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  • BMI Criteria For Anorexia Nervosa | An Ultimate Guide
June 24, 2022

Anorexia nervosa is a serious mental illness that can devastate someone’s health, both physically and psychologically. While many different factors contribute to the development of anorexia nervosa, one of the key diagnostic criteria is having a low body mass index (BMI). In this article, we will discuss the BMI criteria for anorexia nervosa and the potential consequences of this eating disorder.

What is BMI?

Body mass index (BMI) measures body fat based on height and weight. It is a screening tool to identify possible weight problems, but it is not a diagnostic tool. A person’s BMI can be calculated using a BMI chart or a BMI calculator.

It is important to note that BMI is not a perfect measure of body fat. For example, it does not consider muscle mass or bone density. However, it is a reliable indicator of body fatness for most people.

Also, keep in mind that BMI varies by age and sex. For example, a BMI of 25 for a man may indicate overweight, while the same BMI for a woman may indicate obesity.

The Criteria For Anorexia Nervosa

The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) lists the following criteria for anorexia nervosa:

  • Restricting energy intake relative to requirements leads to significantly low body weight in the context of age, sex, developmental trajectory, and physical health. Weight loss must occur when the individual is not dieting despite efforts to maintain weight.
  • Intense fear of gaining weight or becoming fat, even though underweight.
  • Disturbance in how one’s body weight or shape is experienced, undue influence of body weight or shape on self-evaluation, or denial of the seriousness of low body weight.
  • In postmenarcheal females (women who have begun to menstruate), amenorrhea is the absence of at least three consecutive menstrual cycles. A woman is considered amenorrhea if she has not had her period for more than 90 days and is not breastfeeding or pregnant. Nor does she have a medical condition that causes amenorrhea (e.g., polycystic ovarian syndrome)

To be diagnosed with anorexia nervosa, an individual must meet all of the above criteria. In addition, the individual’s BMI must be less than 17.5 or, if their BMI is unknown, they must have lost at least 15% of their body weight.


BMI Criteria For Anorexia Nervosa

BMI, or body mass index, is a way to quantify whether someone is at a healthy weight. BMI is calculated by dividing a person’s weight in kilograms by their height in meters squared. For adults, a BMI of 18.5 to 24.9 is considered healthy, 25 to 29.9 is considered overweight, and 30 or above is considered obese. However, these ranges are different for children and teens, as they are still growing and their bodies are not yet fully developed.

To be diagnosed, a person must have BMI criteria for anorexia nervosa below a certain threshold. For adults, this threshold is typically 17.5. For children and adolescents, the BMI threshold is lower as they are still growing and their bodies are not yet fully developed. The specific BMI threshold varies depending on the individual’s age and sex.

Anorexia is a condition that causes people to weigh 15% or more below the expected weight for their age, sex, and height. The body mass index (BMI) calculation is done by taking an individual’s weight in kilograms and dividing it by the square of their height in meters.

An example would be if someone weighed 66 kg and was 1.7 m tall, their BMI would be 22.8. A “normal” BMI for an adult is considered to be 18.5-25; anything above that is considered overweight, and anything below is considered underweight. For adults with anorexia, their BMI must be below 17.5. If someone is under 18 years of age, a different chart must be consulted to see what their normal weight should be.

It is important to note that BMI is not a perfect measure of someone’s health. Muscle mass, for example, can make a person’s BMI higher than it would be if they had the same weight but less muscle mass. However, BMI is still useful for doctors to assess whether a person is at a healthy weight.

Health Risks Of Low BMI And Anorexia Nervosa

For someone with anorexia nervosa, body weight and shape are extremely important. Maintaining low body weight is often more important than anything else, even if it means making oneself sick or risking death.

Most people with anorexia nervosa have a very low body mass index (BMI). BMI is a measure of body fat based on height and weight. A BMI below 17.5 is considered severe malnutrition.

Anorexia nervosa is a serious mental illness that can have devastating physical consequences. People with anorexia nervosa may suffer from:

1. Chemical Imbalances In The Body

Frequent vomiting or laxative use can lead to dehydration and an electrolyte imbalance. This can cause irregular heartbeat, heart failure, and low blood pressure.

2. Gastrointestinal Problems

Constipation is common in people with anorexia nervosa. This can be caused by a lack of nutrients and fiber in the diet and dehydration. People with anorexia nervosa may also suffer bloating, stomach pain, and nausea due to self-induced vomiting.

3. Musculoskeletal Problems

Osteoporosis is a common complication of anorexia nervosa. This is a condition where the bones become weak due to a loss of bone density. People with anorexia nervosa may also experience muscle weakness and joint pain.

4. Reproductive Health Problems

Anorexia nervosa can disrupt the normal function of the reproductive system. This can lead to missed periods, irregular periods, and infertility. In males, low testosterone levels may result in sexual dysfunction and loss of muscle mass.

5. Skin Problems

People with anorexia nervosa may experience dry skin, yellowing skin, and brittle nails. They may also have a downy growth of hair on their body (lanugo) due to malnutrition.

6. Sleep Problems

Anorexia nervosa can cause insomnia and other sleep problems. This may be due to the physical effects of the illness, as well as anxiety and stress. It is the opposite of binge eating disorders Bulimia nervosa.

7. Social Isolation

People with anorexia nervosa may withdraw from friends and family. They may also avoid social situations where food is present. This can lead to feelings of isolation and loneliness.

8. Weight Loss

People with anorexia nervosa may lose a significant amount of weight. This can lead to malnutrition, organ damage, and death.

Anorexia nervosa is a serious mental illness that requires treatment. If you or someone you know has anorexia nervosa, seek professional help as soon as possible.

BMI Criteria For Anorexia Nervosa

How To Improve BMI And Deal With Anorexia Nervosa?

The first step for the treatment of anorexia nervosa is to improve the body mass index (BMI) to a healthy level. The ideal BMI is between 18.5 and 24.9 kg/m2. For someone with anorexia nervosa, they aim to reach 85% of their ideal body weight. This requires a slow and steady weight gain of about 0.5 to 1 kg per week.

The weight gain rate will differ for each person and will depend on factors such as age, height, current BMI, and how long they have been underweight. A dietitian or doctor can help determine the best weight gain rate for each individual.

  • Treatment for anorexia nervosa often requires a team approach. This may include a dietitian, doctor, counselor, and psychiatrist. The goal of treatment is to reach a healthy BMI, restore menstrual periods in women, and improve overall physical and mental health.
  • Medications may be used to help with some of the symptoms associated with anorexia nervosa. These can include anxiety, depression, and obsessive-compulsive disorder (OCD). Antidepressants are the most commonly prescribed medication for people with anorexia nervosa.
  • Counseling or therapy can also help treat anorexia nervosa. This can provide support and guidance in dealing with the thoughts and behaviors associated with the eating disorder. Family therapy may also be recommended.


Anorexia nervosa is a serious eating disorder that can have life-threatening consequences. Individuals with anorexia nervosa may try to maintain very low body weight by starving themselves or exercising excessively. It is more common in females than males and it often starts during the teenage years.

Recovery from anorexia nervosa requires comprehensive treatment that addresses all aspects of the illness. If you or someone you know is struggling with anorexia nervosa, please seek professional help.

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