Every cell in our body is constantly working to produce the substances and energy needed to sustain life, and metabolism is a process that’s essential for the continuity of these processes.
Despite the fundamental importance to our health and functioning, there’s quite a lot of ambiguity around the concept of metabolism – especially what it means when ours slows down and what we can do about that.
At Atlantic Endocrinology & Diabetes Center we often hear people say, “I have a slow metabolism” or “they just have a fast metabolism,” and we all nod our heads in agreement. But do we understand what that means?
What is your metabolism? Can it be fast or slow? Does having a slow metabolism make you more inclined to gain weight? Does your metabolism really “break” when you diet?
Your Metabolism Is More Than One Thing
We often refer to our metabolism as a singular thing, like it is this black box or small engine that stuff goes into and then comes out of. But the truth is, our metabolism is a collection of many things. In reality, our metabolism is the sum of all the metabolic processes in our body.
One of the most straightforward ways to understand your metabolism is to refer to it as your total energy expenditure. This means that your metabolism is the cumulation of all the energy your body expends to function. We will refer to this as our total daily energy expenditure (TDEE).
What Does Total Daily Energy Expenditure (TDEE) Mean?
This TDEE can be further broken down into three main categories:
resting metabolism (what most of us call our metabolism)
the energy it takes to process the food you eat
physical activity (more on that in a bit)
Your resting metabolism is the sum of all the metabolic processes that are required for you to live. This means your cells use energy to do things like breathe, think, pump blood, etc. This represents about 60-70% of your TDEE.
The Thermic Effect Of Food (Tef)
The next piece is what we call the thermic effect of food (TEF). This is simply the energy it requires to extract the energy you get from your food. This is a relatively small amount of energy and represents about 10% of your Total Daily Energy Expenditure (TDEE).
The last piece that makes up your TDEE is your physical activity, meaning the amount of movement you do throughout the day. This is often broken down into two separate categories: physical activity that is from structured exercise (we call this exercise activity thermogenesis) and physical activity from non-structured exercise (we call this non-exercise activity thermogenesis).
How does Metabolism Work?
When we eat food, our digestive system starts functioning. The digestive system uses different kinds of enzymes to do the following processes:
The initial process is the breaking down of proteins into amino acids.
Enzymes also convert fats into fatty acids.
Carbohydrates have been converted into sugars (Glucose) with the help of enzymes.
When the enzymes convert proteins, fats, and carbohydrates into amino acids, fatty acids, and sugars, the body can use them anytime as an energy source, and these compounds are absorbed by blood which helps in carrying them to different cells for their functioning.
After the blood carries them to the cells, and they enter into the cells, other enzymes start their functioning and act upon it, and a lot of chemical reactions also take place that involve “metabolizing” different compounds. The energy made by these compounds can do different purposes, including being used by the body for performing different tasks, and it can also remain stored inside the body into tissues, such as muscles, liver, and body fat.
A protein acting as a catalyst that facilitates reactions in biological systems is called an enzyme. Each reaction step in Metabolic pathways is catalyzed by an enzyme and it takes control of the biochemical reactions.
Adenosine triphosphate (ATP)
It is an organic compound that provides energy for facilitating many processes in living cells, for example, muscle contraction, chemical synthesis and nerve impulse propagation. It is found in all forms of life, and is often referred to as the “molecular unit of currency”. When consumed in metabolic processes, it is either converted to adenosine diphosphate (ADP) or to adenosine monophosphate (AMP).
Your metabolism adapts to calorie increases and decreases, with a large part of the adaptation coming from changes in physical activity. While metabolisms can decrease, they do not “break.” Lastly, lower resting metabolisms do not appear to be predictive of weight gain and by themselves are not overly helpful measures for most people.
In short: the answer to controlling our metabolic rate lies in following a healthy lifestyle, where we stay physically active, maintain a balanced diet (with plenty of protein) and find ways to de-stress and manage cortisol levels.