If you've had occasional sharp abdominal pain that passes quickly, you may have brushed it off as nothing but gas, constipation, or even stress. But this kind of pain can also indicate the presence of gallstones. These pellet-like accumulations in the gallbladder are surprisingly common, affecting as many as 42 million Americans. Gallstones are most prevalent among women, likely because the hormone estrogen increases risk, says Ray Sahelian, MD, a nutrition scientist in Marina del Ray, California. Newer studies have shown that both women and men with a high waist-to-hip ratio are more likely to develop this painful condition.

The trouble begins in the gallbladder, a small, pear-shaped organ located on the underside of the liver that releases bile — important for digesting fats — into the small intestine. In most cases, a gallstone forms when bile becomes oversaturated with cholesterol from the diet or from the body's natural production; the bile salts are no longer able to keep the cholesterol dissolved in liquid form, so it begins to clump together, eventually forming stones that can be as small as peas or as large as golf balls.

If gallstones are small enough, they may pass painlessly from the gallbladder into the intestines, where they're excreted unnoticed. But if stones grow in size and number, they can cause abdominal pain or inflammation of the gallbladder wall. Larger stones can lodge in the narrow opening of the duodenum (at the start of the small intestine), causing bile to back up into the pancreas, leading to pancreatitis, a life-threatening inflammation of the pancreas. For most people with gallstone symptoms, such as chronic pain, surgery is inevitable. But prevention is possible, say experts, and starts with diet.