Now, doctors say it may also damage your heart -- particularly if you're a woman.
In a study conducted at the University of Michigan Health System, cardiologist Dr. Claire Duvernoy found women who fall prey to the gain-loss-gain syndrome, particularly if it occurs five or more times during their life, face a higher risk of cardiovascular disease beginning shortly after menopause.
"We already know that heart disease is the number one killer of women. And what this study tells us is that gaining and losing weight throughout your lifetime can increase your risks even more," says Duvernoy, director of the Cardiac Catheterization Laboratory at the VA/Ann Arbor Healthcare System.
Duvernoy believes the link between yo-yo dieting and heart disease may involve the endothelial cells, which line blood vessel walls. When people gain and lose weight repeatedly, these cells become damaged so blood can't flow as freely. When blood flow to the heart becomes restricted, the stage is set for heart attack and stroke, especially with women, Duvernoy says.
While obesity is certainly an established risk factor for heart disease -- in men as well as in women -- other heart experts aren't so sure the yo-yo syndrome plays a role.
"What we don't know about the women in this study is how much weight they gained, how many years they were heavy before dieting, and whether their yo-yo losses still left them overweight -- all of which can increase the risk of heart disease," says Dr. Daniel C. Fisher, a cardiologist at New York University Medical Center.
One message women shouldn't take from this study is that obesity is better than dieting, Fisher says.
"The best approach is to lose weight and keep it off," he says. "But even if you slide back up again, it's still important to keeping trying to lose the weight because while we're not sure if yo-yo dieting is going to lead to heart disease, what we do know is that obesity definitely does."
The small study involved 16 postmenopausal women, aged 54 to 66. The women were of varying weights, from thin to obese, and they shared a mixed bag of risk factors for heart disease. Some of the women smoked, some had high cholesterol and some were taking medication for high blood pressure.
The research involved a PET (positron emission tomography) scan of each woman's heart, as well as numerous other tests designed to measure blood flow under varying conditions. The study also recorded the women's current weight, their weight at age 18, their highest lifetime weight and the number of times each had a weight swing -- defined as a gain or loss of 10 or more pounds in a year, excluding pregnancy.
After analyzing all the data, Duvernoy says she found that women who experienced weight gains and loses of 10 pounds or more at least five times in their life had the most problems with blood flow and thus, appeared at greatest risk for heart disease.
For Fisher, the research provides interesting new ground for more study. However, the overall message, he says, is likely to remain the same: "Controlling your weight means controlling a major risk factor for heart disease," he says.
Duvernoy says the best way to do that is "to avoid yo-yo dieting and instead make healthy food choices and get plenty of exercise over the course of your lifetime."
She presented her findings at a recent meeting of the American Heart Association.