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What you Need to Know About Carbohydrates and Running

Sport Nutrition

The Great Carb Debate

Carbohydrates have always been a hot topic, especially for runners.

With the re-rise in popularity of low-carb and extreme no-carb eating, there still seems to be a bit of misunderstanding about what this macronutrient is all about.

Some people claim that carbohydrate intake is absolutely essential for human health, yet others insist that the recommendations for dietary carbohydrates are a bunch of BS, and that the requirement should be ZERO.

So what gives? How can a substance be both essential yet completely unnecessary at the exact same time?

As with most things on the internet that are hotly debated, the right answer is always somewhere in the middle…

But first,

What exactly is a carbohydrate? What are the different types of carbohydrates that we find in our food, and what do carbs do for you as a runner?

I’ll get down to the details and answer the most important carb questions.

So, let’s dive in!

What are carbohydrates?

[Carbohydrates = Sugar]

The term “carbohydrate” is simply the chemical term for sugar. They are molecules made of various combinations of Carbon, Hydrogen, and Oxygen which our bodies are able to break down for energy.

All of the cells in our bodies prefer carbohydrates as their primary energy source.

Carbohydrate is a huge umbrella term that encompasses ALL the different types of sugars out there.

Within the category of carbohydrates there are 3 main groups. Simple Sugars, Complex Carbohydrates (aka Starches), and Fibre. 

Simple Sugars

Simple sugars are structures made up of only 1 or 2 sugar molecules. The single sugars (monosaccharides) are Glucose, Fructose, and Galactose. The various combinations of 2-sugar molecules (disaccharides) are made from these.

Simple sugars are found in foods that tend to taste sweet such as fruit, white sugar, brown sugar, milk, honey, agave nectar, syrups, etc.

These types of sugars are very quickly broken down and absorbed by our bodies for energy because the lack of complexity in the structure means our bodies have to do very little work in order to digest and absorb them. These are great for when we need quick energy before and during our workouts!

Complex Carbohydrates

Complex carbohydrates or starches, are larger, longer chains of these simple sugars bonded together (polysaccharides). They vary by their look and structure but the main components are the same.

These types of carbohydrates take a bit longer for our bodies to break down because our digestive enzymes produced in our gastrointestinal tract need to break every single bond in the chain before the individual sugar molecules can enter our blood stream.

This is why starches/complex carbohydrates don’t taste as sweet to us, and can keep us feeling full for longer after eating them than say, a sugary beverage.

Sugar Is Sugar

What’s important to note however, is that all of these types of sugars and starches are digested and absorbed by our bodies by the SAME mechanisms. 

Sugar is sugar is sugar. We use the same enzymes and transporters to digest bread, fruit, white sugar, milk, and all of the other hundreds of food items that contain carbohydrates.

Once they’re in our gut, our bodies treat them all equally. But despite that, we know that some types of carbohydrate foods are better for our health than others (for example we can probably all agree that pop is less nutritious than brown rice, even if the total carbohydrate content is equaled out). 

It’s also important to remember that when we hear about how “bad” sugar is for our health, we’re usually talking about ADDED sugars specifically. It’s also important to remember that for runners, added sugars are sometimes necessary for performance.

We need quick energy during long runs and races, and completely avoiding all sources of added sugars all the time may actually harm our performance.


What do carbs actually DO?

Carbohydrates are our body’s preferred source of fuel. Carbohydrates are what give all our cells energy, and keep our brain adequately fueled.

During exercise, our muscles need way more energy than at rest to fuel our activity, and that fuel comes mostly from carbohydrates!

If we aren’t eating enough, we can find ourselves hungry, cranky, and with some serious sugar cravings. We might also find our athletic performance seriously impacted (in a bad way!) if we are underfueling.

So what is it that makes some carbohydrate foods more beneficial for our health than others?

Why choose whole grain bread over white bread if the carbohydrates are all broken down the same way? One of the answers to that question is fibre!

