Obesity Changes Heart Muscle

Being overweight or obese can hurt the heart, even in people who don't have heart disease .

New research from Australia spotlights obesity's independent effects on the hearts of healthy people who have excess weight.

The study was conducted by experts including Thomas Marwick, MBBS, PhD, FRACP, of Australia's University of Queensland. Their report appears in the Nov. 9 issue of the journal Circulation.

Marwick and colleagues focused on 142 healthy men and women who averaged 44 years old. None of the participants had heart disease, high blood pressure, type 2 diabetes, or any known symptoms of heart failure.

Based on body mass index (search), an indirect measure of body fat, participants were divided into four groups: severely obese (BMI of more than 35), mildly obese (BMI of 30-34.9), overweight (BMI of 25-29.9), and normal (BMI less than 25).

Although the participants seemed healthy by ordinary screening measures, such as blood pressure reading, electrocardiogram (search), and ultrasound of the heart, the researchers detected subtle effects of excess weight on the hearts of overweight and obese participants.

Many problems of the heart were revealed by a new kind of ultrasound technology, which the researchers used to get an in-depth look at participants' heart muscle and function, as well as treadmill exercise tests and blood samples.

Ultrasound images showed that severely obese participants had significantly reduced pumping function in their hearts' lower chambers, compared with participants with normal BMI. In other words, the left chambers or ventricles in the hearts of severely obese participants had a harder time contracting (systolic function) and relaxing (diastolic function). Therefore people with excess weight had compromised their heart function, even though they were not known to have heart disease.

Mildly obese and overweight patients had the same problem to a lesser, but still significant, degree. The condition could be a warning sign of future heart failure, in which the heart can't pump out enough blood.

Treadmill tests showed that exercise capacity was reduced in participants who were overweight, mildly obese, or severely obese, with the most obese people having the least capacity for exercise.

Likewise, participants' blood samples showed that those with higher-than-normal BMI also had higher insulin levels after fasting. Again, the problem was worst in the severely obese group. High fasting insulin levels (search) could eventually lead to insulin resistance and type 2 diabetes (search), which are both risk factors for heart disease.