What is Metabolism?
Clients who have struggled with their weight throughout their lives often refer to themselves as having a “slow metabolism”. And most people have a friend or know someone who has struggled with being petite or skinny, often saying that they have a “fast metabolism”, which makes it difficult for them to gain weight. But what is your metabolism? How is it measured? Can we set them on a race track and see which one has a faster 40-yard dash?
Metabolism is the sum total of all the chemical processes in your body. This is measured as your Total Daily Energy Expenditure (TDEE), and it is the calculated estimate of the number of calories your body expends per day to keep you alive and perform all its tasks. The more energy (calories) you expend per day, the higher your TDEE is. A higher TDEE - meaning more calories out - requires more calories in to maintain your body as it is.
A calorie is a measurement of energy. One calorie is the amount of energy required to raise one liter of water by one degree Celsius. Your TDEE is measured in calories. The foods you consume contain calories. All calories are equal because a calorie is a unit of measurement, the same way an inch is an inch and a mile is a mile. However, not all sources of calories are equal, the same way a mile of paved highway is not the same as a mile of snowy mountain trail. The composition of the calories you consume - meaning how much processing it has undergone, how many vitamins and minerals it contains, the macronutrient distribution, and the specific types of protein/carbs/fats it contains - will influence how your body weight and body composition are impacted.
When your calories in and your calories out are equal, you are in a calorie balance, which will result in weight maintenance. If you consume more calories than you expend (calories in > calories out) you are in a calorie surplus, which will result in weight gain. If you consume fewer calories than you expend (calories in < calories out) you are in a calorie deficit, which will result in weight loss.
There are four (4) components to your TDEE:
Basal Metabolic Rate (BMR) - 60% of TDEE
You may also see this referred to as Resting Metabolic Rate (RMR)
The amount of energy expended at rest and to maintain cellular functions
Think of this as the number of calories you would need to stay alive if you were in a coma. Your brain, heart, lungs, and other organs need to work and require energy to do so.
Influenced by body weight, body composition, and
Thermic Effect of Food (TEF) - 10% of TDEE
The amount of energy expended to digest and absorb food
Influenced by the number of calories consumed, macronutrient distribution of those calories, and sources of calories
Non-Exercise Activity Thermogenesis (NEAT) - 20% of TDEE
The amount of energy expended through movement that is not exercise
Examples: fidgeting, walking to your car in the parking lot, performing chores, etc
Exercise Activity Thermogenesis - 10% of TDEE
The amount of energy expended directly through exercise
Despite what it may feel like, your metabolism is not static. It is dynamic. BMR and TEF are influenced long-term via habits and behavior, such as increasing your muscle mass and eating foods that are higher in protein and fiber. NEAT and EAT can be influenced on a daily basis via activity, such as increasing your daily steps and exercising more consistently.
Your TDEE is only half of the calorie balance equation. The other half is your calorie consumption (calories in). Most clients think that exercising more frequently or intensely will help them see the results they’re looking to achieve. With calorie expenditure through direct exercise comprising such a small amount of your TDEE, it is often a more efficient route to increase activity through NEAT while simultaneously decreasing your calories by 10%-15%.
For clients that are new to exercise and food tracking, we recommend 2-3 days per week of strength training for 45 minutes, walking 7,000-8,000 steps per day, and eating at maintenance. While this may seem counterintuitive to progress by not doing everything all at once, it is actually backed by research to create the habits of healthy movement and food awareness before trying to adjust other variables.