Losing weight from either a low-carb or low-fat diet lowers body inflammation

Results of the study are being presented at the American Heart Association Scientific Sessions on November 5, 2012.

Inflammation occurs naturally when the body's immune system acts to fight off an irritant or infection or responds to an injury. However, fat cells secrete molecules that also increase inflammation, even when an immune response is not needed. Because these molecules are secreted into the bloodstream, being overweight or obese increases the risk of inflammation throughout the body. This more widespread condition is known as systemic inflammation.

According to the researchers, systemic inflammation increases the chance of a heart attack or stroke by promoting the formation of blood clots, interfering with the ability of blood vessels to contract and relax normally to control blood flow, or causing plaque to break off of vessel walls.

"Our findings indicate that you can reduce systemic inflammation, and possibly lower your risk of heart disease, no matter which diet -- either low-carb or low-fat," says Kerry Stewart, Ed.D., professor of medicine at the Johns Hopkins University School of Medicine and director of clinical and research exercise physiology. "The important factor is how much weight you lose -- especially belly fat."

Stewart adds that there's still some bias in the medical community against a low-carb diet, which, by definition has a higher percentage of fat and protein than a low-fat diet. In their study, 60 people, ages 30 to 65, who were either overweight or obese with excessive fat around their waist, were randomly assigned to go on a low-fat or a low-carb diet for six months. Each group also participated in exercise training three times a week.

The researchers measured the participants' blood levels for three common markers of inflammation -- C-reactive protein, interleukin 6 and tumor necrosis factor-alpha -- at the beginning and end of the study. They also measured body weight, body mass index (BMI) and total body and belly fat. At the start, both groups were similar in the various measures, including elevated levels of inflammation markers.

The participants on the low-carb diet lost more weight, on average, than those on the low-fat diet -- 28 pounds versus 18 pounds. The low-carb diet group also had a greater drop in BMI (4.7 versus 2.9), and a greater drop in belly fat (14.3 versus 8.4 pounds). The level of aerobic fitness increased in both groups by about 20 percent.

"In both groups, there was a significant drop in the levels of all three measures of inflammation," says Stewart, indicating that a diet higher in fat and protein doesn't interfere with the ability to lower inflammation, as long as you are losing weight.

The study was funded by the National Heart Lung and Blood Institute (NHLBI), part of the National Institutes of Health, under contract number R01HL092280.