Loss of Appetite During Cancer Treatment

Several factors can contribute to decreased appetite, such as the side effects of your treatment, the changes within your body, and the emotional burden of cancer and its treatments. These can broadly be grouped in the following ways:

Inflammation and Immune Response

Your body naturally considers cancerous cells as a threat and fights them by releasing chemicals known as cytokines. However, cytokines can affect the part of your brain responsible for regulating appetite, so that you feel less hungry and have less desire to eat (2).

Metabolic and Hormonal Changes

Cancer can also change how your body interacts with hormones. For example, you may become resistant to hormones like ghrelin, which plays a key role in signalling hunger (3). Cancer can also affect your metabolism, making it harder for your body to convert food into energy (4).

Emotional Factors

Most people find their emotions affect their appetite, regardless of a cancer diagnosis or cancer treatment (5). Strong, uncomfortable emotions such as worry, distress and fear can negatively affect your appetite. Concerns about your cancer diagnosis, treatment or outcome can intensify this. 

Cancer treatment contributes significantly to loss of appetite.  Treatments such as chemotherapy, radiotherapy, targeted therapy and surgery can affect your appetite even further, for instance:

Chemotherapy and Appetite

During chemotherapy, loss of appetite is very common. The medicines used can affect your whole body, potentially causing you to experience:

• Nausea and vomiting
• Metallic or bitter taste in your mouth
• Ulcers or pain in your mouth
• Dry mouth
• Fatigue and low energy

Radiotherapy and Appetite

Radiotherapy can cause the following side effects, all of which may affect your appetite: (8)

• Mouth sores
• Dry mouth
• Pain when swallowing
• Nausea
• Thick saliva
• Altered taste

Targeted Therapy and Appetite

Targeted therapies block specific pathways that cancer cells use to grow and spread. It can reduce your appetite by triggering: (9)

• Metabolic changes
• Nausea and fatigue
• Altered taste

Immunotherapy and Appetite 

Immunotherapy aims to fight cancers using your own immune system. During immunotherapy, loss of appetite is common due to side effects such as: (10)

• Fatigue and widespread inflammation
• Irritation of your gut (causing diarrhoea, nausea, and vomiting)

Surgery and Appetite

Surgery can also affect your appetite; however, this varies depending on the type of surgery you are having. 

Hormone Therapy and Appetite 

Hormone therapy (also called endocrine therapy) aims to stop or slow the growth of cancers that need hormones to grow. Anti-oestrogens or progestins can increase hunger and cause weight gain, while drugs for prostate cancer and advanced breast cancer might diminish your appetite, cause nausea, or alter taste. 

Appetite changes can vary based on your type of cancer and the stage of your cancer. Here are some common cancers and how they may affect your appetite:

Lung Cancer

A diagnosis of lung cancer and its associated treatments can cause appetite changes and may increase your risk of malnutrition. With lung cancer, this often worsens as the cancer progresses. (11)

Pancreatic Cancer

Pancreatic cancer can cause several symptoms that are likely to affect your appetite and increase your risk of malnutrition. Your pancreas produces enzymes that allow you to digest and absorb your food; if it's not producing enough, you may get diarrhoea due to malabsorption, which can be upsetting and make you not want to eat. Pancreatic cancer can also be associated with abdominal pain, nausea and vomiting. (12)

Colorectal Cancer

If you have colorectal cancer, you may be advised by your healthcare professionals that you are at risk of an obstruction. If this is the case, they may ask you to follow a special low-fibre diet to manage this. But this should only be done with support and guidance from health professionals. Following a restrictive diet may affect your appetite. As with most other cancers, the side effects of the treatments are likely to also cause changes to your appetite. (13)

Prostate and Bladder Cancer

Prostate and bladder cancers don’t usually cause appetite changes. However, as with other cancers, their treatments can affect your appetite. (14)

Ovarian Cancer

Appetite changes are common in ovarian cancers due to the cancer itself and the associated treatments. It is common for you to feel bloated and full; some people also experience nausea and vomiting. All of which will affect your appetite.

Oesophageal Cancer

Oesophageal cancers sometimes affect your ability to swallow certain foods due to narrowing in your oesophagus; some treatments, such as radiotherapy, can temporarily make this worse. This could restrict what you can eat and cause changes to your appetite and enjoyment of food. (16)

Advanced or Stage 4 Cancer

Appetite changes in advanced cancers are very common; approximately 80% of patients with advanced cancer will experience appetite changes. (15)

If you experience loss of appetite during cancer and its treatment, speak with your medical team for advice tailored to your needs. They may recommend practical strategies to help support your nutritional intake, such as:

Eat Small, Frequent Meals

Small and frequent meals can help you eat more over the course of the day without feeling the pressure to finish large portions all at once. Eating small amounts frequently throughout the day can quickly add up.

Energy-Dense Foods

When you cannot eat much, eat smarter. Choose foods rich in calories and nutrients. Protein helps maintain muscle mass and strength. If you are struggling to eat enough, a dietitian can help you identify protein-rich foods and snacks that are easier to manage. Adding extra fats such as avocados, olive oil, butter, and cheese to foods can help increase the energy you get from your foods without needing to eat more. High-energy snacks such as nuts, cheese, and yogurt are also helpful to have in between meals.

Drinks and Liquid

Embrace “drinking your calories”.  Liquids are easier to consume and can help you stay hydrated. Fortified drinks and smoothies may help you increase your calorie and protein intake when eating enough food becomes difficult. Your healthcare team or dietitian can advise whether oral nutritional supplements would be helpful for you.

Eat by Routine Rather than Hunger

Don’t wait till you feel hungry; instead, have a schedule for meals and stick to it. Where possible, plan so that you have the food readily available. You can also set mealtime reminders and keep a food diary.