What is Metabolism?

What Is Metabolism?


Many people claim that they cannot lose weight because they have a slow metabolism and are constantly looking for ways to boost their metabolism.  A lot of these people do not truly understand the term metabolism.  According to Wikipedia:

“Metabolism is a set of chemical reactions that occur in living organisms in order to maintain life”

In humans the food we eat fuels these chemical reactions.  So when people refer to a fast or slow metabolism they are generally referring to the average amount of calories their body burns in a day.  There are three main factors that affect your metabolism:

1) BASAL METABOLIC RATE (BMR):- This is the amount of energy you use to perform the basic functions that keep you alive e.g. if you lied in bed all day and burned 1000 calories then your BMR would be 1000 calories per day.  You can roughly estimate your BMR by multiplying your weight in pounds by 14 if you are male and by 12 if you are female e.g. if you are male and weigh 150lbs your BMR will be about 2100 calories.  You can also use this BMR calculator.  BMR has the biggest influence on your metabolism and normally accounts for 60% to 65% of the calories you consume.  Your BMR is largely down to genetics but there are a number of things that can affect it:

Building muscle:- This can increase your BMR as muscle requires more calories to maintain than fat.

Dehydration:- This can contribute towards a low BMR as it prevents your body from performing a number of basic functions.

– Illness:- Illness can significantly affect the way your body works and therefore influence your BMR.  Thyroid conditions in particular can have a major influence over your BMR.

– Supplements:- Certain supplements can slightly influence your BMR.

Vitamin or Mineral Deficiency:- This can reduce your BMR if it stops your body from performing basic functions properly.

– Weather:- This has an impact on your BMR because your body will have to use extra calories to warm you up or cool you down depending what the weather is like outside.

2) PHYSICAL ACTIVITY:- Certain people are more active than others.  More active people will burn more calories through physical activity than less active people.  This has the second largest influence on your metabolism using between 25% and 30% of the calories you consume.

The amount of physical activity you do each day is something that you can directly influence.  If you drive to work, sit at a desk all day, drive back home, watch TV, go to bed and repeat then you are not going to burn many calories through physical activity.  However, if you make physical activity part of your lifestyle and do a little bit of activity each day it can quickly add up to a lot of calories burned.

3) THERMIC EFFECT OF FOOD:- Food cannot digest itself.  This process requires calories too.  Digestions has the third largest influence on your metabolism and uses around 10% of the calories you consume.  You cannot hugely increase the amount of calories you burn through the foods you eat.  However, certain foods do have a better thermic effect than others:

Fibre:- Complex carbohydrates that are high in fibre such as fruits, vegetables and whole grains burn more calories during digestion than simple carbohydrates such as white bread, white pasta and sugary foods.

Protein:- Protein is thought to burn two to three times the amount of calories that carbohydrates and fats do during digestion.  Furthermore, according to a study from McArdle et. al (1986) [1] when eating a meal that consists of pure protein up to 25% of the calories consumed can be used during digestion and absorption.

Spicy Foods:- Spicy foods can temporarily increase the amount of calories you burn.  This is because certain spices are thought to stimulate fat burning.  On top of this spicy foods temporarily raise your body’s temperature after you eat them meaning you burn more calories.

So there you have it.  There are three main things that affect your metabolism; your BMR, your physical activity and the thermic effect of the foods that you eat.  Although you can have some influence over your metabolism and increase the amount of calories you burn each day there is no magic way to drastically increase your metabolism (unless you do A LOT of exercise every day).  What you eat and how much you eat has a much larger influence over how much weight you gain or lose.  To maintain or lose weight:

“The Calories you Consume <= BMR + Physical Activity + Thermic Effect of Food”

Now I want to hear from you guys.  Are there any key things I have missed which can raise or lower your metabolism?  Do you agree that the calories you consume is the key to weight loss?  Let me know what you think by leaving a comment.

Do You Need to Increase Your Metabolism? (About.com)
Metabolism (Wikipedia)
Resting Metabolic Rate (BodyBuilding.com)
[1] McArdle, W.D., Katch, F.I., Katch, V.L., (1986) Exercise Physiology: Energy, Nutrition, and Human Performance Lea and Febiger Philadelphia p. 134, 135

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  1. says

    GREAT information. Thanks for including all the non-specific tertiary influences (like the weather).
    I am a huge believer in your BMR and how it is affected by your activity. Personally, I believe my BMR increased over the past year due to my increased activity and my increased muscle mass. So I’m living proof.

    Thanks for the tip on hydration. I’m really bad at hydration. I live in a constant dehydrated state due to my consumption of caffeine (yeah, yeah.. I know). I’m working on it.


    Tom Reply:

    Thanks for your comments Strong One. Hydration is a strange one for me. Monday to Friday I am constantly topping up on water because our office is quite hot and I always want to have some water close by. This keeps me really well hydrated. However, on weekends I drink a lot less water and more caffeine so am a lot less hydrated. Something I need to work on too.


  2. says

    Nice explanation of metabolism and how different things impact it. Hot image too, quite tantalizing. It is surprising to me the effect that thermogenics has on your metabolism. Besides spicy foods, I have also heard that drinking icy cold beverages helps your metabolic rate as well as your body then needs to warm it up in your stomach in order to process it. And then an increase in lean muscle mass is huge too. Thanks for putting this online.



    Tom Reply:

    Glad you like the article Steve.


  3. says

    I haven’t come across much info about metabolims / metabolics rates before, so, thanks for posting this. Also, I have to admit that I’ve never really thought about the thermic effect of different foods before. How much effort should we put into monitoring the thermic rate of our food? Is it a very important consideration to a weight loss program? I guess “reading above” that if you were slightly overweight, eating food with more spices would increase your metabolic rate and help you burn more fat.


    Tom Reply:

    Thanks for commenting Toby. Unfortunately, the thermic effect of food only accounts for around 10% of the total calories you consume. Whilst you can raise this amount slightly your basal metabolic rate and your level of physical activity have a much larger impact on your overall metabolism.


  4. Raeshel says

    Thanks for the info. I am 5’10 160 lbs female and just found out that I have a extremely slow metabolism before I started working again I would work out 6-7 days a week for close to 2 hrs but would fall straight asleep once I got home. I do need to work on my hydration my food intake is pretty good and healthy though it has slipped a bit since I haven’t been able to make it to the gym. Either way thank you for the tips I just need to get my butt back into gear.


    Tom Reply:

    Hi Raeshel – Thanks for commenting. Glad you like the article. Good luck with getting your butt back into gear :).


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