If you're concerned that you're underweight, check your weight using our Healthy weight calculator.
If your body mass index (BMI) is below the healthy range, this is an indication that your weight may be too low.
If you're underweight, your GP or practice nurse can give help and advice. There might be an underlying medical cause for your low weight.
Or you may be underweight because your diet isn't providing you with enough energy (calories). This can happen for a number of reasons. Stress or other emotional problems can sometimes cause a change in eating patterns that is hard to recognise.
If diet is the cause of your low weight, changing to a healthy, balanced diet can help you achieve a healthy weight. Registered dietitian Azmina Govindji has provided the following guidelines.
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 just eating 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' or looking a certain way than on being a healthy weight?
- Are you not eating because it gives you a feeling of control or power?
Talk to someone
There may be emotional issues that are stopping you from eating a healthy diet.
If you feel anxious or worried when you think about food, or feel you may be using control over food to help you cope with stress or low self-esteem, you may have an eating disorder.
If you think you may have an eating disorder, help is available. Find out more about eating disorders.
Why it matters
Being underweight is bad news for your health now and in the future:
- Lack of energy. Being underweight can leave you feeling drained and tired. You may have anaemia (a lack of red blood cells) because you’re not consuming enough iron.
- Nutritional deficiencies. If you’re underweight, you may be lacking vital nutrients that your body needs to grow and work properly. Calcium, for example, is important for the maintenance of strong and healthy bones. Being underweight increases the risk of osteoporosis (fragile bone disease) later in life.
- Weakened immune system. Your immune system is not 100% when you’re underweight, making you more likely to catch a cold, the flu or other infections.
- For women, interrupted periods and difficulty becoming pregnant in the future. Women who are underweight can find that their periods stop. This increases the risk of future problems with fertility.
A healthy diet
If you're underweight, aim to gradually gain weight until you're a weight that is healthy for your height and age.
It’s crucial that you gain weight the right way, and not by eating chocolate, cakes and other high-calorie junk foods full of saturated fat and sugar, or with fizzy drinks. These foods can increase your body fat instead of your lean body mass.
Instead, aim for three meals and three snacks a day and base your diet on healthy eating principles. That means:
- Make meals with starchy carbohydrates such as wholemeal pasta, brown rice, potatoes or lentils as a base.
- Eat five portions of fruit and vegetables a day. For ideas, see 5 A DAY.
- Choose lean protein from meat, fish, beans and pulses.
- Get three portions of calcium a day. One portion is a glass (190ml or 1/3 pint) of milk, a yoghurt or a small matchbox-size 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 and biscuits and sugar-rich soft drinks.
Learn more about the different food groups and how they form part of a healthy diet.
Find out more about a healthy vegetarian diet.
Healthy high-energy foods
If you’re trying to gain weight, eat foods that are not only healthy but are also packed with energy. Try the following:
- for breakfast, porridge with chopped fruit or raisins sprinkled on top, or eggs on toast
- fruit smoothies or milkshakes for a great snack (make them at home and take them to work or college)
- for a healthy lunch, a jacket potato with baked beans or tuna on top, which contains energy-giving carbohydrate and protein
- peanut butter on toast for a high-energy snack
- yoghurts and milky puddings, such as rice puddings
- nuts, which are high in 'good' unsaturated fats (choose unsalted varieties)
