Weight gain after cancer treatment
Some cancer treatments and side effects can make you gain weight. Making positive lifestyle choices can improve your overall health and help you feel more in control.
Weight gain and cancer
A cancer diagnosis and the side effects of cancer treatment can make it hard to have a healthy lifestyle. This can also cause you to put on weight.
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Treatments
Some cancer treatments can cause weight gain. For example, they may increase your appetite. Or they may cause fluid to build up in the ankles, legs, arms or face (oedema or lymphoedema). Treatments that may cause weight gain include chemotherapy, steroids and hormonal therapies such as tamoxifen, anastrozole or hormonal therapies used for prostate cancer.
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Feeling tired
You may feel tired because of the cancer or its treatment. This can make you less physically active than usual.
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Depression and anxiety
For some people, feeling sad or worried about cancer can lead to feelings of anxiety and depression. If you are depressed or anxious, you may eat more and exercise less.
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Stopping smoking
If you smoke and decide to stop smoking, you may gain weight. When you stop smoking, your appetite may increase, and your sense of taste might improve. This could mean you may eat more and gain weight. But there are lots of benefits of stopping smoking and you can gradually lose any weight you may gain after stopping. You will be much healthier after you stop smoking.
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Comfort eating
Some people eat more when they are stressed.
Knowing why you have gained weight can help you think of ways to manage it. If you think you have gained weight because you are feeling anxious or depressed, talk to your GP or nurse. Treatments for this, such as counselling and antidepressants can help.
If you are having hormonal therapy as part of your treatment and have gained weight, talk to your cancer doctor or nurse. It is important to keep taking your medication even if you think it might be causing you to put on weight.
If cancer or its treatment causes your weight to change, your clothes may no longer fit. The cost of buying new clothes can be worrying for some people. If you are worried about money, call the Macmillan Support Line for free on 0808 808 0000 for information and advice. We have more information about getting financial help.
Talk to your doctor, nurse or other healthcare professional
Before trying to lose weight, it is important to speak to your GP, cancer doctor, nurse or other healthcare professional. They can talk to you about the best way for you to lose weight. This can depend on the type of cancer you have and your treatment.
They will ask about your weight before the cancer diagnosis, and any other medical conditions you have. You may also have a blood test to check for any other health conditions that may cause weight gain.
A member of your cancer team, GP or practice nurse may measure your body mass index (BMI). This is a way to check your weight in relation to your height. They may also check your waist measurement and blood pressure. They may give you information about where you can get help and support in your local area.
Your doctor, or another health professional involved in your care, may be able to help you manage your weight. They can also refer you to other health professionals such as a:
- dietitian to advise you about your diet
- physiotherapist to suggest exercises to help improve your physical fitness
- specialist nurse to advise and support you.
You can also get more information about healthy eating and losing weight from the NHS website.
Related pages
The benefits of being a healthy weight
After cancer treatment, many people want to make positive changes to their lives. Trying to have a healthy lifestyle is often a big part of these changes.
Keeping to a healthy weight and being physically active:
- helps you feel stronger
- gives you more energy
- increases your self-confidence
- reduces the risk of heart disease, strokes, diabetes and other health conditions.
- may also reduce your risk of developing some cancers, or the risk of some cancers coming back – your cancer doctor or nurse can tell you more about this.
Choosing to eat healthily is one of the best decisions you can make for your overall health. You get even more benefits if you are also able to be physically active. Making positive lifestyle choices can also help you feel more in control. It can help you focus on what you can do for yourself.
What is a healthy weight for me?
Body mass index (BMI)
Body mass index (BMI) can be a useful measurement. It uses your height and weight to work out if you are a healthy weight. A healthy body weight is also dependent on your sex, age, ethnicity and muscular build. BMI scores are different for older people, some ethnic groups and people who are very muscular. For example, a BMI result cannot tell whether someone is carrying too much fat or a lot of muscle.
The NHS website has a BMI calculator to work out your BMI. Your GP or nurse can also work out your BMI for you.
