While weight loss is often linked with cancer, colon cancer can sometimes lead to weight gain. This can be confusing, as cancer is generally associated with a decrease in body mass. However, colon cancer or its treatments can cause an increase in weight. Understanding these situations can help clarify this less common, yet possible, symptom.
The Typical Relationship Between Colon Cancer and Weight
Weight loss commonly occurs with colon cancer, often due to a metabolic change known as cancer cachexia. This syndrome involves involuntary loss of skeletal muscle mass, even if fat mass is preserved or increased. Cancer cachexia results from systemic inflammation, oxidative stress, and an altered metabolism where the body expends more energy than usual.
Patients may also experience a significant loss of appetite, known as anorexia. This can stem from the physical presence of the tumor, which might cause bowel obstruction, or from inflammatory molecules released by the cancer that interfere with hunger signals in the brain. Colon cancer can also impair the body’s ability to absorb nutrients from food. The tumor can disrupt the intestinal lining’s barrier function and alter gut bacteria, both reducing effective nutrient absorption.
How Colon Cancer Can Lead to Weight Gain
Fluid retention, particularly a condition called ascites, is a way colon cancer can lead to weight gain. As colon cancer advances, it can spread to the peritoneum, the thin lining of the abdomen. This spread can irritate the peritoneum, causing fluid to accumulate in the abdominal cavity. This fluid adds significant weight and often results in noticeable abdominal swelling, even if muscle and fat are lost elsewhere. Malignant ascites is observed in more advanced stages of the disease.
A large tumor’s physical mass also contributes to overall body weight. Colon tumors can range in size, with reported diameters from 0.6 cm up to 15 cm. The pain and fatigue associated with colon cancer can reduce physical activity levels. If food intake remains consistent despite decreased energy expenditure, the resulting caloric surplus can lead to weight gain.
Weight Gain Associated with Colon Cancer Treatment
Medical treatments for colon cancer can also contribute to weight gain, distinct from the disease’s direct effects. Corticosteroids are often given alongside chemotherapy to reduce inflammation, nausea, and prevent allergic reactions. A common side effect of these steroid medications is an increase in appetite and fluid retention.
The emotional stress and physical toll of cancer treatment can alter eating behaviors. While some chemotherapy treatments cause nausea that reduces appetite, other patients may find their appetite stable or increased. When combined with reduced physical activity during recovery, this can lead to a caloric surplus and subsequent weight gain.
Other Symptoms and When to Consult a Doctor
Beyond weight changes, several other symptoms may signal the presence of colon cancer. These include persistent changes in bowel habits, such as new or worsening diarrhea or constipation, or stools that appear unusually narrow. Rectal bleeding, which might manifest as bright red blood or cause the stool to appear dark or tarry, is another indicator.
Individuals may also experience ongoing abdominal discomfort, including cramps, gas, or pain that does not resolve. A feeling that the bowel does not empty completely after a bowel movement, even after passing stool, is also a symptom. Unexplained fatigue or weakness, often due to anemia from slow blood loss, can also be present. If you experience any unexplained weight changes, whether gain or loss, especially when accompanied by these other symptoms, consult a healthcare professional for evaluation.