Most people with cancer will lose weight at some point. When you lose weight for no known reason, it’s called an unexplained weight loss. An unexplained weight loss of 10 pounds or more may be the first sign of cancer. This happens most often with cancers of the pancreas, stomach, esophagus (swallowing tube), or lung.
Your weight can fluctuate for various reasons. A life-changing or stressful event can cause you to lose weight unintentionally. Even having an especially busy schedule for a while can cause a temporary change in your food intake and activity level, causing you to lose a few pounds.
Other cancers, such as ovarian cancer, are more likely to cause weight loss when a tumor grows large enough to press on the stomach. This can make you feel full faster.
Cancer also increases inflammation. Inflammation is part of your body’s immune response to a tumor, which produces pro-inflammatory cytokines and alters your body’s metabolism. This disrupts the hormones that regulate your appetite. It also promotes the breakdown of fat and muscle..
Finally, a growing tumor uses a significant amount of your body’s energy, which may increase your resting energy expenditure (REE). REE is how much energy your body burns at rest.