An Introduction to Calories and Macronutrients

Calories and macros both have an impact on muscle gain, fat loss, and body recomposition. In this guide, you will learn the key differences between calories and macronutrients, and understand how to calculate your personal intake levels to achieve your fitness goals.

What are calories?

Calories (otherwise known as kilocalories) are a unit of energy. In scientific terms, 1 kilocalorie is the amount of heat energy needed to raise the temperature of 1 gram of water by 1° Celsius.

Our bodies use calories as energy, to fuel everything we do from basic cellular function through to exercise. Our body sources calories from food and most drinks.

What are macronutrients?

The food we eat contains calories, and those calories can be broken down further into macronutrients. The three macronutrients are protein, carbohydrates, and fats. There is a fourth – alcohol – which we won’t cover here. It’s important to note that whilst some foods contain high levels of one macronutrient, almost all foods contain more than one. For example, chicken breast is high in protein but also contains some fats.

Macronutrients are different from calories, but the two are linked. All calories come from macronutrients, and all macronutrients contain calories.

Calories per macronutrient

The macronutrients in food carry different caloric weights. For example, protein contains 4 kcals per 1g of protein. This does not mean 4 kcals per 1g of the food itself but 1g of the macronutrient.

Protein: 4 kcals per 1g

Carbohydrates: 4 kcals per 1g

Fats: 9 kcals per 1g


Protein is the most important macronutrient for building and retaining muscle, and for creating all tissue including bones and ligaments. The body can’t make protein from any other macronutrient, so it is important that we eat sufficient amounts of protein every day.

We can get protein from almost all foods, but the highest amounts of protein come from foods like meat, fish, eggs, dairy, and protein powder.


Carbohydrates are important for various functions in the body but are primarily a source of energy. Whilst all calories can be used as energy, glucose (carbohydrate) is the body’s preferred source of fuel. Carbohydrates give us the energy to train hard and be active.

We can get varying amounts of carbohydrates from almost all foods, but the highest amounts are from sugars, fruits, grains, vegetables, beans, and pulses.


Fats carry the highest caloric load of all three macronutrients, at 9 kcals per gram. We need healthy fat for energy, hormone production, cell health, and other important physical functions.

We can find trace amounts of fats in almost all foods, but the highest amount of dietary fat is found in oils, butter, nuts, seeds, oily fish, and high-fat cuts of meat.

How many calories should you eat?

If you have a body composition goal, it’s important to eat the correct number of calories. This figure will differ between individuals due to one’s Basal Metabolic Rate (BMR, the amount of energy you need to fuel basic body function), activity level, muscle mass, age, and other factors.

If you want to gain weight or muscle, you need to eat in a caloric surplus (taking in more than you expend). If you want to lose weight or body fat, you need to be in a caloric deficit (eating less than you expend). And if you want to maintain your weight, you need to eat at maintenance, which means eating the same number of calories as your body expends.

How to calculate your calorie intake

Your body uses calories for much more than just exercise. Here are the different elements that go into your energy output.

BMR: your basal metabolic rate is all the calories your body burns just being alive

TEF: Thermic effect of food is the calories you burn digesting and absorbing food

PA: physical activity is the calories you expend doing exercise, training, and sport

NEAT: non-exercise activity thermogenesis is all the calories you burn being active outside of training

= TDEE: total daily energy expenditure is your personalised daily calorie output

Calories for fat loss

To lose body fat, you need to create a calorie deficit and remain in it consistently for as long as necessary. To do this, you either need to reduce your calorie intake from food and drink or increase your calorie output.

Since it is difficult to increase your BMR in the short term, you should focus on burning more calories through NEAT which includes walking and generally being more active during the day.

You could also increase more calories from PA but be aware that there is an upper limit on how much energy you can expend from training without impacting your recovery capabilities.

Calories for muscle and strength gain

The right amount of calories for muscle and strength gain depends on your current body fat percentage and goals at the gym:

  1. If you’re an individual with a low body fat percentage (10-15%), you need to eat in a caloric surplus to add muscle mass and build strength. This means either reducing your calorie output or increasing your caloric intake. Since your muscle gain goal will naturally involve training, it’s not a good idea to reduce your caloric output. You will therefore need to carefully increase your calorie intake to reach your physique goal. Gradual increase and careful monitoring will provide the best results as you’ll gain muscle at a healthy rate and minimise fat gain.
  2. If you’re an individual with a high body fat percentage (20-30%), it’s possible to stimulate muscle growth while eating at a deficit or maintaining calories as long as your protein intake and training intensity is sufficient. This means that you can lose fat and build muscle at the same time until your body fat percentage is low enough, to where your body requires additional calories to make up for the now depleted fat stores. Generally, this process is known as body recomposition.
  3. If you are not concerned with your body fat percentage, you may choose to eat at a surplus to maximise strength and muscle gain. This is the common route taken by many power-lifting athletes, whose main focus is to maximise strength regardless of body composition.

How to calculate your macronutrient split

Once you have your calorie intake numbers sorted, you will need to think about how much of each macronutrient you eat. Whilst there is no definitive answer to this and you’ll need to monitor what’s best for you, here is a standard approach that some people take.

The 40/40/20 approach:

A common approach to losing fat and maintaining muscle is the 40/40/20 macronutrient split. This means that calories will be made of 40% protein, 40% carbohydrate, 20% fats. Here’s how that would look for an example 2000 kcals intake.

Protein – 40% of 2000 kcals is 800 kcals. At 4 kcals per 1g protein that is 200g

Carbohydrates – 40% of 2000 kcals is 800 kcals. At 4 kcals per 1g carbohydrates that is 200g

Fats – 20% of 2000 kcals is 400 kcals. At 9 kcals per 1g fats that is 45g.

200g protein

200g carbohydrates

45g fats

= 2000 kcals

Once you have figured out your maintenance, deficit, or calorie surplus goal and decided on a macronutrient split, monitor the changes in your body and energy levels for at least 4 weeks. If necessary you can then make adjustments and monitor your body’s changes on a 4-week basis.

The bottom line

In summary, if you want to lose fat, you will need to eat fewer calories or increase your activity throughout the day. While losing fat, it is common that some muscle mass is lost. To preserve as much muscle as possible, you need to eat the right amount of protein. As a rule of thumb, 2.2 grams of protein per kilo of body weight should be enough, but you should monitor your strength at the gym and your physique to ensure that you’re not losing too much muscle while cutting fat.

If you want to put on muscle, you will need to ensure that your body is receiving the right amount of energy. If you have a high body fat percentage, some of this energy can come from existing fat stores, otherwise, if you’re lean, you will need to eat more calories throughout the day. You should always ensure that you’re eating 2.2 grams of protein per kilo of weight while training at the right intensity to stimulate growth. As you get more experienced, you may change these numbers to suit your goals and food preferences.