There are many medical reasons for being underweight. Before trying to put on weight, you need to know that it's safe to do so.
The best way is to make sure you're supervised by someone appropriately qualified.
Check if you're a healthy weight for your height using the BMI healthy weight calculator.
If you're underweight, your GP can check for any health conditions that may have caused you to lose weight, such as:
- an overactive thyroid gland (hyperthyroidism)
- type 1 or type 2 diabetes
- coeliac disease, a condition that prevents your body absorbing food properly
- eating disorders, such as anorexia nervosa
- body dysmorphic disorder
Once the cause of your weight loss has been found, your GP can give you advice about making changes to your diet, sometimes with the help of a dietitian.
The type of food you'll need to eat to put on weight will depend on what's causing you to be underweight.
Read more answers to food and diet questions.
Page last reviewed: 31 August 2018
Next review due: 31 August 2021