Posted on February 28, 2019 by Emily Forbes

It’s February (nearly March eeek!). With this lovely weather and Easter approaching, some people will already be on their “summer body mission”. Some might just be “eating healthier” whilst others may actually be “dieting”. Food and dieting are all about calories. You’ll read on food packaging that men should be eating an average of 2500kcals and women 2000kcals. But what exactly are calories? And how do you go about calculating calories?

What are calories?

One calorie is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius. Kilocalories (kcal) is the amount of heat needed to raise the temperature of 1 kilogram of water by 1 degree Celsius. Calories are our “energy currency”.  We burn calories to provide energy to fuel all our living and daily functions. Everything from breathing, thinking, digestion, moving and exercise require calories to happen. All food contains Calories and is calculated using bomb calorimetry, where the food is burnt and the rise in water temperature is then measured to calculate the Calories.

How many calories do we need?

  • Estimated energy expenditure (EEE) = Basal Metabolic Rate (BMR) * physical activity level (PAL)
  • BMR = The number of calories required to keep your body functioning at rest
  • PAL = Total energy cost of physical activity throughout the day expressed as a ratio of BMR (should not include exercise)


  • An estimation of BMR can be done using the Harris-Benedict equation
  • Males: 66 + (13.7 x BW in kg) + (5 xHeight in cm) – (6.8 x Age)
  • Females: 655 + (9.6 x BW in kg) + (1.8 x Height in cm) – (4.7 x Age)


Lifestyle Description PAL
Sedentary Little or no

activity, desk job

Lightly active Light activity, some of the

day standing or walking

Moderately active Moderate activity levels,

on feet most of the day,

street salesperson

Very active Hard daily activity or

exercise e.g. working long

days on a building site



  • You should now have your estimated energy expenditure. This is the number of calories required to keep you at your CURRENT weight = MAINTENANCE calories
  • If you want to LOSE weight you need to be in a calorie DEFICIT. I wrote another blog on calorie deficits here.
  • To calculate an energy deficit multiply your EEE by a percentage. Example: if you want to reduce your calories by 20% then you will be consuming 80% of maintenance calories; so EEE * 0.80 = new EEE for weight loss
  • These calculations are ESTIMATES. If you don’t lose weight with your calculations then you may have inaccurately estimated, perhaps put your PAL too high. Recalculate using a lower PAL.

Remember THE most important thing to weight loss is an energy DEFICIT. No fancy potion or pills. The diet which works best is the one you can ADHERE to. If you aren’t losing weight (fat)* then you aren’t in an energy deficit. It really is that simple.

Here’s a great blog which gives you an indication of how many calories you burn doing certain activities.

*Sometimes factors like water retention can mask fat loss. So you may be losing fat but not losing weight. But don’t use this as an excuse, it is not the majority of cases. Measurements and clothes sizes should be coming down if you are losing fat. And eventually, the scales will come down too.