Losing weight without trying is a common side effect of cancer. Weight loss can be the result of the cancer itself, its symptoms, or a side effect of cancer treatments. 

Cancer is the name given to a collection of diseases that cause abnormal cell growth, leading to the invasion and destruction of healthy tissues. There are many different types of cancer, as it can occur almost anywhere in the body. Cancers that have the potential to spread to other parts of the body (metastasize) are often referred to as malignant tumours.

Weight loss is very common in cancer patients, and is often one of the first signs people notice that suggests something is wrong. Read on to learn more about lung cancer and how it can affect your health and weight.

What is lung cancer? 

Lung cancer is the most common type of cancer worldwide, with almost 2.5 million people being diagnosed in 2022.^1,2 It accounts for the highest cancer-related mortality rates among both men and women. 

There are two types of lung cancer:

• Primary lung cancer, which begins in the lungs
• Secondary lung cancer, which begins elsewhere in the body and spreads (metastasizes) to the lungs when cancerous cells break off of a tumour and enter the bloodstream

What are the symptoms of lung cancer?

The symptoms of lung cancer include:³

• Shortness of breath
• Unexplained weight loss 
• Chest pain 
• A persistent cough that doesn’t go away
• Fatigue 
• Coughing up blood 
• Reduced appetite 

The symptoms of lung cancer do not typically present until the cancer has advanced to later stages, making it difficult to get a diagnosis and access treatment early. 

How does lung cancer cause weight loss?

Unexplained weight loss is particularly common in lung cancer, with approximately 60% of patients reporting a loss of appetite and significant weight loss at the time of diagnosis.⁴ However, weight loss can also be a side effect of cancer treatment or a result of metabolic changes from the cancer itself. Several different mechanisms of cancer-induced weight loss are discussed below:

Increased resting energy expenditure

Based on the type and stage of your cancer, it can cause systemic inflammation in the body and impact your energy metabolism - increasing the rate at which your body burns calories for energy, even whilst you are resting. This increased energy expenditure, coupled with poor appetite and decreased caloric intake, can quickly lead to weight loss.¹

Impact of symptoms 

Shortness of breath and coughing can make it difficult to eat and breathe, and chest pain may cause nausea that may impact appetite and desire to eat. In addition, some people may feel too exhausted to eat or carry out physical activity, further reducing their appetite. 

Side effects of treatments 

Treatments for lung cancer depend on the type, size, position, and stage of the cancer, as well as the patient’s overall health. Treatments may include surgery, radiotherapy, chemotherapy, immunotherapy, or other targeted therapies. Treatment plans may include one or a combination of treatments depending on the factors above.

Common side effects of cancer treatment include fatigue, gastrointestinal symptoms (nausea, diarrhoea, or constipation), difficulty swallowing (particularly if you are receiving radiotherapy to the chest), pain, mouth ulcers, and changes to your taste buds. 

Cancer-associated malnutrition can cause weight loss. Decreased caloric intake can negatively affect a patient’s quality of life, treatment success, survival, and physical function.¹ Accordingly, weight stabilisation is associated with significant improvements in treatment success and survival rate.^5,6 However, it is unclear whether this is because of dietary management alone, or its combination with traditional cancer treatments. 

Maintaining your weight and adequate nutrition whilst battling cancer can have a significant impact on your quality of life by helping mitigate the side effects of your condition and treatments.

Why am I losing weight when I am eating normally? 

Cancer can cause a condition called cachexia (kak-ex-ee-a), also known as wasting syndrome or anorexia cachexia, which causes significant body fat loss, muscle wastage, and weight loss. 

Cachexia usually develops in those with advanced cancer, and is seen in 61% of lung cancer patients.⁷ Cachexia is the result of cancer increasing your metabolism and changing how your body uses carbohydrates, fats, and proteins. As the body uses more calories than usual, it can become difficult to eat or drink enough to meet the increased calorie demand - making it hard to maintain your weight. 

