDS, Alzheimer’s disease, illnesses or conditions that cause chronic pain, psychiatric illnesses, such as anorexia nervosa, or as a result of side effects from medications. Overnutrition is an epidemic in the United States and is known to be a risk factor for many diseases, including Type 2 diabetes, cardiovascular disease, inflammatory disorders (such as rheumatoid arthritis), and cancer.

Health Risks of Being Underweight

The 2015–2016 National Health and Nutrition Examination Survey (NHANES) estimated that 1.5 percent of adults [2] and 3.0 percent of children and adolescents in the United States are underweight. [3]   Underweight individuals represent a small portion of Americans, yet the health risks associated with being underweight are an essential part of the discussion on nutrition and health.

Being underweight is linked to nutritional deficiencies, especially iron-deficiency anemia, and other problems such as delayed wound healing, hormonal abnormalities, increased susceptibility to infection, and increased risk of some chronic diseases such as osteoporosis. In children, being underweight can stunt growth.

Wasting diseases, such as cancer, multiple sclerosis, tuberculosis, may result severe loss of weight. People with wasting diseases are encouraged to seek nutritional counseling, as a healthy diet significantly affects survival and improves responses to disease treatments.  However,  the most common underlying cause of being skinny in America is inadequate nutrition, which often results from a person intentionally restricting caloric intake due to an eating disorder as discussed in the next section. 

Eating Disorders

The National  Association of Mental Disorders defines eating disorders as “serious and sometimes fatal illnesses that cause severe disturbances to a person’s eating behaviors.”[4] People with eating disorders often experience a preoccupation with food choices and body weight. They frequently have a distorted body image, believing that self-worth is tied to body size and shape.[5]

Eating disorders that result in individuals being underweight affect about eight million Americans (seven million women and one million men). And eating disorders have the second-highest mortality rate of mental illnesses, outranked only by opioid addiction. [6] Prevention and proper treatment of eating disorders must involve a multi-faceted approach, including physical, emotional, and social issues related to each individual’s needs.[7]

A young woman with a worried look on her face is squatting down while standing on a bathroom scale.

Anorexia Nervosa

Anorexia nervosa is often incorrectly referred to as “anorexia,” a word which means lack of appetite.   Because the condition is a  psychiatric illness, most health and nutrition professionals use the actual term, anorexia nervosa.

Description and prevalence of anorexia nervosa

Anorexia nervosa is characterized by an extremely low body weight,  a distorted body image, and a fear of gaining weight.   Anorexia nervosa results in extreme nutrient inadequacy and eventually organ malfunction. It is relatively rare—the NIMH reports that 0.9 percent of females and 0.3 percent of males will have anorexia at some point in their lifetime, but it is an extreme example of how an unbalanced diet can affect health.15 

Anorexia  nervosa frequently manifests during adolescence, although it may emerge much later in adulthood. People with the condition consume, on average, fewer than 1,000 calories per day and exercise excessively. They are in a tremendous caloric imbalance. Moreover, some may binge eat,  followed by purging with self-induced vomiting and using laxatives or enemas. The exact causes of anorexia are  unknown, but many things contribute to its development. It is most prevalent in high-income families. It is a genetic disease often passed from one generation to the next. Complications during fetal development and abnormalities in the brain, endocrine system, and immune system may contribute to the illness’s development.

Signs and symptoms of anorexia nervosa

The primary signs and symptoms  are:

  • Fear of being overweight.
  • Extreme dieting.
  • An unusual perception of body image.
  • Depression.

The secondary signs and symptoms  are all related to the caloric and nutrient deficiencies of the unbalanced diet and include:

  • Excessive weight loss.
  •  A multitude of skin abnormalities.
  • Diarrhea.
  • Osteoporosis.
  • Liver, kidney, and heart failure.

Diagnosis and treatment of anorexia nervosa

No physical test can diagnose anorexia and distinguish it from other mental illnesses. Therefore, a correct diagnosis involves eliminating other mental illnesses, hormonal imbalances, and nervous system abnormalities.

Treatment of any mental illness involves not only the individual, but also family, friends, and a psychiatric counselor. Treating anorexia often includes a nutritionist who helps to provide dietary solutions that are adjusted over time. The treatment goals for anorexia are to restore a healthy body weight and significantly reduce the weight obsession and behaviors associated with the eating disorder. Relapse to an unbalanced diet is high. Many people recover from the disease; however, most continue to have lower-than-normal body weight for the rest of their lives.

