Underweight

Sabine Schrör is a freelance writer for the medical team. She studied business administration and public relations in Cologne. As a freelance editor, she has been at home in a wide variety of industries for more than 15 years. Health is one of her favorite subjects.

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Underweight can have many causes. Sometimes low weight just runs in the family. In other cases it is caused by stress, illness or eating disorders. Too low weight becomes medically relevant if it is associated with deficiency symptoms. Read more on the topic: When is you underweight? What are the possible causes and signs of being underweight? What are the consequences? And how do you treat underweight?

ICD codes for this disease: ICD codes are internationally recognized codes for medical diagnoses. They can be found, for example, in doctor's letters or on certificates of incapacity for work. R63

Brief overview

• Definition: According to the WHO, underweight is a body mass index (BMI) of less than 18.5. However, underweight is only medically relevant if there is evidence of a lack of nutrients.
• Symptoms: tiredness and listlessness if you are slightly underweight. If you are very underweight, e.g. poor concentration, slow wound healing, susceptibility to infection, osteoporosis, menstrual cycle disorders, muscle wasting. Life-threatening underweight exists with a BMI under 14.5.
• Causes: e.g. genetic predisposition, swallowing disorders, stress, depression, cancer, hyperthyroidism, drug or alcohol abuse, eating disorders.
• Diagnosis: based on the BMI. In addition, research into the cause in a doctor-patient conversation and, if necessary, with the help of examinations such as ultrasound and blood tests. The latter also help to identify deficiencies.
• Treatment: If you are slightly underweight, change your diet and provide nutritional advice. In the case of severe underweight: supply of nutrients via nasogastric tube or PEG tube, if necessary infusions with nutrient solution. In addition, gentle training to build muscle. In addition: Treatment of the underlying causes.

Underweight: definition

Being slim is considered an ideal of beauty, at least in the western world. But when does slimness become underweight? When it comes to this question, medical professionals use the Body Mass Index (BMI) as a guide. Accordingly, there is underweight with a BMI below 18.5. The BMI is calculated using a simple formula: body weight in kg divided by body height in m2.

Example: If someone who is 1.80 m tall weighs 75 kg, the BMI is 75: 1.802 = 23.15

In Germany, underweight is comparatively rare. Only around two percent of people over the age of 18 are affected. The situation is different in poorer regions of the world such as India or Africa. Mainly due to the widespread food shortage, a large section of the population is affected by underweight and deficiency symptoms.

Underweight: symptoms and consequences

Anyone who has a BMI of less than 18.5 and is therefore underweight is not automatically at risk for health. Underweight is only harmful if there is malnutrition. Then the body does not get enough nutrients such as proteins, fats, carbohydrates, vitamins and minerals.

The extent to which underweight triggers symptoms depends largely on its severity. The main signs of being slightly underweight are tiredness and listlessness.

Severely underweight shows further symptoms if it persists longer and is associated with a serious lack of nutrients. These include:

• limited physical and mental performance
• Poor concentration
• low muscle strength up to muscle wasting
• poor condition, rapid breathlessness with physical exertion
• slow wound healing
• Bone loss (osteoporosis)
• Water retention in the tissue (edema)
• increased susceptibility to infection
• in women: menstrual cycle disorders up to the complete absence of menstruation and infertility
• in men: infertility
• in children: restricted growth

Life-threatening underweight threatens with a BMI below 14.5, because then the brain metabolism is impaired. Being so severely underweight is dangerous and requires immediate medical attention.

Underweight: causes

The reasons for being underweight vary greatly from person to person. Some people are genetically very slim: They have a fast metabolism, so that they use the calories supplied with food particularly quickly and therefore do not or hardly gain any weight.

In the case of other underweight people, certain illnesses or physical or psychological stress are responsible for the low weight. Common causes of being underweight include:

• Loss of appetite: Especially in old age, many people have less appetite and therefore eat less food.
• Swallowing disorders, e.g. in diseases of the throat or esophagus
• Stress: Persistent negative stress can literally "hit your stomach" and spoil your appetite.
• Depression: Depressed people often have less appetite in the acute phases of their illness.
• Narrowing of the gastrointestinal tract, e.g. in cancer of the esophagus or stomach
• Crohn's disease, ulcerative colitis: These chronic inflammatory bowel diseases can reduce the absorption of nutrients in the intestine.
• Cancer diseases: Tumor diseases increase energy consumption; At the same time, those affected usually feel less appetite.
• Hyperthyroidism: The energy consumption increases due to an excess of thyroid hormones. Even people who have to take thyroid hormones because of an underactive thyroid, for example, can have an increase in energy requirements and become underweight.
• Drugs and alcohol abuse: Illegal substances such as cocaine, but also the legal drug alcohol, can also cause underweight in the long term.
• Eating disorders: Eating disorders such as anorexia nervosa or vomiting addiction (bulimia) occur particularly in adolescents. Depending on the severity of the disease, the associated weight loss can be life-threatening. Professional treatment of the underlying eating disorder is therefore very important.

Underweight: diagnosis

Underweight is diagnosed using the BMI. If it is below a value of 18.5, according to the criteria of the World Health Organization (WHO), the person is underweight.

Once the diagnosis has been made, the next step is to determine the underlying causes in order to derive the appropriate therapy. For this, the doctor can use various examination methods after an initial consultation (anamnesis):

With imaging methods such as ultrasound or magnetic resonance imaging (magnetic resonance imaging, MRT), pathological changes in the gastrointestinal tract or esophagus can be detected, for example. Blood tests provide information about the nutritional status and nutrient supply.

Underweight: treatment

The treatment of underweight depends on the one hand on the causes of the reduced body weight. If, for example, there is a disease behind it, it must be treated. If stress triggers excessive weight loss, relaxation techniques and / or psychological treatment can help to develop more calmness and to practice dealing with stressors more positively.

On the other hand, the treatment depends on the severity of the underweight.

Slightly underweight

Mild underweight can often be treated at home with the help of a professionally supervised change in diet. A nutrition plan, which can be drawn up by a nutritionist, helps.

Tips for those who are slightly underweight:

• Eat what you like. But make sure you eat a wholesome diet according to the recommendations of the German Nutrition Society (DGE).
• It is easier to have five small meals than three large ones.
• Prefer energy and nutrient dense foods like nuts and bananas.

Seriously underweight

Those affected can hardly get a grip on severe underweight alone. Treatment under medical supervision in the hospital is usually required. Those affected are supplied with nutrients via a nasogastric tube in order to slowly increase their weight.

Clinical treatment for severely underweight is indicated, not least in view of the so-called refeeding syndrome: If the calorie increase is too rapid, severely underweight people can develop electrolyte disorders and a vitamin B1 deficiency. They also excrete too little water and sodium, while ammonia levels rise. All of this can seriously disrupt the functioning of the organs - up to and including organ failure.

Refeeding syndrome can be avoided through gentle treatment with a slow increase in daily calorie intake.

If there are problems with the intake of food through the mouth or nose, a so-called PEG tube can be used, which feeds nutrients directly into the stomach. Infusions with nutrient solutions are also suitable in these cases.

In addition, moderate exercise can promote muscle building if you are underweight.

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