Unexplained Weight Loss as a Sign of Colon Cancer

Unintended Weight Loss Needs To Be Evaluated By A Doctor

Weight loss
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Many of us wouldn't want to question unexplained weight loss. We'd just be happy to be losing weight! Though the prospect of losing weight without even trying may seem like a blessing, it really is something to question. It's the old "if it sounds too good to be true..." idea.

Reasons for Unintentional Weight Loss

Possible causes of unintentional weight loss include depression, frequent diarrhea, hyperthyroidism (an overactive thyroid gland), infection, poor nutrition, AIDS, and cancer.

If you're trying to figure out why someone else is losing weight unintentionally, you may also want to look into drug abuse, eating disorders, and smoking.

Unexplained Weight Loss and Colon Cancer

Tumors are their own life form. They require a blood supply and energy to grow, and they also release their own waste products. Since they're living inside you, tumors use your blood and nutrients and release their waste products inside your body. You're unlikely to notice the diversion of blood and nutrients, but sometimes tumors release chemicals that increase the body's metabolism (such as burn calories faster), which can lead to unexplained weight loss. 

The idea of a tumor as its own life form may also partially explain why many people with cancer do not want to eat, so an unusual loss of appetite is another sign to look out for. Aside from the fatigue and nausea of cancer treatments like chemotherapy, eating may feel like a person is "feeding the tumor." 

Medical Attention for Unexplained Weight Loss

According to the National Institutes of Health, adults should consult a medical professional if they've lost more than 5 percent of their body weight over the past 6 to 12 months without trying. (That would be about 10 pounds for a 200-pound person.)

Of course, you should be sure to call your doctor if you are experiencing any unintended weight loss—even if it does not meet the technical criteria above.

Listen to your gut, and get it checked out. 

A Word From Verywell

In addition to unintended weight loss, you should also call your doctor if you experience other potential colon cancer symptoms like

  • Change in bowel habits (persistent constipation or loose stools or narrowing of the stools)
  • Blood in the stool (either bright red blood or black or maroon stool)
  • Cramping or pain in the abdomen 
  • Unusual fatigue or weakness
  • Rectal bleeding
  • Feeling like you need to have a bowel movement that continues despite having one

These symptoms too can be a sign of something else besides colon cancer like an infection or hemorrhoids. But it's best to be safe and have it evaluated by a healthcare professional. 


American Cancer Society. (February 2016). Signs and Symptoms of Colon Cancer

Colon Cancer Alliance. Symptoms.

National Institutes of Health. (January 2015). Weight loss - unintentional