In order to determine how many calories you should eat to lose a specific amount of fat you must first determine how many calories you burn in a day.
The main factors in calorie expenditure are body weight and activity level and also, to a lesser degree, gender. Your calorie expenditure is also known as your maintenance calorie intake or total daily energy expenditure. (TDEE)
The Simple Method
The simplest way to work out your maintenance calorie intake is this:
BW×M=TDEE
BW = Body Weight
M = Multiplier
TDEE = Total Daily Energy Expenditure
The multiplier described here is a number that is affected by gender and activity level.
The Influence Of Gender
Gender makes a significant difference to calorie expenditure which is especially important in more simplistic equations for calculating your calorie needs.
Men tend to have more muscle mass and be more physically active so if you are a man, multiply your bodyweight by 15.
Women tend to have less muscle mass and be slightly less active than men and don’t burn quite as many calories. Ladies, you can multiply your bodyweight by 14.
This isn’t an infallible rule but it’s a fairly accurate guideline.
The Influence Of Activity Level
These values, 15 for men and 14 for women, are average values.
So what is moderate? If you:
- Get a moderate amount of exercise during the week
- Have a job that is neither physical nor sedentary
- Take between 7500 and 12500 steps each day
If this describes you then stick with the original values.
Men = 15
Women = 14
So do you have a low activity level? Do you:
- Have a sedentary job
- Travel by car everywhere
- Do no intentional exercise
- Take less than 7500 steps per day
If you have a low activity level, you should subtract 1 from the original values.
Men = 14
Women = 13
Do you have a high activity level? If you:
- Exercise several times each week
- Play sports frequently
- Have a physically demanding job
- Take more than 12500 steps each day
Then you probably have a high activity level, this is a good place to be and will help you lose fat. In this case you can use the multipliers for those with an average activity to speed up fat loss or alternatively add 1 from the average value:
Men = 16
Women = 15
Do you have a slow metabolism?
Many people cling to the idea that they have a slow metabolism when often it is not the case, this is made worse by many magazines that promote the idea. Instead of telling you that this is false and having you take my word for it, I am going to show you.
Weight: 200 lbs
Gender: Male Activity Level: High 200 x 16 = 3200 calories/day |
Weight: 100 lbs
Gender: Female Activity Level: Average 100 x 14 = 1400 calories/day |
Weight: 250 lbs
Gender: Male Activity Level: Low 250 x 14 = 3500 calories/day |
Not what you may have thought is it?
Person A is typically athletic, with a high activity level his calorie needs are 3200.
Person B is female with an average activity level and as you can see, she has rather low calorie needs of 1400.
Person C is overweight, has a low activity level and yet
has calorie needs of 3500!
Yes, larger individuals who often claim to have a slow metabolism normally have the fastest metabolic rates!
The reason for this is their weight, they may not move as much but they carry a lot more weight. Larger individuals may have more to lose but they are able to lose the weight faster.
Some people genuinely have slow metabolisms. Those who have clinically low levels of thyroid hormones do technically have slower metabolic rates but this doesn’t bypass the laws of physics. If you are one of the unfortunate people with hypothyroidism you can and should follow the guidelines given in this book with your doctor’s approval. More importantly if you are overweight, don’t just assume that you have hypothyroidism, this can only be determined by blood testing.
If you are heavily muscled or obese then this equation may be inaccurate for you, if you want to be sure, try some of these more advanced equations.
The Harris-Benedict Formula
The Harris-Benedict formula is a step up from our simple method, it takes into account not just your weight and activity level but also other factors such as height and age that have small effects on TDEE (Total Daily Energy Expenditure)
The 2-step formula is as follows:
Harris-Benedict Formula: Imperial (original 1918) | |
Men | 66 + ( 6.23 x weight in pounds ) + ( 12.7 x height in inches ) – ( 6.8 x age in year ) |
Women | 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) – ( 4.7 x age in years ) |
Harris-Benedict Formula: Metric (revised 1990) | |
Men | (10 x weight in kg) + (6,25 × height in cm) – (5 × age in years) + 5 |
Women | (10 x weight in kg) + (6,25 × height in cm) – (5 × age in years) – 161 |
The result of this equation is a BMR calculation, which means basal metabolic rate, it is the amount of calories your burn without any additional activity.
In step 2 we take our BMR and multiply it by an activity level multiplier, not unlike the simpler version.
Activity Multipliers | |
Little to no exercise | BMR x 1.2 |
Light exercise | BMR x 1.375 |
Moderate exercise | BMR x 1.55 |
Heavy exercise | BMR x 1.725 |
Very heavy exercise | BMR x 1.9 |
The Harris-Benedict formula is reasonably accurate except in the case of those who are very lean or have a very high body fat percentage. In my experience, the results are often within 100 calories of the simple method.
It is always better to guess low instead of guessing high, very few people will fall under the very heavy exercise category, only use the heavy exercise multiplier if you genuinely do train hard for hours, several days a week.
We’ll use the more complex imperial method for our example. A woman who is 140 pounds and 5′ 4″ and 32 years of age with a moderate activity level would have to calculate:
Step 1: 655 + ( 4.35 x 140 ) + ( 4.7 x 64 ) – ( 4.7 x 32 ) = 1414
Step 2: 1414 x 1.55 = 2192 calories per day
The Katch-McArdle Formula
The Katch-McArdle formula takes lean muscle mass into account in an aim to produce better results because fat mass and fat-free mass have different metabolic properties, in order to use this method you must first know your body fat percentage.
It is beyond the scope of this book to teach the use of skinfold caliper as it is a skill that requires practice for accuracy and some sites are not easily self-measured, I advise that you have skinfold measurements done by a qualified fitness professional with experience using skinfold calipers.
Katch-McArdle Formula: Metric (original) | |
Unisex | 370 + ( 21.6 x LBM ) |
This original formula is for kilograms but it can be adjusted to pounds, the LBM refers to lean body mass, when you know your body fat percentage you can multiply your weight by the percentage of lean mass. If you are 200lbs and 30% body fat, then you are holding around 60 pounds of body fat and 130 pounds of lean mass, (everything else that isn’t fat). We now have a number we can put into the equation.
The Katch-McArdle method can be altered to allow its use in pounds, and it looks something like this.
Katch-McArdle Formula: Imperial (converted) | |
Unisex | 370 + ( 9.82 x LBM ) |
In this case we can put in 130 pounds into the equation. 370 + ( 9.82 x 130 lbs ) = 1647
Or for those inclined to use the metric system using the original 370 + ( 21.6 x 59 kgs ) = 1644
The slight difference is a result of me rounding the numbers when converting from pounds to kilograms, if you want to use both or convert one measure to another then you can, remember that 1 kg = 2.2 lbs.
This method requires a multiplier like the other two methods, use the same multiplier for the Katch-McArdle method as you would for the Harris-Benedict formula. To complete this case, let’s assume that he is moderately active (BMR x 1.55)
1644 x 1.55 = 2548kcal
It is best to use the Katch-McArdle method if you have a particularly high or low body fat percentage.
Whichever you choose to use, just remember to use one! All methods are completely legitimate and suitable for the majority of people.
ACTION POINT
Calculate your total daily energy expenditure using any of the above mentioned formulas. |