Understanding Macronutrients & Calculating Calorie Targets

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In my last post, I set out the role of strength training and its effect on metabolic rate. Today, I want to expand on some of these themes to fully highlight how calories work in regards to your metabolism, and how to effectively calculate the calories you need for your goals. This will form part of a wider series of posts covering each aspect in greater detail. Hopefully, this will increase your knowledge and awareness and provide some guidance on how to apply nutrition effectively towards your goals.


The purpose of this post is to therefore:
- Understand calories and macronutrients.
- Understand macronutrient targets.
- How to calculate macronutrient targets for a fat loss goal.
First, it is important to acknowledge and remember that a calorie - or more specifically, kilo-calorie (kcal) - is a unit of energy. This is an important distinction to be aware of, because the discussion of 'good' calories and 'bad' calories is far too detailed to discuss fully here. For the purposes of this discussion, there are no good or bad calories, but the nutritional value of calories does vary. The sources of calories for your body come from what are called macronutrients. These are the main form of energy which your body requires for fuel.
Macronutrients can be divided into Protein, Fats and Carbohydrates. Which each macronutrient containing a different energy value per gram.
- Protein = 4kcal
- Fats = 9kcal
- Carbohydrates = 4kcal

Before getting into greater depth regarding the role of each macronutrient in the body, I want to spend some time covering how calories work in the body, and how to set a calorie target.

Setting a calorie target requires an understanding of an individual's maintenance intake. Or total daily energy expenditure (TDEE). The total amounts differ from person to person but TDEE consists of three components:
- Resting Metabolic Rate (RMR) = 60-70%
- Active Energy Expenditure/Physical Activity (AEE) = 20-30%
- Thermic Effect of Food (TEF) = 10-20%
Each macronutrient has a different thermic effect when breaking down energy. Your body uses far more energy to metabolise protein compared to fats and carbohydrates, for example. Understanding this split in terms of energy used by the body, allows us to make estimates for total calories required for a given goal and to set targets.

One way to estimate RMR utilises the Katch-McArdle formula, which is based on lean body mass (LBM) and weight in kg. I'll provide a full breakdown example towards the end, but it looks like this when set out. First, you would calculate your total body weight in kg (1kg = 2.205lbs). Then you calculate total body fat with your starting body weight in kg x your body fat percentage. From this point you can calculate your LBM by subtracting the fat mass (kg) from your starting body weight. Knowing this figure, we then bring in the Katch-McArdle formula (21.5 x LBM kg)+370)). This will give us an estimate of RMR. To get a estimate of TDEE from here, we would use an activity multiplier of between 1.4 and 2.2 depending on an indivudual's daily needs.

Now that we can estimate current daily energy needs, starting by estimating calorie and macronutrient targets. An accepted rule for fat loss works on the principle that it takes 3,500kcal to burn 1lb (0.45kg) of body fat. For example, if you were to reduce your intake from maintenance by 500kcal each day, it would, in theory, equal a 0.45kg reduction in body fat per week. This is just a guide as your body will never burn exactly the same number of calories per day. In addition, weight loss can be affected by hydration levels, sleep quality, and hormone fluctuations. Added to the fact that all calorie targets are estimates.

It is therefore, not an exact science. The goal is to find a reasonable starting point that places you close to your target reduction, without being unsustainable. Adjustments can then be made based on how you respond.

With an estimated calorie target set, you can then turn attention to finding your optimal macronutrient amounts this deficit to achieve the desired result.

The first component to set is our protein target. Protein's role in the body is largely structural, with a primary role in building and maintaining muscle. Because of this, and protein taking longer for the body to breakdown, leading to feeling fuller, getting the correct target here is key. Recommended guidelines call for 0.8g per kilogram of total body weight for an average adult. In someone who is in a calorie deficit, or resistance training regularly, this is not suitable. As discussed in my previous post, maintaining and building muscle is essential when seeking to lose body fat, as it increases metabolic rate, and encourages the body to use stored energy as fuel. A higher protein content is required to not only help repair damaged muscle, helping recovery, but preventing further muscle breakdown. The calculations in this scenario, therefore, call for a protein target of between 2g and 2.8g per kilo of LBM (not total weight). Most people will not be used to consuming this amount of protein, so gradually increasing the amount weekly is recommended.

