Underweight teen girls

If you’re underweight, it’s not just your energy that may suffer. How do pallid, blotchy skin, thinning hair and brittle nails sound?

You may have wondered for a while if you're underweight. Perhaps friends or your parents have mentioned it.

You can check by using our interactive Healthy weight calculator.

If you're underweight, your GP, practice nurse or school health visitor can give you help and advice.

There could be an underlying medical cause that needs to be checked out.

Or perhaps you haven’t been eating a healthy, balanced diet. That may be due to stress or other emotional problems.

During your teenage years, your body is changing. Sometimes, teenage girls may feel unhappy about these changes, but they are your body’s way of preparing you for pregnancy in later life.

Whatever the situation, if you're concerned about your weight or your diet, the best thing to do is to tell someone. There’s lots that can be done to help.

Is it an eating disorder?

Even if you already know all about healthy eating, there may be other issues that are stopping you from having a healthy diet.

If you feel anxious when you think about food, or you feel you may be using control over food to help you cope with stress, low self-esteem, or a difficult time at home or school, you may have an eating disorder.

People with eating disorders often say that they feel that the disorder is a way of keeping control over their lives. But that’s an illusion: it’s not they who are in control, but the eating disorder.

If you feel you may have an eating disorder, help is available. Tell someone – ideally your parents or guardians, or another adult you trust.

You can learn more in Eating disorders.

Why are you underweight?

If our healthy weight calculator has told you that you may be underweight, think about why this might be.

  • Have you been unwell?
  • Have you been eating healthily, or have you been skipping breakfast or lunch and eating snacks on the go?
  • Have you lost your appetite because you’re stressed or worried?
  • Have you been trying to lose weight? Are you more focused on being thin than being a healthy weight?
  • Are you not eating because it gives you a feeling of control?

Why it matters

Being underweight is bad for you. It’s bad news for your health now and for the future. The consequences include:

  • Lack of energy –  being underweight can leave you feeling drained and tired. Not very useful if you’re trying to revise for exams, play sport or go out with your mates.
  • Nutritional deficiencies – if you’re underweight, you may be suffering from a lack of the vital nutrients your body needs to grow and work properly. Calcium, for example, is crucial for growing young women because it helps to develop strong and healthy bones. If you don’t get enough calcium, you risk having osteoporosis (fragile bone disease) later in life. Iron is also crucial for good health. After your period starts, you lose more iron through your menstrual blood. Other nutritional deficiencies could leave you with unhealthy skin and brittle or thin hair.
  • Weakened immune system – your immune system is not 100% when you’re underweight, so you're more likely to catch a cold or the flu and other infections.
  • Delayed or interrupted periods – if your period hasn’t started yet, it may be delayed because you're underweight. Or, if you're having periods, these may stop if you're underweight. That’s because being underweight can upset your hormones and stop them from working properly.
  • Damage to future fertility – if your periods stop because you're underweight, you risk having problems getting pregnant later in life.

A healthy diet

If you're underweight, aim to gradually gain pounds until you achieve a weight that's healthy for your height and age.

But it’s crucial that you gain weight the right way. Chocolate, cakes, fizzy drinks and other high-calorie foods full of saturated fat and sugar are likely to increase your body fat, instead of your lean body mass.

Instead, use the following healthy eating principles:

  • Meals based on starchy carbohydrates such as wholemeal pasta, brown rice, potatoes or lentils.
  • Five portions of fruit and vegetables a day.
  • Lean protein from (meat, fish, beans and pulses).
  • Three portions of calcium a day. One portion can be a glass of milk, a yoghurt or a matchbox-sized piece of cheese.
  • Cut down on saturated fat found in processed meats, pies, cakes and biscuits.
  • Cut down on sugary foods and drinks, such as chocolate, cakes and biscuits and sugar-rich soft drinks.

If you’re trying to gain weight, eat foods that are healthy and packed with energy:

  • Make time for breakfast. Try porridge with chopped fruit or raisins sprinkled on top. Or eggs on toast.
  • Fruit smoothies or milkshakes make a great snack. You can make them at home and take them to school.
  • A jacket potato with baked beans or topped with tuna makes a healthy lunch and contains both energy-giving carbohydrate and protein.
  • Peanut butter on toast is a quick, high-energy snack.
  • Try yoghurts and milky puddings, such as rice puddings.

Learn more about healthy eating in Food and diet.

Page last reviewed: 11/03/2013

Next review due: 11/03/2015

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Teen girls 15-18

Read about teen girl health issues, including healthy eating, skin problems and having sex for the first time

Food and diet

Find out how to achieve a healthy, nutritious diet to help you look and feel your best

Overcoming eating disorders

Find out about eating disorders and the support available for people who have problems with food