Fibre is in fact a carbohydrate, but it acts a bit different from simple sugars and starches when we consume it. We get very few calories from fibre (we lack the enzymes needed to digest it properly), but that does not mean that it doesn’t play an important role in our health.

There are different types of fibres in the foods we eat and they play many roles in our digestion. They act as a gel in our digestive tract and slow down how quickly our digested food travels through our intestines, which keeps us from feeling hungry as quickly after eating and helps to keep our bowl movements regular. This is a great thing outside of our workouts, but is the reason why high fibre foods can sometimes lead to GI issues during workouts.

Read more about GI issues and running here

Fibre from foods is the main source of fuel for many of the bacteria that take up residence in our GI tract as well. These bacteria make up what we call the “gut microbiome”, and research consistently demonstrates that a high-fibre diet has positive impacts on the health and diversity of our microbiome.

The World Health Organization recently released a very large scale study on fibre and recommends we eat at least 24 grams per day.


So, are there good and bad carbohydrates?

Not so much… sure there are definitely some carbohydrate-containing foods that are more nutritious than others. Meaning, they generally offer us other nutrients aside from just carbohydrate calories. Of course, when we’re talking about what types of foods we should bring on a long run our priorities need to shift a bit and carbohydrate calories are all we need!

Compare for example, two slices of whole wheat bread, and about 10 fuzzy peaches candies. Both have the same amount of carbohydrate, and similar calories, but the whole wheat bread would be considered more ‘nutritious’. Why?

It’s because the whole wheat bread gives us more than just the sugar, more than just the calories. Whole grains have fibre, vitamins, minerals, and more protein too. This is going to give our bodies important nutrients, but also keep us feeling full and satisfied for longer.

The candy on the other hand contains no additional nutrients, just sugar. It may satisfy a craving for something sweet, but it certainly doesn’t replace all of the nutrients that we get our of a real meal.

Even though our bodies metabolize all sugars in the same way, it’s what other benefits a food can provide that make one a better choice vs a not-so-nutritious one.

For runners, there is also a time and place for different types of carbs. Immediately before and during our training we want to rely on those ‘quick carbs’. At other times of day, more filling whole grains can be a better choice.

How much carbohydrate should we be eating in a day? And when?

Well, it all depends. Think of carbohydrates in your diet like gas in your car. The more driving you do, the more gas you use. People with higher activity levels are going to need more calories (and more carbohydrates) than folks who are sedentary.

Most of the carbohydrates we eat in a day should be from highly nutritious sources, such as fruit, milk, yogurt, whole grains, and starchy vegetables.

An endurance athlete needs about 55-65% of their total diet from carbohydrates, and should consume these carbs before, during and after training to ensure they are properly fueled.

Eating a meal with carbs, protein and fat around 2 hours before training will not only provide a source of fuel, but will give your body some time to digest the meal.

If you’re eating within 30-60 minutes before a workout, its best to consume mostly carbs with no fat and minimal protein and fibre.

I know I mentioned how great fibre is (and YES, it is!), BUT there are times where less fibre may actually be better. Fibre slows our digestion and can lead to GI issues during training. This may cause you to end up with an upset tummy during your run.

You can benefit from some intra-workout carbs if your run is over 60-90 minutes long. After this time, glycogen (or stored carbs) levels are depleted.

Consuming something like an electrolyte drink with a 6-8% carbohydrate solution or piece of fruit such as a banana can help to replenish so you can finish your workout strong.

Whether it’s a post workout snack or a full meal, it’s important to include both carbs and protein to aid in recovery.

But Insulin! Don’t carbs cause diabetes?

A lot of low carbohydrate diet fans talk about minimizing carbohydrate intake to reduce insulin production, because insulin makes us gain weight, and this weight gain leads to health problems such as type 2 diabetes.

They state that carbohydrate intake of any sort (whether it be whole grains, fruit, pop, potatoes, or candy) directly causes us to gain weight. Even more so than any other foods, because the insulin needed to get those sugars into our bodies’ cells also trap fat which makes us unable to lose body fat.