Waist measurement
Your waist measurement can also be used to see if you are a healthy weight. Even if your BMI is within a healthy range, you can carry excess tummy fat. People who have more fat around their waist have a higher risk of health problems such as diabetes. To measure your waist, wrap a tape measure around your waist like a belt. You should do this halfway between your lowest rib and the top of your hip bone.
Your waist measurement needs to be measured in relation to your height. This is called your waist to height ratio.
The NHS website has more information on this. You can talk to your GP about whether you might be at increased risk of health problems, and how to reduce your risk.
Making positive lifestyle changes
It is not always easy to make changes to your lifestyle. Some people try to lose weight with fad diets. These claim to help you lose weight quickly. They are usually made up of only a few foods. With this type of diet, you often miss out important food groups and nutrients. They can also be expensive and difficult to continue with. After stopping a fad diet, you usually gain weight.
Eating a healthy, balanced diet and trying to be more physically active is the best way to manage your weight. It is also better to lose weight gradually. This means you are more likely to reach and stay a healthy weight.
Setting a target for weight loss
Your GP or dietitian can help you set a target weight that is healthier for you.
Dietitians can give you advice about food choices that are healthier but still make you feel full.
Losing weight is a gradual process. It can take time to notice the benefits of losing weight. Be patient with yourself. Most people gain weight over several months or longer. It can take the same amount of time to reach your target weight. You can find ways to make any new lifestyle and activity habits enjoyable. This will help you to stay as healthy as possible.
It is important to eat a healthy, balanced diet. This means you get all the nutrients you need to keep your body healthy. It is reasonable to aim to lose about 0.5 to 1kg (1 to 2 pounds) a week. Another target might be to lose 5-10% of your weight over 3 to 6 months.
If you want to monitor your weight loss, you can:
- weigh yourself each week – do this at the same time each week and use the same scales
- measure your waist using a tape measure.
If you find it hard to get to your target weight, or if you reach it very easily, talk to your doctor, specialist nurse or dietitian. They can help you set a new target. You may find it helpful to use our food and activity planner.
Energy (calories)
Food and drink contain energy. This is measured in units called kilocalories, which are often called calories or Kcals. Our body uses about two-thirds (66%) of the energy for body functions. This includes
controlling body temperature, digesting food and making new tissue. We use the rest of the energy being physically active.
When we eat and drink more calories than we use, our bodies store it as fat. This means we gain weight. To lose weight, we need to use (burn off) more calories than we take in.
You can do this by:
- reducing the number of calories you take in through food and drink
- being more physically active to burn off more calories.
We need fewer calories as we get older. You can ask your GP or dietitian about how many calories you need each day to help you lose weight.
Eating healthy amounts of a variety of low-calorie food types can help reduce the number of calories you take in. Reduce your portion of high-calorie foods and have more vegetables instead. Or try to have a small treat on 2 days of the week instead of every day. This can help you lose weight, especially if you also increase the amount of physical activity you do.
It may help to talk with a dietitian to find out ways you can reduce the number of calories you have in your diet each day. You can ask your doctor if they can refer you to one.
We have more information about healthy eating tips and menu ideas.
The British Dietetic Association has information on helping iwth weight loss.
Being physically active
Doing more physical activity is another positive lifestyle change you can make. Being active helps you burn off energy (calories) from food. This can help you lose weight and make you feel healthier.
Even if you do not lose weight, being more active can boost your immune system. It can also help you recover from treatment side effects. Together with eating a healthy diet, it can help reduce the risk of some cancers coming back.
Physical activities include walking or gardening. More energetic activities include running, swimming, cycling or going to the gym. If you are not very physically active, talk to your GP before increasing how active you are. Any increase in physical activity is good for your health and will help you burn more energy (calories).
Your healthcare professional or member of your cancer team may be able to refer you to an exercise programme run by fitness trainers in your area.
If you are having problems being physically active due to symptoms or side effects of treatment, you can try to find ways to manage these. Talk to your cancer team about this.
If you have problems with walking or balance, your doctor, healthcare professional or member of your cancer team may refer you to a physiotherapist. They can assess you and show you how to exercise safely.
We have information about physical activity during and after cancer treatment.
The NHS has useful tools, including ways to move more, eat well and be healthier. You can also download them as free apps using your mobile phone or tablet.
