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Looking at All Sides of the Carbohydrate Debate

Understanding if, when, and how to eat carbohydrates is a hotly debated topic among endurance athletes.

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Many people swear by them, while others vow to avoid them at all costs. Carbohydrates have long been both the enemy and the friend of the endurance athlete, but do we really know why? To view carbohydrates as a polarizing topic of conversation with a simple “yes” or “no” answer goes against common sense as well as current scientific literature. There are so many factors to consider. How can we use carbs as part of a periodized nutrition approach? What should we know about the different types of carbs? Does the gut need to be trained to deal with the number of carbs required for racing? With all of these questions in mind, let’s discuss carbohydrates.

What Are Carbs?

Carbohydrates are one of three types of macronutrients used by the body—the other two being fat and protein. Carbohydrate is a term that can encompass sugar, fruits, vegetables, fibers, and legumes. Vegetables, fruits, whole grains, milk, and milk products are the major food sources of carbohydrates in the modern human diet. 

In their simplest form, carbohydrates are glucose, and this is converted by your body into energy. They provide four calories per gram (protein also provides four calories per gram and fat provides nine). There are many forms of carbohydrates: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Think of mono- and disaccharides as simple carbs, with oligosaccharides and polysaccharides as complex carbohydrates. 

Why Consider Carbohydrates for Training and Racing?

The simple answer is: They provide you with energy! If you want to perform at the highest possible level then you absolutely should consume carbohydrates, especially if you want a place on the podium. In a 2018 expert panel review, Dr. Mitch Kanter explained: “Although dietary protein and fat can provide the necessary energy to perform physical activity, carbohydrate is the substrate most efficiently metabolized by the body and the only macronutrient that can be broken down rapidly enough to provide energy during periods of high-intensity exercise when fast-twitch muscle fibres are primarily relied upon.” 

The more detailed answer to the “why” of carbohydrates should be consumed, is found in how and when they provide you with energy. This is dictated by the form of carbohydrate. It’s important to consider that not all carbohydrates are created equally and need to be addressed in this manner when using them as part of your nutritional program. When discussing carbohydrate availability with clients I use the simple analogy that anything with a barcode is going to be high to moderate availability and anything from the ground is going to be low availability. 

Foods and Carbohydrate Content

There is a common misconception that carbs are only found in foods like bread, pasta, and oats—however, these are just simple carbohydrates. But what many people don’t realize is that plants also provide carbohydrates; these are complex carbohydrates and usually consist of a low to medium glycaemic load. Plant-based carbohydrates are great for everyday general diet, energy during exercise and are fine to eat in abundance.

When considering carbohydrates as part of your fueling strategy for your training and racing, it is important to consider how quickly and just how much glucose they deliver to your system. Simple carbs such as gels, chews, sugar, honey, jam, fruit juice, and white bread will do this task very quickly. This makes them ideal for use in training sessions that require high-intensity efforts, during racing and also for immediate refueling when you’re doing multiple sessions in a day. 

The Problem With Carb Consumption During Racing

It is a common belief that carbohydrate loading during sessions under 90 minutes is not necessary. This is not always the case, as it depends on what you are attempting to achieve with your nutritional strategy. 

A clear example of this is the following situation:  

Tim is a triathlete, training for a 70.3, yet time-starved the majority of week due to work commitments. His training sessions are limited to 60-90 minutes for both bike and run. As a result, he does not practice any intra-session carbohydrate fueling and gets through his sessions just fine. When race day comes along he uses gels, bars, and carbohydrate drinks as he knows he will require instant energy during the race. What follows is an all-too-familiar situation: Tim is vomiting, cramping, and having to dash off behind a bush during the race for an emergency toilet stop. 

Why does this occur? Put simply, Tim’s gut was not trained to cope with that many carbohydrates at once. As a result, his gastric emptying rate is inefficient and results in fluid being pulled into his small intestine. Nausea, bloating, cramps, and gas are all common symptoms of poorly tolerated carbohydrates.

