Better understanding through science: Metabolism
A basic knowledge of metabolism can help with the understanding of what goes on in the body in regards to energy requirements, nutritional requirements, fitness, and overall health.
TOPICS ON THIS PAGE:
TOPICS ON THIS PAGE:
- Cellular metabolism
- Base metabolic rate (BMR) and Resting metabolic rate (RMR)
- Things that can mess with your metabolism, both good and bad
Cellular metabolism
Metabolism is a term that is used to describe the processes of converting food and drink into energy. The processes are very complex, however put simply, these chemical reactions occur when oxygen is combined with the calories from food and drink and the result is energy for the body. There are 2 main types of metabolic activity: catabolism and anabolism.
Metabolism reactions, like most reactions, result in some waste. In humans, the waste that is produced in the metabolic reactions are carbon dioxide (CO2), water (H2O), ATP (adenosine triphosphate), Urea, and heat.
Metabolism is a very complex set of processes and the above explanation is a very BASIC understanding of how metabolism works. Below are some diagrams to illustrate how complex metabolism truly is.
- Catabolism is the metabolic process of breaking down food molecules into smaller chemical units. This breakdown often releases energy and breaks the bonds between the food molecules that we have consumed, which produces energy for all of our activities.
- Anabolism are the chemical reactions that build bigger and more complex molecules from the smaller molecules. Anabolism requires energy, in the form of ATP (adenosine triphosphate).
Metabolism reactions, like most reactions, result in some waste. In humans, the waste that is produced in the metabolic reactions are carbon dioxide (CO2), water (H2O), ATP (adenosine triphosphate), Urea, and heat.
Metabolism is a very complex set of processes and the above explanation is a very BASIC understanding of how metabolism works. Below are some diagrams to illustrate how complex metabolism truly is.
As one can see, metabolism is no simple process. Metabolism and nutrition go hand in hand. If there is a basic understanding of how metabolism works, one can better understand how consumption and restriction of certain foods and substances can enhance or hinder physical fitness/activity/life.
This is a simple diagram to show catabolism and anabolism. Again, this is a very basic understanding.
This diagram shows a slightly less complicated way of understanding what happens when food (nutrients) are ingested.
Base metabolic rate (BMR) and Resting Metabolic Rate (RMR)
The amount of calories that a person burns at rest is called the base metabolic rate or BMR. BMR is very close to RMR, known as resting metabolic rate. The difference between the two has to do with how each is calculated. BMR is calculated under strict lab conditions where a person has been asleep for 8 hours in a darkened room, 12 hours of fasting, and remains in a reclined position. RMR is calculated under less strict lab conditions where a person doesn't have to spend the night sleeping in the lab facility prior to the calculation. Since most people don't have lab access, several formulas exist to obtain a rough estimate of BMR and RMR.
BMR and RMR account for the amount of calories a person burns at rest. Even at rest our bodies are constantly needing energy (calories) to function. Typically, a person doesn't think of all the functions that the body does 24/7/365 until the day you die, but it takes energy to breathe, to circulate blood, to grow and repair cells, the list goes on. BMR and RMR are the minimum caloric values needed to sustain body function.
The equations used for BMR today, have changed over time, due to exercise physiology research. The Harris-Benedict and Mifflin St Jeor BMR equations are the most common equations used today. The Harris-Benedict equation has been updated a few times and in 1990 the Mifflin St Jeor equation came into play. The issue with these equations is that they don't differentiate between the metabolic demands of fat tissue VS lean muscle mass. Lean muscle mass has a higher metabolic demand than fat tissue. To incorporate lean body mass, two other equations have been developed; Katch-McArdle equation and the Cunningham equation. The Cunningham equation is for RMR.
Calculating your BMR can give you an idea of how many calories you burn at rest. Having this knowledge can help when trying to determine how many calories you need to consume to reach your fitness and exercise goals. Below are the two most common equations used for calculating BMR.
