You hear this word thrown around a lot these days.

You might blame a slow one for how much easier it is for you to gain weight than it was a few years ago!  If you’re like me, you remember the days where you could eat whatever you wanted and you didn’t think twice. But as you got older you found you needed to pay careful attention to what you eat!

So what is it? Technically, metabolism is the word used 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 stay alive. Without this amazing biochemistry you would not be possible.

Metabolism includes how the cells in your body:

  • Allow activities you can control (your physical activity.)

  • Allow activities you can’t control (your heart beat, healing, processing of nutrients, etc.)

  • Allow storage of excess energy for later use

When you put all of these processes together into your metabolism you can imagine that these processes can vary in speed – they can be fast, slow, or just right.

Which brings us to your metabolic rate, which is how fast your metabolism works and it’s measured in calories.

The calories you eat can go to one of three places:

  • Work (exercise and other activity).

  • Heat (from all those biochemical reactions).

  • Storage (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 your metabolic rate:

  • RMR – This stands for resting metabolic rate, which is how much energy your body uses when you’re not being physically active.

  • TDEE – This stands for total daily energy expenditure which measures both the resting metabolic rate as well as the energy used for “work” (exercise) throughout a 24-hour period.

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.

Another factor is your size – Larger people have higher metabolic rates; but your body composition is crucial! As you can imagine, muscles that are worked need more energy than body 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 you lose weight without exercising, you tend to lose muscle. That loss of muscle causes a decline in your metabolic rate.

Once the diet is over (let’s face it, none of them last forever!) and you resume your regular diet, your body now needs fewer calories to exist than it did before, which is why you often gain weight back after dieting, plus a few extra pounds!

So you definitely want to offset that by having more lean muscle mass.

Another factor is your activity level – Aerobic exercise also temporarily increases your metabolic rate.  Your muscles are burning fuel to move so they’re doing work.

How Your Diet Affects Your Metabolism

Did you know that 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 the fat or carbs in your diet 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.

Let’s not 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.

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Disclaimer: I am not a medical doctor or Registered Dietitian. The information presented is purely to share my experience and for entertainment purposes. As always, check with a doctor before making any fitness or nutrition changes. The author and blog disclaim liability for any damage, mishap, or injury that may occur from engaging in any activities or ideas from this site.