How to Adjust Your Gut to Tolerate Carbohydrates

The good news is that it is possible to “train” your gut. The GI system is adaptable and can be trained to improve gastric emptying and gut discomfort. Strategically placing carbohydrate feeds and fluid consumption into specific sessions and practicing race conditions is a simple strategy that is supported by scientific research. By consuming carbohydrates in your diet and during sessions and forcing them to be utilized, you can alter your intestinal system for improved efficiency. The result will be better carbohydrate absorption and utilization. In practical terms, this means diminished chances of GI symptoms occurring, leading to improved performance in training and on the race course.

A recent study investigated the effect of practicing carbohydrate fueling within training sessions to see if GI distress symptoms could be improved. A group of runners were split into consuming 20g carbohydrate gels, 20g carbohydrate food, or 0g carbohydrate placebo. Carbohydrate consumption was every 20 minutes, i.e. 60g carbohydrates every hour (60g carbs for two groups versus 0g carbs for the placebo group). The researchers investigated the effect on gastrointestinal (GI) symptoms, maximal oxygen uptake (VO2max), carbohydrate malabsorption rates, carbohydrate/fat utilization, blood glucose rates, and running distance. The results found that the two groups who consumed carbohydrates at this rate during the training sessions had significant improvements in gut discomfort, upper and lower GI symptoms, and reduced nausea when compared to the placebo. Blood glucose availability and glucose malabsorption rates were improved in both carbohydrate groups (gels better than food) and this correlated to improved running performance in both the carbohydrate groups compared to the placebo group.

The gel and food group came out fairly similar in this study with respect to the GI symptoms. Some further research exists that might push you towards choosing gels as a fuel source for running races. In this study, carbohydrate comprising of fructose and maltodextrin was ingested every 20 minutes via commercial drink, gel, bar, or a mix of all three, providing 80g carbohydrate per hour to 12 well-trained male cyclists. They were studied performing a cycling test lasting just over 90 minutes. Their GI symptoms, GI distress, power, and perceived exertion were investigated. The results revealed fewer GI symptoms and distress with gels compared to fluids and bars. There was also a small yet possibly significant reduction in power in relation to the consumption of bars versus gels and fluids. This is all practical information that should be noted when choosing your form of carbohydrate for fueling for training and racing.

But How Much Do I Need?

Once again, there is no definitive answer to this question—it will depend on your individual goals. “Fuel for work” was a term coined by Dr. James Morton and his team in relation to the “train low, compete high” debate. They proposed a model of carbohydrate availability being adjusted according to the intensity and volume of training sessions. The aim is to maximize cellular adaptation while also ensuring that training intensity is not compromised. 

This type of pre-planning and nutritional strategy ensures key sessions are completed with high carbohydrate availability, so as to promote performance, gut adaptation to carbohydrates and recovery. The actual amount of glucose that can be oxidized sits at around 60-65 grams/hour. By combining fructose, this rate can be pushed further up to around 95 grams/hour. This is because glucose and fructose utilize different transporters to enter the bloodstream from the small intestine. Women may struggle to ingest more than 65 grams/hour of carbohydrates. Given the increased prevalence of GI symptoms in women, it is not recommended to consume above this amount. For men, the 95 grams/hour of mixed carbohydrates is achievable, yet also takes practice, as mentioned above. Taking into account current research findings, it may well be that women should start with a prescribed amount around 0.8 grams/hour/bodyweight and men 1 gram/hour/bodyweight for carbohydrate recommendations during racing. You can then start to practice this and increase amounts depending on your gut symptoms. This in practical terms would look like the following:

Women: (0.8 x body weight in kg) e.g. 0.8 x 50kg = 40g/hr)
Men: (1 x body weight in kg) e.g 1.0 x 80kg = 80g/hr)

The caveat to this recommendation will be at what intensity you are performing during racing. If you are pushing the limits and have visions of personal records, then training your gut to cope with these volumes of carbohydrates is certainly a valid consideration. 

To Carb AND to Not Carb—That Really Is the Answer

Being strategic with your consumption is paramount to your success. Understanding what carbohydrates are, how they provide energy, which types provide immediate versus sustained energy, how much you require for fueling for specific sessions, is a great beginning to implementing a periodized program designed to reach your fitness aspirations.

Scott Tindal is a performance nutrition coach with 20 years of experience working with pro and amateur athletes. He has a Masters degree in sports medicine and a post-graduate diploma in performance nutrition. He is the co-founder of FuelIn, an app-based personalized nutrition coaching program.