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Video: Underweight

Video: Underweight
Video: Health Topics: How does being underweight affect pregnancy? 2023, December


About six percent of the world's population is underweight. From a global perspective, food shortages are the most important causes. In Austria, around two percent of the population is affected. These are mainly women under the age of 50. This is due, among other things, to some diseases (e.g. hyperthyroidism), which are more common in women at this age. However, despite many counter-initiatives in recent years, the socially recognized and desired body image of the thin, girlish woman still plays an important role.

Beyond the age of 70, the risk of developing underweight also increases again somewhat. The most common causes include depression and multimorbidity - i.e. the simultaneous presence of several diseases.


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  • What causes can be underweight?
  • What are the symptoms?
  • How is underweight diagnosed?
  • How is underweight treated?
  • Whom can I ask?
  • How are the costs going to be covered?

What causes can be underweight?

The many causes for the development of underweight have one thing in common: the body has less energy (substrate) available than it needs to fulfill its functions. The causes can be divided into three groups:

Inadequate food intake e.g

  • loss of appetite: depression, pain, stress, certain medications (e.g. chemotherapeutic agents), smoking, some illegal drugs (e.g. cocaine and ecstasy) and alcoholism, stomach, liver and gall bladder diseases;
  • after serious injuries or extensive operations;
  • from injuries and diseases of the brain;
  • from injuries or diseases of the mouth, throat or jaw;
  • with swallowing disorders;
  • through narrowing of the gastrointestinal tract: gastric and esophageal cancer, narrowing in the esophagus (esophageal stenosis) or at the stomach outlet (pyloric stenosis);
  • in case of malnutrition - during sport, through low-energy diets or fasting;
  • in case of malnutrition of the unborn child: due to malnutrition of the mother, injuries to the placenta, poor blood circulation in the placenta (eg when smoking during pregnancy), alcohol during pregnancy;
  • in the case of neglect of children and old or sick people by caregivers;
  • in case of food shortages.

Decreased nutrient absorption in the intestine, e.g

  • in Crohn's disease and ulcerative colitis;
  • Genetically caused enzyme malformation or a genetically determined enzyme deficiency (e.g. lactose intolerance, celiac disease);
  • with certain parasite infections.

Note These diseases only lead to underweight if the disease is severe.

Increase in energy expenditure (catabolism) e.g.:

  • for chronic diseases that cost a lot of energy (consuming diseases): - e.g. cancer or certain infections (e.g. tuberculosis, AIDS); with chronic obstructive pulmonary disease (COPD) - high energy expenditure due to difficult breathing (mostly with reduced food intake at the same time);
  • from certain medications (e.g. thyroid hormones);
  • in metabolic diseases: predominance of hormones that increase energy expenditure (e.g. thyroid hormones in hyperthyroidism).

eating disorder

All three of the above groups of causes can play a role in anorexia nervosa. The eating-vomiting addiction (bulimia) is characterized by the ingestion of large amounts of food and the subsequent self-induced vomiting. Laxatives are often taken as well. The aim is to lose energy. Depending on how much energy those affected with bulimia absorb or lose, they can be underweight as well as normally or rarely overweight.

Note Underweight can also be genetic. In this case it is seldom a disease.

What are the symptoms?

The imbalance between food intake and nutrient consumption usually leads to an undersupply of important nutrients (malnutrition). These include proteins, carbohydrates, saturated and unsaturated fatty acids, vitamins and trace elements.

Note Malnutrition refers to a generally reduced intake of food or an insufficient intake of individual important food components (e.g. vitamins, trace elements or protein). Therefore normal and overweight people can also be malnourished.

Those affected do not always notice symptoms if they are slightly underweight. Often, however, mental disorders such as tiredness, exhaustion and listlessness occur.

Severe underweight goes hand in hand with a pronounced lack of nutrients. This reduces physical and mental performance. Muscle strength decreases and the affected person becomes out of breath more quickly. The risk of developing infectious diseases is higher, illnesses are generally more severe, and complications are more common among the underweight. They also recover more slowly after illness. Wounds also heal worse. Severely underweight people often suffer from concentration and memory problems.

If a nutritional deficiency develops as part of a severe chronic illness, body composition changes after a while. A loss of skeletal muscles and / or fatty tissue can be observed. Pronounced emaciation due to the loss of lean body mass and fat mass is called cachexia.

A lack of protein can lead to the development of edema. Body fat isolates the body from the cold. Since the body fat percentage is low, underweight people freeze more easily than those of normal weight.

In women, the menstrual cycle becomes irregular; if you are severely underweight, the menstrual cycle stops (amenorrhea). Underweight women and men can suffer from fertility problems or even infertility.

If you are underweight for a long time, osteoporosis often develops. Organs - such as the heart, liver or kidneys - can also be damaged.

How is underweight diagnosed?

