Why Do Some People With Diabetes Lose Weight?

Diabetes is a metabolic disorder in which the body is unable to properly control blood glucose levels, aka blood sugar. One of the symptoms of diabetes is unexplained weight loss.

Weight loss caused by diabetes may occur even if a person is eating and drinking much more than normal — which is likely, because excessive hunger and thirst are two of the other common symptoms of untreated diabetes.

In order to understand diabetes-related weight loss, we first need to understand how diabetes works.

Glucose, or sugar, is the body's main source of energy. The body converts the compounds in food (mainly carbohydrates) into glucose, according to the U.S. National Library of Medicine. The hormone insulin moves glucose out of the bloodstream and into the cells, which use it for energy.

But people with diabetes either don't make enough insulin or can't use insulin properly. This leads to a buildup of glucose in the bloodstream, resulting in high blood sugar — a potentially dangerous health condition.

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When glucose gets left in the blood, it doesn't reach the cells — and the cells therefore don't get energy. They then send a signal to the brain that they need more fuel, which prompts the brain to trigger the hunger response. This is the reason that a person with untreated diabetes experiences excessive hunger: It's the body's way of saying the cells need more fuel.

This condition of the cells not getting enough fuel leads to weight loss. But, as explained by Diabetes.co.uk, eating more food can't fix the problem, because more food just creates more glucose. Without proper insulin action, glucose can't get into the cells to give them energy; instead, it backs up into the bloodstream, resulting in high blood sugar levels.

In addition to triggering the hunger response, the body of someone with untreated diabetes will attempt to generate fuel by breaking down fat and muscle tissue, the Cleveland Clinic explains. This increases the unintended weight loss.

The longer that a person's diabetes goes undiagnosed, the more weight they could lose unintentionally. Once a person begins treatment, however, they tend to gain weight, which is a good outcome, Elizabeth Halprin, MD, clinical director of adult diabetes at Boston's Joslin Diabetes Center, tells LIVESTRONG.com.

In addition to unexplained weight loss and excessive hunger, excess thirst and increased urination are two of the other most common symptoms of diabetes. High blood sugar levels forces the kidneys to work overtime in order to clear the excess glucose through urine, according to JDRF. This causes a person with untreated diabetes to urinate more frequently. To make more urine, the kidneys need more water, causing excess thirst.

Dr. Halprin points out that excessive urination can also play a major role in the unintentional weight loss related to diabetes. "The reason a person [with untreated diabetes] pees a lot is because the body is trying to get rid of all the [excess blood] sugar," she notes — meaning the glucose that was supposed to go to the cells. "The body's not holding onto it. So that's where all the calories go: down the toilet."

According to the Mayo Clinic, additional symptoms of diabetes can include fatigue, blurred vision, slow-healing sores, frequent infections and/or numbness in the hands or feet.

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According to the Cleveland Clinic, you should talk to a doctor if you have an unexplained weight loss of 10 or more pounds, as this may be a sign of diabetes.

If you experience other symptoms — particularly excessive urination, thirst or hunger — also be sure to inform your doctor as soon as possible.