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Underweight facts for kids

Kids Encyclopedia Facts
Body images for obesity
Body images to illustrate Obesity: Images 1 to 5 show people who are underweight
Underweight 01
Image of an uderweight woman

The term underweight refers to humans that have much less weight than they should. Being underweight is bad for the overall health of the person affected. It is normal what a person's weights changes over time. Being underweight is often defined using a measure called the body mass index which calculates a score, based on height and weight. If this score is below 18.5, a person is generally said to be underweight. This is only a general indication, though as the scores must not be calculated for everyone. It does not apply to children and adolescents, for example.

Being underweight can have different causes:

  • Malnutrition, not eating enough, or eating the wrong kinds of foods. The right kinds may not be available, or they may be too expensive to buy.
  • The weight of a person is also determined by genetic factors. One of these factors is that some people have a "lighter build" than others.
  • Stress, anxiety and depression can influence weight
  • There are eating disorders that cause people to become underweight. The most common of these are anorexia nervosa and bulimia nervosa
  • Sudden unexplained weight loss can point to a disease, such as cancer, tuberculosis, hyperthyroidism, Type 1 diabetes or inflammatory bowel disease
  • Sometimes the use of drugs leads to weight loss
  • Organs of the digestive tract may not be working as expected
  • People who train sports too much may be using more energy than they get.


There are problems that are related to being underweight. Very often being underweight is not the first problem. Rather, it often is the effect of another condition or disease. Unexpected weight loss requires the attention of a doctor. There might be another disease. If that disease is treated, the weight problem also disappears.

Another problem underweight people face is that the weight problem affects their health: Their immune system is weakened, and they may get sick more often. People who are underweight because they cannot get or afford the right food need special attention. Women who are underweight may not have their menstruation and face difficult pregnancies.

Once they were being underweight, psychically, they may feel sad and worried about their health. Therefore, family and friends should support them to help them get rid of their unhappiness.

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