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Understanding Calories

Updated: Apr 26, 2021

What are calories? We have all heard of them, we know too many calories leads to weight gain, but what exactly are they? Well, they are not little creatures that live in wardrobes shrinking your clothes to make them not fit. The truth is not overly exciting. Calories (Kcal) are a unit of measurement, like a metre measures distance, calories measure energy. Living and moving uses energy, therefore, we must fuel our bodies (like petrol in a car or logs on a fire). Our fuel is the food and drink we consume, giving us the energy we require, measured in calories.

The human body is not built to waste energy, this comes from historical times when we were hunter gatherers and man did not know where the next meal would come from, therefore, our bodies evolved to store any excess energy. Still to this day when we consume more calories than we require, our bodies store the excess for a later time and it is stored as body fat. Food however is a lot easier to come by and there are a lot of unhealthy and high calorie foods readily available to us daily too.

To lose this excess body fat we may have gained over time we need to put our bodies into a healthy calorie deficit of negative 500kcal a day. An example of this would be your average woman requires 2000kcal a day, if we reduced their calorie intake to 1500kcal a day they would lose 1-2lbs of body fat that week. Sounds simple? Well, if you take away eating habits, emotion, hidden calories in foods, socialising etc then it is. 1lbs of fat is 3500kcal. Overeat by that amount and gain 1lbs, get the deficit right and lose 1lbs.

Everyone leads different lifestyles and has different activity levels, so you will need to work out YOUR required calories. This is known as your Basal Metabolic Rate or BMR, simply put it is the amount of energy or calories your body requires to function and live. There are different equations out there to work this out, I tend to use the Harris-Benedict equation. You will need to know your weight in Kg, your height in cm and your age in years to complete it. Once you have this figure, you will need to then account for how active you are, this is known as you Physical Activity Level or PAL. You multiply your BMR by your Pal (BMR X PAL) and the answer is your estimated calorie expenditure for 1 day (For equations see the end of the article).

Once we know how many calories to target for our goals the next stage is to look at the foods we eat. The basics of a balanced diet consist of fats, carbohydrates, proteins, a mixture of vitamins and minerals, fibre and water. All have calories (except for water) and in different amounts. 1g of fat consists of 9kcals, 1g of carbohydrates consists of 4kcals and 1g of protein consists of 4kcals. Alcohol also contains a lot of calories (1g consists of 7kcals) but offers no nutritional value so is not considered part of a healthy balanced diet. Food gives you the nutrients your body needs, it is also fuel, and calories are the measurement of that fuel. There are basic guidelines to this, men require 2500 Kcal (calories) and women 2000kcal a day (on average). My advice here is be incredibly careful and work out your own bodies requirements.

A few points to consider are, I have never met a single person who requires the “average” calories as recommended. Therefore, it is so important to make it specific to you. I have had a client who was pretty inactive and on the upper side of 60 years old who was overweight and with their calorie deficit required only 900kcal a day. Had they gone with the “average”, they would have been over eating by 600kcal a day (4200kcal a week). If you are going to be upping your exercise, base your calculations on what you have been doing rather than what you are aiming to do, and in time adjust when necessary. And finally, it is especially important not to go over the negative 500kcal a day, as this is a healthy amount that your body can cope with, eating less will mean your body will be malnourished and it will start to take what it requires from your healthy muscle tissue and cells, reducing your lean healthy tissue and your health.

Harris-Benedict equation (BMR)


(10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) + 5 = BMR


(10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) – 161 = BMR

Physical Activity Level (PAL)

Weekly activity level

Little to no exercise BMR x 1.2

1-3 days BMR x 1.375

3-5 days BMR x 1.55

6-7 days BMR x 1.725

7-14 sessions (heavy) BMR x 1.9

BMR x PAL = Estimated Calorie expenditure

* (Too lose body fat healthily - 500 from this total)

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