Causes and Mechanism of Weight Loss in Cancer

Why does weight loss occur in cancer? Weight loss is a common symptom in cancer patients and can often be the first noticeable sign of the disease. Approximately 40% of patients diagnosed with cancer experience unexplained weight loss. The primary cause of weight loss in cancer is loss of appetite (anorexia). This can result directly from the cancer itself or as a side effect of cancer treatments. Other factors contributing to weight loss include: Altered metabolism and increased energy demands of cancer cells Nausea and vomiting Constipation Mouth sores Difficulty chewing and swallowing Loss of taste sensation Malabsorption and malnutrition Depression Pain How does weight loss progress in cancer? Unexplained weight loss of more than 5% of body weight over 6 to 12 months is considered a warning sign of cancer and often begins before diagnosis. The extent of weight loss varies depending on the type and location of cancer. The greatest weight loss is seen in cancers of the upper gastrointestinal tract (esophagus, stomach, small intestine, pancreas, and liver), followed by lung cancer, where about 60% of patients experience weight loss. Cancer treatments such as chemotherapy and radiotherapy can also reduce appetite and cause side effects like mouth sores, nausea, fatigue, and general weakness, further contributing to weight loss. Appetite stimulants may be prescribed during treatment to help manage anorexia and weight loss. How much weight loss is significant? Cancer is often diagnosed in patients who have lost at least 5% of their body weight within 6 to 12 months. Rapid weight loss (e.g., about 1.5 kg per week) or loss exceeding 5% over a year warrants immediate medical attention, especially if accompanied by weakness, confusion, or inability to eat or drink. Complications of weight loss in cancer The most serious complication is cachexia, a syndrome characterized by severe muscle wasting and fat loss due to increased energy demands and metabolic alterations caused by cancer or its treatment. Cachexia leads to physical weakness, reduced ability to perform daily activities, depletion of protein, vitamins, and minerals, and worsens prognosis. Patients who were overweight before cancer diagnosis may not appear wasted despite cachexia, so laboratory tests are necessary for accurate diagnosis. Cachexia also impairs tolerance to cancer treatments such as chemotherapy, radiotherapy, and surgery, and negatively impacts quality of life. Which patients are at higher risk for weight loss? Weight loss is more common in cancers affecting the gastrointestinal tract, pancreas, and lungs. However, tumors like ovarian cancer can cause fullness and early satiety by pressing on the digestive organs, also leading to weight loss. Can cancer patients gain weight? Some cancer patients may gain weight, especially those with breast, ovarian, or prostate cancer, due to hormone therapies that increase weight, reduced nausea when eating, fluid retention caused by medications, or increased tumor mass. Recommended supplements for preventing and managing weight loss in cancer Supplement use should always be supervised by an oncologist or specialized nutritionist since some supplements may interfere with cancer treatments or affect cancer risk. Commonly recommended supplements include: Protein powders (e.g., whey protein or powdered milk) that can be added to foods or consumed as shakes Ready-to-use high-protein enteral formulas suitable for tube feeding or oral intake, ideally used as snacks or between meals Multivitamins and minerals, provided they do not exceed 100% of the recommended daily allowance (RDA)