There are many causes of fast and unintentional weight loss during a cancer diagnosis. Here are some of the most common reasons.

For many people, weight loss is the first visible sign of cancer. About 31 to 87 percent of people with cancer report an unintentional weight loss.

A combination of weight and muscle loss, also known as cachexia, is also common among cancer patients. Cancer cachexia is mainly driven by changes in how the body makes and uses energy.

There are some cancers that are more commonly associated with weight loss, and certain cancer treatments can also be the cause of unintentional weight loss. Here’s what you need to know.

Unexplained rapid weight loss can be a sign of cancer or other health problems. The American Cancer Society recommends that you see your doctor if you lose more than 5 percent of your total body weight in a year without trying or you lose more than 3 pounds in a week. To put this into perspective: If you weigh 160 pounds, 5 percent of your body weight is 8 pounds.

The American Cancer Society also reports that an unexplained weight loss of 10 pounds or more could be the first sign of cancer. The types of cancer often identified with this type of weight loss include cancers of the:

According to Cancer Research UK:

  • 80 percent of people with pancreatic cancer, esophageal cancer, or stomach cancer have lost a significant amount of weight by the time they’re diagnosed.
  • 60 percent of people with lung cancer have lost a significant amount of weight by the time of their diagnosis.

Cancer treatments can also lead to weight loss. Radiation and chemotherapy commonly cause a decrease in appetite. Weight loss can also be attributable to radiation and chemotherapy side effects that discourage eating, such as:

Unintentional weight loss, according to the NHS, can be attributed to a number of causes other than cancer including:

Depending on your specific situation, your doctor might recommend curbing weight loss with medication. This may include progesterone hormones, such as Megestrol acetate (Pallace, Ovaban), or steroids, such as Pancreatic enzyme (lipase), Metoclopramide (Reglan) or Dronabinol (Marinol).

However, there are no standard medications for cancer-related weight loss. Currently, clinical trials are emerging, and your cancer team can work with you to consider various short-term and long-term options.

In addition to medications, other potential interventions include exercise and diet plans that are specific to people living with cancer, especially when weight loss is recognized early.

Additionally, some cancer patients who have difficulty swallowing or chewing are given intravenous (IV) nutrient therapy. For instance, people with esophageal or head and neck cancers often have difficulties eating or drinking.

Rapid, unexplained weight loss may be an indication of cancer. It can also be a side effect of cancer treatment.

If you’re diagnosed with cancer, good nutrition is important for your recovery. If your calorie intake is too low, you not only lose weight, but also lower your ability to physically and mentally cope with your treatment.

If you’re experiencing unintentional weight loss, talk with your doctor. They can provide an accurate diagnosis and recommend an effective treatment plan.