When people cannot lose weight, they sometimes blame it on a slow metabolism. A slow metabolism means your resting metabolic rate, the rate at which your body burns energy when you’re not exercising and haven’t just eaten a meal, is slow. Therefore, you burn fewer of the calories you eat as energy and store more of them as fat.
But how would you know if your resting metabolic rate is too slow? To know what your resting metabolic rate is, you’d go to a place that makes these measurements. Most use a technique called indirect calorimetry that looks at gas exchange at rest. They would put you in a chamber and measure how much oxygen you use and how much carbon dioxide you breathe out at rest. Resting metabolic rate for the average person varies with the amount of lean body mass they have.
Indirect calorimetry takes time and can cost a lot of money, but it’s accurate. However, you can get a rough idea of your resting metabolic rate using calculators available online. To use these calculators, you input specific information, including your gender, height, weight, and age. Plus, the calculator also asks about your stress level and how physically active you are.
Based on the input, they give you an estimate of your resting metabolic rate, how many calories you burn over 24-hours. You could then use this information to determine how many calories you need per day to stay in energy balance and avoid weight gain or weight loss. This method isn’t as accurate as indirect calorimetry, but it also doesn’t require significant time or money.
The most common type of calculator is based on the Harris-Benedict equation, an equation that gives an estimate of your metabolic rate. Using this equation is a way to get a rough estimate of how many calories you burn in a day. By knowing this, you can adjust your calorie intake in a way that makes it easier to lose weight, but you can also ensure that you don’t drop your calorie count too low if you’re trying to maintain your current body weight.
Factors that Affect Your Metabolic Rate
You might also wonder what some factors are that determine how many calories you burn each day. Here are some of the most important ones and how they affect your resting metabolic rate.
Men have a higher ratio of muscle to body fat. They’re also larger and have bigger organs. More muscle and larger organs require more calories each day to maintain. In contrast, women have less muscle and more body fat, and body fat is less metabolically active. Men often lose weight faster than women, and these factors partially explain why.
Metabolic rate is highest during childhood when your body is growing and developing. Resting metabolic rate starts to decline in adults after the age of 20 at a rate of around 2 to 3 percent per decade. Strength training helps maintain a healthy resting metabolic rate by increasing the ratio of muscle to body fat on a person’s frame. So, your resting metabolism will slow somewhat with age.
Height and Weight
Being taller and weighing more also increases resting metabolism since bigger, taller people have more mass to maintain. If you’re larger, when you do any type of activity, you burn more calories than someone smaller and slimmer.
If you spend time in a hot or cold environment, it may affect your metabolic rate too. If you sit or work for a prolonged time in a hot environment, it will boost your resting metabolic rate, but the exposure has to be prolonged. You also experience a rise in resting metabolic rate when you have a fever. In contrast, you might expect your metabolism to slow in cold temperatures. However, cold temperatures can also activate metabolically active brown fat and boost the rate at which your body burns fat as fuel.
What You Eat
Your resting metabolic rate can slow or speed up based on your diet. If you adopt a low-calorie diet to lose weight, your resting metabolism may drop as much as 20% and the degree of metabolic slowing will vary with how low you drop your calorie intake. That’s why experts don’t recommend reducing calories by over 500 calories per day, even when you’re dieting. Focus more on diet quality.
If you strength train, the extra muscle you build will boost your resting metabolic rate. You’ll also burn more calories while you’re exercising. If you do high-intensity exercise, your metabolism may rise and stay up for up to 24 hours after a vigorous workout.
Thyroid Gland Health
The thyroid gland is the master gland for regulating resting metabolic rate. If you have a condition called hypothyroidism, you don’t produce enough thyroid hormone to keep your metabolism humming along and you may experience weight gain. Likewise, if you have an overactive thyroid gland, known as hyperthyroidism, your metabolic rate will speed up and you’ll lose weight.
The Bottom Line
You can’t get an exact picture of what your resting metabolic rate is at home, but you can use an online calculator to get an estimate of how many calories you need each day for weight maintenance. These are widely available on many fitness sites.
- American Council on Exercise. “Resting Metabolic Rate: Best Ways to Measure It—And Raise It, Too”
- org. “Resting Metabolic Rate: Best Ways to Measure It—And Raise It, Too”
- com. “RMR: What Is Resting Metabolic Rate?”
- The American Journal of Clinical Nutrition, Volume 82, Issue 5, November 2005, Pages 941–948.
- ‘The factors affecting basal metabolic rate/resting metabolic rate in the planning of dietary treatment of obesity: Review.’ January 2011Turkiye Klinikleri Cardiovascular Sciences 23(1):54-60.