Weight loss can occur for many reasons. It can be either voluntary (on purpose) or involuntary (not on purpose). It is due to one of three causes: decreased calories being consumed, increased calories being used, or loss of calories in the urine or stools. Voluntary weight loss is a sign of good health for patients who are overweight. It is usually due to significant attempts at eating less and exercising more.
If the involuntary weight loss is associated with increased calorie intake patients often have increased appetite or thirst. These causes include intestinal disorders that cause lack of absorption of food (like chronic diarrhea), endocrine disorders that cause the body to burn more energy (like hyperthyroidism), and uncontrolled diabetes, which cause the body to lose excess calories by spilling sugar into the urine.
Diabetes is a disorder of elevated blood sugars. Sugars become quite elevated before the diagnosis is made. As the blood sugar level goes up, the body cannot reabsorb all of the sugar that is naturally filtered through the kidneys. So the sugar is spilled in the urine.
The higher the sugar level, the more sugar is spilled into the urine. This causes people who have very high sugars to be very thirsty, and to have to urinate very frequently. Patients will often have sudden significant weight loss associated with these symptoms. These same patients will be so thirsty they will often drink sugary drinks (such as sodas, juices or sweetened coffee drinks) which causes the sugars to be even higher, and the weight loss to be more severe. It can become a sudden dangerous cycle.
In a frustrating outcome, a long-term weight-loss program/diet to control diabetes aimed at overweight adults with diabetes didn't cut the rate of heart attacks and strokes, a major study showed. But losing weight did provide at least one major benefit by cutting the development of chronic kidney disease, a leading cause of premature death in people with type 1 and Type 2 diabetes.
If you suddenly develop significant involuntary weight loss, especially associated with significant thirst or an increased need to urinate, it is critical to see a health care provider as soon as possible.