The Nutrition Series: Carbs 101

Carbohydrates: Energizing the Body

There are widespread misconceptions about carbohydrates in both the fitness space and general public. Indeed, opinions regarding carbs tend to swing from attributing fat gain solely to excess carbohydrate intake all the way to understanding that carbs are a necessity not only for performance in sport, but also for life. Let’s explore the seemingly complex world of carbohydrates and attempt to falsify some of the existing beliefs surrounding this important macronutrient.

Simple vs. Complex

Carbohydrates come in a wide variety of forms you are likely already familiar with. Think starches (pasta, rice, bread, potatoes), fiber, sugars and even vegetables and fruits contain carbohydrates in varying quantities. Fundamentally, carbohydrates provide the body with glucose which is utilized by the body for energy. Without getting too deep into the world of biochemistry, the body breaks down glucose into adenosine triphosphate (ATP); aka, the body's energy currency.

There are two types of carbohydrates: simple and complex.

Simple carbohydrates are digested quickly by the body, thus supplying a quick source of energy. There are both added (sugar) and naturally occurring (think fruits, honey, milk etc.). While both supply ample sources of immediately accessible fuel, added sugars tend to lack the additional minerals, nutrients and fiber present in naturally occurring simple sugars that are vital for optimal functioning.

Complex carbohydrates are made up of long-chains of glucose and generally take longer to digest. These include, but are not limited to, such foods as peas, beans, whole grains and vegetables.  There are essentially, two types of complex carbohydrates: refined and unrefined.

Refined carbohydrates have undergone some type of processing such as white rice, pizza dough, many breakfast cereals, white bread, pasta prepared from white flour etc. This processing effectively removes crucial nutrients and fiber important for ideal health.

Unrefined carbohydrates, such as brown rice, whole-wheat pasta, multi-grain bread, whole-wheat cereal etc., have not undergone processing and thereby retain all of the nutrients and fiber lacking in refined carbohydrates. Eating unrefined carbohydrates provides a rich source of nutrients, B-vitamins and fiber, which is essential for maintaining satiety and avoiding overeating.

It’s worth highlighting that consuming refined carbohydrates is certainly not detrimental to your health, so don’t immediately toss all of the refined carbohydrates in your pantry into the garbage. Refined carbs aren’t bad for you, perse, there are simply better options.

You may have also heard that refined carbohydrates spike your blood sugar, due to having a high glycemic index (GI), while unrefined carbohydrates do not. Some may even use this quality to their advantage and consume refined carbohydrates before and after a workout, when having ample glycogen stores is desirable. Current nutrition literature, however, has discovered that the assigned GI to foods is a poor predictor of subsequent blood sugar levels in humans after consumption. In fact, responses tend to be quite variable between subjects within studies. Therefore, basing your dietary choices on GI alone may not be the most ideal way to structure your diet.

Function Within the Body

As mentioned above, the body utilizes carbohydrates for energy via ATP, the energy currency of life. It’s worth unpacking exactly how the body utilizes carbs however, to highlight the importance and discredit any misconceptions you may hold about carbs.

Energy Production: in the simplest terms, carbohydrates are chains of sugar molecules. They vary in length from single units (monosaccharides; glucose, fructose, sucrose etc.), two units (disaccharides), three to ten units (oligosaccharides) and beyond (polysaccharides). Once in the body, these chains are broken down through metabolic processes to produce ATP. Within cells, ATP transfers a phosphate molecule through phosphorylation, releasing chemical energy between bonds that we utilize to power our cellular processes and bodies.

Brain Function: the most critical use for carbohydrates and ultimately, glucose, is energy for the brain. The brain is the most demanding organ when it comes to energy utilization; a whopping 20% of our energy usage is by the brain alone. That’s a whole lot of energy! Glucose readily crosses the blood-brain barrier via a transport protein and is metabolized by brain cells to create energy for cognitive functions.

Muscle Fuel: During physically demanding exercise, energy stores in the form of muscle glycogen are broken down into glucose. This metabolic process provides the energy for muscle contraction, movement and performance. Carbohydrate intake prior to, during and after can help sustain your energy levels, delay fatigue and improve recovery. Carbohydrates are FUEL. No one knows this better than endurance athletes, but adequate carbohydrate intake around any physical activity can assist in improving performance.

Glycogen storage: Excess glucose not utilized by the body is stored in the liver and muscle as glycogen. This provides a readily available source of energy during fasting or periods of intense physical activity when levels of glucose in the bloodstream decrease. As your body can only store so much glycogen, it is important to readily take in carbohydrates to support an adequate supply of glycogen.

