Why Does Cancer Cause Weight Loss?

Why Does Cancer Cause Weight Loss?

Staff Writer
6 minute read

Why Does Cancer Cause Weight Loss?

It is very typical to see someone battling cancer or receiving treatment for cancer lose a significant amount of weight. That raises the question, why does cancer cause weight loss?

The following are the primary topics that will be discussed throughout this article:

  • Cancer and unexplainable weight loss

  • Why does cancer cause weight loss?

  • How fast does it happen?

  • When should you be worried about unexplained weight loss?

  • What nutrients are most important in cancer? How do they help?

  • How to manage weight loss while having cancer?

Cancer And Unexplainable Weight Loss 

Many people who have cancer experience unexplained weight loss. According to studies, it is believed that more than forty percent of people experience unexplained weight loss when they are first diagnosed with cancer.  In essence, weight loss in cancer can be classified into two types.

Calorie deficiency

The first type of weight loss is still considered normal and treatable, and it is caused by a calorie deficiency in the body due to the loss of appetite that cancer patients experience. This condition can be reversed with proper nutrition and a healthy diet


The second type of unexplained and rapid weight loss is known as cachexia. Patients with cachexia will experience a loss of a significant amount of skeletal muscle, an increase in their metabolism, exhaustion, and loss of appetite. This occurs due to more advanced kinds of cancer, and it is impossible to entirely reverse the condition with nutrition alone.

Different types of cancer have different statistics regarding weight loss, with upper gastrointestinal cancers having the highest percentage. Upper gastrointestinal cancers such as stomach, esophagus, and liver cancer generally have an average 80% weight loss possibility.

Why Does Cancer Cause Weight Loss? 

To better understand why cancer causes weight loss, we need to look at the issue from three different angles: the weight loss that is linked with the disease itself, the weight loss that is associated with cancer treatment, and other contributing factors.

Weight loss associated with cancer itself

According to a study, over 38% of people who experienced unexplained weight loss were mainly suffering from cancer of the digestive system. Cancer or tumor might block a passageway that makes swallowing difficult or create a sense of fullness. 

Cancer could also affect how your hormones work, interfering with the signaling process that tells you when your body needs nutrients. This means that you don’t feel the need to eat even when your body craves it.

Weight loss associated with cancer treatment

The second reason for weight loss in cancer patients is the treatment itself, which may include chemotherapy, hormone therapy, radiotherapy, or other options. These therapies can cause unpleasant side effects such as nausea and vomiting and alterations in smell and taste, ultimately resulting in a lack of appetite.

Other causes

After a diagnosis, a patient may experience various physiological symptoms, including stress, pain, and depression, which can contribute to weight loss. It has been discovered that feelings of stress and depression cause a person's metabolism to speed up as a result of the "flight or fight" reaction while at the same time reducing their hunger. Both of these conditions will result in a reduction in the amount of weight carried by the body.

How Fast Does Weight Loss Happen? 

Rapid weight loss can occur in patients who have not been diagnosed with an illness within six months to one year. The length of time it takes to complete varies on the type of cancer and the degree to which it has progressed.

However, because of the potential side effects of treatment, patients who are currently receiving treatment may experience weight loss, albeit a moderate amount, within the first few weeks of medication. It is of the utmost importance that you have your weight checked immediately if there is any sign of sudden weight loss and that you maintain your weight within a healthy range so that it does not impede your recovery.

When Should You Be Worried About Unexplained Weight Loss? 

Whether you should be concerned about your unexplained weight loss counts on the condition. If you lose more than 5% of your body weight in 6 to 12 months, you should visit a physician because this might be a cancer symptom.

You should also be worried about losing too much weight during cancer treatment, as high weight loss is associated with a lower chance of survival. 

If you lose more than 2 to 3 pounds in a week or more than 5% of your body weight in a year while receiving treatment, you should get in touch with the members of your care team.

What Nutrients Are Most Important In Cancer? How Do They Help?


Protein is essential for developing, maintaining, and repairing human tissue and properly functioning our immune systems. If your body does not receive enough protein, it may resort to breaking down muscle to obtain the fuel it requires. Because of this, getting better after an illness takes more time and can make one less resistant to infection. 

Cancer patients typically have an increased requirement for protein. In most cases, additional protein is required to facilitate the healing of tissues and aid in the fight against infection after undergoing medical procedures such as surgery, chemotherapy, or radiation therapy.

Fish, lean cuts of red meat, eggs, poultry, low-fat dairy products, nuts, nut butter, dry beans, peas, and lentils, as well as meals made with soy, all provide excellent protein sources.


Omega-3 can inhibit proteolysis or the breaking down of protein in the body. So not only will this reduce the rate of muscle deterioration in cancer patients, but it will also preserve the body’s protein in general. 

Vitamins and minerals

You'll get plenty of vitamins and minerals from a balanced diet. Cancer treatment side effects might make eating a healthy diet difficult. Your doctor or dietician may recommend a multivitamin and mineral supplement if you encounter treatment side effects. If you've lost weight because of treatment, inform your doctor.


Antioxidants include the vitamins A, C, and E; the minerals selenium and zinc; and certain enzymes that may absorb and attach themselves to free radicals (destructive chemicals), preventing them from damaging normal cells. 

To increase your intake of antioxidants, it is recommended by health professionals that you eat a wide variety of fruits and vegetables.

Take Away

Why does cancer cause weight loss? It could be associated with the disease's nature or the cancer treatment's effects that cause appetite loss. 

There are ways to manage weight loss during cancer but this could be difficult, as patients will experience loss of appetite due to cancer treatments. Nevertheless, managing weight loss is crucial because the body will need extra calories and energy for recovery, proper nutrition, and the appropriate cancer treatment.

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