What do heart disease, diabetes, Alzheimer's, stroke and cancer have in common? Scientists have linked each of these to a condition known as chronic inflammation, and they are studying how high-fat foods and excess body weight may increase the risk for fatal disorders.

Inflammation is the body's natural response to injury and outside irritants. But when the irritants don't let up, because of a diet of high-fat foods, too much body fat and smoking, for example, the immune system can spiral out of control and increase the risk for disease. Experts say when inflammation becomes chronic it can damage heart valves and brain cells, trigger strokes, and promoteresistance to insulin, which leads to diabetes. It also is associated with the development of cancer.

Much of the research on chronic inflammation has focused on fighting it with drugs, such as cholesterol-lowering statins for heart disease. A growing body of research is revealing how abdominal fat and an unhealthy diet can lead to inflammation. Some scientists are investigating how certain components in foods might help. Dietary fiber from whole grains, for instance, may play a protective role against inflammation, a recent study found. And dairy foods may help ease inflammation in patients with a combination of risk factors.

Chronic inflammation is perhaps best understood in its relation to cardiovascular disease. The immune system's white blood cells rush to the arteries when the blood vessels are besieged by low density lipoprotein, or LDL -- the 'bad' cholesterol. The cells embed themselves in the artery wall and gobble up the invading cholesterol, causing damage to the arteries that can lead to heart attack or stroke.

'You need to have inflammation when you have a wound and the immune system goes in to heal it. Yet we don't want too much inflammation in our system causing damage to our arteries' and other harm, says Wendy Weber, a programdirector at the National Center for Complementary and Alternative Medicine, part of the National Institutes of Health.

One significant discovery concerns obesity and the ways it promotes inflammation. Fat cells, particularly those in the visceral fat that settles in the belly and around organs, were long thought merely to store excess weight. Instead, fat cells act like small factories to churn out molecules known as cytokines, which set inflammation in motion, says Peter Libby, chief of the division of cardiovascular medicine at Brigham and Women's Hospital in Boston and a professor at Harvard Medical School.

'We've learned that abdominal fat tissue is a hotbed of inflammation that pours out all kinds of inflammatory molecules,' Dr. Libby says. The most important step patients can take is to lose excess weight, which can reduce inflammation in a matter of weeks or months, he says.

A substance known as C-reactive protein, measured with a simple blood test, is an indicator of inflammation in the body. A report published in Archives of Internal Medicine in 2007, which analyzed results of 33 separate studies, found that losing weight can lower C-reactive protein levels. For each one kilogram, or 2.2 pounds, of weight loss, whether by dieting, exercise or surgery, the mean reduction in C-reactive protein among participants was 0.13 milligram per liter.

According to the American Heart Association, a C-reactive protein level of less than 1 mg/L indicates a low risk of cardiovascular disease, 1 to 3 mg/L indicates moderate risk, and greater than 3 mg/L equals high risk. Doctors increasingly are ordering the test for patients at moderate risk for heart disease.

At a meeting in Quebec City last week on abdominal obesity and its health risks, experts in cardiology, endocrinology, nutrition and related specialties presented a wide range of new research linking obesity to inflammation-related diseases.