Why Does Cancer Cause Weight Loss?
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Understanding the Connection Between Cancer and Weight Loss

People with cancer commonly experience progressive and often profound weight loss. This is usually a combination of loss of body fat and muscle mass. It is frequently accompanied by extreme weakness, reduced appetite and anemia.

Understanding Cancer Cachexia

This syndrome where the body wastes away is referred to as cancer cachexia. Cancer cachexia is more frequently associated with advanced cancer, although unexplained weight loss of more than 5 percent of body weight can sometimes be the first sign in early cancer.

It occurs in about 50 – 85 percent of cancer sufferers and is more commonly associated with particular types of cancers, such a pancreatic, bowel and lung cancer. Cancer cachexia affects quality of life and makes cancer treatments more difficult to tolerate.

Most people will be surprised to discover that cancer cachexia is directly responsible for death in about a quarter to a third of cancer patients. Greater weight loss is associated with a poorer prognosis.

Cachexia Causes

The cause of this cancer-induced wasting syndrome is not fully understood. Cancer cells do use up a lot of energy as they replicate constantly. However, a human fetus grows more rapidly and uses more energy than most cancers, yet pregnant women do not waste away.

Even small tumors can cause cachexia. So, energy used by the cancer is not responsible for the weight loss.

Cancer does commonly cause reduced appetite. This may be due to changes in taste and also due to changes in the areas of the brain that control appetite. However, studies show that reduced appetite alone is not enough to explain weight loss in cancer and, indeed, not all people with cachexia have reduced appetite.

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However, anorexia does contribute. Cancer causes profound changes in the body’s metabolism, with significantly increased body-wide energy use. Uniquely, cancer promotes the break-down of muscle, as well as fat, to provide for this increased energy need. This is different to the mostly fat loss that occurs with deliberate weight loss or even starvation.

Looking at the Research

Scientists are beginning to work out some of the mechanisms responsible for the muscle wasting and fat loss in cancer. Current research indicates that multiple factors are involved.

The cancer cells themselves produce substances that promote weight loss. Scientists recently discovered one such substance, called MIC-1. This is a protein that is found in the blood of non-cancerous people. However, many cancer cells produce large amounts of MIC-1, causing the levels in the blood to rise to 10 to 100 times normal levels.

Studies have shown that MIC-1 contributes to weight loss solely by suppressing appetite and food intake. Cancer cells also directly produce substances that tell the body to breakdown muscle and fat. One such substance is called PIF.

The body also responds to cancer by producing substances called cytokines, which sends the body’s immune system into overdrive. These inflammatory cytokines have multiple effects on the body’s hormones and metabolism, causing the breakdown of muscle and fat and increasing the body’s resting metabolic rate.

Researchers have found one specific effect of these cytokines is to turn white fat into brown fat. Brown fat is the main fat babies have, which burns energy to keep them warm. Why the white fat is turned into brown fat is unknown, but it commonly occurs in cancer patients and causes an increase in the body’s resting energy needs.

It seems there are many substances involved in weight loss in cancer. Science is still in the early stages of finding out what these substances are and how they cause this cancer-induced wasting syndrome.

Outside Factors

While weight loss is commonly caused directly by the cancer or the body’s response to the cancer, weight loss can also be exacerbated by other factors. Decrease appetite can be caused by pain, nausea, vomiting, changes in taste, and mouth sores from radiation therapy or chemotherapy.

Also, while destroying cancer cells, chemotherapy and radiation therapy cause damage to other areas of the body, such as the blood, skin and intestines. It takes energy for these areas to repair themselves.

Cancers involving the stomach or intestines can also reduce the nutrients extracted from food. Diarrhea and vomiting from treatment can also cause loss of nutrients. Fatigue can also cause reduced activity, which can contribute to muscle wasting.

Cachexia is a horrible side effect of cancer. Currently, there is no treatment and it cannot be prevented or adequately counteracted by increased nutrition.

Scientists are working hard to understand why this wasting syndrome occurs. In the future they hope to be able to target the precise mechanisms responsible for the wasting syndrome with a view to restricting cancer-induced weight loss.

If you are suffering from weight loss due to cancer, try to eat as much nutritious food as you can tolerate. While you may not feel hungry, weight loss means the body is not getting the energy it needs.

You will need to stay as strong as you can for cancer therapies. Eat well, do strengthening exercises to maintain muscle tone, and ask your doctor if there are any therapies or medications that might help.