There are currently no effective medical interventions to reverse cachexia. Adequate nutrition support is the main form of treatment used to minimise its effects on your health.^7,8

How can I stop unwanted weight loss? 

As discussed above, it can be very difficult to manage your weight whilst living with cancer. However, there are some things you can do that can help reduce the impact of cancer on your weight. 

Here are 5 top tips to help prevent weight loss in cancer:

• Eat little and often: aim to have 4-6 small (but high calorie and high protein) meals each day. Suggested meals include cheese and crackers, Greek yoghurt, hummus and vegetable sticks, and fruit and nut butter. Try to prioritise foods you like, rather than eliminating or restricting foods for health reasons, to encourage your appetite
• Beef up your meals: large portions may feel overwhelming for those struggling with poor appetite. As such, it is vital to find ways to make the most of the foods you can eat to avoid missing out on essential calories and nutrients whilst eating smaller portions

Foods can be combined, or supplements added to meals and drinks to increase their nutritional and caloric content without increasing the portion size. This practice is known as food fortification. 

For example, scrambled eggs on 2 slices of toast with a thin scraping of butter contains approximately 300 calories and 15-20 grams of protein (depending on the size of the eggs). In comparison, scrambled eggs made with 30 grams of cheese and 30 ml of double cream on 2 slices of toast with a thick scraping of butter contains approximately 600 calories and 23-28 grams of protein.

Some common foods used for food fortification, also called ‘food enrichers’, include:

• butter
• cheese
• cream
• jams and spreads (e.g. chocolate spread, nut butters, and marmite)
• cooking oils
• crème fraiche
• cream cheese
• and milk powder

Plant-based versions of dairy products would also work for fortifying meals. 

• Make the most of your drinks: higher-calorie drinks can help you consume calories more easily. A few good examples are:
  • Milk (choose full-fat milk or add milk powder to further increase its caloric content) 
  • Fortified plant-based milks (oat and soy milk contain the most calories)
  • Fruit juice (fresh)
  • Hot milky drinks e.g. coffees/hot chocolate/milky tea/Horlicks 
  • Milkshakes
  • Smoothies

Some people may find drinks easier to consume than food, so choosing high-calorie drinks can help you get extra nutrients without having to eat. 

Milk powder can be found in most supermarkets and can be added to milk to increase its calorie and protein content. It’s recommended that cancer patients use fortified milk (instead of normal milk) in milkshakes, cereals, scrambled eggs and more. Fortification of milk also works using vegan milk powder in plant-based milks. 

Note: it’s important to avoid ‘light’ or ‘fat-free’ versions of foods if you’re trying to increase your caloric intake and minimise weight loss. ‘Light’ foods often do not contain natural fats, which are higher in calories and help the body absorb important nutrients from food.

• Choose softer foods: shortness of breath and coughing can cause fatigue and make it difficult to eat and chew. Choosing softer foods can help reduce this problem and make it easier to manage meals and snacks. Ensuring meat is tender, cooking rice and pasta until soft, and steaming vegetables can help
• Get spicy! Get creative using herbs, spices, and marinades to help increase the flavour profile of foods and make them more tasty and appealing. Choosing foods that smell good can further help improve your desire to eat. If sweet tastes are unpleasant, try sharp or tart-tasting foods

Summary 

Weight loss is a common side effect of lung cancer, and it can negatively impact treatment efficacy, survival rates, and quality of life if left unmanaged. If you’re losing weight without trying or struggling to maintain your weight after a cancer diagnosis or during treatment, reach out to your doctor or a registered dietitian to help you with an appropriate nutrition treatment plan. 

It's also important to note the impact cancer and weight loss may have on a person's mood, as well as their loved ones. Talking regularly with loved ones or seeking support from your doctor or cancer nurse and cancer charities may help work through feelings associated with weight loss during a cancer diagnosis.