Regulation of blood glucose levels: As we’ve discussed, breaking down carbs produces glucose, which in turn causes blood sugar levels to rise. This results in a cascade of signalling causing the pancreas to release insulin. This peptide hormone assists with glucose uptake into the cells by essentially instructing cells to take in more glucose (by way of additional transport proteins on the cellular membrane). More transport proteins, glucose levels go down and stabilize, everybody is happy. This process prevents glucose levels from becoming too high (hyperglycemia). The body raises blood sugar levels through the peptide hormone glucagon, which signals for the breakdown of glycogen in the liver to produce glucose which then enters the bloodstream and prevents blood glucose from becoming too low (hypoglycemia). Both of these conditions can have adverse health effects and adequate carbohydrate intake can assist in maintaining blood glucose levels in healthy individuals.

Fuel for Red Blood Cells: Another crucial function of carbohydrates is for providing energy to red blood cells. Wait what? “My red blood cells require energy?”, you say. You bet! Just like any other cell, red blood cells utilize glucose for ATP production the only difference is, red blood cells do not have mitochondria and therefore rely solely on glycolysis (the breakdown of glucose) for energy. While other types of cells have different options for energy production during periods of glucose scarcity, red blood cells do not have this luxury. Therefore, it is crucial that an adequate supply of carbohydrates and glycogen be available for energy production.

Supporting metabolic processes: Aside from energy production, carbs can play a crucial role in metabolic processes and specifically, in supporting digestive health. Certain carbs high in fiber support digestion and removal of waste products of the body. Individuals require fiber as part of their diet for optimal health. Therefore, it is key to select a wide range of carbs when structuring your diet to ensure you are getting a rich source of fiber (among other minerals and nutrients).

Whole Food Sources

So, let's talk about some of these sources! When it comes to carbohydrates, there are numerous sources to choose from, including both from whole food sources as well as carbohydrate supplementation (we’ll get to that later).

When we think about carbs, many individuals leap first to obvious choices, pasta, bread, rice etc. These are, indeed, rich sources of carbohydrates, but there are many other sources you may not be aware of.

Fruits: fruits contain carbohydrates in the form of the simple sugar (monosaccharide) fructose. As you can expect, there are fruits that are lower in fructose like bananas, and those that are higher in fructose such as pineapple. Fructose has often been touted mistakenly as bad for your health. This couldn’t be further from the truth. This myth has its origins in the negative connotations surrounding high-fructose corn syrup (very different from naturally occurring fructose). For context, high-fructose corn syrup is a sweetener derived from the processing of corn syrup, which converts some of its glucose to fructose. This is then added to many commercially available products such as sodas, candy and dessert.

For comparison, 100g of high-fructose corn syrup contains almost 80g of carbs, while 100g of pineapple contains approximately 10g of carbs. Huge difference, not to mention the fructose contained in the high-fructose corn syrup is heavily processed versus the naturally occurring fructose in fruit. Processed sugar cause a rapid and massive spike in blood sugar, which over time has been linked to a host of health conditions such as diabetes, cardiovascular disease, weight gain, cancer and many others.

I’ll say it again louder for the people in the back, FRUIT IS NOT BAD FOR YOU. As part of healthy diet, you should be consuming a wide variety of fruits of a spectrum of colors.

Vegetables: Our second commonly missed source of carbohydrates are vegetables (and yes, potatoes are vegetables). Most vegetables contain carbohydrates in varying amounts except for green leafy vegetables (spinach, kale, lettuce etc.), cucumber, tomato and celery, to name a few. Vegetables contain carbohydrates in varying amounts; from barely any carbs to rich sources such as sweet potatoes, peas and corn.

Vegetables typically contain carbohydrates as starch; a polysaccharide mixture of two polymers known as amylose and amylopectin. Starches occur in plants, seeds and tubers and are utilized by the plant as a source of glucose and energy. Starch is, in essence, to a plant what glycogen is to other life.

In addition to being an excellent source of carbs, vegetables also provide key nutrients (minerals, vitamins, antioxidants, phytonutrients) and are both low in fat and calories making them a crucial component for structuring your diet. While often overlooked for other higher sources of carbohydrates and protein, with all of benefits they provide, you would be remiss to pass on the veggies at your next meal!

