Resting Metabolism

By Scott McDoniel
November 2004

One of the most popular new trends in fitness centers is offering weight-management programs. Most of these programs have a common theme: Eat less and exercise more.

Energy balance occurs when the consumption of calories equals the amount of calories burned in a day, commonly called total energy expenditure (TEE). Individuals will not gain or lose weight when energy balance is achieved. However, the 64 percent of the American public that is overweight or obese has a positive energy balance, meaning these individuals consume more calories than they burn. So, how can health and fitness professionals reverse positive energy balance? Successful weight management is dependent on several factors, including reducing the amount of calories consumed each day. However, the amount of calorie reduction is unique to the individual and to weight-loss goals.

How RMR fits in

The total amount of calories used in a day is comprised of lifestyle (occupational level), exercise and resting metabolism. Resting metabolic rate (RMR) represents the vast majority of total calories burned in a day (approximately 75 percent), and is the missing piece when developing an accurate calorie budget for weight loss, weight gain or weight maintenance.

Most fitness professionals use predictive equations to determine RMR. To predict an individual's resting metabolic rate, most equations use basic demographics (age, height, weight and gender). Therefore, according to the equations, all individuals of similar demographics will have a similar resting metabolic rate. However, studies indicate a significant difference between actual and estimated resting metabolic rate, and these differences can be as much as 10 to 35 percent.  The best equation has a 10 percent margin of error 70 percent of the time, and can impede individuals from achieving their weight-management goals. Ten percent of 1,500 calories is 150 calories, which will result in a weight gain of approximately 1pound per month.

Predictive equations are not able to track physiological changes such as hormones, genetics and improvements in lean muscle mass. Individual changes in hormone levels affect RMR. For example, testosterone can increase RMR by increasing lean muscle mass. And, post-menopausal women can have a significant reduction in RMR.^{11, 2} Experts recommend using indirect calorimetry for determining appropriate energy levels for women who are post menopausal.⁷ Based on current health and fitness facility trends, women represent 52 to 55 percent of memberships, and 74 percent of women join a facility to lose weight.⁸ Therefore, accurately determining RMR is imperative for women who have weight-management goals.

Calorie restriction also affects RMR. Calorie restriction can result in decreased lean muscle weight and a significant reduction in RMR.¹⁰ In one study, researchers noted a 10 percent reduction in RMR over the initial 12weeks. However, individual variability was approximately 20 percent during the first two weeks of the weight-management program.¹ Individual RMR variability cannot be determined using predictive equations.

Determining RMR

Resistance training can increase RMR during a weight-management program. Resistance training has proven to increase RMR when individuals increase the percentage of lean muscle mass. This improvement has been noted in post-menopausal women, as well.^{13, 4} Predictive equations are not capable of adjusting calorie intake if 5 pounds of muscle are developed and 5 pounds of fat is removed. The individual will have the same bodyweight, and the estimated RMR will remain the same.

Resting metabolism is the missing link in all weight-management programs. The use of predictive equations is often imprecise and irrelevant to an individual's actual RMR; however, technology is now available to determine an individual's unique RMR. To improve your client outcomes, stop guessing and start measuring metabolism.

References upon request.

What Do the Experts Say About the WatchWT™ MedGem^® Device

“ The MedGem can be used to accurately measure oxygen consumption and  RMR in capacities where a traditional metabolic cart would not be practical or cost-effective.”     Stewart et al. 2005

"The MedGem provides a quick and convenient estimate of RMR in children that  is accurate and reliable, and should facilitate the process of pediatric weight management counseling.”      Nieman et al. 2005

 "The MedGem hand-held indirect calorimeter has potential application in clinical evaluations in which typical metabolic carts or other standard methods  are not practical.”                                     Fields et al. 2006

"The use of the MedGem may provide clinicians a diagnostic tool for tailoring a nutrition message specific to each client."                               McDoniel et al. 2008

"The portable MedGem may assist research dietitians in determining energy needs of racially diverse populations of middle-aged overweight and obese women."                             

Spears et al. 2009