6 Autoimmune Diseases That Mess With Your Weight

Of the 29 million Americans who have diabetes, only around 1.25 million have type 1, which occurs when the immune system attacks the cells that produce insulin in the pancreas. (Type 2 diabetes, the more common form, is not considered an autoimmune illness.) Because insulin plays a key role in how your body uses and stores glucose for energy, many people with undiagnosed type 1 diabetes experience unexplained weight loss. If you're having any other symptoms—like excessive thirst, frequent urination, fatigue, or blurred vision—talk with a doctor.

Weight gain isn't technically a symptom of rheumatoid arthritis, but it's common for people with RA to see the number on the scale start creeping upward. The steroids commonly used to reduce inflammation can cause weight gain and water retention, and the symptoms—joint tenderness, stiffness, and fatigue—can make it hard to maintain your normal activity level. But Engelman says patients often get discouraged when they can't work out at "warrior" level and end up doing nothing at all. "Put your sneakers on, and walk for 15 minutes or half an hour at a reasonable pace," he says. 

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We hear a lot about gluten sensitivity these days, but only around 1% of the population actually has celiac disease, an autoimmune disorder in which eating gluten causes the immune system to attack the cells of the small intestine. People with celiac "don't absorb food well, so they're frequently thin," Engelman says. Other symptoms can vary greatly, but may include abdominal pain, bloating, headaches, joint pain, or anemia. Your doctor can do a simple blood test to screen for it—just be aware that you have to be consuming gluten for the screening to work properly, so call your doctor before attempting a DIY elimination diet.

This autoimmune disorder affects the adrenal glands, which regulate the hormones that help you cope with stress and regulate your blood pressure. When the adrenal glands don't produce enough of these hormones, it can cause decreased appetite, nausea, and sudden weight loss. If you've been exhausted or lightheaded lately, or your mood has been off, mention it to your doctor. (Here are 8 things you should know about Addison's disease.)

When your immune system messes with your thyroid, it can cause unexplained weight changes. Your thyroid helps control your metabolism, so if it's underactive (hypothyroidism), everything slows down. That's why common symptoms include weight gain, fatigue, constipation, hair loss, and depression. 

The flip side is an overactive thyroid, which is often caused by Graves' disease. When your thyroid makes too much thyroid hormone—you guessed it—everything speeds up, including your metabolism. "You lose weight even though you're eating like a lunatic," Engelman says. Other symptoms can include rapid heartbeat, frequent bowel movements, and difficulty sleeping. If you suspect your thyroid might be out of whack, your doctor can check with a simple blood test. (In as little as 30 days, you can be a whole lot slimmer, way more energetic, and so much healthier just by following the simple, groundbreaking plan in The Thyroid Cure!)

Crohn's and colitis tend to get lumped together, because both are inflammatory bowel diseases caused by an abnormal immune response. The difference: ulcerative colitis only affects the colon, whereas Crohn's can affect any part of the gastrointestinal tract. Both diseases can cause diarrhea and cramping, and since this can make eating pretty unpleasant, weight loss is also a common symptom. If you have ongoing tummy troubles, talk with your doctor.