Whole-Grains: When considering carbohydrates, whole grains are traditionally thought of as the main source of carbs in our diet. Whole grains contain all parts of the grain kernel meaning they are comprised of the brain, germ and endosperm and thereby retain all inherent fiber, nutrients and minerals. Examples of whole grains include whole wheat, brown rice, oats, quinoa, barley, buckwheat, millet and bulgur.

As mentioned, there are a host of benefits to eating whole grains. Firstly, they contain crucial vitamins such as B vitamins (thiamin, riboflavin, niacin, and folate), iron, magnesium, and zinc, which are important for energy metabolism, nerve function, and immune health. Secondly, whole grains are rich in phytonutrients and antioxidants that reduce inflammation and protect against chronic disease. Finally, they are rich in fiber which aids in digestion and promotes satiety and also slow digestion and result in a gradual release of glucose into the blood providing sustained energy levels and feeling of fullness.

Aside from whole grains, there are also endless options of refined grains commercially available including, flour, white rice, pasta, cereal, pastries etc., to name a few.

Other Sources: It’s worth highlighting the additional sources of carbohydrates in our diet. On top of fruits, vegetables and grains, carbohydrates are also obtained as starches from legumes and pulses, root vegetables and tubers and dairy products in the form of lactose.

All of the above sources contain a variety of nutrients and it is vital to include a diverse array of carbohydrate sources as part of a rich diet.

Carbohydrate Supplementation

Generally, the average individual has little trouble meeting their carbohydrate intake however, select individuals that are burning significant calories as part of exercise may require supplementation. For example, due to limitations in glycogen storage within the body, endurance activities lasting longer than 90 minutes require some type of carbohydrate supplementation in order to sustain effort. This is generally in the form of simple carbohydrates that provide an immediately available source of energy to the body.

Moreover, high intensity exercise that require quick bouts of activity (think basketball, soccer, high-intensity interval training), may have greater energy demands then the body can supply from glycogen stores alone. While these activities are generally shorter in duration than sustained endurance training sessions, they require rapid energy production and supplementation may assist greatly to support performance.

Carbohydrate supplementation can also assist in speeding up recovery. The requirement for protein supplementation following exercise is commonly known however, supplementing with carbohydrates post training can enhance glycogen resynthesis, reduce muscle breakdown, and facilitate muscle repair and growth. Therefore, you may consider a carbohydrate powder to add to your protein shake to reap further benefits from your training session.

Importantly, carb supplementation can also enhance performance. Indeed, increasing carbohydrate intake the days leading up to a competition, event or other physical feat demanding maximal effort can dramatically improve performance. For example, runners often go through a period of carb-loading prior to a race to ensure they are operating at peak performance.

Lastly, supplementing with carbohydrates can be beneficial for those engaging in multiple training sessions per day, under restrictive diets and for the population that generally has higher energy demands (elite athletes, manual labor positions, pregnant or breastfeeding women etc.).

Carbohydrate Requirements

Carbohydrate requirements can vary widely depending on sex, age, activity and overall health. For the average individual, current carbohydrate recommendations are 45 – 65% of your current daily caloric intake. Thus, for the average recommended intake of 2,000 calories per day, this translates roughly into 225 to 325g of carbohydrates per day. Of course, when we look at active individuals, the story becomes a little different and even greater so when we consider individuals on the higher end of the activity level spectrum.

Current recommendations for active individuals range from 5–12 g/kg/day, with the upper end of this range (8–10 g/kg/day) reserved for those athletes that are training at moderate to high intensities (≥ 70% VO2max) upwards of 12-hours per week. So, for a 80kg (~180lb) athlete training fairly hard at least 12-hours per week, carbohydrate requirements could range anywhere from 640 to 800g per day. That is a whole lot of carbs, which makes it blatantly clear why supplementation is necessary in some individuals.

Adequate carbohydrate intake and ultimately, glucose, is crucial for powering the body. Not only is is glucose utilized for ATP for movement, body also essential bodily functions and most importantly, brain power. Carbs are also brimming with nutrients for ensuring optimal health, especially unrefined carbs. And, while carbs have historically gotten a bad rap (mostly due to overconsumption and subsequent weight gain), a full-well rounded diet is most certainly inclusive of plenty of carbohydrates.

References

1.      Kerksick, C.M., Arent, S., Schoenfeld, B.J. et al. International society of sports nutrition position stand: nutrient timing. J Int Soc Sports Nutr 14, 33 (2017). https://doi.org/10.1186/s12970-017-0189-41