The word “metabolism” is thrown around a lot these days. What does it refers to?
You know that if yours is too slow you might gain weight. But why is that?
What is metabolism?
Well technically “metabolism” is the word to describe all of the biochemical reactions in your body. It's how you take in nutrients and oxygen and use them to fuel everything you do.
Your body has an incredible ability to grow, heal, and generally stay alive. And without this amazing biochemistry you would not be possible.
Metabolism includes how the cells in your body:
allow activities you can control (e.g. physical activity, house chores, walking to and from places, etc.);
allow activities you can't control (e.g. heart beat, body temperature, wound healing, processing of nutrients and toxins, etc.);
allow storage of excess energy for later use.
So when you put all of these processes together into your metabolism you can imagine that these processes can work too quickly, too slowly, or just right.
Which brings us to the “metabolic rate”.
What determines the metabolic rate?
This is how fast your metabolism works and is measured in calories (yup, those calories!). Calorie is a measure of energy: one calorie unit refers to the approximate amount of energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere.
The calories you eat can go to one of three places:
work (i.e. exercise and other activities);
heat (i.e. from all those biochemical reactions);
storage (i.e. extra leftover “unburned” calories stored as fat).
As you can imagine the more calories you burn as work or creating heat the easier it is to lose weight and keep it off because there will be fewer “leftover” calories to store for later.
There are a couple of different ways to measure metabolic rate. One is the “resting metabolic rate” (RMR) which is how much energy your body uses when you're not being physically active. That is the amount of energy necessary to think clearly, breathe normally, maintain an optimal body temperature, and
The other is the “total daily energy expenditure” (TDEE) which measures both the resting metabolic rate as well as the energy used for “work” (e.g. exercise) throughout a 24-hour period. Anything above a “resting” state adds up energy expenditure to your body.
What affects your metabolic rate?
In a nutshell: a lot!
The first thing you may think of is your thyroid. This gland at the front of your throat releases hormones to tell your body to “speed up” your metabolism. Of course, the more thyroid hormone there is the faster things will work and the more calories you'll burn.
But that's not the only thing that affects your metabolic rate.
How big you are counts too!
Larger people have higher metabolic rates; but your body composition is crucial!
As you can imagine muscles that actively move and do work need more energy than fat does. So the more lean muscle mass you have the more energy your body will burn and the higher your metabolic rate will be. Even when you're not working out.
This is exactly why weight training is often recommended as a part of a weight loss program. Because you want muscles to be burning those calories for you.
The thing is, when people lose weight their metabolic rate often slows down which you don't want to happen. So you definitely want to offset that with more muscle mass.
Aerobic exercise also temporarily increases your metabolic rate. Your muscles are burning fuel to move so they're doing “work”.
The type of food you eat also affects your metabolic rate!
Your body actually burns calories to absorb, digest, and metabolize your food. This is called the “thermic effect of food” (TEF).
You can use it to your advantage when you understand how your body metabolizes foods differently.
Fats, for example, increase your TEF by 0-3%; carbs increase it by 5-10%, and protein increases it by 15-30%. By trading some of your fat or carbs for lean protein you can slightly increase your metabolic rate.
Another bonus of protein is that your muscles need it to grow. By working them out and feeding them what they need they will help you to lose weight and keep it off.
And don't forget the mind-body connection. There is plenty of research that shows the influence that things like stress and sleep have on the metabolic rate.
This is just the tip of the iceberg when it comes to metabolism and how so many different things can work to increase (or decrease) your metabolic rate.