The diagnosis begins with the calculation of the body mass index (BMI) in order to be able to assess the extent of the underweight and to document an initial value for the therapy control. According to the criteria of the World Health Organization (WHO), the threshold for underweight was set from a BMI below 18.5 kg / m². In children, weight is assigned percentiles based on age. In addition, the mean upper arm circumference can be measured. Here, too, there are age-dependent normal values. If the cause is not known, the doctor makes a note of the patient's medical history and living conditions and then initiates detailed examinations. Depending on how severe the underweight is, the diagnosis is carried out by a resident doctor or in a hospital.

Various laboratory tests can provide information about the cause, but also about the consequences of the lack of energy and nutrients. Imaging methods - e.g. ultrasound, computed tomography (CT) or magnetic resonance tomography (MRT) - are also used if necessary. Information on imaging procedures can be found here.

How is underweight treated?

The therapy is carried out at home or in the hospital, depending on the severity of the underweight. In addition to treating the cause of the underweight, nutritional therapy is started. If you are slightly underweight, a change in diet is initiated. In most cases, the person affected works out a nutrition plan together with a dietician. When eating food, attention is paid to the intake of high amounts of energy and sufficient nutrients.

Diet recommendations for underweight:

  • Prefer foods with a high energy density: eg fruit juices, nuts, bananas;
  • at least five small meals - large meals often cause nausea and general malaise;
  • whole food (see: food pyramid);
  • less consumption of “empty” foods rich in fat or sugar with a low content of vitamins, minerals or fiber (eg chips or lemonade);
  • Consideration of individual preferences.

Note The units for the energy content of food are kilocalories (kcal) or kilojoules (kJ).

If you are severely underweight, food is also given through energy-dense food supplements or through the nasal tube (nasogastric tube). If food cannot be ingested through the mouth or the esophagus in the long term, it can be fed through a PEG tube. For this purpose, an artificial connection between the abdominal wall and stomach is established as part of an endoscopic procedure. A closable gastric tube is inserted through this connection and then fixed. This allows food to be administered directly into the stomach. If food ingestion through the mouth or gastrointestinal tract is not possible, nutrient solutions can also be administered via infusions into a vein. This form of nutrition is called parenteral nutrition.

Exercise is beneficial for weight gain if it does not use too much energy. After physical activity, protein or carbohydrates should be supplied within two hours in order to ensure sustainable muscle building and replenishment of the carbohydrate stores (glycogen stores). Muscle strengthening exercises support muscle building. Stretching exercises can relieve tension and are generally relaxing. Accompanying memory training accelerates the regression of memory disorders.

For people who depend on the support of other people, a change in the care situation may be necessary. Sometimes this is the only way to achieve a satisfactory gain in weight or the maintenance of normal weight. Then it is necessary to organize helpers or accommodation in a care facility. Children and young people can be supported by the youth welfare office. Elderly and sick people in need of help receive support from a social worker.

Treatment problems

When a nutrient supply is restarted, a so-called refeeding syndrome can occur. Serious disturbances of the electrolyte balance as well as a lack of vitamin B1 (thiamine) develop and there is a reduction in the excretion of water and sodium. The ammonia level can also rise through protein intake. Refeeding syndrome is characterized by various severe, potentially life-threatening organ dysfunction. Therefore, the treatment of severe underweight must always take place under medical supervision. The development of a refeeding syndrome can be prevented by an initially low-calorie diet with a slow increase in the daily amount of energy supplied in the further course.

In the case of severely underweight people, the body is only “geared towards survival”. The activity of the immune system is greatly reduced. If the immune system recovers from treatment, it can react intensely to infections. This can lead to severe courses of infectious diseases. Therefore, infections must be carefully managed during weight gain.

Long-term severe underweight can lead to small intestine damage. Most of the nutrients are absorbed in the small intestine. This can make treating underweight difficult.

Whom can I ask?

If the cause of the underweight is not known, the family doctor is the first point of contact. He / she carries out the first examinations himself. If necessary, she / he issues referrals to specialists or to a hospital. If the cause is known, treatment will be initiated by the general practitioner or a specialist in the relevant area.

The change in diet should - if possible - be initiated by a nutritionist and can then be accompanied by a dietician. Physical training can be planned by a specialist in physical medicine and carried out together with a physiotherapist.

Note The cause of an unclear weight loss or serious underweight should be identified and treated as soon as possible.

How are the costs going to be covered?

All necessary and appropriate diagnostic and therapeutic measures are taken over by the health insurance carriers. Your doctor will generally settle accounts directly with your health insurance provider. With certain health insurance providers, however, you may have to pay a deductible (treatment contribution) (BVAEB, SVS, SVS, BVAEB). However, you can also use a doctor of your choice (ie doctor without a health insurance contract). For more information, see Costs and Deductibles.

For certain examinations (e.g. MRI), approval from the health insurance provider responsible (medical service - "chief physician") may be required, as well as for certain drug or non-drug treatments (e.g. physical therapy), in some cases only when the disease has reached a certain extent. For certain services (e.g. inpatient stays, aids and medical aids) - depending on the health insurance provider - patient co-payments are provided. Most health insurance providers provide for a permit, sometimes depending on the type of medical aid. The prescription fee has to be paid for medication on a “cash prescription”. For more information about the respective provisions, please contact your health insurance provider, for exampleon your social security website.