Underweight people are often called "beanstalk", "ironing board" or "asparagus resin": those who are extremely thin do not always have it easy. From a medical point of view, "being thin" does not automatically mean "being healthy". Almost 2 million people in Germany are underweight, as shown by the information provided by the Federal Statistical Office. Significantly more women than men are affected, especially in the age group between 14 and 29 years.
Similar values apply to the other western industrialized countries: in the US, around 3.5% of the population weigh too little, in France almost 5%. By contrast, almost 50% of adults in the developing world are too light. Under the guidelines of the World Health Organization WHO is underweight who has a body mass index (BMI = body weight in kilograms divided by height squared in meters) of less than 18.5.
Genetic predisposition and chronic diseases
The discussion about anorexic models has brought the pathological BMI under 17 in the foreground. However, not only people with proven eating disorders are affected, but especially those who simply do not gain weight or who suffer from chronic diseases. Reasons for unintentional weight loss are often inflammatory bowel disease. The cause may be, for example:
- Ulcerative colitis
- Crohn's disease
In AIDS patients, sudden, unexplained weight loss can often be the first indication of the virus infection.
Underweight and malnutrition
Those who are underweight are not automatically malnourished. There are people who, because of their individual metabolism, do not increase and stay thin throughout their lives. Especially in the western industrial nations such genetic factors or metabolic disorders are more often the reason for underweight than, for example, malnutrition as in developing countries.
When differentiating between underweight and malnutrition, one must continue to distinguish between inadequate nutrition on the one hand and nutrient losses due to lack of or poor recovery on the other hand. For example, patients with chronic oropharyngeal infections may only have limited intake of food, while lactose-intolerant patients may be poor at ingesting the ingested food.
That eating disorders such as bulimia and anorexia can lead to malnutrition and underweight to death is well known. Much less well-known, however, is the fact that older people are increasingly malnourished and thus underweighted. Loss of appetite, physical and mental limitations are often a reason for the so-called "pudding seniors" in addition to financial problems and acute illnesses.