Unlike protein, fat and carbohydrate intakes are assigned as a percentage of total calories. This is because the primary function of both macronutrients is to provide the body with an energy source. I address the targets for both together, as the target for fat determines the target for carbohydrates. Fat targets would be set at either 25%, 30% or 35% of total calories, depending on preference and energy levels. Your remaining calories would then be allocated to carbohydrates, and you would then adjust the levels of fats and carbs based on your energy levels. Because fats and carb intakes can be more about personal preference, you can chose to only focus on your protein and total calories. Although tracking all variables does help with meal planning. Your total calculation would look like this:
Step 1: Calculate protein target and apply it to LBM in kg = LBM (kg) x Protein multiplier (2g-2.8g)
Step 2: Calculate total protein calories = Protein target x 4
Step 3: Calculate fat target. Select fat target and multiply it by calorie target = Calorie target x Fat % target in decimal form (e.g. 0.35)
Step 4: Calculate total fat grams = Fat calories /9
Step 5: Calculate carbohydrate target. Add protein and fat calories together and subtract from daily calorie target = Calorie target - (Protein calories + Fat calories).
Step 6: Calculate total carbohydrate grams = Carbohydrate calories /4

The example below is designed to show how this all works in practice, with all values rounded off to the nearest kcal.
Client A:
- Bodyweight = 80kg
- Body fat = 20%
- Occupation = Construction worker
- Activity = Recommended levels
Estimated RMR using Katch-McArdle Formula
- 80kg x 0.2 = 16kg body fat
- 80-16 = 64kg LBM
- Katch-McArdle part 1 (21.6x64) = 1382
- Katch-McArdle part 2 (1382+370) = RMR of 1750kcal
Client A has a physically demanding job and is committed to four resistance sessions per week. Based on this, and activity multiplier of 1.8 will be applied.

Multiplier calculation
- 1750 x 1.8 = Maintenance level of 3150kcal
Daily calorie target:
- 80 x 0.0075 (0.75%) = Target weight loss of 0.6kg per week.
- 0.6 x 7700kcal = Weekly deficit of 4620kcal
- 4620/7 = Daily deficit of 660kcal
- 3150 - 660 = Daily calorie target of 2490kcal

Calculating protein target:
- 64kg x 2.8g = 180g
- 180g x 4 = 720kcal protein

Calculating fat target:
- 2490 x 0.25 = 623kcal
- 623/9 = Daily fat target of 70g

Calculating carbohydrate target:
- 2490 - (720+623) = Daily carbohydrate intake of 1147kcal
- 1147/4 = Carbohydrate target of 285g

The final number for Client A's target would be:
Total daily calories = 2490kcal
Total daily protein = 180g
Total daily fat = 70g
Total daily carbohydrates = 285g

To conclude, the aim with this post was to provide a greater understanding of how calories are used within the body, and how understanding the macronutrient split of these calories can be applied to give you the best chance of losing body fat. It should also, hopefully, build on the previous post highlighting the role of strength training and fat loss. If you are able to ensure that you are fuelling your body correctly in a calorie deficit. By which I mean, ensuring that you are able to maintain consuming fewer calories than you burn, but ensuring that of this number, you are getting enough protein to maintain your existing LBM. In this scenario, you are giving your body the best chance of requiring your body to use it's stored energy for fuel, and as a result, able to sustain this without the need for drastic reductions to the point where you do not have enough energy for daily functions. As a note of caution, any calorie and macronutrient figures are based on a set of estimations, and can - and should - be adjusted based on how each individual responds.

In my next posts I'll be looking into the different macronutrients in greater depth, starting with protein. Hopefully you found this useful and if you have any questions please get in touch. If there are specific topics you would like me to discuss, please drop a note in the comment section.

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