Chasing the ultimate caloric burn remains a top priority for many avid gym-goers. Personal trainers have long promoted muscle mass and definition as powerful tools in attaining this goal. Could we have been misleading our clients…and ourselves…about how much muscle really “raises” metabolism?
Metabolism encompasses every chemical process required by the body as it sustains life. Basal or Resting Metabolic Rate (BMR) refers to the amount of energy (in terms of calories) utilized during these processes. The Thermic Effect of Food (TEF) takes into account the calories burned during digestion. TEF is usually small, certainly not sufficient enough to outweigh the calories ingested.
“Many factors have an impact on metabolism,” says Allison Knott, MS, RDN, a registered dietitian based in Brooklyn, NY. While this statement merits consideration, it does not imply a total inability on our part to expend calories in an effective manner. A few points need to be considered.
The Real Cost of Weight Loss
“In general, losing weight leads to a lower resting metabolic rate and fewer calories burned, including during activity,” says Sarah Gold Anzlovar, MS, RDN, LDN. “Smaller bodies require less energy to function than larger bodies–just like a small apartment requires less energy to heat than a larger house.”
A body weighing 150 pounds requires fewer calories to efficiently function than a 200-pound body. While 150 pounds may represent a healthier weight for an individual, the weight loss goes hand in hand with a reduction in BMR.
Sheer body weight accounts for the sum total of fat, muscle, bone and water. Our clients often lose sight of the fact that weight loss often comes at an unexpected cost: the loss of muscle tissue along with the desired fat loss. This explains how a reduction in overall body weight could inadvertently depress metabolism.
“This is one reason why you see a change in metabolism over the lifespan,” Knott says. “As you age, you naturally lose muscle mass, which results in a decreased metabolism. This can be influenced by maintaining muscle mass throughout the lifetime with weight-bearing physical activity…. (which) remains one of the ways that metabolism can be significantly impacted, due to additional energy requirements as well as the optimal shift in body composition.”
Metabolism and Training Approach
Ultimately, we cannot place sole blame upon genetics when it comes to our metabolisms; we must own some culpability in our quest for metabolic changes. Clients, especially women, often need reminding that instead of relying heavily on cardiovascular exercise to alter body composition, weight-bearing movements go a long way towards facilitating the overall re-shaping of the body.
While a treadmill session may confer a higher total caloric expenditure, hard-earned lean muscle mass often gets burned in the process, along with adipose tissue. As we often preach to our clients, including two to three days of strength training per week can facilitate weight loss while preserving lean muscle mass.
The body’s ratio of adipose tissue to lean muscle mass exerts a powerful effect on metabolic rate. According to Sarah Gold Anzlovar, “More muscle mass means a higher metabolism, so don’t be afraid of weight training.” While most research supports this notion to a certain extent, precise data remain elusive.
Muscle tissue does in fact metabolize energy at a higher rate than any of the other 3 tissue types, although perhaps not at the rate we would like to believe. The previous-held notion that amassing 5 pounds of lean muscle tissue results in the burning of up to 250 calories a day appears to lack accuracy. If we keep in mind that the effort of such mass gains represents a Herculean challenge even for elite bodybuilders, we begin to see the problem of offering such an unsubstantiated statement to our average clientele.
Dr. Cedric X. Bryant, Chief Science Officer at the American Council on Exercise, adheres to the belief that 1 pound of muscle only burns about six to seven calories a day. While this number does represent a significantly lower estimate than the aforementioned statistic, keep in mind that this amount is still triple the number of calories burned by 1 pound of adipose tissue. Thus, muscle mass can always benefit body composition.
Optimizing Realistic Goals
Although such discrepancies frustrate scientists and fitness trainers alike, the problem stems from the fact that every study utilizes a variety of different mechanisms to assess post-exercise metabolic changes. Accounting for the other factors that we know affect metabolism — gender, age, and overall levels of activity – we conclude that the relationship between elevated metabolic rate and lean muscle tissue is not clear-cut.
The best advice trainers can provide to clients with weight loss goals encompasses a balance between prudent nutrition/calories consumed, exercise/energy output, and a reduction in overall adipose tissue while preserving muscle mass.