Digestive Health Current Topics in Digestive Health

The Fat Inside: The Concealed Consequences of Obesity

People who are obese probably already know they're more likely to develop heart disease and diabetes. But they may not realize they are also heading toward a whole range of gastrointestinal (GI) problems, from acid reflux to fatty liver disease to some GI cancers.

"Having excess body fat means not just having excess fat inside fat tissue, but also having excess fat in organs, particularly the liver," says Dr. Samuel Klein, director of the Center for Human Nutrition at Washington University in St. Louis. "Having excess fat in the liver causes liver dysfunction and even can lead to serious long-term liver disease. For example, if you're obese and have diabetes and hypertension, you have about a 75 percent chance of having fatty liver disease." In fact, fatty liver disease is now the most common cause of abnormal liver tests in the U.S.

Normally, nutrient-rich blood passing from the stomach and intestines through the liver is converted into energy when food is processed. But the metabolism of excess fat, and the subsequent increase in fatty acids, can damage the liver and impair its function. Fat in the liver can lead to non-alcoholic fatty liver disease, which resembles the damage to the liver done by alcohol abuse. It then can progress to cirrhosis of the liver, in which liver cells are replaced by scar tissue. As a result, liver disease due to obesity has become a common cause of liver transplantation in the United States.

Obesity is also a risk factor for gastroesophageal reflux disease, or GERD, which causes chronic heartburn. GERD involves a malfunction in the lower esophageal sphincter, a muscle that acts as valve between the esophagus and stomach. The valve fails to close properly, allowing acid, enzymes and partially digested food in the stomach to slip back up into the esophagus, causing heartburn. Losing weight, especially if people improve their diets in the process, can ease GERD symptoms.

The relationship between weight and gallbladder disease is a more complex one. Gallbladder disease is characterized by the development of gallstones. Gallstones are small masses of solid material —mainly cholesterol in most cases— that form in the gallbladder when it cannot dissolve all of the cholesterol in bile, or when the gallbladder is not emptying properly.

"People who are obese, particularly obese women, have a much higher risk of gallstones than non-obese women," Klein says. "But losing weight initially increases your risk of having gallstones because weight loss itself changes the composition of bile." However, gradually losing weight, and then keeping it off, can help lower the risk of developing gallstones.

While obese people are not more likely to get pancreatitis, or inflammation of the pancreas, they are more likely to have a severe form of it. "The reason for that is unknown," Klein says. "It might be due to excess fat around the pancreas that gets digested by leaky pancreatic enzyme releasing fatty acids and toxic products around the pancreas." In addition, obese patients with gallstone disease are at risk of developing gallstone pancreatitis. This is thought to result from a temporary blockage of the pancreatic duct as small gallstones pass from the gallbladder into the small intestine.

Obese people may also have a higher risk of colon and rectal cancers than leaner people do, for reasons that are not yet clear. The same is true when it comes to liver cancer, which can arise from cirrhosis related to fatty liver disease.

"I think it's important to recognize that, in addition to the diseases we associate with obesity—diabetes, hypertension and heart disease—being overweight can also increase risk of GI disease," Klein says. "These diseases need to be on the radar screen."