Being overweight or obese-which 66 percent of Americans are, according to the Centers for Disease Control and Prevention-is a major risk factor for heart problems. Staying active and not smoking can mitigate some of the adverse effects of obesity, but cant erase them altogether, says a new study published in the June 9 online edition of Circulation that undermines the idea that you can be both fat and fit. "Quitting smoking and getting more exercise benefit heart health," says Carolyn Snyder, RD, an ambulatory dietitian in Cleveland Clinics Department of Nutrition Therapy. "But carrying excess weight still trumps that benefit." The study tracked 54,783 participants ages 50 to 64 for seven years. Researchers found that developing acute coronary syndrome (ACS, a group of symptoms that includes unstable angina and heart attack) was significantly associated with increased body mass index (BMI). BMI is a ratio of weight to height, calculated by dividing your weight in pounds by your height in inches squared, and multiplying the result by 703; a score of 25 or more is considered overweight, while 30 or more is considered obese. For each unit of BMI increase-from a BMI of 25 to 26, for example-ACS risk increased by five percent in women and seven percent in men.