The human metabolism represents the sum total of the living cells’ energy-producing and energy-utilizing reactions. Total daily energy expenditure describes how much energy (calories are burned) is used within a 24 hour period.
It is made up of four components.
Resting metabolic rate (RMR)
Thermic effect of physical activity (TEPA)
Thermic effect of food (TEF)
Non-exercise adaptive thermogenesis (NEAT)
In order to achieve energy balance, energy intake must meet the energy expenditure.
RMR, which accounts for 60%–75% of all calorie-burning processes, is the amount of energy required to keep the homeostatic processes (the regulation of organ systems and body temperature) performing.
TEPA, which accounts for 15%–30% of daily calories burned, depends upon an individual’s activity level, including both structured exercise and non-structured activities such as shivering and fidgeting. This non-structured activity is what establishes the term NEAT.
TEF, the energy required to digest, absorb, and transport consumed food, accounts for approximately 10% of the daily expenditure.
How Much Does Resistance Exercise Affect Metabolism?
Muscle creates a higher demand for energy, since muscle needs to maintain itself at rest and during exercise.
Perhaps one of the most meaningful benefits of resistance training during a reduced-calorie diet is that it helps to prevent the loss of fat-free mass.
Every pound of muscle garners roughly 11 calories. Maintaining, and adding muscle can be a valuable part of weight loss.
What Effect Does Diet Have on RMR?
To lose weight, individuals must burn more calories than they consume; to gain weight, they must consume more calories than they burn. Very low calorie diets often fail because the dieters do not consume enough calories to fuel physical activity, and this underfeeding can diminish metabolic processes.
Intense energy-restrictive diets are not only tough to maintain; they actually trigger the body to suppress RMR by as much as 20%. Biological processes adapt to what the body perceives as a state of famine. The body increases metabolic efficiency by burning fewer calories to do a given amount of work.
Underfeeding may also interfere with the body’s ability to synthesize muscle because of a lower production of insulin-like growth factor (IGF-1) and the body’s decrease in power-producing capacity.
As we can see, it is important to be able to perform exercises at high intensities to maintain muscle. Otherwise, we fall into a state of reversibility, a term that will be covered later.
Just as a body adapts to exercise intensity that increases, it will adapt to intensity that decreases. Finding a calorie range, and macronutrient ratios that allow you to perform exercises at or better than before will help maintain and build muscle, and keep metabolism faster.
With carbohydrates as our main source of energy, low carbohydrate diets can make our workouts suffer. Eating carbohydrates provides a “protein-sparing” effect; a person who eats too few carbs needs to use some protein for energy, rather than for building and repairing muscle. Therefore, low-carbohydrate diets are not recommended for individuals training to enhance muscular fitness or maintain muscle.
How Does Age Affect RMR?
Due to many circumstances, resting metabolic rate lowers over age. Some are preventable. For example, due to inactivity, resting metabolic rate decreases over age from loss of muscle mass. Regular resistance training can prevent this. Children and growing adolescents have faster metabolic rates than adults because their organs are larger in proportion to their body. Organs are high in metabolic demand and therefore as bodies grow, the metabolic rate per kilogram of body weight lowers.
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