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Underweight teen boys

If you’re underweight, you could be damaging your body. It can cause stunted growth, weakened muscles and a lack of energy: bad news if you want to keep up with your mates.

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


If you are underweight, your GP, practice nurse or school health visitor can give you help and advice. There may be an underlying medical cause for your low weight that needs to be checked out. Perhaps you haven’t been eating a healthy, balanced diet. Or maybe you're having emotional problems, and have changed your eating habits.

Whatever the situation, if you're concerned about your weight, or if something about your diet is worrying you, the best thing to do is to tell someone. There a lot 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 eating 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, then you may have an eating disorder.

People with eating disorders often say that they feel their eating habits help them keep control of their lives. But that’s an illusion: it’s not them 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, guardians or another adult you trust.

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 skipping breakfast and lunch and just grabbing snacks on the go?
  • Have you lost your appetite, perhaps 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 news for your health now, and for the future. 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 sports or go out with your mates.
  • Nutritional deficiencies If you’re underweight, you may be suffering from a lack of the vital nutrients that your body needs to grow and work properly. Calcium, for example, is crucial for the development of strong and healthy bones. You build half the strength of your adult skeleton during adolescence.
  • Weakened immune system Your immune system is not at 100% when you’re underweight so you're more likely to catch a cold, the flu and other infections.
  • Stunted growth and poor muscle development Your body needs the right foods if it is to grow properly. If you stay underweight you could be shorter and weaker as an adult than you would have been if you’d eaten a healthy diet.

A healthy diet

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

It’s crucial that you gain weight the right way, so avoid reaching for chocolate, cakes, fizzy drinks and other high-calorie foods full of saturated fat and sugar. They are likely to increase your body fat, instead of your lean body mass.

Instead, eat three meals and three snacks a day. Follow these healthy eating principles:

  • Meals with starchy carbohydrates, such as wholemeal pasta, brown rice, potatoes, or lentils.
  • Five portions of fruit and vegetables a day.
  • Lean protein (from meat, fish, and beans and pulses).
  • Three portions of calcium a day. One portion is a glass of milk, a yoghurt or a matchbox-sized 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, choose foods that are healthy and packed with energy. Try the following:

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


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