RMR: Your Body's Calorie-Burning Engine

How many calories should I eat?

I can't remember how many times I've been asked that question! In a culture focused on dieting and body weight, everyone seems to want to know how many calories they should eat to drop that first 20 pounds or the last five.

Until recently, almost every health professional and online interactive calorie counting page used something called the Harris-Benedict equation to estimate calorie needs. Talk about antiquated, Harris-Benedict was first published in 1919 based on an equation using height, weight, age, sex and activity level to determine calorie intake. Only 136 men and 103 women participated in the study ‑- not a large number by anyone's definition. So, it's not surprising that this method is wrong 5 to 15 percent of the time!

Even relying on a 1,200-calorie diet to lose weight is outdated. A better way to determine your optimum calorie intake is by finding your resting metabolic rate (RMR), which is simply the amount of calories our bodies burn at rest. Once you have your RMR measured, you know exactly how much food you can ‑- and should ‑- eat to lose weight, gain weight or just stay healthy.

Indirect Calorimetry
We don't estimate blood sugar, blood pressure or cholesterol levels ‑- we measure them. So, why would we not measure RMR? Actually, technology to measure calorie intake has existed for years. Unfortunately, you had to be involved in a research study at a major university to use it! Fortunately, recent advances have led to hand-held, portable devices that work just as well as the large, expensive machines used by hospitals and universities. And the cool thing is, they're showing up at health clubs, outpatient divisions of hospitals and private nutritionists' offices across the country.

Although calorimetry might sound like it involves some hardcore mathematics, it's actually incredibly easy with today's devices. Here's how they work: You just breathe. That's it! Indirect calorimetry machines measure the amount of oxygen you breathe in ‑- and subtract the amount of oxygen you exhale ‑- to get the amount of oxygen your body uses. Your body uses oxygen to provide energy. So, through a mathematical equation programmed into the device, you can find your RMR in about 10 minutes.

Resting Metabolic Rate
Even when we don't move, our heart beats, lungs breathe and brain functions. When we're at rest, we're like an idling car ‑- still burning gas, but not as much as when we're mobile.

Since RMR accounts for as much as 75 percent of our total calorie expenditure, it's an important number to know. The rest of our calories burned come from exercise, daily activity and digesting food. If we keep our calorie intake the same as our RMR, we should lose weight.

What determines RMR?
Forget about pills, potions or teas that promise they will "rev up" your metabolism. Instead of promoting safe weight loss, they stress your body and potentially increase your blood pressure. RMR is primarily determined by our genetics. The same way we can't control the color of our eyes or height, RMR is determined before we're born. Larger people ‑- both in height and weight ‑- tend to have higher RMR values, similar to the way a large SUV burns more gas than a compact car. Muscle mass also uses more energy, so people with more muscle mass have higher RMR values. That's the same reason RMR can decrease as we age ‑- if we lose muscle, we don't need as much energy to exist, and our RMR goes down.

Put RMR to work for you
There are two main indirect calorimetry devices on the market today, which are manufactured by HealtheTech and Korr Medical. You can find a location near you that uses one of the HealtheTech products at MetabolicFingerprint.com.