How much should you eat? – The Diet Set up Part 1

If you have 30 seconds, read the summary
If you have 10 minutes, read the entire post.


  1. Use the Mifflin St Jeor formula to calculate your basal metabolic rate
  2. Multiply your basal metabolic rate by an activity factor to arrive at your maintenance calories
  3. Adjust your maintenance calories up/down depending on whether you want to gain weight or lose weight

Before we start

This is going to be a bit of a lengthy post with lots of numbers but remember to stay with me! For those of you who don’t like numbers there will be a spreadsheet at the end of this series to walk you through everything and do the calculations for you. However, I would still encourage you to read this so you have an understanding of the reasoning behind the calculations.

This series of posts will outline the basic diet set up – help you calculate an estimate of calories to eat and how to split it between the different types of macronutrients. I strongly advise that these should be used as a guiding framework rather than rigid black and white numbers. Obsessing over your diet can often lead to an unhealthy relationship with food and body image issues in the long run.

Note that this information should only be applied if you are over 18 years old. The reason being is that most of these calculations will be inaccurate for teenagers as their metabolism tends to be much higher in a growth phase. There are alternative ways to do these calculations for teenagers but I won’t list them here as I believe you should simply enjoy the process of exercise and diet when you are that age.

Energy Balance revisited

So let’s first look at energy balance. In the previous post, we discussed the concept of calories in vs calories out. The next question from here would be how many calories to be taking in? There’s a few ways to calculate this, please keep in mind that these are just initial starting points which then have to be adjusted for each individual as the diet progresses.

To find out how much you need to eat we first need to look at how much energy we use. This varies from person to person, hence the need for calculations as a rough baseline.

Some basic terms/definitions:

BMR = Basal Metabolic rate – this is literally your ‘base’ amount of calories you burn if you did nothing and were in a coma all day long.

NEAT = Non-Exercise Associated Thermogenesis – this is the amount of calories burned that is NOT related to exercises ie. Walking around, fidgeting, moving your hands etc.

EAT = Exercises associated Thermogenesis – this is the calories burned when you are doing intentional or planned exercise

TEF = Thermic effect of Feeding – this is the calories used in order to process food that you eat. This tends to vary across different macronutrients, for example digesting protein requires slightly more energy than digesting carbohydrates and fats (more on this in a later post).

TEE = Total Energy Expenditure – This is your total energy requirement and is the sum of all the above. Makes sense right?

Total Calories Burned = Calories you burn as if you were in a coma + non-exercise related calories burned + exercise related calories burned + digestive related calories burned

Now as far as calculations is concerned, there are many many ways to do this. Because there is a lot of variation between individual EAT/NEAT/TEF, these 3 factors are bunched together into what we will call an “activity factor”. The most common way is to estimate BMR and then multiply it by an activity factor to arrive at our total energy expenditure. The graph below may help to visualise what happens in real life and how we are estimating it:


There are also many formulas to calculate BMR, the formula that you choose does not matter too much as they all have their pros/cons and will give similar results. At the end of the day what we are looking for is a starting point from which we can make subsequent adjustments.

You can read more about alternative BMR calculations here. I personally like using the Mifflin-St Jeor method, although it tends to overestimate requirements in the overweight I find that not many people know their body fat percentage to be able to use Katch-McArdle Formula.

BMR: Mifflin-St Jeor Formula
MEN: BMR = [10 x weight (kg)] + [6.25 x height (cm)] – [5 x age (years)] + 5
WOMEN: BMR = [10 x weight (kg)] + [6.25 x height (cm)] – [5 x age (years)] -161

Multiply it by the following activity factors:
1.2 = Sedentary (Desk job, and Little Formal Exercise)
1.3 – 1.6 = Sedentary plus 3-6 days of weight lifting
1.5 – 1.8 = Lightly active plus 3-6 days of weight lifting
1.7 – 2.0 = Active plus 3-6 days of weight lifting
1.9-2.2 = Very active plus 3-6 days of weight lifting

These are again, ranges/estimations. If you feel you have a slow metabolism, choose from the lower end of the range, the opposite is true if you feel you have a faster metabolism. Multiplying your activity factor by your BMR will give you a rough estimation of your TEE (total energy expenditure) and this is also known as your maintenance calories. The reason it’s called maintenance calories is because if you eat this amount of calories each day, then you would in theory maintain your weight  – not gain and not lose any weight (assuming it’s an accurate estimation). From our previous discussion about energy balance, it would be fairly obvious what the next step is right?