Bulimia Nervosa

Bulimia nervosa  is also a psychiatric illness that can have severe health consequences.[8]

Description and prevalence of bulimia nervosa

Bulimia nervosa is characterized by episodes of eating large amounts of food followed by purging, which is accomplished by vomiting or use of laxatives and diuretics. Unlike people with anorexia, those with bulimia nervosa often have a normal weight, making the disorder more difficult to detect and diagnose. The NIMH reports that 0.5 percent of females and 0.1 percent of males will have bulimia at some point in their lifetime.

Signs and symptoms of bulimia nervosa

The primary  signs and symptoms are similar to anorexia:  fear of being overweight, extreme dieting, and bouts of excessive exercise.

Secondary ones include gastric reflux,  tooth enamel erosion, dehydration, electrolyte imbalances, lacerations in the mouth from vomiting, and peptic ulcers. Repeated damage to the esophagus puts people with bulimia at an increased risk for esophageal cancer.

Diagnosis and treatment of bulimia nervosa

Like anorexia, there are no  physical tests that can be used to diagnose bulimia and distinguish it from other mental illnesses. Therefore, a correct diagnosis involves eliminating other mental illnesses. The disorder is also highly genetic, linked to depression and anxiety disorders, and mainly occurs in adolescent girls and young women.

Treatment often involves antidepressant medications and, like anorexia, has better results when both the family and the individual with the disorder participate in nutritional and psychiatric counseling.

This photo shows an open mouth with both the upper teeth and lower teeth in view. The lower teeth show erosion caused by bulimia. For comparison, the upper teeth were restored with porcelain veneers.

Figure 12.6. This photo shows the erosion of the lower teeth caused by bulimia. For comparison, the upper teeth were restored with porcelain veneers.


Binge-Eating Disorder

Like those who experience anorexia and bulimia, people with the  binge-eating disorder have lost control over their eating. This disorder was only recently classified as a distinct psychiatric illness, becoming formally recognized as a diagnosable eating disorder in 2013.

People with binge-eating disorder will periodically overeat to the extreme, but their loss of control over eating is not followed by fasting, purging, or compulsive exercise. As a result, people with this disorder are often overweight or obese. Their chronic disease risks are those linked to an abnormally high BMI,  such as hypertension, cardiovascular disease, and type 2 diabetes. Additionally, they often experience guilt, shame, and depression. Binge-eating disorder is commonly associated with depression and anxiety disorders.

According to the NIMH, binge-eating disorder is more prevalent than anorexia and bulimia. It affects almost 3 percent of individuals at some point during their lifetime.15 Treatment often involves antidepressant medication as well as nutritional and psychiatric counseling.

Other Specified Feeding or Eating Disorders (OSFED)

Many individuals have an eating disorder that does not meet the strict psychiatric diagnostic criteria of the three eating disorders described above. Therefore, the American Psychiatric Association developed  the category Eating Disorder Not Otherwise Specified (EDNOS) and  was  considered a “catch-all” for conditions that did not precisely meet the criteria of other disorders. The name ENDOS was  changed to Other Specified Feeding or Eating Disorder (OSFED) in 2013.   OSFED  is a serious, life-threatening, and treatable disorder like the other eating disorders.

Conditions under this category include:

  • Atypical anorexia nervosa  (weight loss is in the normal range)
  • Binge eating disorder of low frequency and limited duration
  • Bulimia nervosa of low frequency and limited duration
  • Purging disorder  (purging without binge eating)
  • Night eating syndrome (excessive eating after the  evening meal or waking from sleep to eat)


 Avoidant Restrictive Food Intake Disorder

Avoidant restrictive food intake disorder (ARFID) was  previously known as a selective eating disorder. It is characterized by individuals limiting the types and amounts of foods they will consume. Unlike anorexia nervosa, people with ARFID are not afraid of gaining weight and do not have a distorted body image or extreme fear of gaining weight  

Generally, the onset is  during middle childhood instead the teen or early adult years like eating disorders.   Many children go through phases of picky eating.  However, the picking eating continues and  worsens for those diagnosed with ARFID.  They eventually  do not eat enough calories to grow and develop properly. If not treated,  the condition may persist into adulthood.

Signs and symptoms of ARFID include:

  • Dramatic restriction of types or amount of food eaten
  • Lack of appetite or interest in food
  • Dramatic weight loss
  • Limited number of foods eaten


Orthorexia  was first defined in 1998, but it has yet to be formally  classified by the American Psychiatric Association as an eating disorder, making it difficult to determine how prevalent it is. Research suggests it may be identified as a form of obsessive-compulsive disorder.19 While focusing on a healthy diet isn’t inherently a bad thing, in orthorexia situations, the individual emphasizes  healthy eating, or “clean” eating, to the extreme.  Healthy eating  becomes a fixation, putting their health at risk.19 

Although awareness of orthorexia nervosa is increasing, it is not formally recognized in the Diagnostic Statistical Manual and thus it is difficult to get an estimate of how many persons are affected by orthorexia nervosa. Additionally, the lack of formal diagnostic criteria makes it impossible to know if orthorexia nervosa occurs with other types of existing disorders like anorexia or a form of obsessive-compulsive disorder (OCD) or if it’s a stand-alone eating disorder. Studies show that many persons with orthorexia nervosa also have OCD. Many experts view orthorexia nervosa as a variety of anorexia or OCD. Treatment usually involves psychotherapy and weight restoration as needed.[9] OCD may be a consequence of malnutrition, being underweight and a starved brain thus weight restoration may resolve the OCD.

