For most people, dropping a few pounds without meaning to is a welcome surprise. But it's important to know when unexpected weight loss is a cause for concern.

There are many possible reasons for unintentional weight loss, including:

• Changes in diet or activity level. Skipping meals, eating on the run, eating less fat or preparing food in new ways may contribute to unexpected weight loss. A particularly hectic schedule may cause you to drop a few pounds as well.
• Mood changes. Anxiety, stress and depression can affect your weight.
• Medication. Some antidepressants and other medications may cause weight loss.
• Difficulty chewing or swallowing. Dental problems can make it difficult to chew, and many conditions can interfere with swallowing. With esophageal dysphagia, food feels as if it sticks or gets hung up in the base of your throat or chest. Certain neuromuscular problems can weaken your throat muscles, making it difficult to move food from your mouth into your throat and esophagus.
• Poor absorption of nutrients. This may be a problem with disorders such as celiac disease, a digestive condition triggered by consumption of the protein gluten. This protein is found in bread, pasta, cookies, pizza crust and other foods containing wheat, barley, rye and some oats.
• Nausea. If you're feeling queasy, you may eat less and lose weight. Many conditions can trigger nausea. Viral and bacterial infections, hormonal changes and various digestive disorders can all make you nauseated.
• Inflammatory bowel disease. Ulcerative colitis and Crohn's disease are the two most common forms of inflammatory bowel disease. These often painful and debilitating conditions cause chronic inflammation of the digestive tract, which may prevent you from digesting or absorbing much of what you eat.
• Pancreatitis. Pancreatitis is a condition in which digestive enzymes attack the pancreas rather than break down food in the small intestine. Chronic pancreatitis may cause weight loss, even when your appetite and eating habits are normal.
• Lack of blood supply to the bowel. If the blood flow to your small intestine or colon is reduced, you may develop a condition called intestinal ischemia. Signs may include unintentional weight loss.
• Hyperthyroidism. The thyroid hormones regulate every aspect of your metabolism, from your heart rate to how quickly you burn calories. When your thyroid gland produces too much of the hormone thyroxine, you develop hyperthyroidism. This condition causes sudden weight loss, even when your appetite is bigger than normal.
• Diabetes. Diabetes affects the way your body uses blood sugar. Even when you eat as much as usual, you may lose weight if your muscle tissues don't get enough glucose to generate growth and energy. This is especially true with type 1 diabetes, in which very little sugar gets into your cells. With uncontrolled diabetes, sugar lost in the urine may also contribute to weight loss.
• Cancer. Many types of cancer cause unintentional weight loss, including cancers of the pancreas, gallbladder and stomach. Cancer treatment may have the same effect.

If you're losing weight and you're not sure why, consult your doctor — especially if you lose more than 5 percent of your weight within a few weeks or 10 percent within six months. The doctor will determine what's causing the weight loss and the best way to treat the problem. You may need a special diet to prevent further weight loss or regain lost pounds.