Unexplained weight loss is losing weight without trying. A medical or mental health condition may cause this weight loss.
There isn't an exact number for when weight loss becomes a medical concern. In general, see your healthcare professional if you lose more than 5% of your weight in 6 to 12 months when you aren't trying to lose weight.
For example, a 5% weight loss in someone who is 160 pounds (72 kilograms) is 8 pounds (3.6 kilograms). In someone who is 200 pounds (90 kilograms), it's 10 pounds (4.5 kilograms).
Unexplained weight loss is more common in older adults and people who live in nursing homes.
Your calorie intake, activity level and overall health affect your weight. Also, your weight is affected by how well your body takes in and uses nutrients from food. Economic and social factors may play a role.
Unexplained weight loss also may be called unintended, unexpected or involuntary weight loss.
Unintended weight loss may have medical and nonmedical causes. Often, a combination of things results in changes in your health and related weight loss. Sometimes, a specific cause of weight loss isn't found.
Most often, medical or mental health conditions that cause weight loss have other symptoms.
Potential causes of unintended weight loss include the following.
If you're losing weight without trying, talk with your healthcare professional. As a rule of thumb, losing more than 5% of your weight over 6 to 12 months is a concern if the weight loss is not intentional. If you're an older adult or have ongoing medical issues, even a smaller amount of weight loss may be an important sign.
Your healthcare professional can work with you to try to figure out what's causing the weight loss. In addition to a complete exam, a health professional asks questions about:
- Patterns of weight loss and other symptoms.
- Diet and exercise.
- Recent changes in diet, appetite or sense of smell.
- Social activities.
- Recent life changes.
- Medicines, dietary supplements and herbal remedies.
- Use of alcohol, cigarettes or other substances.
- Allergies or sensitivities to foods.
- Financial concerns that affect grocery shopping.
- Changes in mood, such as depression.
Your healthcare professional likely also will review any recent cancer screenings. These may include a colon cancer screening test, breast exam and mammogram, or a prostate exam. This can help determine if more testing is needed.
Your healthcare professional may order blood and urine tests that can give information about your general health. Based on the results or other symptoms, you may have other tests, including imaging tests.
Sometimes, if the tests do not show a cause, watchful waiting for 1 to 6 months is a next step. Your healthcare professional may suggest you keep a food diary and track your weight.
Your health professional may suggest that you stop following a diet that limits healthy food choices and calorie intake. You may need a special diet to prevent further weight loss or to regain lost pounds. Your health professional can refer you to a dietitian, who can offer suggestions on getting enough calories.
Show References
- AskMayoExpert. Abnormal weight loss. Mayo Clinic; 2021.
- Involuntary weight loss. Merck Manual Professional Version. https://www.merckmanuals.com/professional/special-subjects/nonspecific-symptoms/involuntary-weight-loss. Accessed May 25, 2022.
- Goldman L, et al., eds. Approach to the patient with gastrointestinal disease. In: Goldman-Cecil Medicine. 27th ed. Elsevier; 2024. https://www.clinicalkey.com. Accessed May 25, 2025.
- Gupta R, et al. Approach to the patient with unintentional weight loss. https://www.uptodate.com/contents/search. Accessed May 25, 2022.
- Medical review (expert opinion). Mayo Clinic. July 9, 2025.
Original article: https://www.mayoclinic.org/symptoms/unexplained-weight-loss/basics/when-to-see-doctor/sym-20050700