What are carbohydrates? | The nutrition guide

Friend or enemy? Sugar is both loved and loathed. It's our main source of energy and one of the pillars of our diets. But do you actually know what carbohydrates are?

What are carbohydrates? | The nutrition guide

For our bodies to function properly and stay healthy, they need three things: carbohydrates, protein, and fat. Each plays an important role. However, we're all familiar with those tempting mentions of "sugar-free", "no added sugar" and even "low in sugar".
So why have carbohydrates got such a bad name? If we actually knew what they did, we might be a bit more aware of their importance and make better food choices… Let's demystify things together! 

What are carbohydrates?

Carbohydrates are sugars. They represent 50% to 55% of the total energy our bodies need to function normally.
And it's not just our bodies that need this energy: an average adult will eat 180 g of carbohydrate per day, 140 g of which is used by their brain!
Carbohydrates are part of the macronutrients family, just like fat and protein. 

The difference between carbohydrates and sugar

Sugar is the simplest form - the baby of the carbohydrate family. It's what makes food taste sweet. 

The 4 main roles of carbohydrates

Like with fat and protein, it's impossible to sum up what carbohydrates do in just one sentence. Their varied, complementary roles are involved in numerous biological processes.

Providing energy

One gram of carbohydrate provides 4 kcal (the same as protein). They can therefore quickly provide energy to the body's various tissues. When we eat carb-heavy foods, they're transformed either quickly or slowly into glucose: the fuel that powers our bodies and in particular our brains.

This glucose is either used by the body immediately when it needs an instant energy hit, or is transformed into glycogen and stored in the liver and muscles. This store comes in handy whenever we start to feel a bit limp, and is particularly useful to sports users during competitions. 

Regulating our appetite

It's mainly the complex form of carbohydrates - rich in dietary fibre - that leads to a feeling of fullness. Carbs therefore help us eat a balanced diet.

Encouraging good sleep

When we eat carbohydrates, we increase the availability of tryptophan in our bodies. Tryptophan is an amino acid that's a precursor to serotonin and melatonin, among others. These two substances help us fall asleep.
Want to find out more about amino acids?  Read our full article.

Providing taste

Carbs give our meals - especially our desserts - their sweet, comforting side and make lots of foods far more tasty. Which means it's very easy to become addicted. Bear this in mind, and remember to eat in moderation.
Check out our article on sugar addiction. 

Absorption of carbohydrates

In the mouth

The carbohydrate family is the only one for which digestion begins in the mouth. Saliva is actually composed of digestive enzymes, which divide this macromolecule into smaller parts. For example, lactase is an enzyme whose basic function is to separate lactose into two smaller molecules that can be more easily digested: glucose + galactose.
These enzymes, each in their own way, break carbohydrates down into simpler forms that can be absorbed by the small intestine. 

In the intestines

The carbohydrates absorbed by the small intestine arrive in the liver in the form of glucose. Some of this glucose is stored as glycogen which, if necessary, can be turned back into glucose to be used. The brain can only use carbohydrates if they're in the form of glucose. These reactions are how the body accesses the energy provided by carbs.  

As you can see, carbohydrates are broken down at every stage of their journey through the digestive system by enzymes operating everywhere, from the mouth all the way through to the intestines.

The different families of carbohydrate

Carbohydrates can be divided into two categories with very different effects on our bodies.

Fast or simple sugars

The main sources of simple carbohydrates are: 

* the sugar derived from milk (lactose);
* the sugar contained in the cells of fruit (fructose, glucose, saccharose);
* the sugar purified from beet (saccharose and white table sugar).

This family of carbs is digested very quickly and serves as the main source of energy for the brain in particular, as well as for the muscles during short, intense exercise. For longer efforts and endurance exercise, fats take over and provide the body with the fuel it needs to do the activity.

Slow or complex sugars

There are other sources of carbohydrate. Around half of digestible (easily absorbed) carbs come from the starch found in cereals and legumes. This starch is composed of long chains of glucose molecules that are absorbed in the small intestine.
There are also other starches, known as "resistant starches" because they can't be absorbed in the small intestine and therefore reach the colon intact. We refer to this as dietary fibre. It's found in vegetables, legumes and seeds, and doesn't have a sugary taste.

Not all types of carb can be digested: 

either the form they're in is too big (e.g. certain starches);
or the presence of vegetable fibres makes them inaccessible to digestive enzymes, and so they'll be fermented by bacteria in the colon. When this happens, these fibres feed our gut flora - also known as the microbiome - and have a "bulking" action that speeds up intestinal transit.

Take a look at our article on gut health, prebiotics and probiotics.

Refined sugar

Also known as hidden sugar, there's nothing natural about this sugar. It's created by humans and added to many of the processed products that manufacturers use to make our favourite sweet and salty foods (ham, deli meats, crisps, etc.). Why? To trigger our brains' reward systems and encourage consumers to buy more!

As you can imagine, this sugar should be avoided at all costs. It has a high glycaemic index and doesn't provide our bodies with any nutrients. And it actually leads to all sorts of health problems, including:

* diabetes;
* cardiovascular disease;
* digestive disorders;
* chronic fatigue;
* anxiety and stress.

Sadly, this list isn't exhaustive.
Read our article on healthy carbohydrate alternatives to be sure you're getting the energy you need without damaging your health!

All about the glycaemic index

The glycaemic index (or GI) is a scale used to classify carbs according to their impact on our blood sugar. In other words, how they affect our blood sugar levels in the minutes and hours after we eat them.

The glycaemic index tells us which foods are rich in carbs, and helps us understand that different types of carbohydrate have different consequences for our blood sugar.
The GI is divided into 3 families according to how much the food raises our blood sugar levels:
* Low GI: less than 55;
* Medium GI: 55 to 70;
* High GI: over 70.

The top of the scale is 100, which corresponds to pure sugar. So it's best to eat low- or medium-GI foods, and avoid ones with a high GI.
Check out our special article all about the glycaemic index. 

Foods rich in carbohydrate

Most foods sources are composed of carbohydrates, whether simple or complex.  The main sources of carbs are cereal-based products, fruit, certain vegetables, and legumes. 

For example, one portion (100 g) of:
* grapes contains: 80 g of carbohydrates;
* quinoa contains: 57 g of carbohydrates;
* dates contains: 33 g of carbohydrates;
* sweet potato or banana contains: 24 g of carbohydrates;
* whole milk contains: 5 g of carbohydrates.

Sugar-free foods:
Here, we're not talking about processed, reduced-sugar foods, but rather foods that are naturally low in sugar or carbohydrates.  These naturally "sugar-light" foods include: green vegetables, lean meats, fish, nuts and seeds, and vegetable oils.

In general, all non-processed foods limit sugar consumption and are therefore a healthy alternative. 

Carbohydrates aren't necessarily sweet foods, but they're present in many of the things we eat. They're a major source of energy for our bodies, making them essential. Provided that the ones you're eating are of good quality and that you're eating the right amount for your needs, it's unwise to go without them! So, friend or enemy?

What are carbohydrates? | The nutrition guide


Naturopath & Yoga Teacher - Diet and Sport Consultant

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