Pinehurst, N.C. — A breathing test can help people learn how many calories they consume each day and form a plan to lose weight.

Many people fail at diets because they don't know how many calories they can consume per day and still lose weight safely.

So when Lisa Smith wanted to lose weight, she turned to registered dietitian Kathy Hefner at the FirstHealth Center for Health and Fitness for help.

Hefner gathered information about Smith's normal activity levels and sleep habits.

She used a breathing device, called the Med Gem, to measure the least number of calories Smith needs each day. The Med Gem measures how much oxygen Smith consumes, which indicates her resting metabolic rate.

"Just like a campfire needs oxygen to burn, our body actually uses oxygen in order to create energy," Hefner said.

A 5- to 10-minute test with the Med Gem, combined with Smith's personal data, yielded a plan for her to lose one to two pounds a week. Under the plan, Smith can consume about 1,450 calories a day.

"It's nice to know what I can eat," Smith said. "She (Hefner) said I can come back for the follow up for the meal plan, so that'll be nice."

The Med Gem provides a more accurate measure than the estimates given by magazines and Web sites. The device gives a user a sense that the calorie limit "is my number. It becomes unique to them," Hefner said. With that knowledge, it's easier to create a personalized meal plan for weight loss.

The Med Gem measures within 40 calories of a much more complex test – in which a person is placed in a small room equipped with devices that measure body heat and oxygen exchange – that is considered the gold standard for the science of calorimetry.

The federal Department of Agriculture's Web site provides another source for a good personalized calorie estimate.