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Are you worried about being underweight? Or perhaps your friends or parents have mentioned it?

We all grow and develop at different rates. You may have friends who are taller, heavier and more muscular than you. Lots of boys do not reach their adult height and weight until they are over 18.

You can check whether you're a healthy weight by using our BMI healthy weight calculator.

If you are underweight, a GP, practice nurse or school nurse can give you help and advice.

Why are you underweight?

There may be an underlying medical cause for your low weight that needs to be checked out. Gut problems such as coeliac disease, for example, can make people lose weight.

Read more about unintentional weight loss and some of the medical conditions what can cause it.

Maybe you're having mental or emotional problems that have affected your eating habits. Depression and anxiety, for example, can both make you lose weight.

Or perhaps you have not been eating a healthy, balanced diet.

Whatever the reason, if you're concerned about your weight or your diet, the best thing to do is tell someone you trust, such as a parent, your school nurse or GP. There's a lot that can be done to help.

Why being a healthy weight matters

Being underweight can cause you to have low energy and affect your immune system. This means you could get colds or other infections easily.

If your diet is unhealthy, you may also be missing out on vitamins and minerals you need to grow and develop.

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.

Healthy diet for teen boys

It's important that you gain weight in a healthy way. Try not to go for chocolate, cakes, fizzy drinks and other foods high in fat or sugar.

Eating these types of foods too often is likely to increase your body fat, rather than building strong bones and muscles.

To have a healthy diet you should:

  • base your meals on potatoes, bread, rice, pasta or other starchy carbohydrates, choosing wholegrain versions where possible
  • have at least 5 portions of fruit and vegetables a day
  • have some dairy or dairy alternatives, such as soya drinks
  • eat some beans, pulses, fish, eggs, meat and other proteins including 2 portions of fish every week, 1 of which should be oily, such as salmon or mackerel
  • choose unsaturated oils and spreads, such as sunflower, rapeseed or olive, and eat them in small amounts
  • drink 6 to 8 cups or glasses of fluid each day

We all need some fat in our diet, but it's important to keep an eye on the amount and type of fat we're eating.

Try to cut down on the amount of saturated fat you eat – that's the fat found in foods such as sausages, salami, pies, hard cheese, cream, butter, cakes and biscuits.

Cut down on sugary foods, such as chocolate, sweets, cakes, biscuits and fizzy drinks.

See more healthy eating tips for teenagers.

Strength training can also help to build strong muscles and bones. Find out how to increase your strength and flexibility.

How to boost your calories

Aim to eat 3 meals and 3 snacks each day to boost your energy intake in a healthy way.

Make time for breakfast. Try porridge made with milk and sprinkle some chopped fruit or raisins on top. Have whole milk until you increase your weight.

Or how about eggs on toast with some grilled tomatoes or mushrooms?

A jacket potato with baked beans or tuna on top makes a healthy lunch and contains both energy-rich carbohydrates and protein. Adding cheese will provide calcium. Or try pasta salad with chicken breast and tomatoes.

Have a healthy snack before bed. Lower-sugar cereal with milk is a good choice, or some toast. Go for wholemeal where possible.

See Change4Life for more healthy meal ideas.

Find out how many calories the average teenager needs.

Ideas for healthy snacks

Aim for 3 snacks each day to boost your calorie intake. Try:

  • Crumpets, bananas or unsalted nuts
  • Hummus with pitta bread, carrots sticks or celery sticks
  • Beans or eggs on wholemeal toast
  • Toast with lower-sugar, lower-salt peanut butter
  • Fruit teacake, hot cross bun, malt loaf or fruit bread
  • Wholemeal bagel and lower-fat cream cheese

You should also make sure you get plenty of sleep. About 8 to 10 hours each night is ideal for teenagers.

Avoid smoking and alcohol.

Teen boys and eating disorders

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.

If you feel you may have an eating disorder, tell someone, ideally your parents, guardians or another adult you trust.

The charity Beat Eating Disorders has a youth helpline where you can get confidential advice. Call 0808 801 0711 (12pm to 8pm Monday to Friday; 4pm to 8pm Saturday and Sunday).

Page last reviewed: 18 February 2020
Next review due: 18 February 2023