Harris-Benedict Equation for BMR
Step 1: Calculate BMR
Men BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age in years)
Women BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age in years)
Step 2: Apply the Harris-Benedict Principle (TDEE or Total Daily Energy Expenditure)
Little to no exercise, desk job, student: Daily kilocalories needed = BMR x 1 . 2
Light exercise (1–3 days per week): Daily kilocalories needed = BMR x 1 . 375
Moderate exercise (3–5 days per week): Daily kilocalories needed = BMR x 1 . 55
Heavy exercise (6–7 days per week): Daily kilocalories needed = BMR x 1 . 725
Very heavy exercise, twice per day, extra heavy workouts, physically demanding job: Daily kilocalories needed = BMR x 1 . 9
**kilocalories and calories are synonymous**
Katch-McArdle Equation
For this equation, which incorporates lean body mass, a person needs to know what their body fat percent is.
Step 1: Calculate Lean Body Mass
Your body weight x (1 - body fat %) = Lean Body Mass (LBM)
Step 2: Convert LBM from pounds to kilograms
LBM in pounds / 2 . 2 = LBM in kilograms
Step 3: Calculate BMR
370 + (21 . 6 x LBM in kilograms) = BMR
Step 4: Use the TDEE table to calculate Total Caloric Maintenance
BMR x TDEE = Total Caloric Maintenance
Total Daily Energy Expenditure Table
Little to no exercise, desk job, student: Daily kilocalories needed = BMR x 1 . 2
Light exercise (1–3 days per week): Daily kilocalories needed = BMR x 1 . 375
Moderate exercise (3–5 days per week): Daily kilocalories needed = BMR x 1 . 55
Heavy exercise (6–7 days per week): Daily kilocalories needed = BMR x 1 . 725
Very heavy exercise, twice per day, extra heavy workouts, physically demanding job: Daily kilocalories needed = BMR x 1 . 9
**kilocalories and calories are synonymous**
For those who don't want to calculate their own BMR or RMR can use an online calculator on the inter-webs. Again, this is an estimate of BMR/RMR. The calculator doesn't take into account exercise and activity.
BMR and RMR account for the amount of calories a person burns at rest. Even at rest our bodies are constantly needing energy (calories) to function. Typically, a person doesn't think of all the functions that the body does 24/7/365 until the day you die, but it takes energy to breathe, to circulate blood, to grow and repair cells, the list goes on. BMR and RMR are the minimum caloric values needed to sustain body function.
The equations used for BMR today, have changed over time, due to exercise physiology research. The Harris-Benedict and Mifflin St Jeor BMR equations are the most common equations used today. The Harris-Benedict equation has been updated a few times and in 1990 the Mifflin St Jeor equation came into play. The issue with these equations is that they don't differentiate between the metabolic demands of fat tissue VS lean muscle mass. Lean muscle mass has a higher metabolic demand than fat tissue. To incorporate lean body mass, two other equations have been developed; Katch-McArdle equation and the Cunningham equation. The Cunningham equation is for RMR.
Calculating your BMR can give you an idea of how many calories you burn at rest. Having this knowledge can help when trying to determine how many calories you need to consume to reach your fitness and exercise goals. Below are the two most common equations used for calculating BMR.
Harris-Benedict Equation for BMR
Step 1: Calculate BMR
Men BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age in years)
Women BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age in years)
Step 2: Apply the Harris-Benedict Principle (TDEE or Total Daily Energy Expenditure)
Little to no exercise, desk job, student: Daily kilocalories needed = BMR x 1 . 2
Light exercise (1–3 days per week): Daily kilocalories needed = BMR x 1 . 375
Moderate exercise (3–5 days per week): Daily kilocalories needed = BMR x 1 . 55
Heavy exercise (6–7 days per week): Daily kilocalories needed = BMR x 1 . 725
Very heavy exercise, twice per day, extra heavy workouts, physically demanding job: Daily kilocalories needed = BMR x 1 . 9
**kilocalories and calories are synonymous**
Katch-McArdle Equation
For this equation, which incorporates lean body mass, a person needs to know what their body fat percent is.
