If you’ve been trying to lose weight but not having as much success as you would like, you may wonder if your lack of results are due to a low metabolism. While some food and activity habits can influence your metabolism, for better or for worse, and a few health conditions can result in an abnormally low or high metabolism, odds are your metabolism is within what would be considered a normal range for your gender, age and body size.
What Is Metabolism?
Metabolism refers to all the physical and chemical processes in your body that convert or burn energy. These processes include digesting food and nutrients, breathing, eliminating waste, controlling body temperature, circulating blood, contracting muscles, and operating the brain and nerves. Your metabolic rate is the number of calories you burn during all of these processes. To know if your metabolism is low, you would first need to know your resting metabolic rate, or RMR, which is similar to your basal metabolic rate, or BMR.
Determining Your Base Metabolism
Your BMR is the energy your body burns just to survive. Your RMR is the energy you burn while resting in a fasted state. They are similar, but RMR is easier to measure. RMR accounts for about 60 to 80 percent of the calories you burn. Genetics affects your RMR, and so does your gender and age, because muscle tissue burns more calories, even at rest. In general, men have more muscle than women, and younger adults have more muscle than older adults. That’s why men need more calories and why calorie needs decrease with age.
Increasing and Decreasing Metabolism
If you are overweight, you may need more calories to maintain your weight than someone of same age and gender who weighs less, because some of your extra weight is muscle. When you eat, your metabolism increases because digestion means more work for your body. Your metabolism also goes up when you move, especially during exercise, because your muscles have to contract and your lungs and heart have to work harder. Physical activity is the biggest variable in your overall metabolism, or total energy expenditure.
Your body adjusts your metabolism to meet your needs. An extreme example is the slowing of metabolism that can follow a starvation diet. A few health conditions, such as hypothyroidism, can also slow metabolism. One way to calculate your estimated RMR is the Harris-Benedict Equation. For example, A 5-foot-7-inch, 140-pound, 30-year-old woman would have an estimated RMR of 1,448 calories. If you have your actual RMR measured using a handheld indirect calorimetry device, you could compare the two numbers to see if you are in a normal range.
- MedlinePlus: Metabolism
- “Modern Nutrition in Health and Disease (11th Edition)”; A.C. Ross, B. Caballero, R.J. Cousins, K.L. Tucker, T.R. Ziegler; 2013
- National Endocrine and Metabolic Diseases Information Service (NEMDIS): Hypothyroidism
- GlobalRPH: Harris-Benedict Equation: Determination of the Basal Metabolic Rate (BMR)
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