Dear Doctors: You always hear how unintended weight loss is a symptom of different diseases. How does that happen? Does the disease actually make you lose weight, or is it just that you've lost your appetite because you don't feel well and are eating less?
Dear Reader: It's true that when you're not feeling well, it's easy to lose your appetite. This leads to eating less and, eventually, losing weight. But what you are asking about is more accurately described as unexplained weight loss. This is a decrease in body weight that isn't readily explained by changes to diet or activity level. It is sometimes quantified as a loss of 5% or more of total body weight that takes place over the course of six to 12 months.
For most of us, weight fluctuates from week to week and even from day to day. But sustained and unexplained weight loss is a symptom of several serious illnesses. These include gastrointestinal diseases, hormonal disorders, infections, autoimmune diseases and cancers. Unexplained weight loss can also be a side effect of some medications and an indicator of mental health or substance use disorders.
How much you eat and how active you are each affect body weight. So does overall health. Part of the general health equation is how well the body takes in and uses the nutrients in the foods we eat. Cancer, particularly when it occurs in the digestive system, can interfere with nutrient absorption. So can gastrointestinal illnesses such as celiac disease and inflammatory bowel disease. Unexplained weight loss can also be caused by chronic infection. This can occur due to the ongoing immune response, which revs up energy demands. In fighting infection, the immune system also releases specialized molecules that can alter metabolism and lead to the breakdown of muscle and fat.
Hormonal disorders can cause weight loss through several mechanisms. Hyperthyroidism, which is when the thyroid gland becomes overactive, accelerates metabolism. This increases the body's energy needs and can lead to a calorie deficit. Diabetes, by contrast, makes it more difficult for the body to access the energy sources that are already present. When the body isn't making enough insulin or can't use it effectively, it's harder for glucose to move from the blood and into the cells. This can cause glucose to be lost in the urine. With glucose now less available, the body begins to break down fat and muscle to use for energy.
If anyone experiences unexplained weight loss, check in with your healthcare provider to try to pinpoint a cause. They will review your medical history, including whether you are up to date on recommended cancer screenings. These can include prostate and colorectal cancer screening, and mammograms. If a metabolic issue is suspected, blood tests may be recommended. These can include testing for thyroid function, and blood glucose or A1C for diabetes. Unexplained weight loss doesn't automatically mean something is seriously wrong. But finding the cause can offer answers and also peace of mind.
(Send your questions to [email protected], or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
