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.

They say it also might explain the fact that while 47 percent of Americans are trying to lose weight at any given time, an estimated 30 to 64 percent of dieters end up gaining back more weight long term then they lost in the short term.

Tomiyama says this study doesn’t mean people should give up on trying to reach a manageable weight. But she says it does mean you should be smart about how you go about it – and perhaps focus on other things like exercising and not overeating.

“I’m saying there are so many ways to get healthier,” Tomiyama says. “Maybe there are better ways out there than just cutting your calories.”

But other experts feel that the study has serious limitations.

W. Scott Butsch, MD, a weight loss expert at Massachusetts General Hospital in Boston, says it’s hard for him to draw conclusions from this research because we don’t know how many calories the participants were taking in before the study. Therefore, he says, it is difficult to know how much, or even if, people were really restricting their food. 

He also points out that those in the study had average body mass indexes of 24 or 25, which is considered the high end of normal body weight. His patients have an average BMI in the range of 43 to 45. 

“Is this really a good sample population for the general public?” he asks. “Probably not. Two-thirds of our population is either overweight or has obesity.”

Dr. Butsch says he also believes weight loss and weight gain are based on a variety of biological and environmental factors and changes, and he says stress probably does play a role in weight control.

“We know there are many complex pathways involved in weight gain and weight loss and stress is one of those responses,” Dr. Butsch says.

And he agrees with Tomiyama, however, that it’s important to be thoughtful about weight loss. He says there are ways to find a weight-loss plan that won’t add stress.

“What we try to do here is we try to individualize diets. It’s not a restrictive diet where you’re off carbs,” Dr. Butsch says. “The thought is to have a balanced diet and something that’s comfortable for you. The same with exercise – let’s try something that’s comfortable for you."