While many more people suffer from excess appetite, and would rather decrease it so they can lose weight, some people find that they have insufficient desire to eat food and thereby lose weight even though they don’t want to. Mild weight loss can occur in relatively healthy people with stomach problems such as dyspepsia or gastric atonia (sluggish action of the stomach). More severe loss of weight can occur among people who are receiving cancer chemotherapy or have serious diseases such as HIV, emphysema (COPD), Crohn’s disease, or congestive heart failure. In extreme cases, inadequate caloric and fat intake leads to a form of starvation (cachexia) that can hamper recovery and increase the risk of death.

Conventional treatment of undesired weight loss primarily involves concentrated protein-calorie supplements, often taken in liquid form. However, among people who have cancer, simply increasing nutritional intake may not help. Cancer can cause a condition called tumor-induced weight loss (TIWL), in which symptoms of starvation occur despite apparently adequate nutrition. The cause is thought to be a particular form of inflammation caused by the cancer. For this reason, nonsteroidal anti-inflammatory drugs have been tried for the treatment of TIWL, with some positive results.1 Progesterone-related drugs may be helpful for TIWL as well, for reasons that are not clear.

Note: This article does not cover psychological eating disorders, such as bulimia or anorexia.

Fish oil contains omega-3 fatty acids, “good fats” that have many potential health-promoting properties. As noted above, cancer-induced weight loss involves inflammation and responds to treatment with anti-inflammatory drugs. Fish oil also has anti-inflammatory effects. According to some, though not all, studies, fish oil supplements can help people with cancer gain weight.2-4

A typical dosage of fish oil used for cancer-induced weight loss is about 12 g daily. For more information, see the full Fish Oil article.