Adjusting calories based on your goals

Using our calculated maintenance calories above, you then need to adjust these based on your goals. In the simplest terms you are basically decreasing your calories if you want to lose weight and increase your calories if you are trying to gain weight. There are a number of ways to do this but I will outline two:

  1. Percentage based increase/reduction:
    For most people adding or subtracting 10-20% of your TEE is a good starting point:

    • To gain weight – Add 10-20% to your maintenance calories from above
    • To lose weight – Subtract 10-20% from your maintenance from above

    This will give you your daily calorie target. The reason for using a percentage based calorie adjustment rather than an absolute number is because this takes into account your total energy expenditure. For example, a generic recommendation of reducing calories by 500 per day for a large active male whose maintenance is 3500 calories will have a different impact to a small female whose maintenance might only be 1500 calories a day. In the second case, 500 calories are one third of your current intake which is generally too big of a decrease and not recommended for various reasons.

  2. Absolute calorie targets based on % of weekly weight loss/gain
    Another way to find the adjustment in maintenance is looking at how fast you want to gain or lose weight based on a percentage of your current weight. This tends to be in the 0.5%-1.5% range but is a little trickier depending on where you are at with your training and fat loss goals. I will write more about this in a future post.This calculation is essentially:

    1. Calculate what percentage of your weight you wish to lose/gain per week
    2. Convert that weight loss/gain to a calorie deficit/surplus per week
    3. Divide by it by the number of days to arrive at average daily deficit/surplus
    4. Subtract/add it to your maintenance calculated in the previous step

    What you need to know for this calculation is that 1 pound(~0.5kg) of fat equals to approximately 3500 calories (this is a generally accepted simplification).

    So for example if you weighed 100kg, and wanted to lose 1% of your weight each week:

    1. 1% of 100kg = 1kg – this is the amount of weight you wish to lose PER WEEK
    2. 1kg =~ 7000 calories (~0.5kg = 3500 calories as above)
    3. So that means you need to DECREASE your weekly calories by 7000 calories and if you want to subtract this evenly across the 7 days of the week that would be 1000 calories per day
    4. You then need to subtract 1000 calories from your maintenance calories to arrive at your daily target calories

    Note: it is important to look at these two calculation methods side by side ie. If you choose to lose 1.5% of your weight and the calorie calculation recommends to subtract 1000 calories from your 1500 diet (67% decrease) then you know your initial choice of 1.5% was too high. Choosing a more conservative 0.5% might translate to a 300 calorie deficit (20% drop from 1500 calories) which appears to be closer inline with the first method.

    I will outline a few guidelines for percentages of weight gain/loss below. The reasoning behind these will be further discussed in a later post. For the moment, please leave your ego at the door (don’t aim to lose 3% of your body weight per week because you have a special event coming up) when calculating your own numbers and trust the process:

    For losing weight: 0.5% – 1%
    For Gaining weight: 0.5% – 1.5% depending on your level of experience in training. Generally speaking if you are a beginner who just started training, you are able to gain weight much faster due to neural adaptations so you would choose the higher end of 1.5%. If you have been training for years and years, you cannot expect to grow a tonne over night. In fact, most advanced trainees will only see their progress when viewed month to month or even year to year so they would choose something very conservative such as 0.5% or even lower.

And there you have it! A very rough starting point for the amount of calories you should be eating based on your goals. In the next post I will discuss what proportion of these calories should be allocated across protein, carbohydrates and fats and a few other areas important for your diet set up. Stay tuned!



Toni is management consultant by day and an amateur powerlifter also by day.. he sleeps at night. He loves to strive for personal development and he achieves this through training, reading and maybe even writing.

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