How Many Calories Should You Eat?

For Fat Loss in particular, this is the most important thing to address, truly nothing else matters anywhere near as much. Your energy needs to go here. Now I’m about to blow your mind. Are you ready for this? Ok here we go: You either need more, less or the same number of calories that your body requires to sustain itself. Da-da. See mind blown right? Now let's get a bit more specific for you.

For Fat Loss - You need less calories
Muscle Gain - You need more calories (most of the time)

Annoyingly the amount of calories you need will vary - sorry, it’s annoying but it’s true so let’s get over it. I’d like you to think of your calorie requirements as a moving target or better yet a moving target range

Why is it a range? Simply because your body can adapt to your current level of energy intake. Now don't let people freak you out with odd sounding terms and claims, it doesn't happen through weird or magical means and it's quite normal. As you'll see as we go it may even be a sensible reaction. For example, increasing or decreasing your bodyweight is a direct adaptation to a different level of energy intake. 

As you begin to diet your body detects that there isn't enough calories for your body's daily needs and begins to adjust. As a result it starts to utilise your fat stores to fuel your bodily processes (which we'll cover shortly) and this has a couple of effects. 

  1. Reducing your bodyweight
  2. Reducing the energy demands of the body itself

Simply put it takes less energy to sustain and move around a smaller body than a larger one

While this is occurring your body starts to send out various hormones (a messenger system that carries information - like the postal service) that keep delivering the same message, getting gradually louder and louder and harder to ignore - EAT YOU FOOL! This means it starts to get harder to resist delicious food and that you'll find yourself thinking about food more frequently. Sound familiar? I don't care who you are, there’s only so long you can ignore the bloody doorbell.

To add another level to this you’ll also start to become more lethargic - slowing down the amount you fidget and move about. Simply put you have less energy to do things. 

Think of dieting as being akin to taking a pay cut. You and your body have to assess which outgoings you can maintain and whether or not you'll need to downsize the house. There are Three Ways your body uses energy:

  1. Cost of Maintaining Bodily Functions (BMR)
  2. Cost of Digestion (TEF)
  3. Cost of Movement (EAT & NEAT)

Basal Metabolic Rate (BMR)

This is the amount of calories your body uses per day at rest. It is the cost of maintaining your body and its organs in a rested state. Can this change? Well, it could  potentially do two types of things to adapt:

Reduce the size of your organs which means they require less energy to sustain them (as a result you weigh less)
Increase the efficiency of the tissues themselves (they weigh the same but use less energy to exist at that weight)

The thing is, when we lose weight we mainly see the former. Our weight and body mass decrease rather than seeing a huge increase in the efficiency of the tissues themselves. They can adapt a little bit but the largest I’m aware of is 15%; which were in conditions that were used to mimic the POW camps. In other words - it's probably not that applicable to you.

Different organs have different energy demands. Elia (1992) identified them as: 

  • Brain = 240kcal/kg/day
  • Liver = 200kcal/kg/day
  • Heart = 440kcal/kg/day
  • Kidneys = 440kcal/kg/day
  • Skeletal Muscle = 13kcal/kg/day
  • Fat Mass = 4.5kcal/kg/day

Now if we know the weight of the organs and how metabolically demanding they are we can effectively calculate BMR, so here we go:

And so on and so forth for the rest.

And so on and so forth for the rest.

Fat loss is a balancing act of getting enough calories to be able to function, train well (by holding on to your non fat mass) and not die while consuming few enough that your body has to mobilise its own stored energy (fat mainly) to do this whole living thing. Again, you need calories. The key is in the amount.

Now we’ve covered BMR (resting calories) we have to add on the others, so lets start with the cost of Digestion.

Thermic Effect of Food (TEF)

TEF is the amount of calories you use to break down the foods you eat into their basic blocks; either to store them or use them. TEF varies for different foods due to its macronutrient (Protein, Carbohydrate & Fat) breakdown. It accounts for roughly 10% of your Total Daily Energy Expenditure (TDEE) - all of the calories you use for everything in a day added together.

For Protein around 20-30% of the energy is lost to TEF
For Carbohydrate around 5-10% is lost to TEF
Fat Fat around 0-3% is lost to TEF

For Alcohol around 10% is lost to TEF

For example if you ate all your calories from Protein, Carbohydrate or Fat only the difference in available calories can make quite a difference.

Note - in real life this will never happen but it illustrates a point about Net Calories versus Gross calories. 

We end up in a scenario where the total NET calories consumed can be quite different depending on the food choices made. So even though some diets may look like they allow you to eat more than others (and they do), it’s the GROSS amount of calories they give you rather than the NET amount. 

