Are you looking to enhance your nutrition or weight loss efforts? Understanding how your body utilizes fuel sources and how to potentially increase your metabolism can provide a significant advantage. A Resting Metabolic Rate (RMR) test can offer valuable data to optimize your fitness journey. When it comes to nutrition and weight loss, numerous factors are at play, and your resting metabolic rate (RMR) is a crucial one. It significantly influences how quickly and effectively you can lose weight. Understanding its role is essential for weight management and maintaining a healthy diet.
Understanding Metabolic Rate
Your metabolic rate represents the number of calories your body requires to perform essential functions such as breathing, circulating blood, adjusting hormone levels, and cell growth and repair. This is also known as your Basal Metabolic Rate (BMR). When the body is at rest, the calories burned are referred to as your Resting Metabolic Rate (RMR).
Your RMR accounts for approximately 60-75% of the total calories you burn each day. Therefore, understanding your RMR can provide valuable insights into how many calories you should consume and burn for effective weight loss. The remaining percentage comes from physical activity (exercise or non-exercise movement) and the thermic effect of food (the energy required to digest and process food).
The Role of Resting Metabolic Rate in Nutrition and Weight Loss
The relationship between your RMR and weight loss is straightforward: a higher metabolic rate means more calories burned at rest, leading to more significant weight loss. Conversely, a lower metabolic rate means fewer calories burned at rest, making it harder to lose weight. This explains why some people can eat more without gaining weight, while others struggle to lose weight despite strict diets. Individual metabolic rates play a crucial role. Understanding your resting metabolic rate can be a game changer when it comes to nutrition. Knowing how many calories your body needs just for basic functions can help you plan your diet more effectively.
If you consume fewer calories than your RMR requires, you may not provide enough fuel for essential bodily functions. This could lead to fatigue, nutrient deficiencies, a weakened immune system, and other health problems over time.
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Factors Influencing Resting Metabolic Rate
Several factors can affect your RMR. These include:
- Age: RMR decreases with age.
- Gender: Men generally have higher RMR due to more muscle mass.
- Genetics: Genetic predispositions can influence metabolic rate.
- Body Size and Composition: More muscle mass increases RMR.
- Temperature: Cold weather can increase RMR as the body works harder to maintain normal temperature.
- Nutritional Status: Consuming protein-rich foods can increase your metabolism because they require more energy for digestion compared to fats or carbohydrates.
Can We Calculate Our RMR?
Resting metabolic rate is the total number of calories burned when your body is completely at rest. RMR supports breathing, circulating blood, organ functions, and basic neurological functions. Direct calorimetry measures the amount of heat produced by a subject enclosed within a small chamber to calculate energy expenditure. As a result, more accessible and affordable techniques that estimate RMR have been developed over the past 100 years. Perhaps the most common methods utilized today are mathematical formulas.
Mathematical Formulas for Estimating RMR
Revised Harris-Benedict Equation
The commonly used metabolic equation, called the Harris and Benedict equation, was first designed in 1918 (and updated in 1984). While it was intended to estimate BMR, it actually estimates RMR, according to the National Academy of Sports Medicine. It uses height, weight, biological sex, and age to determine RMR and is based on average lean mass levels. Below are examples of how to calculate your RMR using the revised Harris and Benedict equation.
Men: (88.40 + 13.40 x weight in kilograms [kg]) + (4.80 x height in centimeters [cm]) - (5.68 x age in years)
For example, if a man is 180 pounds, 5'11", and 43, his RMR is 1,804 calories.
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Women: (447.60 + 9.25 x weight in kg) + (3.10 x height in cm) - (4.33 x age)
For example, if a female is 130 pounds, 5'3", and 36, her RMR is 1,333 calories.
Mifflin-St Jeor Equation
The Mifflin-St Jeor equation is another equation that uses the same variables but may be more accurate, Church says.
Here’s what the Mifflin-St Jeor equation looks like for men and women:
Men: (9.99 x weight in kg) + (6.25 x height in cm) - (4.92 x age in years) + 5
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For example, if a male is 180 pounds, 5'11", and 43, his RMR is 1,734 calories.
