Everyone has a unique metabolic rate that can affect how well he or she loses or gains weight. If your metabolic rate is lower than average, you may gain weight, even on a diet. If it's higher than normal, you may have trouble keeping weight on.
Your resting metabolic rate, or RMR, is essentially how many calories your body burns at rest each day just to maintain basic bodily functions. These numbers can vary from person to person by as much as 1,200 calories a day or more.
Formulas can help you determine your resting metabolic rate, but they just measure age, gender, height and weight (try www.bodybuilding.com/fun/calrmr.htm).
Those formulas don't tell the whole story; all sorts of other factors, particularly genetics, can alter your metabolism.
"Definitely, estimating how many calories you burn can help you lose weight in the long run," says Natalie Allen, a dietitian with Barnes-Jewish Hospital.
Until a few years ago, the only way to measure your RMR was to get tested on expensive research equipment at hospitals and universities, using a method called indirect calorimetry. But now, commercial devices are popping up in some gyms to help you learn your RMR.
Most experts say the devices used at gyms are similar to indirect calorimetry, though not quite as accurate. "And they certainly can't hurt you," Allen says.
In the case of two area people, the RMR readings certainly helped.
When Kathy Brooks joined Fitness in a Flash in O'Fallon, Mo., one of the first things she did was get her resting metabolic rate checked.
She sat down and breathed normally -- well, as normally as possible with her nose pinched shut -- into a tube that measured how many calories she burned in a day in a state of rest, with no walking to the car, no getting up to fix dinner and no working out.
What she found out surprised her.
"My metabolism was actually really high," says Brooks, 62. The test showed she had an RMR of about 2,400 calories, which is 38 percent faster than it should have been for someone of her age and size.
"When I heard that, I realized I had a chance," Brooks says. "I didn't have the excuse that I just had a slow metabolism. It actually gave me the initiative to work harder."
And after nearly a year of working harder, Brooks has lost more than 40 pounds and gotten so healthy she no longer takes 10 medications that she used to take. She's since had her RMR retested; her metabolism is 45 percent faster than it should be for someone of her age and size.
"That's one of the goals of this RMR testing," says Angie House, personal trainer and co-owner of Fitness in a Flash. "It can break the denial for anyone; they can't just blame bad metabolism for their heaviness."
Many, though, don't get that kind of good news when they learn their RMR. Karen Fields, 27, found that her metabolism was quite low when she had it tested recently at Bally's Total Fitness in St. Charles, Mo.
"The test showed I was at 1,380 (calories a day)," she says. "I think that's pretty darned low."
When she saw the diet Bally's wanted to put her on, she realized how much she had been overeating.
"It was shocking to see how low in calories I had to go. But I guess the test confirmed some stuff that I thought all along. I figured I had a low metabolism, but I didn't figure it was quite that low. I'm pretty active with my job" as a veterinary assistant, she says.
Using Bally's plan, Fields has started to see some weight loss, and hopes to shed 40 pounds. "It helps to have this information," she says.