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Three macronutrients

What are proteins, carbs and fats?

Published 2 years ago at 01 Oct 2019 by Alexandra Soare

A healthy diet starts with understanding two main nutrients: macro and micronutrients. I am a registered dietitian and this is a complete guide on what are macronutrients and why are they important.

The name macro already gives you an idea. Macronutrients are elements needed in large amounts. For example, an adult needs around 60g/day of protein (=macro) compared to 1.5 micrograms of Vitamin B12 (=micronutrient).

The main role of macronutrients is to build, grow and provide your body with energy. A complete nutrition is composed of three main macros:

  • Carbohydrates = 4 kcal per gram
  • Protein = 4 kcal per gram
  • Fat or lipid = 9 kcal per gram

Certain studies suggest alcohol as a macronutrient, providing 7 kcal per gram.

The function of the 3 macronutrients

All macronutrients provide energy. However ... there is a reason why there are 3 macronutrients instead of 1! Each element has its own special function. The best way to explain it is by using the house metaphor. 


Imagine your body like a wooden house. Wood is a great material because it can be used for heating, storage, or as a construction material. Expert architects can tell you that certain wood is better suited for certain tasks.  The same happens in our bodies with macronutrients. Carbs are great as fuel to be used immediately. Fats function better as energy storage. Proteins have a special chain side (like Legos) that allows them to be fit in together and build huge structures.

Macronutrient function

PROTEIN = structure

In order to build a house, we need a material that is flexible and can be combined in different ways. That is why for our house we will use a series of 20 amino acids. Like Lego pieces, each amino acid has a unique form that can be combined to form proteins.

combination of aminoacids = protein

The biggest combination possible is 34,350 amino acids. This giant protein Titin is responsible for muscle elasticity. It is also known because its official scientifical name is the longest word in English with 189,819 letters and takes around four hours to pronounce correctly. The smallest combination is 44 amino acids. This is a protein that can code a small part of mRNA. As you can see, proteins can cover a whole variety of functions. Many think they only form muscles, but in reality they are also hormones, enzymes, immune system components, etc. Insulin for example? A protein. Antibodies are? Proteins.

In case you are in shortage of proteins and you need a fast boost, choose from the foods below!

Carbohydrates = the main source of energy

Carbohydrates are called this way because they are composed by carbon and water (h20). You might be curious ... why take energy from this element? All living creatures (at least on Earth) are carbon-based. The advantage with this type of element is that it is stable enough to create long-chains, like for example in polysaccharides!

In food you will often find these types of carbohydrates:

  • simple carbs (monosaccharides and disaccharides)
  • complex carbs (polysaccharides)

All living creatures are carbon-based!

What is a sugar?

The main sugars are Glucose, Fructose and Galactose. A sugar is a molecule composed by 6 carbon atoms and a specific C=0 bond. The difference between them is the position of this C=0 bond and whenever a h20 is found on the left or right. Because there is only one molecule, Glucose, Fructose and Galactose are considered Monosaccharides.

To not confuse with table sugar! This is a specific combination (disaccharide) between two sugars: Glucose + Fructose. Here are other combinations: Gluctose + Galactose = Lactose; Glucose + Glucose = Maltose. 

Glucose frucose and galactose structure

and fiber...

When people think about carbs, they sometimes forget about fiber because to be fair, it gives a small dosage of energy. It is mainly there for the gut bacteria.

The main role of fiber is to act as a “filler” or “bulk.” 

This is very beneficial for the gastrointestinal system, helping in colonic lubrication and transit.

Fiber rich foods

Fat = storage

All that you need to know about fat was covered in a previous article fat-all-you-need-to-know. Over here I will mention some interesting facts about it.

The main purposes of fat are storage and protection from cold. There are diets that consist of 80% fat. For example, the Inuit´s main sources of food are whales, walrus, seals and occasionally some berries and tubers. Having a high ratio of fat helps them endure the cold winter. Luckily they developed over time a genetic modification (CPT1A gene) that allows their body to not enter the state of "ketosis", which can endanger the body. In the US and Europe, a diet full of fats is recommended to patients that suffer seizures.

As you can see, fat is an important ally, so pick the healthy ones from the list below!

Healthy fat rich foods

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1. Smallest protein in the human body

2. Why life is carbon-based

3. Life beyond carbon

4. Role of fiber

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