This triggers overeating, further increases in insulin levels, and finally when the body is unable to keep up, type 2 diabetes develops. They believe that if we kept insulin levels in our bodies to a minimum, we’d be home free from weight gain and developing diabetes forever.

Some of the most vocal advocates of low carb dieting don’t believe exercise, genetics, or anything else plays a role. It’s all about the insulin and the carbs.

Myth Busting

Yes, insulin is a hormone that plays a role in glucose metabolism, by which it allows sugars to enter our bodies cells to either be stored, or used for energy. But insulin itself is not the sole driver of weight gain. Read more on understanding type 2 diabetes, here.

Our bodies automatically adjust insulin levels to match blood sugar levels and keep them stable. If we’re gaining weight, it isn’t insulin’s fault- it’s that were taking in more calories than our bodies’ truly need, and we’re storing the extra energy as fat. We don’t become insulin resistant because we eat carbs. We become insulin resistant because our body’s fuel stores are full.

It is important to recognize as well that a diet very high in saturated fat has actually been shown to contribute to insulin resistance, which is one of the major factors that leads to developing type 2 diabetes. Physical inactivity has also been shown to contribute to this issue.

Plus, this “carbohydrate-insulin model of obesity” has been studied. A few times actually, and has not been found to be true. Excess calories from any source will cause us to gain weight, there is absolutely nothing special about the impact of carbohydrates on the development of type 2 diabetes.


But, are they really necessary? Do we really NEED to eat carbs?

Honestly… no. I’m not one to tell anyone what they can and can’t do when it comes to what they put in their bodies (unless it’s raw water- don’t drink that!), however there’s a few pretty big BUTs that go along with my statement. Just because carbohydrates are not an essential nutrient, that does not mean it makes sense to bypass them altogether. This is ESPECIALLY true for athletes who want to perform their best. While we technically can survive without carbohydrates in our diet, that doesn’t mean we’ll thrive without them.

Here are a few reasons why:

  1. While our bodies do have the capacity to create new glucose molecules in the liver (you can read more about that process here), it comes at a hefty price. Amino acids from protein are required to complete this process. Some very low-carb high fat diets recommend a relatively low protein content, in which case the body has to turn to the amino acids stored in our body’s muscle mass in order to keep making glucose. That’s bad news for our strength and metabolism!
  2. While carbohydrates themselves may not be essential, many of the vitamins and minerals that come packaged with them in the food we eat are. If we become too focused on eliminating carbs from our diet we might wind up cheating ourselves out of even more important nutrients. If we try to cut all the carbs out of our diet we’re also going to have a heck of a time eating enough fibre, which is something you don’t want to skimp on.

  3. Carbohydrates ARE essential to athletic performance, and not just for elite athletes! Time and time again, carbohydrates have been shown to be absolutely key for fueling moderate to vigorous intensity exercise. Trying to follow a low-carb diet while maintaining a high level of physical activity is basically like shooting yourself in the foot and trying to run a marathon. You may FEEL like you’re working really hard when you’re eating low-carb and hitting the gym, but the performance gains just won’t be as fruitful as when you include carbs as part of your pre and post-workout meals.

  4. There’s just no reason to! Most people like eating foods that have carbs in them, and that should be the only reason we really need to go ahead and enjoy them.

The bottom line

There’s no need to be afraid because carbohydrates aren’t so bad after all! They keep our bodies fueled and energized, and able to perform in every aspect of our lives, including big race days!

Without carbs, we can feel fatigued, have trouble with memory, cognition, and mood. All you need to do is practice eating the right amount of carbohydrates for your activity level, and choosing carbohydrates sources that provide you with the best overall nutrition.

Carbs are key to athletic performance! To figure out what works best for you, you might find working with a Registered Dietitian like myself helpful for meeting your fueling needs!



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