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

For many people, a cancer diagnosis and cancer treatment can make it hard to have a healthy lifestyle. People do not usually expect to gain weight during cancer treatment. But some treatments, side effects or even lifestyle changes can cause you to gain weight:

  • 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.

  • Feeling tired

    You may feel tired because of the cancer or its treatment. This can make you less physically active than usual.

  • Depression

    For some people, feeling sad or worried about cancer can lead to depression. If you are depressed, you may eat more and exercise less.

  • Stopping smoking

    You may decide to stop smoking if you are diagnosed with cancer. If 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 it is important to remember that you will be much healthier if you stop smoking. You can gradually lose any weight you have gained.

  • Comfort eating

    Some people eat more when they are stressed.

  • Kind offers of food

    Friends, family or neighbours may offer food as a way of showing support and wanting to help. It can sometimes be hard to say no to these kind offers.

Do not be too upset if you find you have gained weight. Sometimes knowing why it has happened can help you think of ways to manage it. If you think you have gained weight because you are depressed, talk to your GP or nurse. There are treatments for depression, such as counselling and antidepressants.

If you are having hormonal therapy as part of your treatment, it is important to keep taking it, even if you think it is causing weight gain. Talk to your cancer doctor or nurse if you are worried about this. Eating healthily and being more physically active can help you manage your 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 on 0808 808 00 00 for information and advice. We have more information about getting financial help.

Talk to your doctor and nurse

Before trying to lose weight, it is important to speak to your GP, cancer doctor or nurse. They can talk to you about the right way for you to lose weight. They do this by looking at the type of cancer you have and your treatment. They will also ask about your weight before the cancer diagnosis, and any other medical conditions you have.

Your doctor or nurse will measure your body mass index (BMI) to see if you are a healthy weight for your height. They may check other things, such as your waist measurement and blood pressure. You may also have a blood test to check for health conditions that may cause weight gain.

They may suggest you talk to other health professionals, such as:

  • a dietitian, for advice about your diet
  • a physiotherapist, for exercises to help improve your fitness
  • a specialist nurse, for advice and support about managing weight gain.

Your doctor or nurse may also give you information about where you can get help and support in your local area.

Booklets and resources

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.

Being a healthy weight reduces the risk of heart disease, strokes and diabetes. It 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 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) is a way of measuring if you are a healthy weight for your height. Your GP or nurse will work out your BMI for you. There is also a BMI calculator on the NHS website.

Your BMI score shows which weight category you are in:

  • A BMI of less than 18.5 is underweight.
  • A BMI between 18.5 and 24.9 is a healthy weight.
  • A BMI between 25 and 29.9 is overweight.
  • A BMI of 30 and over is obese (well above the healthy weight range for your height).
  • A BMI over 40 is very obese.

BMI scores are different for older people, some ethnic groups and people who are very muscular. Talk to your doctor or nurse about your BMI before you start trying to lose weight. They can help you set a target weight that is healthy for you.

You can use the chart below to work out your BMI. Find the line that matches your weight and follow it until it crosses the line that matches your height. Talk to your GP or nurse if you are below or above the healthy range.

BMI chart

Waist measurement

Your waist measurement can also be used to see if you are a healthy weight. People who have more fat around their waist have a higher risk of health problems. 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.

A healthy waist measurement for:

  • women is less than 80cm (31½ inches)
  • men of South Asian origin is less than 90cm (35 inches)
  • men not of South Asian origin is less than 94cm (37 inches).

Making changes to your diet

It is not always easy to make changes to your lifestyle. Some people try to lose weight with ‘fad’ diets. Fad diets 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 as only some foods are allowed, fad diets can often be boring and difficult to continue with. They can also be expensive to follow. When people stop the diet, they usually gain weight.

If you eat a healthy diet and are physically active, you will lose weight gradually. This means you are more likely to reach and stay a healthy weight.

Setting a target for weight loss

Try to keep your weight within the healthy range for your height on the BMI chart above. Your GP can also advise you on your ideal weight. If you are worried about your weight, ask your GP or a dietitian for advice and support. Dietitians can give you advice about food choices that are more healthy but still make you feel full.

Losing weight is a gradual process, so be patient with yourself. It can help to set yourself a target weight to work towards. Talk to your doctor, specialist nurse or dietitian about this. Most people gain weight over several months or longer. It can take the same amount of time to reach your target weight. 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.

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 planner.

Energy (calories)

Food and drink contains energy. This is measured in units called kilocalories, which are often called calories or Kcals.

Recommended daily calorie intake for adults

We need fewer calories as we get older. You can ask your GP or dietitian about how many calories you need.

If we take in the recommended amount of calories, our body will use about two thirds of the energy for body functions. This includes controlling body temperature, digesting food and making new tissue. We use the rest of the energy when we are physically active.

When we take in 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.

Many weight loss programmes include calorie-controlled diets. Some food types have more calories than others. For example, a handful of biscuits has more calories than a handful of diced carrots. Eating healthy amounts of different food types can help reduce the number of calories you take in. This can help you lose weight, especially if you also increase the amount of physical activity you do.

We have more information about healthy eating tips and menu ideas.

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.

Being physically active can mean doing activities like walking or gardening. Or it can mean more energetic activities, such as running, cycling or going to the gym. Any increase in physical activity is good for your health and will help you burn more energy (calories).

If you have problems with walking or balance, your doctor may refer you to a physiotherapist. They can assess you and show you how to exercise safely. Some doctors may be able to refer you to an exercise programme run by fitness trainers in your area.

If you want more information about exercise you can download our booklet about Physical activity and cancer. We also have information on our website about physical activity during and after cancer treatment.

The NHS has useful tools, including how to move more, eat well and be healthier. You can also download them as free apps using your mobile phone or tablet.

Who can help?

Family and friends

Tell your family and friends what you are doing and ask them to support you. They might even join you in healthy eating and exercising. This can encourage you, and it is good for them too.

If you are getting used to life after cancer treatment, it can help to talk to people going through the same thing. Our Online Community is a place where you can make friends, blog about your experiences and join groups to meet other people going through the same things.

Healthcare team

Your doctor or nurse can give you advice or refer you to a dietitian. If you are struggling, your GP may refer you to an NHS weight loss clinic. 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.

Exercise groups

You can find more information about local exercise groups at your local library, healthy living centre, community centre or leisure centre. You can also look online.

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.

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. Body image is the picture you have in your mind of how you look. It is how we think and feel about our bodies and how we believe others see us.

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. You may find it hard to accept that you look different because you have gained weight. You may feel angry, anxious or sad. It is natural to feel like this. It is part of adapting to the way you see yourself. You may meet other people who have similar thoughts and feelings.

You may worry that the change in your appearance will affect relationships with a partner, family and friends. You may be anxious about what people think of you or about being rejected. Or you may feel self-conscious about eating at home or out with your family and friends.

Talking about how you feel

People often keep their thoughts and feelings about their bodies to themselves. But keeping your worries hidden can make them grow into something bigger. So, it is important to talk to someone.

Many people find it helps to talk to someone close to them. If you find it difficult to talk about your feelings with a partner, family member or a friend, you could talk to your doctor or specialist nurse. You may also find it helpful to speak to a counsellor. Your GP or nurse can give you advice on how to contact one.

If you are close to someone who has had physical changes, it may take you time to adjust and accept the changes. You may need to talk about your feelings too.

About our information

  • Reviewers

    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. It has been approved by Chief Medical Editor, Professor Tim Iveson, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

Date reviewed

Reviewed: 01 August 2020
Next review: 01 August 2023

This content is currently being reviewed. New information will be coming soon.

Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.