How many calories should I eat? The ultimate guide to determining how many calories you should eat to lose fat or gain muscle.

Ever asked yourself "How many calories should I eat?" In this 5 part series we go over what really matters when it comes to losing fat and gaining muscle.

Huw Williams
April 29, 2021

When it comes to nutrition, much like training, it’s easy to get caught up in the details. With the number of nutrition methodologies out there – from regular protein feeding to intermittent fasting, high protein diets to ketogenic diets and the carnivore diet – it’s no surprise if you’ve found yourself questioning which is best. You don’t have to look far to find someone who swears by one diet while ridiculing another.


So which diet is actually the best? And what really matters when trying to lose weight or gain muscle?


While over the years people have created new names for diets in order to sell products or be seen as the next big thing, the reality is that the fundamentals have not changed.


And they really aren’t that complicated.


When it comes to achieving your fitness goals, whether that’s gaining muscle, losing fat or just improving your fitness, it’s useful to frame things in the context of 5 fundamental building blocks – energy balance, macronutrients, micronutrients, nutrient timing and supplementation.


In this blog series, Nutrition 101, we are going to work through each of these building blocks, starting this week with the most important – Energy balance.


Ladder showing energy expenditure, macronutrients, micronutrients, nutrient timing and supplements as the 5 important building blocks of a nutrition plan. Energy Balance, highlighted in green, being the most important and supplements being the least important.



An introduction to the concept of Energy Balance


Energy balance = calories in vs calories out. ‘Calories in’ refers to the number of calories you are consuming per day (or more accurately, per week), while ‘calories out’ is determined by your energy expenditure. When considering energy expenditure, it is important to remember that it is subject to a large degree of individual variation. It is unfortunately not as simple as saying women should consume 2,000 calories per day and men2,500 calories. Your energy expenditure is not only dictated by your level of exercise (eg. the length and intensity of your training sessions or whether or not you do manual labour) but also by your NEAT – ‘Non exercise activity thermogenesis’. As the name suggests, NEAT refers your energy expenditure when you are not exercising. For example, if  like me you fidget or tap your leg while you work, the number of calories you burn as NEAT may be as much as a few 100 higher than someone who sits still. Similarly, if you engage more postural muscles while you work (for example by using a standing desk) then you’re NEAT will also be higher. (we’ll talk more about NEAT later when we come to calculate how many calories you should be eating).


Getting this balance right will have the biggest single impact on the success of your nutrition plan.


If you’re eating 1800 kcal per day but burning 2000 kcal, you’re not going to put on weight or gain muscle regardless of whether you're getting all of your micronutrients and timing your meals perfectly. Conversely, if you’re looking to lose fat but are consuming 300 calories more than you burn each day, you simply won’t get the results you’re after – no matter how much you focus on macronutrient breakdown and supplementation.


So you may be asking “how many calories should I eat?”



How do you calculate how many calories you should eat?


You need to start by determining your maintenance calories– ie. the number of calories you need to eat each day to remain exactly the same weight. There are a number of online calorie calculators you can use to dothis or alternatively you can use the simple calculation below as a starting point.


Start with your bodyweight in lbs. Multiply by 10. Then multiply by an activity multiplier, which accounts for NEAT. For roughly 90%of people, this activity multiplier is likely to fall between 1.3 and 2.3 dependingon your level of daily exercise and NEAT. Our recommendation would be to make a sensible estimate based on how active you think you are.


Let’s take Matt as an example.

Matt weighs 180lbs.

180 multiplied by 10 = 1800

Matt is somewhat active but his NEAT is relatively high (he’s fidgets quite a lot), so he has an activity multiplier of 1.6.

Therefore, to calculate his maintenance calories we need to multiply 1800 x 1.6.

Matt’s maintenance calories are therefore 2880 kcal per day.


Now it’s time to adjust for your goals – ie. weight loss or weight gain.


If your goal is to lose fat and get leaner (while maintaining your performance) you’re going to want to aim to lose 0.5% - 1% of your body weight per week. Utilising the knowledge that 1lb of fat is equivalent to roughly 3500 kcal and that therefore to lose 1lb of fat per week you need to be in a calorie deficit of roughly a 500kcal per day (3500kcal/7 = 500kcal), we can calculate the size of deficit needed to for you to lose weight at the desired rate. We would then subtract this required deficit from your maintenance calories.


Returning to our beautiful model Matt to demonstrate this in practice:


-      At a bodyweight of 180lbs he is going to be aiming to lose about 0.9lbs – 1.8lbs per week. (ie. 0.5% - 1% of 180lbs)

-      In order to achieve this he will need to be in a calorie deficit of 450kcal – 900kcal per day. (calculated by (3500 x 0.9)/7 for the lower end weight loss and (3500 x 1.8)/7 for the higher end).

-      Therefore to lose weight Matt will need to be consuming between 2430kcal – 1,930kcal.


It’s worth noting that this deficit does not all need to come from your nutrition. You can also add in more activity to achieve this same energy balance.


On the other hand, if your goal is to gain weight you’ll need to make sure you’re in a calorie surplus. Gaining muscle takes a lot more time than losing fat and so it makes more sense to look at changes at the month by month level. In addition, the desired rates for lean muscle gain will vary depending on your training experience (beginner, intermediate or advanced) and your gender (this is due to hormonal differences between men and women).


For men, you’ll be looking to gain between 2-3lbs /month asa beginner and 1-2lbs /month as an intermediate.


Women on the other hand should be looking to gain roughly half of this:  1-1.5 lbs /month as a beginner and roughly 1lb /month as an intermediate.


For advanced athletes the focus shifts from weight gain to performance and recovery. This is because at this point that rate of weight gain is so slow that it no longer makes sense to use as the primary metric for determining your calorie intake.


To determine the required calorie surplus to gain weight at these rates, we’ll utilise the same energetic principles as discussed earlier(in the weight loss section – ie. 3500kcal deficit = 1lb of weight loss).


Therefore, as a beginner you should be aiming for a calories surplus of 300kcal per day, as an intermediate you should aim for 100kcal per day and as an advanced athlete you should look to consume maintenance calories(or just above) each day.



It’s not a perfect science – experimentation is key


While these methods are a great place to start when determining the number of calories you need to fuel your goal, they are not hard and fast rules.They are subject to a huge degree of individual variation, and so it’s important that you learn to experiment you’re your intake and expenditure until you find what works for you. This is where you need to own your nutrition.


At any point you can determine whether your calories are correct by averaging your bodyweight over the preceding couple of weeks and looking at the change. How is your weight changing? Are you losing or gaining weight at the desired rate or are you staying the same?


Once you’ve determined this, you’ll be able adjust your calorie intake or expenditure to match you goal.


In my view this phase of personal experimentation is where things really get interesting. You’ll learn how to manipulate your body and your weight to do exactly what you want. Guess work and surprise changes in your weight will become a thing of the past.


Understanding energy balance and your calorie requirements is like finding the key to unlock control over your physique. It's worth taking the time to figure out.



Don’t get caught up in details.

The first thing to do when starting any diet is to ask yourself “Am I getting the right number of calories to support my goal”.Getting this right will have the single biggest impact on whether you achieve your physique goals.

Individual experimentation will teach you how to be completely in control of your weight and any changes you want to make.


In the next instalment of this nutrition series we will be covering macronutrients - what they are how to determine your requirements and much more.

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