The Role of Carbohydrates in our Bodies

By: Amber Whittemore RD, BSN, MHSc(c)

Did you know that March is Nutrition Month in Canada? In honour of this we will be spending the next few weeks focusing on some of the most important nutrients our bodies need for proper physical and mental functioning: complex carbohydrates, fibre, amino acids from protein, and essential fatty acids!

All of these come from the “big three”: carbs, protein, and fat. These are the macronutrients that provide our body with energy!

While mainstream media has played a large role in demonizing some of these macronutrients, we are here to tell you that each one of them play an essential role in our health. We will be diving into some of the research that supports why we need these nutrients, (hopefully) dispelling common myths surrounding them, and providing tips for increasing these nutrients and recipe ideas to optimize these nutrients through your diet.

The focus of today’s blog is complex carbohydrates!

The Basics & Their Role in Our Health

Carbohydrates are the preferred energy source for the human body, and despite many of the current diet trends – we do need them for proper metabolic, physical, and mental functioning.

Our bodies digestive tract breaks all the carbs we eat into their most simple form to be absorbed into our bloodstream: glucose. All of the body’s cells depend on glucose, which is why it is our preferred and most essential energy source. Once glucose enters the bloodstream, it provides the fuel needed for proper brain and central nervous system functioning, metabolic and enzymatic reactions, and physical activity and/or movement.

When we are not eating enough carbs some of the most common symptoms may include the following: fatigue or lack of energy, brain “fog”, preoccupation or constant thoughts of carbohydrate rich foods, and impaired metabolism which may be leading to weight fluctuations and muscle loss (rather than fat loss).

Because carbs are so essential to human life and functioning, we undergo biological and chemical changes as a response to restricting them. Some of these changes include the breakdown of muscle to create the glucose needed, the metabolic shift to a “starvation state” (which looks like creating ketones for energy), a decrease in metabolism (which is linked to weight gain or re-gain), and hormonal changes linked to increased carb cravings and preoccupation with food1.

Where to Find Them

Carbohydrates is a large umbrella term for all the foods that are broken down into glucose in our body, underneath this umbrella we find three main categories:

  1. Simple carbohydrates
  2. Starches or complex carbohydrates
  3. Fibre

Simple carbohydrates are the items that our bodies don’t have to put tons of work into to break down, and can be subcategorized three more ways:

  1. Added or processed sugars: candy, chocolate, desserts, pop, juice, canned fruit in syrup, cereals. These items are readily absorbed into our body since the added sugar is commonly already in the form of glucose.
  2. Dairy products: milk, yogurt, etc. These include the sugar lactose, which gets broken down by our body with ease, coining it a “simple carb”.
  3. Fruits: apples, bananas, kiwis, etc. These have fructose in them, which is a natural sugar that our body turns into glucose fairly simply.

Note: this does not mean these items need to be avoided, it simply is referring to the work the body needs to put into digesting and absorbing them. Simple carbs, especially from dairy products and fruit, are still great nutrient sources to include in your day. Fruit is also an awesome source of fibre, which we will get more into next week!

Complex carbohydrates are the foods that take a bit more work for our bodies to break down, since they are made of multiple sugars strung together – each bond therefore needs to be broken to absorb the glucose into our bloodstream. Complex carbs can be broken down into some common branches, which are:

  1. Grains: bread, noodles, rice, cereals, quinoa, oats, couscous, etc. When choosing grains it is best to choose whole grains more often, such as whole wheat bread, brown rice or pasta, large flake or steel cut oatmeal.
  2. Legumes: beans, lentils, peas. These are plant-based proteins, which also contribute some complex carbohydrates to our diet.
  3. Starchy vegetables: carrots, yams, potatoes, etc. Our body digests these more slowly than the refined grains, coining them “complex carbs.

Fibre is found in the majority of plant-based food sources, many of which are also the complex carbs listed above. We will dive into where to find fibre, and its importance, in the next blog post!

The Benefits of Complex Carbs

Complex carbs are broken down into glucose more slowly in our digestive tract, meaning the impact they have on our blood sugars is both lower and more sustained than the quick spikes and drops we might see with more refined or processed sugars. Because of this, complex carbs are great for regulating our blood sugar levels throughout the day and preventing “crashes”.

These carbs therefore provide us with a more sustained fullness and satisfaction after eating, as well as with an abundance of nutrients such as B-vitamins, magnesium, potassium, selenium, fibre and more. Many of these nutrients are removed in refined grains, making the case for choosing whole grains and complex carbs more often even stronger.

Complex carbs are also great for regulating our blood-lipid levels, such as cholesterol, because the fibre found in these sources can bind to these fats and help them pass through our digestive tract rather than all being readily absorbed. So, if you are struggling with elevated cholesterol levels, choosing more complex carbs is a great place to start!

How Much Do We Need?

In general, it is recommended that 45-65% of the calories we get on a daily basis come from carbohydrates. Ideally, more often than not we are choosing complex carbs like whole grains, starchy vegetables, and legumes to ensure we are optimizing our energy and blood sugars throughout the day.

Everybody is different and depending on factors like your activity levels your needs may fall on the lower or higher end of the recommended range mentioned above. High performance athletes tend to require more carbs since they are burning more through their exercise. While elderly adults or those who are more sedentary will likely fall on the lower end of the spectrum.

Regardless of where you fall, carbs are still vital for adequate functioning, and we know that choosing complex carbs at least 50% of the time is the optimal way to fuel our brains and bodies to get us through the day.

Tips for Increasing Them in Your Diet

  1. Try to fill 1/4 of your plate with your starch sources at mealtimes. The current Canada’s Food Guide2 is a great visual for this.

Canada's Food Guide

  1. Aim to choose whole grain sources at least 50% of the time, some examples could include:
  • Whole grain bread or tortillas
  • Steel cut or large flake oats
  • Whole wheat pasta
  • Wild or brown rice
  • Quinoa
  • Whole wheat couscous

The Bottom Line

Carbohydrates are essential for proper mental, physical, and metabolic functioning. When we lack carbohydrates our body lets us know with a myriad of symptoms and bodily changes. We get carbs from many different sources in our diet, including simple carbs and complex carbs. It is recommended to choose complex carbs, like whole grains, legumes, and starchy vegetables, more often – which could look like aiming to choose them at least 50% of the time.
Choosing more complex carbs help us to regulate our blood sugars as well as energy levels throughout the day, while also providing us with the necessary glucose we need to fuel all of our cells and daily activities.
We hope you found today’s blog helpful! Make sure to come back next week to read more about why fibre is so important for our health, and where we can find it in our diet!


1Tribole, E. & Resch, E. (2020). Intuitive Eating, 4th edition.  St. Martins Publishing Group.

2Canada’s Food Guide: