The overweight/obesity trend in the United States has been increasing at an alarming rate over the past few decades. Approximately 61% of Americans are overweight and almost 26% are obese. The Surgeon General recently identified overweight/obesity as the second leading cause of preventable death in the United States.
For years health professionals have developed and implemented weight management programs that included the necessary components for successful weight management-behavior change, nutrition education, and exercise prescription-yet the overweight/obesity trend continues to rise. The reason these programs have not succeeded in the past is because they are missing one key component – >the foundation must be centered on the energy balance equation and resting metabolic rate (RMR).
The energy balance equation is a very simple concept – calories in versus calories out. More specifically, if a person wants to lose weight, he/she must be in negative energy balance (consumption < expenditure). If a person wants to gain weight, he/she must be in positive energy balance (consumption > expenditure). And if a person wants to maintain weight, they must be in stable energy balance (consumption = expenditure). The concept is simple, but the implementation is very difficult because health professionals have not understood what each component of the energy balance equation is and what each contributes to weight management.
The energy balance equation has two sides: the energy in (consumption) and energy out (expenditure). The consumption side is comprised of the macronutrients – carbohydrates, protein, and fat – and is very simple to understand. Carbohydrates and protein yield four calories of energy per gram while fat yields nine calories of energy per gram. This side of the equation is very absolute and is only affected by the amount of food a person eats.
The expenditure side is much more complicated because biology has more of an impact on each component, which makes it more difficult to balance. The expenditure side is comprised of the thermic effect of feeding (TEF), the thermic effect of physical activity (TEPA), and resting metabolic rate.
The thermic effect of feeding (TEF) constitutes approximately 10% of total daily energy expenditure (TDEE) and includes obligatory thermogenesis (the result of the energy-requiring processes of digesting, absorbing, and assimilating food nutrients) and facultative thermogenesis (the activation of the sympathetic nervous system and its stimulating effect on metabolism). The magnitude of the TEF can vary greatly depending on both the quantity and type of food eaten. TEF is usually not a primary factor in weight management nor is it the primary focus on the expenditure side of the equation due to its low relative amount of contribution.
The thermic effect of physical activity (TEPA) constitutes approximately 15-30% of TDEE and includes occupational and lifestyle activity, and purposeful exercise. This is the most variable component and can contribute the most to negative energy balance (and weight loss) by increasing the amount of purposeful physical activity.
Resting metabolic rate (RMR) constitutes approximately 60-75% of TDEE and includes sleeping metabolism, basal metabolism, and arousal metabolism. RMR refers to the sum of the metabolic processes of the active cell mass related to the maintenance of normal body functions during rest. More simply stated, RMR is the amount of calories a body needs at rest to perform basic functions such as the heart beating and the brain functioning. RMR is the most important component on the expenditure side of the energy balance equation because it represents up to 75% of the total calories burned by the body.
The reason the U.S. has seen overweight and obesity trends significantly increase in the past decades is because health professionals have been estimating RMR. Estimating RMR based on prediction equations could be very inaccurate. In fact, one research study, conducted at the University of Pennsylvania in 1988, predicted and measured the RMR of 80 females of the same height and weight. The researchers found a variance of approximately 500 calories between the predicted and measured RMR’s. Because RMR can represent up to 75%, a 500-calorie inaccuracy automatically sets a person up for failure before they even begin a program. A caloric inaccuracy of 500 calories per day adds up to a 52-pound weight gain in 1 year!
Since the number one factor that influences RMR is body mass, a loss of body weight will decrease a person’s RMR, and vice versa. Therefore, the key factor that will determine success with weight management is measuring resting metabolic rate frequently in order to accurately provide a person the amount of calories they need to eat and the amount of exercise they need to perform in order to reach their weight goals.
The easiest way to measure resting metabolic rate is by using an indirect calorimeter. Indirect calorimetry is the process of measuring a person’s respiratory oxygen consumption (VO2). After VO2 is measured, the value is placed into the Weir equation, the universal standard for converting gas exchange measurement into caloric metabolic rate, and metabolic rate in calories per day is calculated. This is done by algorithms inside the indirect calorimeter so the health professional does not have to configure it with pen, paper, and calculator. All indirect calorimeters can measure VO2 and provide resting metabolic rate in calories per day, including those in human performance labs and hospitals, and newer, handheld indirect calorimeters now found in some fitness centers in the United States.
The key to weight management is not following a certain fad diet or banning certain foods or macronutrients. The key is to measure RMR and use each component of the energy balance equation to balance the amount of calories consumed and burned each day to produce a deficit for weight loss, a surplus for weight gain, or a balance for weight management.
Estimating RMR is the worst thing a health professional could do for a person who wants to change the way their body looks. Remember, you can’t manage what you can’t measure.
My next article will detail how to achieve weight loss and weight gain goals using RMR and the energy balance equation.
- McArdle, Katch & Katch. (1996). Exercise Physiology: Energy, Nutrition, and Human Performance. Fourth Edition.
- “Call to Action”. United States Surgeon General. December 2001.
- Foster, G. et al. (1988). Resting Energy Expenditure, Body Composition, and Excess Weight in the Obese. Metabolism, 37(5), 467-472.