What Effects Do Underweight Teens Go Through?

Updated February 21, 2017

Underweight teenagers can be affected both physically and emotionally by their condition. It is important to define what "underweight" means before labelling a teenager as having a problem. Teenagers need to know their Body Mass Index, or BMI, to know if they are really underweight. A teen with a BMI below the 5th percentile of a standard BMI chart is considered underweight, as described by Kids Health.

Feeling Generally Unwell

Underweight teens can feel generally slow, tired and lethargic on a regular basis. They may even begin to feel depressed. It can be difficult to spot this during puberty because it is common for teens to feel occasional periods of slowness and low mood. However, if the teenager consistently complains of feeling tired, lacking in energy or feeling ill a lot, their low weight and inadequate calorie consumption may be a factor. A low intake of vitamins can also contribute to a general feeling of tiredness and lethargy because vitamins help boost the body's natural responses.


Coughs, stomach cramps, diarrhoea, loss of menstruation and continued physical fatigue are symptoms of a problematically low weight and poor quality diet. Also, the immune system may not function as effectively, they may experience muscle weakness, low blood pressure, anaemia, swollen joints and even hair loss, as described by Troubled Teen 101. If these issues continue for more than a week or two, help should be sought from the family doctor. Bulimia or anorexia nervosa are serious, sometimes life-threatening, illnesses that can cause dramatic weight loss in teens. A teen with either illness will suffer physically and psychologically, so it is essential they get help from their doctor.

Growth Inhibition

A teen with a restricted, low calorie diet can have a reduced growth rate. This not only affects their height, size and stature, but it also means their sexual development may be slowed or inhibited. A balanced, carefully planned diet may be required to reset their body to ensure they get enough of the right vitamins and minerals to help them grow properly and develop at the same rate as an average weight teen. Broken fingernails, dry skin and hair and a light growth of soft hairs all over the body can also result from being very underweight.

Pressure From Friends and Family

The pressure to fit in, wear the right clothes and look a certain way can affect any young person, but thin or fat teens can get more pressure to conform than most. Sometimes that pressure can turn into bullying and cause the teen to feel victimised, singled out, ugly and worthless. Often their underlying fears of being different are compounded by the continual reference to the fact that they look different to an average person their age. Some well-meaning family members can put pressure on their teenage children to change their weight and appearance, but they may actually need professional help to do so safely.

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About the Author

Natasha Parks has been a professional writer since 2001 with work published online and in book format for "Thomson Reuters," the "World Patents Index" and Her areas of expertise are varied and include physics, biology, genetics and computing, mental health, relationships, family crises and career development. She holds a Bachelor of Science in Biophysics from King's College, London.