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Metabolism Explained
What is “metabolism?” Metabolism is the total amount of energy your body burns in one day. Your body uses energy, measured as calories, every time you move. From breathing to running to thinking, you burn calories continuously; even when you’re sleeping you burn calories. The calories you burn in 24 hours are based on 3 factors:
- Resting Metabolic Rate (RMR)
- Thermic Effect of Food (TEF)
- Physical Activity (PA)
Resting Metabolic Rate (RMR) is the number of calories you burn each day to maintain normal body functions such as heart rate, breathing and brain activity. RMR is the largest component of your daily metabolism. It accounts for 60-75% of your total energy expenditure. RMR varies between individuals and is impacted by body size, muscle mass, age, sex and hormonal status as well as illness and injury (see table below). Many of the factors that impact RMR are out of your control. However, a person’s RMR may be increased by including resistance training and increasing muscle mass (muscles burn more energy than fat). This can be particularly helpful when losing weight to help offset the natural decrease in RMR that occurs as your body size gets smaller.
Factors Affecting RMR |
| Note |
| Body Size | Larger body size = higher RMR | Taller and heavier people use more energy. |
| Body Composition | Greater muscle mass = higher RMR | Muscle is more active, using more energy, than fat. |
| Age | Older individuals = lower RMR | Muscle mass declines and hormone levels change with age. |
| Sex | Men = higher RMR | Men typically have more muscle than women. |
| Hormonal Status | Variations occur with menstrual cycles and with impaired thyroid hormone levels. | |
| Illness and Injury | Illness or injury = higher RMR | Fighting infection and healing wounds requires energy. |
Thermic Effect of Food (TEF) is the amount of energy your body uses to digest and process your food for fuel or storage. TEF is the smallest component of your daily metabolism, about 10%. The more difficult the food is for the body to process the more energy it uses and the higher the calorie burn. Fat is the easiest for the body to break down and process, while protein is the most difficult and carbohydrate is somewhere in between. Although the TEF and content of your diet has a small effect on your daily metabolism, following a menu that is lower in fat, includes protein and carbohydrates could help increase your daily burn.
Energy expenditure through Physical Activity (PA) is the most variable component of daily metabolism. Physical activity can account for 15 to 30% (or even more) of your metabolism. If you spend the day lounging around, you will burn fewer calories than if you spend your day cleaning your house or exploring the zoo. PA is the one area in which you have the most control. The more you move the more you’ll burn!
Take-home message: How do you increase your metabolism? Move more!! Getting more physical activity will have the biggest impact on increasing your daily metabolism. Include some resistance training; by losing fat and increasing muscle, you'll burn more calories without even trying. You can do resistance training easily at home with a DVD and basic exercise equipment like resistance cords; gym equipment works great too. Other activities like Pilates and yoga also incorporate resistance type training movements. Start including some resistance training 2-3 times per week to compliment your cardio.