Warning signs and symptoms of orthorexia nervosa:[10]

    • Compulsive checking of ingredients lists and nutritional labels
    • An increased concern about the health of ingredients
    • Cutting out an increasing number of food groups such as all sugars, all carbohydrates, all dairy or all animal products
    • An inability to eat anything but a narrow group of foods that are deemed ‘healthy’ or ‘pure’
    • Unusual interest in the health of what others are eating
    • Spending hours per day thinking about what food might be served at upcoming events
    • Showing high levels of distress when ‘safe’ or ‘healthy’ foods are not available
    • Obsessive following of food and ‘healthy lifestyle’ blogs on social media
    • Body image concerns may or may not present

Signs and symptoms of orthorexia

Signs of orthorexia include compulsively reading food labels, cutting several food groups out of the diet, spending an unusual amount of time focusing on what foods may be available at upcoming events, and experiencing a high level of stress when healthy foods are not available. The obsession with healthfulness comes with a high social cost as it is often difficult to enjoy eating out or sharing meals with friends and family.

Treatment of orthorexia

There is no formal treatment plan for orthorexia, but many eating disorder experts treat it similarly to anorexia and obsessive-compulsive disorder.[footnote]Orthorexia. (2018). National Eating Disorder Association. Retrieved November 7, 2019, from https://www.nationaleatingdisorders.org/learn/by-eating-disorder/other/orthorexia.[/footnote]

If you think you or someone close to you might have an eating disorder and you want to learn more or find resources for help, check out these organizations and links.


Learning Activities

Technology Note: The second edition of the Human Nutrition Open Educational Resource (OER) textbook features interactive learning activities.  These activities are available in the web-based textbook and not available in the downloadable versions (EPUB, Digital PDF, Print_PDF, or Open Document).

Learning activities may be used across various mobile devices, however, for the best user experience it is strongly recommended that users complete these activities using a desktop or laptop computer.



  1. Hunger in America: 2016 United States Hunger and Poverty Facts. World Hunger Education Service. Retrieved from http://www.worldhunger.org/articles/Learn/us_hunger_facts.htm. Accessed April 15, 2018.
  2. Prevalence of underweight among adults aged 20 and over: United States, 1960–1962 through 2015–2016. (2018). Centers for Disease Control and Prevention. Retrieved November 4, 2019, from https://www.cdc.gov/nchs/data/hestat/underweight_adult_15_16/underweight_adult_15_16.htm.
  3. Prevalence of underweight among children and adolescents aged 2–19 years: United States, 1963–1965 through 2015–2016. (2018). Centers for Disease Control and Prevention. Retrieved November 4, 2019, from https://www.cdc.gov/nchs/data/hestat/underweight_child_15_16/underweight_child_15_16.pdf.
  4. Eating disorders. (2017). The National Institute of Mental Health. Retrieved November 4, 2019, from https://www.nimh.nih.gov/health/statistics/eating-disorders.shtml#part_155061.
  5. Body image. (2018). National Eating Disorder Association. Retrieved November 4, 2019, from https://www.nationaleatingdisorders.org/toolkit/parent-toolkit/body-image.
  6. Statistics and research on eating disorders. (2018). National Eating Disorder Association. Retrieved November 4, 2019, from https://www.nationaleatingdisorders.org/statistics-research-eating-disorders.  
  7. Prevention. (2018). National Eating Disorder Association. Retrieved November 4, 2019, from https://www.nationaleatingdisorders.org/learn/general-information/prevention
  8. Bulimia nervosa. National eating disorders Association.  Retrieved on February 3, 2022 from https://www.nationaleatingdisorders.org/learn/by-eating-disorder/bulimia
  9. Orthorexia. (2017, February 26). National Eating Disorders Association. https://www.nationaleatingdisorders.org/learn/by-eating-disorder/other/orthorexia 
  10. Orthorexia. (2017, February 26). National Eating Disorders Association. https://www.nationaleatingdisorders.org/learn/by-eating-disorder/other/orthorexia 


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Introduction to Nutrition and Wellness Copyright © 2022 by Janet Colson; Sandra Poirier; and Yvonne Dadson is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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