Underweight teen girls

You may be wondering 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 GP, practice nurse or school nurse can give you help and advice.

There could be a medical cause that needs to be checked out. Or perhaps you haven't been eating a healthy, balanced diet. That may be because of stress or other emotional problems.

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?

Why being underweight matters

Being underweight isn't good for you. It can leave you with low energy and affect your immune system. This means you could pick up colds and other infections more easily.

Plus, you may be missing out on important vitamins and minerals like calcium and iron, which you need to grow and develop.

If you're underweight, it can also affect how your hormones work. This means your periods could be delayed if they haven't started yet or, if they have started, you could miss some.

The good news is that, with a little help, you can gradually gain weight until you get to a weight that's healthy for your height and age.

What to do if you're underweight

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.

Base your meals on starchy carbohydrates, such as wholemeal pasta, brown rice or potatoes.
Have at least 5 portions of fruit and vegetables a day.
Have some lean protein (from lean meat, fish, beans and pulses).
Have some dairy or dairy alternatives each day – have whole milk until you build your weight back up.
Cut down on foods that may be high in saturated fat, including processed meats, pies, cakes, pastries and biscuits. Vegetable oils, nuts, nut butters and seeds are good sources of healthier fats.
Cut down on food and drinks high in sugar, such as chocolate, ice cream, cakes, biscuits and sugary soft drinks.

Healthy ways to gain weight

Make time for breakfast – try porridge with chopped fruit or raisins sprinkled on top, or mashed avocado or eggs on toast.
A jacket potato with baked beans or topped with tuna makes a healthy lunch and contains both energy-giving carbohydrate and protein.
A handful of nuts or toast with unsalted and unsweetened nut butter make quick, high-energy snacks.
Try whole milk yoghurts and milky puddings, such as rice pudding, to help build your weight up.
Aim to eat 3 regular meals a day with some healthy snacks in between.
It may help to increase your portion sizes at mealtimes, too.

Learn more about healthy eating.

Is it an eating disorder?

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.

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

The eating disorders charity Beat has a free Youthline, where you can get confidential advice – call 0808 801 0711.

Page last reviewed: Thu Nov 2017 Next review due: Mon Nov 2020