Underweight people are often called “beanpole,” “ironing board” or “asparagus tarzan.” Those who are extremely thin don’t always have it easy. Even from a medical perspective, “being thin” does not automatically mean “being healthy.” According to the World Health Organization (WHO) classification, someone who has a Body Mass Index (BMI = body weight in kilograms divided by height in meters squared) of less than 18.5 is underweight.
Prevalence of underweight
Just under 2 million people in Germany are underweight, according to data from the Federal Statistical Office. Significantly more women than men are affected, especially in the age group between 14 and 29 years.
Similar figures apply to the other western industrialized countries: in the USA, around 3.5% of the population weighs too little, in France almost 5%. In contrast, nearly 50% of adults in developing countries are too light.
Causes: Genetic predisposition and chronic diseases.
The discussion about anorexic models has brought pathological BMI below 17 to the forefront. However, this does not only affect people with designated eating disorders, but especially those who simply do not gain weight, for example due to genetic predispositions, or suffer from chronic diseases. Reasons for unintentional weight loss are often also inflammatory bowel diseases.
Other causes of underweight may include, for example:
- Ulcerative colitis
- Crohn’s disease
- Tuberculosis
- Cancers
In AIDS patients, sudden unexplained weight loss can often be the first indication of viral infection.
Underweight and malnutrition
Someone who is underweight is not automatically malnourished. There are just people who do not gain weight due to their individual metabolism and remain thin throughout their lives. Especially in Western industrialized nations, such genetic factors or metabolic disorders are more often the reason for underweight than, for example, malnutrition as in developing countries.
When distinguishing between underweight and malnutrition, one must further distinguish between insufficient food intake on the one hand and nutrient losses due to missing or inadequate utilization on the other hand. Patients with chronic inflammation of the mouth and throat, for example, have limited ability to absorb food, whereas patients with lactose intolerance have poor ability to utilize ingested food.
Underweight in the elderly
That eating disorders such as bulimia and anorexia can lead to malnutrition and underweight and even death is well known. However, it is much less well known that malnutrition and thus underweight occur more frequently in the elderly. In this context, loss of appetite, physical and mental limitations, in addition to financial problems and acute illnesses, are often a reason for the so-called “pudding seniors.”
