Physical causes
One of the most common physical reasons for being underweight is hyperthyroidism (Latin: hyperthyroidosis: hyper = over, thyroid = thyroid gland). The thyroid gland is the central organ that controls our metabolism and can accelerate it in such a way that nutrients are excessively burned and converted into energy and no nutrients are transported into the body. The central hormone of the thyroid gland is the so-called thyroxine, which can easily be measured in a blood test.
The examination of the thyroid function in the blood is one of the first and simplest examinations in the clarification of underweight. Since the absorption of nutrients takes place from the intestine, the logical consideration is that of an intestinal disorder in underweight. All chronic inflammatory bowel diseases such as Crohn’s disease and ulcerative colitis can be the cause.
In these diseases, parts of the intestinal mucosa are almost permanently inflamed and the intestinal cells can no longer fulfill their function and can only absorb insufficient nutrients, which in the long run leads to underweight with the resulting deficiency symptoms. Previously unrecognized intolerances of sugars such as lactose or fructose can also be the cause of intestinal disorders and thus be responsible for underweight. In most cases, a so-called sprue is already noticeable in childhood.
Here, the destruction of the intestinal cells through an allergy to the cereal protein gluten leads to malnutrition. Even when the intestine is functioning, nutrients can still be lost through the intestine if the absorption is not possible, for example, due to a lack of splitting (as after stomach removal or due to bile stasis or pancreatic dysfunction). In rare cases, parasites or worms in the intestine can also impede the absorption of nutrients.
Causes for unwanted weight loss and underweight can also be far from the digestive system. Many serious diseases can consume the body’s reserves due to high energy requirements and lead to underweight. These diseases can be tumors that require a lot of energy due to their rapid cell growth. Furthermore, tuberculosis or AIDS can increase the body’s energy requirements and lead to underweight. Until a definite cause is found, these diseases cannot be excluded and must be kept in mind.