When dieting you can really take advantage of this. Using higher protein foods can let you eat more total food for your calories than if you chose other macronutrient dominant foods. It also has the happy bonus of making you feel fuller. Both of these make it likely that you'll consume less NET calories.

Exercise Activity Thermogenesis (EAT)

This one’s pretty straight forward; it’s the amount of calories you burn through exercise itself. As you would imagine some exercises burn more calories than others. A burpee demands more energy than a crunch. A sprint more than a walk. 

The bigger the movement being done means more calories used and the longer the movement is done for means more calories are used. We measure these in Metabolic Equivalents or MET’s. 

One MET is equivalent to the amount of oxygen conusmed while sitting quietly at rest in a chair (it’s equal to 3.5ml/O2/kg/min). The higher the MET the more energy it uses compared to sitting at rest, so a MET of 10 means that the activity in question is TEN TIMES more energy demanding than sitting at rest.

Metabolic Equivalents of Activities 

This system isn't perfect as the authors of the study note: A larger person would be expected to have a larger resting oxygen uptake compared with a smaller person. Individuals with the same body mass, but differing in percent body fat and lean body mass (LBM), will have different resting metabolic rates, with resting energy expenditures proportional to the quantity of muscle present (LBM). But it does give us a good place to start from, and it is fair to say that we are likely to see similar increases in your specific level of MET as the level of physical exertion increases regardless of body size and composition.

The authors also give us this handy guide: Three levels of intensity: light; when the activity results in only minimal perspiration and only a slight increase in breathing above normal; moderate; when the activity results in definite perspiration and above normal breathing; heavy; when the activity results in heavy perspiration and heavy breathing…

For instance, a person participating in a game of tennis with only a slight change from normal state would be exercising at approximately 4 METS. A patient showing slight perspiration, accompanied by increased breathing, would be exercising at 6 METS. However, a person who shows heavy perspiration and heavy breathing while performing would be working at 10 METS. - M. Jette et al. : METS in exercise testing

Obviously the amount of calories you need in your diet will be affected by how much exercise you do and the level you perform it at. Simply:

If you do lots of exercise, you’ll need more calories. 
If you sit at desk all day, you’ll need less calories. 

All things being equal if you're striving for Fat Loss you should pick high levels of MET as they use more energy BUT this also depends on how long you can perform them for. You may sprint for 10 seconds at a high MET but get over it, it's only 10 seconds. Finding that sweet spot of high expenditure over a longer period of time will require a little bit of playing around. We'll explore this more in the What's The Best Cardio for Fat Loss article. 

Non-Exercise Activity Thermogenesis (NEAT)

You may be asking what in the blue hell NEAT is, well simply it is the total amount of movement in your day that isn't chalked up to exercise. While you sit there and read this on your phone or your computer, you're blinking, fidgeting in your seat, smiling, chewing, cracking your knuckles and a whole host of things that we do unconsciously that require energy. After all your head doesn't hold itself up for free. This is also the section that will have the largest differences from person to person (If you're curious the word thermogenesis means the production of heat, usually in an animal body).

So How Big A Difference Are We Talking?

Levine et al, fed a group of 16 non-obese volunteers 1000kcals more than they needed for 8 weeks to see what happens. He calculated how much weight (LBM &/or Fat Mass) they should have gained and compared it to what they did gain. There are roughly 3500kcal in each pound of body fat. If we take an over simplified view of this we can say that for every 3500 calories we overfeed someone we should expect to see them gain one pound of Fat.  So what did Levine find? 

That on average only 432 of the 1000 calories eaten ended up being stored. 
BMR didn't really change so that doesn't explain it.
TEF was calculated and accounted for and doesn't explain it.
And they didn't change any Exercise Activity so that can't explain it.

Changes in the participants Non-Exercise Activity Thermogenesis are how we explain this. Levine actually coined the term in response to his findings. And while NEAT is fascinating in itself, the most interesting part is the variation he found between people.

One person increased their NEAT response by 692kcals a day
One person decreased their NEAT response by 98kcals a day

Remember both of those people were given the same stimulus (they did the same thing). But even though they were both overfed 1000 calories, one of them was only overeating by 308 calories a day while the other was nailing 1098 calories more than they needed. If you've ever noticed that your leaner friends tend to be fidgety or that your larger friends often sit quite still and are less physically animated, you've witnessed NEAT differences in action. This can be one of the reasons that explains that friend we all have who seems to eat and eat without really gaining any weight. 

If you can just eat and eat without adding any size, don't worry this can be overcome and we'll get to it shortly.
If you feel you only need to look at a doughnut for the squidge to appear, don't worry this can also be overcome and we'll get to it shortly.

