Stressed? It could be your diet.

A study suggests that people feel more stressed when they track what they eat, even if they’re not cutting calories.

And even if you’re not noticeably tense, the study found that people who cut calories have higher levels of a stress hormone – so your body could be feeling the effects, one of which, unfortunately, is to store more fat around the midsection.

“This is the first time we can say, ‘Yes, dieting is stressful in a biologically meaningful way,’” says A. Janet Tomiyama, PhD, lead author of the study and a Robert Wood Johnson Foundation Health & Society Scholar at the University of California, San Francisco.

Researchers in California and Minnesota set out to see what happened to dieters’ stress levels when they employed two common weight loss strategies – cutting calories and counting calories.

To do that, psychologists recruited 121 women who wanted to go on a diet and randomly assigned them to follow one of four regimens: One group was asked to track the number of calories they normally ate; a second group was asked to track their calories and restrict them to just 1,200 a day; a third group got pre-packaged meals that totaled 1,200 calories a day, but were told they didn’t have to count calories; and a fourth group of controls didn’t do anything differently. Regular tests monitored how much stress each group felt and how much of a stress hormone, cortisol, they made.

After three weeks, people in the groups that held their calories to 1,200 a day, lost an average of about 2 pounds each. Those in the groups that didn’t cut calories gained an average of nearly 3 pounds each.

The groups that counted calories reported feeling more stressed, even if they weren’t restricting what they ate.

The group that got the pre-packaged meals, however, didn’t report feeling any more stressed, but their hormones told a different story. Dieters in this group saw an average increase in their cortisol levels of about 15 percent.

Researchers also accounted for the affects exercise, stressful events, general health, pain, and alcohol and caffeine consumption had on cortisol levels. However, cortisol levels remained high for those counting calories, despite these external factors.

Cortisol has the attention of obesity researchers because one of its many functions is that it tells the body to store fat around the belly.

“What we’re saying is you might not even realize it, but that diet is changing all sorts of things like, in this study, your stress hormone levels,” Tomiyama says.

The study was published online in Psychosomatic Medicine.

Tomiyama and her team say their findings have far reaching implications since chronic stress not only promotes weight gain, but has also been linked to cancer, diabetes, heart disease and many other health problems.