5 Easy Steps For Calculating Energy Requirements & Adjusting For Weight Loss

If you are a calorie counter you will love this! I don't like getting too caught up with the 'mathematics' of energy in and energy out but for those of you who do here are 5 easy steps to calculate your daily energy requirements and adjust to achieve a weight loss of 0.5 - 1kg per week. Don't read any further without your calculator!








Step 1: Calculate Your Ideal Body Weight

If you are not overweight or looking to lose weight your energy requirements can be calculated using your 'actual weight' and calculating your IBW is not necessary - if this is you, skip to step 2.

If you are trying to lose weight it's important that energy requirement calculations are based on your ideal body weight (IBW) to avoid over estimating  A simple method to calculate IBW is to work out what your body weight would be at a body mass index (BMI) of 25. Calculate your estimated IBW using the equation below.

IBW (kg) = Your Height (m) squared x 25

Example: My current body weight is 88kg and my height is 1.78m, ((1.78 x 1.78) x 25) which equals 79kg. 


Step 2: Calculate Your Basal Metabolic Rate

Next we need to calculate your basal metabolic rate (BMR). BMR is the amount of energy the body expends at rest - the energy required to sustain vital physiological functions. BMR can be thought of like the 'body's furnace' which burns energy fairly consistently all day, everyday. Calculate your BMR using your 'actual weight', or, your ideal body weight calculated in step 1.

BMR (kj) =

Men:
10 – 17 years: (17.7 x Weight (kg) + 657) x 4.2
18 – 29 years: (15.1 x Weight (kg) + 692) x 4.2
30 – 59 years: (11.5 x Weight (kg) + 873) x 4.2
60 + years: (11.711 x Weight (kg)  + 587) x 4.2

Women:
10 – 17 years: (13.4 x Weight (kg) + 692) x 4.2
18 – 29 years: (14.8 x Weight (kg) + 487) x 4.2
30 – 59 years: (8.3 x Weight (kg) + 846) x 4.2
60 + years: (9.082 x Weight (kg)  + 658) x 4.2

Example: I am 29 and male, (((15.1 x 79) + 692) x 4.2), which equals 7916kj, rounded to 7900kj. If you are trying to lose weight always round down. 

Step 3: Apply An Activity Factor

Now we need to account for the energy you expend with activity, this includes structured exercise, occupational and leisure actiity. This is achieved by multiplying your BMR (calculated in step 2)  by an activity factor. Determine which activity factor best describes you and multiply it by your BMR to calculate your estimated energy requirements (EER). 

If you want to lose weight be careful not to overestimate your activity factor, it may be better to even choose one factor less to keep your energy estimation on the lower end.

EER (kj) = BMR (kj) x Activity Factor (choose from below)

Sedentary people of both genders should multiply by 1.3

Sedentary is very physically inactive, inactive in both work and leisure.

Lightly active men should multiply by 1.6 and women by 1.5.

Lightly active means the daily routine includes some walking, or intense exercise once or twice per week.

Moderately active men should multiply by 1.7 and women by 1.6.

Moderately active means intense exercise at least three time per week, or a job with a lot of walking, or a moderate intensity job.

Very Active men should multiply by 2.1 and women by 1.9

Very active means intense exercise 6-7 days per week, or a heavy physical job, such as a mail carrier or an athlete in training.

Extremely active men should multiply by 2.4 and women by 2.2

Extremely active means an athlete on an unstoppable training schedule of 2 or more training sessions per day, or a very demanding job, such as working in the armed forces or shoveling coal.

Example: I exercise 6 days a week (sometimes twice per day) fairly intensely so I would use a 'very active' activity factor of 2.1, (7900kj x 2.1) which equals 16590kj rounded to 16500kj. 

Step 4: Adjust For Weight Loss

Your EER calculated in step 3 represents the total energy intake required to maintain your weight. If you want to lose weight you need an intake less than this. A healthy weight loss of 0.5-1kg per week should be your target. Calculate the daily energy intake you require to achieve your desired weight loss result.. 

Weight Loss of 0.5kg / Week
Adjusted Energy Intake for Weight Loss (kj) = EER (kj) - 2100kj

Weight Loss of 1kg / Week
Adjusted Energy Intake for Weight Loss (kj) = EER (kj) - 4200kj

Example: I want to lose 1kg per week, (16500 - 4200kj), which equals 12300kj, rounded to 12000kj. This is the energy intake I require per day to lose 1kg per week. 


Step 5: Convert to Calories (if you wish)
If you prefer to work in kilojoules (kj) ignore this step.  I like to work in kilojoules (kj) however I can appreciate that a lot of people are more familiar with calories (cal) or kilo calories (kcal) - which are both the same thing. 

Adjusted Energy Intake for Weight Loss (cal) = Adjusted Energy Intake for Weight Loss (kj / 4.2 

Example: My adjusted energy intake to achieve 1kg of weight loss per week is 12000kj, (12000 / 4.2), which equals 2857cal, rounded to 2800cal.