That worked fine for our ancestors, Peeke said, but the brain can't tell the difference between survival stress and chronic, daily stress.

CNN: Health - Stress is bad, but one expert says it's also fattening

"It temporarily impairs the prefrontal cortex, the smarty-pants part of the brain that allows you to think clearly and rein inimpulsivity, " Peeke says.

CNN: Wine or your waistline? 3 rules to follow

But relaxation techniques may not be enough, Peeke said, since the best way to block stress hormones is through beta endorphin -- produced during exercise.

CNN: Health - Stress is bad, but one expert says it's also fattening

"Weightlifting on a routine basis -- meaning twice a week vigorously for 30-40 minutes -- for both men and women is really the key, " Peeke said.

CNN: Health - Stress is bad, but one expert says it's also fattening

"There are special receptors on the fat cells deep inside the abdomen which are specifically intended to hook up with stress hormone -- and stress hormone stimulates them to accept fat, " said Peeke, a former senior scientist at the National Institutes of Health.

CNN: Health - Stress is bad, but one expert says it's also fattening