NEW YORK (Reuters Health) - Contrary to their expectations, British researchers have found that when exposed to psychological stress, obese people show smaller changes in their heart rate compared with normal-weight individuals.

Dr. Douglas Carroll at the University of Birmingham, and colleagues there and at the University of Glasgow, examined the association between obesity and the magnitude of heart reactions to stress in 1,647 adults living in the community.

Blood pressure and heart rate were measured at rest and in response to psychological stress -- performing mental math problems under a time deadline. Measurements were taken when the study began and 5 years later.

Contrary to expectations, heavier individuals and "those categorized as obese displayed smaller heart rate reactions to stress," Carroll and colleagues report in the journal Psychosomatic Medicine.

Moreover, "high heart rate reactivity was associated with a reduced likelihood of becoming obese in the subsequent five years," they write.

Low nervous system activity, which leads to smaller heart rate changes, may be associated with weight gain and the findings of this study "are certainly in line with that notion," the investigators say.

Carroll's team notes that other researchers have suggested that reduced nervous system activity may increase food intake.

Be that as it may, they conclude that low heart rate reactivity may be a risk factor for developing obesity.

SOURCE: Psychosomatic Medicine, July/August 2008.

Related MedlinePlus Pages:

• Obesity - http://www.nlm.nih.gov/medlineplus/obesity.html
• Stress - http://www.nlm.nih.gov/medlineplus/stress.html