What Are Macronutrients And Why Do You Need Them?

What Are Macronutrients And Why Do You Need Them?
What Are Macronutrients?
What Are Macronutrients?

Following on from the post on calories (read it here), today we look at macronutrients.

Macronutrients, also known as macros for short, are the three primary sources of calories. Even if you are new to the term macronutrients you will undoubtedly be aware of the macros by their individual names: protein, carbohydrates and fats.

Each macro plays a specific role in the body and provides a number of calories per gram.

  • Protein has 4 calories per gram
  • Fat has 9 calories per gram
  • Carbohydrate has 4 calories per gram

Knowing the number of calories provided by each macronutrient allows you to effectively meet your daily calorie needs. To determine how much of each macronutrient you need in your diet you first need to understand the roles they play in your body once they’ve been eaten.


Protein is very important and is used to break down and rebuild the cells in your body. This process is called protein synthesis and is vital for growth and maintenance of your body.

When you eat protein, it’s broken down into amino acids by your digestive system in order to be used.

In total, there are 20 amino acids, 9 of these amino acids are called essential, which means your body cannot produce enough of them and you must get them from food sources. The remaining 11 are called non-essential as the body can produce them in high enough quantities that it’s not essential that you get them in your diet.

Overall, protein plays an important role in building, repairing and regenerating your body’s tissues and cells. It helps in the preservation of muscle mass, immune function and aids in the production of essential hormones and enzymes. It’s particularly important if you exercise regularly (more on this later).


Fat in the diet allows you to absorb fat-soluble vitamins, provide essential fatty acids and in some circumstances, provide a source of energy.

When eaten, fat is broken down into fatty acids (mostly in the small intestine) to be used by the body and depending on total calorie intake fat is commonly stored for future use, which can lead to the accumulation of body fat and weight gain.

Fat is vital for the absorption of fat-soluble vitamins, maintenance of cell membranes and hormone production. It can also be used as energy by the body and as insulation to help maintain a normal core body temperature.


Carbohydrate can be metabolised by the body very quickly and is your preferred source of energy.

When you eat carbohydrates, they get broken down into glucose to provide energy to your body. Any glucose not used is converted into glycogen and stored in your muscles and liver for future use.

Your liver can store approximately 100g of glycogen which is used to maintain blood glucose levels between meals. Whereas, your muscles can typically store 400 – 500g of glycogen which is used to provide movement.

Carbohydrates aids in the proper function of your heart, brain, kidneys and muscles. It is also important for intestinal health and digestion.

What’s More Important, Calories or Macros?

There’s no arguing that calories and macros are heavily intertwined but a good way to think of the difference is like this.

  • Calories are the main factor in weight change i.e. will you lose or gain weight?
  • Macros as the main factor in body composition i.e. will you lose fat or muscle or gain fat or muscle?

As for what’s more important, it really depends on your goal:

1. Weight change with not too much concern about body composition

If this describes your goal then aim to hit your total calorie goal within 100 kcals either side and you’ll be fine. You’ll change your weight at a steady pace and your daily calories will balance out over the week.

2. Weight change with the primary purpose to improve body composition

If this describes your goal then aim to hit your macronutrients within 5 – 10g and this by default will keep you close to your calorie goal. Whilst also allowing you the benefits of the a well-structured macronutrient breakdown.

Summing Up

Macronutrients are your body’s primary source of food and together make up your total calorie allowance for the day. Each macronutrient has a specific calorie value per gram and plays an important role in your body.

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