How can we determine calorie needs?

To determine how many calories you need there are a few different methods. The most accurate way is to record everything that you eat over a few days while you are not gaining or losing weight, then take an average of what calorie amount you have consumed during that time. This works great for those who are used to measuring their calorie intake and who have a relatively consistent diet (basically, people who are doing all of this anyway) but for people new to the concept this has some issues.

Primarily, the simple act of focusing upon something alters its behaviour, be that an animal, a sub atomic particle, or you when you’re rummaging in the fridge. If you just happen to have stayed weight stable by accident over the last few weeks then suddenly start to record your intake you will probably change what you’re doing. Not only that, people are terrible at recording their food. We’ll cover this a lot more in the module about tracking food, but for now just trust us that this process is great in theory, but less so in practice.

A much faster and potentially more accurate means (given the above) is to use what we know about the factors which make up RMR and then estimate that. When we consider the average weight of all different tissues in a given individual and the average amount of calories those tissues require per kilogram, we can get to a pretty good number for estimating it, which makes the whole thing a lot more straightforward.

There are many complex formulae which you can use to estimate your BMR/RMR (depending on the formula) with the most popular probably being the Harris Benedict Equation which looks like the below:

• Men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)
• Women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.339 x age in years)

These look a little intimidating but with a calculator they are simple to use. With that said, you can get to a very close figure to what you’d get by doing the above by simply doing the following:

• Men: Bodyweight in kilograms x 24
• Women: Bodyweight in kilograms x 22

The difference in both is mostly because men carry more lean tissue at a given level of ‘leanness’, as women’s essential fat (the amount of bodyfat they have to carry to stay alive) is far higher. A man and a woman who are at the same level of visual leanness, will have a bodyfat % which differs by about 8-10%, with the man being lower. This doesn’t really mean anything, but it’s good to note for reference, and it explains why the BMR of the two is different in part. The remainder of the difference isn’t entirely clear, but it follows logic that the reasons are primarily hormonal.

Note: For individuals who are extremely lean, extremely overweight or muscular, very old, peri or post-menopausal, or suffering from certain health issues relating to metabolism (thyroid issues, for example, or PCOS) the figures may be different. These individuals should use the more complex formulae to get a good estimate, but really estimating the TDEE of these individuals is beyond the scope of this course and in fact practically very difficult to do.

After you have estimated someone’s BMR, your next step is to account for the activity which you might take part in during the day. To do this, we can use the following ‘activity modifiers’:

• If someone is largely sedentary, perhaps someone with a sedentary job who doesn’t really engage in activity at all, an estimate of their daily kilocalories needed would be: BMR x 1.2
• If someone is a light exerciser (2-3 exercise sessions per week) and has an inactive office job, or they engage in little to no exercise but have a moderately active job like a hairdresser, their daily kilocalories needed would be: BMR x 1.375
• If someone is a moderate exerciser (2-3 sessions per week) and they also have a moderately active job like a hairdresser, or if they engage in heavy exercise (3-5 sessions per week) while working an office job, or if they have a very demanding job but don’t formally exercise daily, kilocalories needed would be: BMR x 1.55
• If someone did a lot of heavy exercise (6-7 exercise sessions per week) and a moderately active job, or moderate exercise and manual job, their daily kilocalories needed would be: BMR x 1.725
• A very heavy exerciser, twice per day exercise, or heavy exercise and a manual job, their daily kilocalories needed would be: BMR x1.9

Note: THESE ARE ESTIMATES. If you aren’t sure, go with the lower figure as most people overestimate their calorie expenditure and we will show you later in the course how to verify the figure you come to. This calculated figure is an average across 7 days, and as such would be eaten on both training and resting days.

Practical Example: An 85kg male would have a BMR of around 2040 calories according to our shortened calculation (weight in kg x 24). If he lifted weights 4 times per week, took a long walk on his lunchbreak and stayed reasonably active during the weekend he would comfortably fall into the category of ‘moderately active’, so we would take this 2040 figure and multiply that by 1.55 to get an estimated TDEE of 3162. This could be rounded to 3100-3200kcals. As this calculation is an estimate, and because (as you will see in the food label module) food labels are not precise either, it’s a good idea to use a calorie range instead of an exact figure to make dietary adherence far easier.