Underweight teen girls

5 min read

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

You can check by using our healthy weight calculator. If you're underweight, your doctor, 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 the result of stress or other emotional problems.

During your teenage years, your body is changing. Sometimes teenage girls can 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.

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 being underweight matters

Being underweight isn't good for you. It could cause:

  • lack of energy – being underweight can leave you feeling drained and tired. You may find it difficult to revise for exams, play sport or go out with your mates.
  • nutritional deficiencies – if you're underweight, you may be missing out on vital nutrients your body needs to grow and work properly. Calcium, for example, is very important for young women because it helps to develop strong and healthy bones. If you don't get enough calcium, you risk having
    (fragile bone disease) later in life. Iron is also crucial for good health. After your periods start, you lose 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 isn't 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 periods haven't started yet, they may be delayed because you're underweight. Or, if you're having periods, they may stop if you're underweight. That's because being underweight can upset your hormones and stop them working properly.

What to do if you're underweight

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

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

Instead, try:

  • 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, biscuits and sugar-rich soft drinks

If you're trying to gain weight...

If you'd like to put on some 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.

Is it an eating disorder?

Even if you already know all about healthy eating, there may be other issues stopping you 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 they feel the disorder is a way of keeping control over their lives. But that's an illusion: it's not them who is in control, but the eating disorder.

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

Bear in mind that, if you are underweight because of an eating disorder, your treatment may include eating a diet that’s higher in sugar, fat and calories for a while.

Get informed about dodgy diet pills sold online.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.