Putting on some extra weight over winter or during a super-stressful time may not seem like such a big deal, as long as you slim down again when the weather gets warmer or your schedule calms down. But new research suggests that yo-yo weight fluctuations are bad for the heart. For some women, these ups and downs may even raise their risk of dying from cardiac disease.

The study, which was presented today at an American Heart Association conference, followed nearly 160,000 postmenopausal women for about 11 years. Women who were normal weight at the start of the study and lost and regained at least 10 pounds had about 3.5 times higher risk of sudden cardiac death than women whose weight remained stable. This type of “weight cycling” was also linked to a 66% increased risk for death related to coronary heart disease in those women. (Coronary heart disease occurs when fat and other substances block blood vessels to the heart.)

Yo-yo dieters who started the study overweight or obese, however, had no increase in either type of death. They also found no increase in death for women who gained weight but did not lose it, or for women who lost weight but did not gain it back.

Lead author Somwail Rasla, MD, internal medicine resident at Memorial Hospital of Rhode Island and Alpert Medical School of Brown University, says that normal-weight women seem to be more vulnerable to the dangers of weight fluctuations. 

“Normal-weight women usually have less adaptive mechanisms in their body, compared to overweight and obese women, when they [are] exposed to…the hazardous effects of weight cycling,” he said in a video on the American Heart Association website. Previous research has shown that these effects include changes in metabolism, blood pressure, and cholesterol; and animal studies have shown that practices like yo-yo dieting can damage DNA. 

That doesn’t mean that it was healthier to be heavier in the study, or that overweight women didn’t face their own health risks. Although it wasn’t the focus of the research, obesity still raises the risk of cardiac disease, Dr. Rasla stresses, as well as several types of cancer, diabetes, and other chronic conditions. 

“For those who have normal weight, they should preserve their body weight and avoid, as much as they can, fluctuations,” Dr. Rasla said. “But for those who are overweight or obese, actually the worst thing for them is being overweight and obese.”

So if you’re overweight, losing those extra pounds (through exercise or a balanced diet) will almost always be a good thing. This group of people “should not worry about weight cycling or fluctuations in body weight, because basically they are not increasing their risk,” Dr. Rasla said. 

Weight gain and loss in this study were self-reported, and the researchers did not collect information on the causes behind the changes. But Dr. Rasla says that often, weight cycling is tied to stress eating and crash diets.

The new findings have not yet been published in a peer-reviewed medical journal, and the researchers say that more studies are needed before any clinical recommendations can be made—especially since theirs did not include men or younger women. Plus, the study was observational (and not a placebo-controlled intervention, for example), so it was only able to determine a link between weight fluctuation and heart disease risk, not a cause-and-effect relationship.

Even so, Dr. Rasla is still comfortable providing some advice to people concerned about their weight and their heart health: “Our main message [is] that those who are, in their adult life, normal-weight, should stick to, as much as they can, with a stable weight,” he said.

American Heart Association spokesperson Suzanne Steinbaum, DO, agrees that while the study should not be seen as the “end all be all” of the health effects of yo-yo dieting, the findings are certainly important—especially for women who have trouble keeping off extra pounds after menopause.

“Here is a study which shows the real true negative effects of what yo-yo dieting can do on our hearts, and this is very, very relevant and important for us to see and understand,” said Dr. Steinbaum, who is director of Women and Heart Disease at Lenox Hill Hospital’s Heart and Vascular Institute in New York City, in a video.

“One of the things I often say to women is, ‘Train for menopause like you’re training for a marathon because you’re in it for the long haul,” she added. In other words, make lifestyle changes you can actually maintain.

Yo-yo diets are characterized by extremes and quick fixes, says Dr. Steinbaum (think slashing calories, cutting out entire food groups, or over-exercising). “We know that’s not sustainable, so there’s significant weight gain that comes back,” she said. “That pattern is very hard on our hearts. It’s important to take home the message that a healthy lifestyle is about a lifestyle…It’s really about making choices that can sustain you in a heart-healthy way.”