Modest weight gains – even among those who aren’t overweight – can cause dangerous changes to the heart, but small amounts of weight loss can improve the condition, new research from UT Southwestern Medical Center cardiologists shows.

The report, published in the Journal of the American Heart Association, found that weight increases of as little as 5 percent can result in a remodeling of the heart. That’s the equivalent of a 6.5–pound gain for a 130–pound woman or about a 7.5–pound gain for a 150–pound man.

“The take–home message is that weight gain is linked to abnormal changes in the heart muscle,” said cardiologist Dr. Ian Neeland, Assistant Professor of Internal Medicine at UT Southwestern and senior author of the study. “Regardless of the weight you start at, gaining weight damages the heart whereas losing weight improves the heart.”

Researchers reviewed MRI images of the heart before and after seven years and found that weight gain caused the heart to get bigger and thicker, with its thicker walls reducing the amount of space left to hold and pump out blood, which can lead to heart failure, Dr. Neeland said.

“You get larger, thicker, smaller–cavity hearts that can’t fill very well with blood, and so the blood backs up to the lungs,” said Dr. Neeland, who specializes in evaluating and managing patients with obesity, diabetes, and other forms of metabolic disease coupled with heart–related concerns.

The good news from the study is that even small amounts of weight loss can improve the condition of the heart, even for those who were not overweight, said Dr. Neeland.

But the more important message is don’t gain, Dr. Neeland said.

“The people who were not obese, when they started gaining weight, it was worse for them than gaining weight was for the people who were obese,” he said. “Even if you can’t lose weight, focus on not gaining weight.”

Maintaining weight might be hard for many. American adults tend to gain progressively through middle age, according to the Agency for Healthcare Research and Quality. On average, they add 1.1 to 2.2 pounds per year – an amount that can lead to obesity over time even for those who started at a normal weight.

UTSW researchers looked at MRIs for 1,262 participants in the Dallas Heart Study, an ongoing multiethnic study of adults in Dallas County. Tests were taken between 2000 and 2002, and again between 2007 and 2008, then examined to determine the heart’s left ventricular mass and diastolic volume, mass–to–volume ratio, wall thickness, and ability to eject blood.

The researchers will now look at the effect of gaining weight in the belly versus gaining weight in the hips and thighs, Dr. Neeland said. They hope to have those findings next year.