Resting Metabolic Rate: Accuracy Brings Results

Shannon Miller

October 22, 2018


Let’s face it, whether it’s losing fat or gaining muscle, your body composition goals are personal. Since every body is different, everybody’s approach to achieving a goal is unique. The most important piece of knowledge required to drive results through nutrition is a clear understanding of your unique metabolism. Knowing how efficiently your body uses the food you consume can help shape a nutrition plan informed by your own physiology.

Resting Metabolic Rate

The body burns – and stores – calories from food as a source of fuel to power basic bodily functions and physical activity. However, the rate at which the body uses calories differs from person to person depending on individual characteristics such as age, lean muscle mass, sex, and activity level. For example, a 50-year old male with a sedentary lifestyle and little lean muscle mass is likely to burn energy at a different rate than a 20-year old female collegiate athlete. In some cases, both type of individuals could have similar goals in weight loss, but because of their metabolic differences, both require a tailor-made approach to nutrition and caloric intake. This is where measuring metabolism comes into play.

The most accurate assessment of how the body uses energy is through a Resting Metabolic Rate (RMR) measurement, also referred to as Basal Metabolic Rate (BMR). Well over half of all calories consumed are burned performing basic functions like digestion, breathing, thinking, and other uses of energy apart from physical activity. RMR provides a baseline measurement of the number of calories the body typically burns in a 24-hour period while at rest. From there, a nutrition plan that results in a daily calorie deficit (or surplus, depending on goals) can be developed that is specific to a baseline caloric needs, while also considering calories burned during physical activity. For instance, to lose fat, a 20% reduction in daily caloric intake is typically recommended – but to figure out where to start reducing from requires an accurate baseline measurement.

Know Your Numbers

Knowledge is power when it comes to getting results through nutrition. The key to changing body composition (losing fat mass and/or gaining muscle mass) is understanding the body’s specific caloric needs. Predictive calculations have been developed to estimate the amount of energy an individual burns at rest, but many are inaccurate, which leads individuals to wrongly estimate how many calories needed in a day. This can significantly impact body composition over time if calories are over or underestimated. Therefore, an accurate RMR measurement provides the tools necessary to have a better understanding of daily caloric intake needed to reach body composition goals.

Online Calculators – How Accurate Are They?

RMR is typically calibrated using individual factors including height, weight, age, sex, and activity level. When curious about RMR, many turn to online calculators for a simple estimate. A typical online RMR/BMR calculator uses the following data to calculate a suggested daily caloric expenditure:

  • Age
  • Sex (M/F)
  • Height
  • Weight
  • Activity Level (sedentary/light activity, active or moderately active, vigorously active)

Many online calculators draw from equations developed within the scientific community to estimate RMR/BMR, including the Harris-Benedict (later revised by Mifflin-St Jeor), Schofield, and Institute of Medicine equations. For instance, the Harris-Benedict equation follows a specific mathematical equation (see below) to determine BMR in men and women, then amplifies each calculation depending on an individual’s typical daily activity level.

Harris-Benedict Equation:

  • BMR (Men) = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
  • BMR (Women) = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161

While calculating RMR may seem like simple math, this method risks inaccuracy. Unfortunately, online calculators and equations do not always result in the most accurate measurement, which can lead an individual astray if their baseline RMR is incorrect. In fact, many online RMR calculators have been shown to have a variance of +/- 300 calories, equivalent to a small meal each day, which can drastically affect results over time. Since accuracy is particularly important for setting goals around nutrition, it’s crucial to turn to a professional source for RMR testing.

The RMR Test Difference

To truly understand the amount of energy your body burns at rest, receiving an RMR test from a licensed facility is ideal. RMR testing involves breathing into a small device for approximately 10 minutes. The machine accurately calibrates the number of calories the body burns at rest (Resting Energy Expenditure), and estimates calories burned through lifestyle and activity, as well as dedicated physical exercise. From there, a report is generated that shows how many calories are needed in a day in order to maintain or lose weight, and how long it will take to meet a goal when following a nutrition plan that fits within a customized caloric intake zone. The test also provides data on where the metabolism lies on a spectrum from slow to fast, and compares metabolism data to others with the same sex, height, age, and weight. After receiving a full RMR report, a nutrition coach can help design a tailored plan that aligns with a specific caloric intake zone.

A one-size-fits-all recipe when it comes to reaching goals through nutrition won’t drive optimal results. It’s necessary to obtain the most accurate measurement of caloric needs based on a specific weight loss (or gain) goal, which is only possible with the right tools. RMR testing far surpasses basic metabolic rate calculations in terms of accuracy and can provide a helpful guide to nutrition planning to achieve results. Connect with a nutrition coach today to know your numbers and learn more about your specific metabolic needs.

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