Booklets and resources
Weight loss injections
For some people losing weight can be difficult. In some situations, doctors may prescribe weight loss injections. The decisions to prescribe these weight loss drugs is based on factors like the person’s body mass index (BMI) and whether they have other weight-related health problems. These drugs work by making people feel fuller for longer and reducing their appetite. These injections should be used alongside lifestyle changes such as a healthy diet and increased physical activity.
More research is needed to find out if weight loss injections may affect cancer treatments. It is important to check with your cancer doctor before using these injections. Your cancer doctor or healthcare team can talk to you about the possible risks and side effects from using weight loss injections when you have cancer or are going through cancer treatment.
Who can help you make lifestyle changes?
Family and friends
Tell your family and friends what you are doing and ask them to support you. They might even want to join you in healthy eating and exercising.
It may help to talk to people going through a similar experience. Our Online Community is a place where you can make friends, blog about your experiences and join groups to meet other people in a similar situation.
Healthcare team
Your doctor, nurse or another healthcare professional can give you advice. If necessary, they may refer you to a dietitian, physiotherapist, exercise specialist or exercise group. If you are struggling, your GP may refer you to an NHS weight loss clinic, if this is available in your area. If you have experienced eating disorders or struggle with your body image, you may find it helpful to speak to a counsellor or other mental health professional.
Financial help
If cancer or its treatment causes your weight to change, your clothes may no longer fit. The cost of buying new clothes can be worrying for some people. If you are worried about money, call the Macmillan Support Line for free on 0808 808 0000 for information and advice. We have more information about getting financial help.
Exercise groups
Your GP can help you to find out about services to help with weight management. These could be exercise classes or health and well-being sessions. You can also find information about local exercise groups online or at your local library, healthy living centre, community centre or leisure centre.
Weight loss groups
These can be a good way to meet other people who can encourage and support you. Remember that weight loss programmes should be based on:
- a healthy balanced diet
- regular physical activity
- weight loss of no more than 0.5 to 1kg (1 to 2 pounds) a week or between 5 and 10% over 3 to 6 months.
Your feelings about weight gain
Weight gain can be upsetting and difficult to cope with. This is because it can be a visible reminder of your illness. It can also affect your body image. This is how we think and feel about our bodies.
If you gain weight because of cancer or its treatment, you will see a different image of yourself from the one you are used to. It’s normal to have different emotions such as feeling angry, anxious or sad. You may find it hard to accept that you look different because you have gained weight.
You may worry that the change in your appearance will affect relationships with a partner, family or friends. You may be anxious about what people think of you. Or you may feel self-conscious about eating in front of people.
Talking about how you feel
If you have depression or feel upset about changes to your body, it can help to talk to someone about how you feel. If you find it difficult to talk about your feelings with a partner, family member or friend, you could talk to your doctor, specialist nurse or other healthcare professional. You may also find it helpful to speak to a counsellor. Your GP, nurse or healthcare professional can give you advice on how to contact one.
Macmillan is also here to support you. If you would like to talk, you can:
- call the Macmillan Support Line free on 0808 808 00 00.
- chat to our specialists online
- Visit our emotional support forum to talk with people who are dealing with the emotional impact of cancer, share your experience, and ask your questions.
About our information
This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer.
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References
Below is a sample of the sources used in our information about weight gain after cancer treatment. If you would like more information about the sources we use, please contact us at informationproductionteam@macmillan.org.uk
National Institute for Health and Care Excellence. NICE. Obesity: identification, assessment and management. CG189. Last updated: 26 July 2023. Available from www.nice.org.uk/guidance/cg189/chapter/Recommendations#identifying-and-assessing-overweight-obesity-and-central-adiposity [accessed July 2025]
World Cancer Research Fund WCRF. Weight, Obesity and Cancer. Available from Be a healthy weight - Cancer prevention recommendations | World Cancer Research Fund (wcrf-uk.org) [accessed July 2025]
British Dietetic Association BDA. Obesity and overweight. Available from www.bda.uk.com/food-health/your-health/obesity-and-overweight.html [ accessed July 2025]
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