Women: (9.99 x weight in kg) + (6.25 x height in cm) - (4.92 x age in years) - 161
For example, if a female is 130 pounds, 5'3", and 36, her RMR is 1,249 calories.
Cunningham Equation
Other metabolic equations, such the Cunningham equation, use your total level of lean body mass, which is a primary determiner of BMR and therefore RMR. But calculation requires you to measure your body’s levels of fat versus free-fat mass, Church says.
Are Mathematical Formulas Accurate?
These formulas imply that all individuals of the same gender, age, height and weight have the same RMR, a fact that is certainly not accurate. Genetics and epigenetics can also play a significant role. While RMR is an important component of TDEE, an accurate measurement remains elusive for many. Subsequently, we resort to mathematical formulas, but considering their potential errors, the values determined should always be considered a general estimate rather than an accurate value.
Can We Influence RMR?
Resting metabolic rate is modulated by the amount of calories consumed in the diet relative to energy expenditure. Excessive consumption of energy appears to increase resting metabolic rate while fasting and very low calorie dieting causes resting metabolic rate to decrease. Since the metabolic rate at rest is the primary component of daily energy expenditure, its reduction with caloric restriction makes it difficult for obese individuals to lose weight and to maintain weight that is lost. Several lines of evidence suggest exercise may modulate resting metabolic rate. Bed rest in sedentary individuals leads to a reduction in resting metabolic rate. Similarly, in highly trained runners, cessation of daily exercise training lowers resting metabolic rate by about 7 to 10%. Resting metabolic rate is depressed in previously sedentary obese individuals on a very low calorie diet, but it quickly returns to the predieting level when exercise of sufficient frequency, intensity and duration is undertaken while dieting. These findings suggest caloric intake and daily exercise can modulate resting metabolic rate.
Building lean body mass is another effective method for boosting RMR. The ability to preserve muscle mass or even better, build muscle mass can help preserve our age-related losses. Even a small gain of 2-to-4 pounds of muscle mass can provide a 7-to-8% boost in metabolism, which can add approximately 90-to-110 kcal to TDEE per day or 9-to-11 lbs per year if diet remains constant.
The Impact of Exercise on Resting Metabolic Rate
Whether exercise has a carry-over effect on resting metabolic rate remains controversial, even though this question has been studied extensively during the last 90 years. Reasons for contradictory results include variations in control of prior diet and exercise patterns, inadequate exercise frequency, intensity and duration, and the possibility of response to exercise varying between individuals.
Regular exercise increases the amount of energy you burn while you are exercising. But it also boosts your resting energy expenditure - the rate at which you burn calories when the workout is over and you are resting. Because resting energy expenditure accounts for 60% to 75% of the calories you burn each day, any increase in resting energy expenditure is extremely important to your weight-loss effort. The kinds of vigorous activity that can stimulate your metabolism include walking briskly for two miles or riding a bike uphill. Another benefit of regular physical activity of any sort is that it temporarily curbs your appetite.
Caloric Deficit and Weight Loss
Knowing your BMR or RMR can help you better determine your total daily energy expenditure in order to create a caloric deficit, defined as consuming fewer calories each day than you burn for energy. A caloric deficit is required to lose weight.
Dieting and Metabolism
Excessive consumption of energy appears to increase resting metabolic rate while fasting and very low calorie dieting causes resting metabolic rate to decrease. If one person cuts back on calories without exercising and another person increases exercise without cutting back on calories, the first person would probably find it easier to lose weight. That's because it's easier to cut 500 calories a day from your diet than it is to burn 500 extra calories through exercise. But if you only cut back on calories, you're more likely to regain the weight you lose. Why? The body reacts to weight loss as if it is starving and, in response, slows its metabolism. When your metabolism slows, you burn fewer calories - even at rest.
Hunger vs. Appetite
Regular physical activity of any sort is that it temporarily curbs your appetite. Of course, many people joke that after a workout they feel extremely hungry - and promptly indulge in a snack. But because exercise raises resting energy expenditure, people continue to burn calories at a relatively high rate.