Set Point Theory - Your body has a weight it is used to and it will try to maintain and defend that weight in the face of potential change. When we mentioned earlier that hormones start to be produced to tell you that you're hungrier than normal this is Set Point Theory working. As is the increase and/or decrease in NEAT variance. If we consume less calories and we're trying to defend our current weight then it makes sense that the body may slow down some of it's physical processes and the most obvious one is how much low level movement we do. That feeling of lethargy during a diet is a normal response and could be said to exist to get us to conserve our energy to maintain our Set Point. 

All of that together can make it seem like it's going to be for you to lose weight. That's simply not true and there are plenty of examples of people successfully losing weight and keeping it off. But it does help us explain why some people struggle more than others and why lots of people who diet will regain all the weight that they lose (and often more). This is a really large topic and goes beyond the scope of this article so we'll stick to what you need to do in practice.

How To Set Your Calories - A Practical Guide

Now you know the factors and how they are subject to change, let's show you exactly what you need to do to set your calorie targets. We will then give you some useable ideas to give you the best chance of maximising your results for these. 

Note - Before you use the calculators, consult the activity level table below as you will need the multiplier that applies to you.

For the Gents >>> use this Calculator
For the Ladies >>> use this Calculator

Want To Know How All This Is Worked Out?

10 x weight (kg) + 6.25 x height (cm) - 5 x age (y) - 161.

10 x weight (kg) + 6.25 x height (cm) - 5 x age (y) + 5

This is called the Mifflin St-Jeor equation, but you could also use Katch-McArdle, Alan Aragon or Lyle McDonald’s. They will all give you ever so slightly different numbers, don’t worry and try to  remember that they are a best estimate not a precise number. If needed we can adjust from this point later on.


Lisa is 75kg (11st,11lbs), 166cm tall (5'4") and 42 years old

  • Times 75 x 10 which equals 750
  • Then times 6.25 x 166 giving us 1038
  • Adding those two together equals 1788
  • Then we times 42 x 5 giving us 210
  • We take that 210 away from our 1788 and we are left with 1578
  • Finally we subtract 161 giving us Lisa's BMR of 1417 Calories

Tom is 94kg (14st,11lbs), 187cm tall (6'1") and 33 years old

  • Multiply 94 x 10 which equals 940
  • Then Multiply 6.25 x 187 to give us 1169
  • Adding those two together equals 2109
  • Then we Multiply 33 x 5 giving us 165
  • Take that 165 away from the 2109 leaves us with 1944
  • Finally we add 5 to the 1944 to give us Tom's BMR of 1949 Calories

Once you have your BMR you'll need to add on an total daily activity. Use this table to help guide you on the level you should pick.

Now we have figured out your maintenance calories you need to decide whether you should have more or less of them. Follow the guide below to suit your needs. If you need to understand a little more on How Long It Should Take You read here.

Muscle Gain 

As a Beginner Lifter
Eat at maintenance
Improve your gym performance

If you're an Intermediate or Advanced Lifter
Add 200-500 Calories
Improve your gym performance


Fat Loss

For Fat Loss at 0.5% of Bodyweight per week
Minus 500 Calories or
Remove 20% of the total Calories

For Fat Loss at 1.5% of Bodyweight per week
Minus 800-1000 Calories or
Remove 30% of the total Calories


Then Comes The Hard Part

Calculating all of this means less than nothing if you can't stick to it. Finding a way of sticking to your calorie requirements will be the difference between glory, success and proud glances in the mirror and yet more guilt, shame and Yo-Yo behaviour. 

Monitor your intake and make sure you are actually consuming what you think you are. Every day not just the good days. Include your coffee, alcohol and condiment consumption in this. BE HONEST. Really honest here. Seriously. Remember you'll only be cheating yourself.

The best way to make sure you are hitting your calories is to use a daily tracker. The best is My Fitness Pal. Go and download it now. It's free for some reason. Set yourself up and then go to the menu in the app and do the following:

Go to Goals
Then Calorie & Macronutrient Goals
Set Calories to those you've calculated
Get to work

If you like to eat the same thing every day then creating a Meal Plan that meats your calorie and macro requirements is a sensible way to go. When the time comes that you want something different start playing with tracking and substituting foods that have similar calorie and macronutrient breakdowns. This is a skill and takes some time. 

Tips for maximising your Fat Loss by understanding all of the above

  • BMR - Try not to lose LBM by dieting too quickly. Not sure what that pace means - go here.
  • TEF - Pick high Thermic Effect Foods - High Protein & Starchy Carbohydrates are your best friends (they will also keep you feeling as full as possible)
  • NEAT - Set either a target number of steps per day or a number of standing hours to help you out. Fitbits, Apple Watch or UP bands can be great for this.
  • EAT - Pick exercises with a higher MET rate as often as you can (this gets more difficult as you get further into a diet and have less energy)