Step 1: Calculate Lean Body Mass
Your body weight x (1 - body fat %) = Lean Body Mass (LBM)
Step 2: Convert LBM from pounds to kilograms
LBM in pounds / 2 . 2 = LBM in kilograms
Step 3: Calculate BMR
370 + (21 . 6 x LBM in kilograms) = BMR
Step 4: Use the TDEE table to calculate Total Caloric Maintenance
BMR x TDEE = Total Caloric Maintenance
Total Daily Energy Expenditure Table
Little to no exercise, desk job, student: Daily kilocalories needed = BMR x 1 . 2
Light exercise (1–3 days per week): Daily kilocalories needed = BMR x 1 . 375
Moderate exercise (3–5 days per week): Daily kilocalories needed = BMR x 1 . 55
Heavy exercise (6–7 days per week): Daily kilocalories needed = BMR x 1 . 725
Very heavy exercise, twice per day, extra heavy workouts, physically demanding job: Daily kilocalories needed = BMR x 1 . 9
**kilocalories and calories are synonymous**
For those who don't want to calculate their own BMR or RMR can use an online calculator on the inter-webs. Again, this is an estimate of BMR/RMR. The calculator doesn't take into account exercise and activity.
Things that can mess with your metabolism, both good and bad
Many factors can determine and effect a person's BMR
- A larger person will have a higher BMR than a smaller person. For example, a 130 lb, 30 year old, 5'5" female has a BMR of around 1311 calories per day, where a woman who weighs 200 lbs at the same height and age will have a BMR around 1628 calories per day. The heavier woman will also burn more calories while exercising.
- The amount of lean body mass (muscle) can increase the BMR. Muscle tissue has higher caloric demands than fat tissue. Men tend to have a higher BMR than women due to more muscle mass.
- Age plays a role in metabolism. Typically, as we age we lose muscle mass. The loss of muscle tissue causes a decrease in metabolism.
- One factor that plays a role in metabolism that many seem to overlook is genetics. Our genetics plays a larger role than we think. Many metabolic disorders occur due to genetic factors. Disorders such as diabetes, hypothyroidism, hyperthyroidism, metabolic syndrome, are just a few examples.
- Too much calorie restriction or starvation will slow down metabolism. During starvation the body will store anything and everything that is consumed because the body doesn't know when it will get nutrients again. Slowing down the metabolism is the body's way of energy conservation.
- Exercise. Both cardio (aerobic) and weight lifting/strength training (anaerobic) have positive metabolic effects. HIIT (high intensity interval training) is a very effective way of combining both cardio and strength training into a workout. Interval training causes the heart rate to increase during activity and decrease during rest. This type of increase and decrease is hard on the body, in a good way. Because this type of workout is taxing on the body, it takes the body longer to recover. Recovery takes energy.
- Strength training. Strength training typically leads to muscle hypertrophy (increase in muscle size). Increase in lean muscle mass/tissue, increases metabolism because lean muscle tissue requires more energy to function than fat tissue does.
- Thermogenic effect of food. It takes energy for the body to break down food. This is called the thermogenic effect of food (TEF). Protein has a TEF of 25%, meaning that 25% of the calories of each gram of protein is burned off during digestion. The TEF for carbohydrates is 5% and for fats is 2%. It takes more energy to digest protein than fats or carbohydrates.
- Eat more often. Roughly every 4-6 hours depending on metabolism, activity level, and what has been consumed, food/nutrients pass from the stomach through the small intestine and into the large intestine. From start of digestion to excretion (pooping) can take anywhere from 30-40 hours. Eating 5-6 small meals a day keeps metabolism elevated. When only eating 3 meals a day, the body will slow metabolism down because it doesn't know when it will get food again; it will conserve as much energy as possible.
- Be aware of processed foods and preservatives. Processed foods and those heavy in preservatives are harder for the body to digest. Also, during the processing and adding of preservatives, some of the essential and nonessential nutrients are lost.
- Drink water. Water flushes out waste products and aids in digestion. Being hydrated cuts down on cravings and helps digestion move along more smoothly.
- Decrease the amount of stress. When the body becomes stressed it causes certain hormones to be released, which causes fat to be stored. Attempt to decrease the amount of stress in your life and it will help decrease the amount of stress hormones being released and fat being stored.
- Get plenty of sleep. 7-9 hours is the typical range of sleep needed. The body does many of its repairs and recovery during sleep. Rest and recovery takes energy. Sleep is also a "reset" button for the brain and dreaming is a way for the psyche to process the day's activities.