Basal Metabolic Rate

As we’ve determined in our diet overview, weight loss is achieved when there is a calorie deficit i.e. your body has used more energy than you’ve consumed.

A calorie, or kcal as it’s often labelled, is a unit of energy that is often used when referring to:

  • How much energy is in the food or drink we’ve consumed. For example, a cheeseburger contains 350 calories
  • How much energy is used by our bodies to move and exist. For example, a 20 minute run will burn about 300 calories (will vary depending on weight of runner and running speed)

That all sounds great, but how can you know how much energy you’ve consumed?

We can get a solid guideline to the amount of energy our bodies have used by calculating our Basal Metabolic Rate (or BMR). Our BMR is the amount of calories (or energy) our bodies would use if you lay down and didn’t move all day; the amount of energy our bodies need to function and exist. This can be worked out with the formula below, or more simply by using this BMR calculator:

Women: 655 + ( 9.6 x weight in kilos ) + ( 1.8 x height in cm ) – ( 4.7 x age in years )
Men: 66 + ( 13.7 x weight in kilos ) + ( 5 x height in cm ) – ( 6.8 x age in years )

Now that we’ve worked out our BMR, we need to take into account our levels of activity; the amount of extra energy we’ve used. This will obviously vary greatly from person to person and is roughly worked out by multiplying your BMR rate by an amount that is equated with your levels of weekly activity:

  • If you are sedentary (little or no exercise) multiply your BMR by 1.2
  • If you are lightly active (light exercise/sports 1-3 days/week) multiply your BMR by 1.375
  • If you are moderatetely active (moderate exercise/sports 3-5 days/week) multiply your BMR by 1.55
  • If you are very active (hard exercise/sports 6-7 days a week) multiply your BMR by 1.725
  • If you are extra active (very hard exercise/sports 2 times daily or physical job) : multiply your BMR by 1.9

This is obviously not exact and could vary from week to week but it gives a good guideline.

Now we’ve gone though all the figures and equations, let’s put it into practice on me:

I am a 1.83m tall, 29 year old, 81kg male. Taking into account these factors, if I laid completely still all day I would use 1894kcal of energy. That is my BMR.

I would consider myself to be between ‘moderately active’ and ‘very active’. I am on my feet most of the day and I train hard 5-6 days of the week. Therefore I am using x 1.65 as my activity level multiplication. This is probably underestimating slightly but I’d prefer that than overestimating. So, multiplying my BMR of 1894 with my activity multiplier of 1.65 brings my total energy expenditure to:

3125 calories per day

I have used this figure as part of my food diary to help me understand whether I have a calorie deficit (consuming less energy than I’m using) or a calorie surplus (consuming more energy than I’m using). If there is a calorie surplus, the extra calories will be stored on my body as fat. If there is a calorie deficit energy will be taken by using the energy from fat on my body. Simple as.

So there you have it – using the method detailed on this page you can get a good idea of how much energy your body uses in a day, something that I think is beneficial for everyone to know, regardless of their goals or weight.

Of course, if you have any desire to increase or decrease your weight or to change your body composition (what your body is made up of – fat, muscle, bone etc) then it is essential that you know your BMR.

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