Resting energy expenditure (REE) is defined as the energy expended by a person at rest. More precisely defined, resting metabolic rate (RMR) is the REE measured just after awakening in the morning, which is used to qualify REE relative to calories burned. RMR is approximately one kilocalorie per kilogram (2.2 pounds) of body weight expended per hour.
No matter how it’s defined, research has determined that REE is the largest component of the total amount of energy expended in a day – roughly 65% of calories used, which makes REE an important facet for successful weight management.
In my numerous hospital affiliations over the last 40 years, I have consistently measured REE - among other important variables, as part of my comprehensive weight management programs. It was quite common to find post-menopausal women and women with an undiagnosed low thyroid condition to have a significantly lower REE than expected – all of which required additional laboratory testing to support the finding.
Research – Potential Causes of Elevated REE After High-Intensity Exercise – which appears in the November 2018 issue of Medicine & Science in Sports & Exercise, comments that, “fat-free mass (FFM) has a large influence on REE, explaining 25%–30% of its variance, whereas fat mass (FM) normally explains less than 10% of the variation in REE.”
Furthermore, “other factors that may influence REE include variability in protein turnover due to muscle damage, sympathetic (muscle tone), and uncoupled phosphorylation (heat production) in adipose tissue and/or muscle,” – all representing the cost of doing business inside the human body.
Researchers from the Universities of Alabama, Birmingham and Tennessee reference that “REE is increased for 18–24 h after a high-intensity aerobic exercise bout of at least 70% maximal oxygen uptake,” which equates to roughly 85% of maximum heart rate.
As such, they chose to look at the influence of exercise - moderate and high intensity - on REE, resulting from the effect of any associated muscle damage and other metabolic regulators under energy balance conditions.
Thirty-three untrained, premenopausal women were recruited. Evaluations occurred at baseline, after 8–16 weeks of training, and 22 h after either moderate-intensity, continuous aerobic exercise (MIC) – corresponding to 50% of their maximum endurance capacity (peak VO2), or high-intensity interval exercise (HII) at 84% of their peak VO2.
Participants were sequestered in a room calorimeter during and after the exercise challenge. Food was modified to provide energy balance across twenty-three hours. 23-hour urine samples and muscle biopsies were obtained – looking for mitochondrial muscle status and fat oxidation.
The researchers observed that REE increased by more than 100 kilocalories (kcal) twenty-two hours after the high-intensity exercise and more than 60 Kcals, after moderate-intensity exercise in aerobically trained women in energy balance. “The primary observation of this study that is unique is that under energy balance conditions, REE increased after both the HII and MIC exercises, although the increase after HII was larger,” as noted.
The findings led the researchers to conclude:
“These results suggest that if increased REE is the goal of aerobic exercise training, periodic bouts of exercise training must occur regularly throughout the week. This in turn may enable better weight maintenance and potentially offset weight gain, which may improve metabolic health. Indeed, the combination of energy expenditure from the exercise plus the increase in REE, after the exercise may enable individuals to do a better job of remaining in energy balance and avoid weight gain.”
The take-away message from my experience - with a cross section of overweight and obese male and female adults of various ages - is that it’s never too late in the game to increase your metabolic rate. It’s been said that we’re as young as we’re metabolically active.
Circuit training, in conjunction with short duration interval training in heart rate ranges between 72-87% of maximum heart rate, seems to get the job done.
Consult your physician first.