Metabolism refers to the amount of energy used in a set period of time, or more commonly, the rate at which the body burns calories. The resting metabolic rate (RMR) is a measure of the amount of energy used by the body in an inactive state to simply maintain basic life functions; including respiration, circulation, digestion, brain activity, etc. RMR measurements are usually taken after eight hours of sleep and an overnight fast.
The resting metabolic rate varies from person to person and is influenced by weight, age, height, gender, physical activity, muscle mass and normal caloric intake. Men automatically burn more calories than women. As a person ages, his RMR lowers; lower height, weight and muscle mass also result in decreased RMR. A number of formulas have been created to estimate RMR, but they are somewhat inaccurate since they cannot distinguish between body types and muscle mass. Handheld devises known as indirect calorimeters use breath tests to measure oxygen consumption and are a more accurate means of measuring RMR.
It is important to determine a person’s resting metabolic rate in order to design a successful, individual weight loss program. The RMR should account for at least three-fourths of the calories required to maintain a person’s current weight. Someone who is overweight may actually have a higher RMR than a person who is not overweight. This is the reason a person loses weight faster at the beginning of a diet, and more slowly as he reaches his goal weight.
A person is not always at a state of rest, so the actual calories burned throughout the day will be higher than the RMR. Weight loss logic states that you can lose weight by consuming fewer calories than you burn. This is true, up to a degree, but if a person consumes significantly less calories then his body requires, he will actually lower his resting metabolic rate, thus making weight loss even more difficult. To maintain a healthy weight loss the daily caloric intake should never go under the RMR.
There are things a person can do to increase his RMR and to enhance weight loss. The first step is to determine the optimal daily caloric intake, and then to divide this into six meals or snacks. Digestion requires energy, and metabolism increases for a period of time after eating. If someone eats smaller, more frequent meals, he can maintain a higher RMR. Conversely, going too many hours between meals slows the metabolism and can actually make weight loss much more difficult.
Exercise is also a great way to increase a person’s resting metabolic rate. Thirty minutes of intense exercise can increase metabolism for one to two hours. Strength training and impact exercises may not offer the same immediate increase in calorie consumption, but are actually more effective in creating a long-term change in metabolism because muscle burns more calories than fat. As a person ages, his resting metabolic rate decreases steadily, making it necessary to cut the number of daily calories to prevent weight gain. A strength training program designed to increase muscle mass can be effective in preventing this trend.