Understanding how many calories your body actually requires is a good starting point for your health and fitness goals.
The first of three numbers you will need to find is your Basal Metabolic Rate (BMR), this is essentially how many calories our body will burn by just being alive.
Next you will need to know what your activity level is during the day, ie. how active are you in the day (outside of planned exercise). Each level has a number associated with it, and with the BMR will equate to your daily energy requirement.
Finally, if you are exercising through the week we will need to know roughly how many calories you are burning during your exercise, this can be researched through Google searching databases, but the best way to do this is to use Heart Rate monitor and complete your week of training. Remember to keep recording how many calories you burn during exercise as this is likely to change as you get fitter.
Putting it all together
To find this there are a number of different formulas out there, an accurate one is the Harris-Benedict formula which we will use below, I will further simplify this at the end of the post.
Basal Metabolic Rate:
Men = (10 x Body Weight (kg)) + (6.25 x Height (cm)) - (5 x Age (yrs)) + 5
Women = (10 x Body Weight (kg)) + (6.25 x Height (cm)) - (5 x Age (yrs)) - 161
Activity Level (outside of planned exercise):
Sedentary (office job) = 1.4
Moderately Active (shop worker stacking shelves etc) = 1.7
Very Active (carpenter, builder, labourer etc) = 2.0
Now take your BMR and multiply it by the corresponding number next to your activity level (be honest!).
This will give you your daily energy expenditure. This is of course not including planned exercise, but this would ideally be gathered through an average training week and the calories accounted for within each day.
For example, if you are running for an hour 5 days a week and burning 500 kcal per session, then this should be added to your figure above. A good way of doing this is to add up all the calories burned in one average week of a planned programme (so that there is consistency) and divided by 7 (days of the week), you can then add this average daily figure to your daily energy requirement.
Gary here is 73kg, 29 years old and 184cm tall, he currently works full time as an administrator and therefore sits down for prolonged periods.
Gary's BMR = (10 x 73 (weight in kg)) + (6.25 x 184 (height in cm)) - (5 x 29 (age in yrs)) + 5
BMR = 730 + 1150 - 145 + 5
BMR = 1740 kcals (per day)*
*This is the amount of energy required to keep Gary functioning normally every day.
Daily Energy Expenditure
1740 x 1.4 = 2436 kcals
*This is the amount of energy required each day for Gary to maintain weight at his current activity level (outside of planned exercise).
Gary has started running three times per week and doing one spinning class per week which he has found through his Heart Rate monitor to equal 2000 kcals per week.
2000 / 7 = 285 kcals
This is the amount of calories burned during exercise which need to be accounted for in his daily energy expenditure. He could just add the individual amounts for each exercise to each day, in this case this is roughly 500 kcals per training session. Or he could divide the total weekly calories burned (through exercise) by 7 and add this to his daily energy expenditure. In this case, this would be an extra 285 kcals per day.
BMR x Activity Level + Average Exercise Energy Expenditure
New Daily Energy Expenditure = 2722 kcals per day*
*This is the amount of calories per day that Gary would have to consume to MAINTAIN his current weight.
If we are to try and lose weight, we MUST BE IN A CALORIE DEFICIT, in this case we could subtract a percentage for a healthy fat loss deficit. In most cases, a 15-20% deficit is healthy and easier to adhere to.
To find this, we simply subtract the given percentage from our total Daily Energy Expenditure.
Gary wants to lose some body fat and has decided to commit to a 15% calorie deficit.
BMR x Activity Level + Average Exercise Energy Expenditure - 15%
Gary's daily calorie needs within a healthy deficit = 2300 kcals
Ultimately, this is a little over complicated, although the majority of the calculation is as simple as it can be, there is a easier way of calculating this is you are an average person trying to shift a bit of weight. this is the method learned from Martin MacDonald though the Mac Nutrition Uni:
Men: Body Weight (kg) x 24
Women: Body Weight (kg) x 22
Now you can multiply by your activity level above and hey-presto! you have your daily energy expenditure. Don't forget at this point to add on your exercise calories if you are working out several times a week. If you are going for the odd run, walk or swim or go to the gym once maybe twice a week (a total exercising time of 2-3hrs per week of moderate exercise) then you need not bother adding on the exercise energy expenditure as this will take you into a manageable calorie deficit.
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