Cancer and weight loss

Weight loss and cancer are closely linked. In fact, weight loss is one of the most common side-effects in people diagnosed with cancer1. Although common, it’s not something that should be ignored as it can affect treatment and recovery2.

Do you always lose weight with cancer?

Between 30% and 80% of patients may lose weight at some point during their disease, depending on the site of the tumor1. Worryingly, malnutrition is considered the cause of between 20% and 40% of all cancer-related deaths3.

Why do you lose weight with cancer?

There are lots of reasons why patients lose weight when they have cancer. Before diagnosis, unexplained weight loss may be an early sign that something is wrong, particularly in cancers affecting the lungs, pancreas, stomach or oesophagus4. This is caused by the body releasing substances called cytokines, which help fight the disease but also have the unfortunate side effect of causing weight loss and muscle loss, as well as a loss of appetite5.

Before and especially during treatment (e.g. chemotherapy, radiotherapy), a person may not feel like eating or drinking because of a lack of appetite or because of mouth ulcers, a dry mouth, constipation, diarrhoea, nausea, vomiting, taste changes or pain.

Treatment can also negatively affect how well the body absorbs and uses the nutrients it gets from food5, further worsening weight loss.

Although weight loss is common in cancer, eating less can mean the body may not get the energy, protein and other nutrients it needs at a time when it needs to be at its strongest to undergo treatment. It should therefore not be ignored.

What is cancer cachexia?

Losing weight can be seen as a good thing, especially for those who have always struggled to manage their weight - but when undergoing cancer treatment is not the right time. This is because when cancer patients lose weight, they mostly lose the strong, protective muscle tissue needed to help fight cancer, rather than fat tissue6. This loss of muscle tissue (or ‘lean body mass’) is known as cachexia6. Cachexia can lead to mental and physical tiredness but also, perhaps more importantly, can lower a patient’s tolerance to their treatment which could negatively affect their chances of survival1,6.

How does a patient’s body mass index affect treatment success?

The optimal chemotherapy dose for a patient is based on, amongst other factors, weight and height, also known as body mass index (BMI). Any changes in a patient’s weight from when they were first diagnosed can have a direct and negative impact as the patient may no longer be able to tolerate the full dose; more seriously, a significant reduction in BMI could delay treatment altogether7-9. By maintaining good nutritional intake, patients can help reduce the risk of losing additional muscle weight in the future, helping to ensure the body can tolerate the optimum treatment dose.

What nutrients are most important in cancer?

Good nutrition is all about getting the balance right - the balance of nutrients that a patient’s body needs to function well, to cope with treatment and to keep as active as possible. However, in cancer, some nutrients are particularly important:

  • Protein: important for building and repairing body cells, getting enough protein is important for cancer patients wanting to maintain or regain lean body mass. International guidelines recommend cancer patients consume almost twice the amount that a healthy person needs (>1g of protein/kg of body weight and preferably 1.5g/kg vs 0.75g/kg for the general healthy population)10
  • Omega-3 polyunsaturated fatty acids: with anti-inflammatory properties, this nutrient can help stabilize or improve appetite, food intake, lean body mass and body weight10
  • Micronutrients, such as vitamins, minerals and trace elements: cancer patients often have micronutrient deficiencies due both to reduced food intake and the aggressive nature of some treatments11,12
  • Dietary fibre: essential to a balanced diet, cancer patients can benefit from consuming the right quality of fibre to improve stool consistency, especially those who are suffering from diarrhoea as a side effect of their radiotherapy or chemotherapy13

What to do if you are struggling to eat or losing weight?

If a cancer patient is struggling to eat and drink, has lost weight unintentionally, or has concerns about their diet, they should talk to their healthcare professional. It is important to remember that they don’t need to wait to be asked about their concerns. It is ok to start the conversation with the oncologist and the supporting healthcare team.

Medical nutrition is important to keep the body strong

If after dietary counselling by a qualified healthcare professional a patient is still struggling to eat and drink and/or maintain weight, they may be advised to start taking medical nutrition supplements, also known as oral nutritional supplements (ONS). Medical nutrition (or ONS) are specially designed foods and drinks that help people with disease-related malnutrition meet their nutritional needs, providing the extra energy, protein, vitamins and minerals they need. They are known as ‘foods for special medical purposes’ and should be used under medical supervision.

Medical nutrition, particularly if given to patients early in their cancer journey, has been clinically proven to reduce weight loss. This is important to continue cancer therapy and is therefore related to better treatment outcomes14. Medical nutrition is available in a range of flavours and formats including milkshakes, juice style, yoghurt style, powders and desserts.

  1. Ryan et al. Proc Nutr Soc. 2016;75(2):199-211.
  2. Bozetti 2008 and 2001; Bosaeus 2001; Hebuterne et al, 2014 JPEN J Parenter Enteral Nutr.;38(2):196-204.
  3. Andreyev HJ et al. Eur J Cancer. 1998;34(4)p.503-9.
  4. Hebuterne X et al. JPEN, 2014;38:196.
  5. Argilés JM, et al. Curr Opin Support Palliat Care 2009; 3: 263–68.
  6. Fearon K et al. Lancet Oncol, 2011;12(5):489-95.
  7. Capuano G, et al. Head Neck 2008;30:503-8.
  8. Andreyev HJ, et al. Eur J Cancer, 1998;34:503-9.
  9. Rickard KA, et al. Cancer 1983;52:587-98.
  10. Arends J, et al. ESPEN guidelines on nutrition in cancer patients Clin Nutr, 2016; epub.
  11. Grober U, et al. Nutrients, 2016;8(3):163.
  12. Ströhle A, et al. Oncology Reports, 2010;24(4):815-28.
  13. Garcia-Peris P, et al. Eur J Clin Nutr, 2016;70(2):170-174.
  14. Martin L Senesse P et al. J Clin Oncol 2015 Jan 1: 33(1):90-9.


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