Cancer and cancer treatment (e.g. chemotherapy, radiotherapy or surgery) can affect what you are able to eat and how well your body absorbs and uses the nutrients it gets from food.

You may not feel like eating and drinking because of a lack of appetite or because of mouth ulcers, a dry mouth, constipation, diarrhoea, nausea, vomiting, taste changes or pain.

It is not uncommon to lose weight without meaning to (unintentional weight loss) when you have cancer, it’s often what alerts people that something is wrong and prompts them to talk to their doctor which then leads to investigations and the diagnosis of cancer.

Losing weight can be seen as a good thing, especially you’ve always struggled to manage your weight. But it is important to know that losing weight unintentionally or weighing less than is healthy for your height (low body mass index or ‘BMI’) can affect both your treatment and your recovery. This is even the case for people who were or are overweight.

Body weight is a measure of how heavy you are. Our body is made up of different amounts of fat, bone, muscle and water; this is called body composition.

Losing weight can mean losing fat, but it can mean losing muscle too; this is often the case in cancer.

Muscles help you move. Losing muscle can affect how strong you feel and what you are physically able to do in your day e.g. get out of bed, go for a walk, stand up to cook a meal.

When we can’t or don’t eat enough protein, the body breaks down muscle to get the building blocks of protein (amino acids) to make cells that it needs for other processes in the body such as healing and fighting infection. This can intensify the muscle loss (muscle wasting).

Inflammation is one of the ways that your body fights infection and disease. It happens when the immune system detects something harmful in the body such as bacteria or damaged cells. It can affect the way your body handles nutrients. This response can also make you feel very tired (fatigue), have no appetite, lose weight and lose muscle.

Maintaining your weight can help your body to better tolerate your treatment. This is because the optimal dose of your chemotherapy has been specially calculated for you based on your weight and height. Any changes in your weight from when you were first diagnosed could affect your treatment dose or delay your treatment. By maintaining good nutritional in-take you can help reduce the risk of losing additional strengthening muscle weight in the future. This can help ensure your body can better tolerate your treatment.

Talk to your healthcare professional about any problems you’re having with eating, drinking or weight loss. Some symptoms that interfere with eating and drinking can be managed with medication and others thorough dietary changes or a combination of both. And remember some days, such as when you are particularly tired or in the week after chemotherapy, may be worse than others. Check the Here to help page for information that can help with taste changes, nausea and other problems that get in the way of eating and drinking well.

As your cancer treatments can affect your ability to eat and drink, your healthcare team should take this into account. They can help you anticipate and prepare for managing any symptoms or bad days and advise you on how long this might be expected to last. As many cancer treatments are long and complex, it is not uncommon to be referred to a dietitian who can work out an individualised nutrition plan with you. This can help you manage symptoms and issues as the arise, especially those that you find most bothersome.

Physical activity or keeping active is important and goes hand in hand with good nutrition. This is especially true for supporting muscle health and helping you keep up your usual activities.

Keeping active may include doing as much as you feel able to do of your normal daily activities, this is hugely variable for each of us. For some this might be having the energy to shower, prepare a meal or snack, do some light housework or get out for a walk. For others this might be going for a cycle or swimming, it’s all about what is normal for you. As keeping active can help you to feel more positive, try and make the most of your good days to get out and about.

For some people, specific advice on exercises and activity to support maintaining or building muscle or muscle strength may be provided. Members of the healthcare team including physiotherapists, may be available to provide specific advice.

If you are considering taking on new forms of exercise or physical activity that you wouldn’t ordinarily do, you might want to check with your healthcare team first.