What is a "Carb"?

What is a "Carb"?

Carbohydrates or “carbs” are often discussed as a “thing” that is bad or damaging to our health. However, in sport nutrition the opposite is true; carbohydrates are often discussed favorably because of the proven benefits for performance. When you ask someone what a “carb” is, you will often get varying answers. The goal here is to briefly clarify what a “carb” is and its relevance in endurance sport performance. 

What is a carbohydrate?

The term “carbohydrate” was first used in 1844 by German chemist Carl Schmidtt. Simply, a carbohydrate is one of the key macronutrients composed of carbon, hydrogen, and oxygen. Carbohydrates can be found in the body (endogenous carbohydrates) or consumed (exogenous carbohydrates). Carbohydrates contain the energy necessary for bodily functions that occur at rest and during exercise. Other terms often used interchangeably with carbohydrates are “saccharides”, “sugars”, “starches”, etc. despite their distinct differences. 

Types of carbohydrates

Carbohydrates can be classified based on how many individual carbohydrate molecules (units) that are bound together. Within the body, endogenous carbohydrates can be found mostly in forms of glycogen or glucose. Glycogen are chains of glucose primarily found in the liver and muscle while glucose is found primarily in the blood. 

While there are various types of carbohydrates such as starches, the most common types of carbohydrates used in sport nutrition products include monosaccharides, disaccharide, as well as oligosaccharides and polysaccharides. Mono- being one carbohydrate unit, di- being two, oligo- includes three to nine units, and poly- more than nine. Examples include dextrose (glucose), fructose, sucrose/table sugar (glucose + fructose), glucose syrups (multiple glucose units), maltodextrin, and Cluster Dextrin™ (multiple glucose units). 

The amounts, ratios, and types of these carbohydrates are often carefully chosen to develop a product. In the Carbs Fuel Original Gel, a combination of maltodextrin, sucrose, and fructose were chosen to achieve a balance of taste and texture, while delivering a high density of carbohydrates in an ideal glucose to fructose ratio. 

Molecular structures of various carbohydrates 
Glucose Molecule.    Glucose Molecule
Glucose molecule (monosaccharide) depicted as different projections
Fructose Molecule 
Fructose molecule (monosaccharide)

Carbs Fuel Logo
Carbs Fuel Logo (abstract representation of the 2:1 glucose:fructose ratio)
Sucrose Molecule
Sucrose molecule (disaccharide)
Maltodextrin Molecule
Generic maltodextrin (n = number of glucose units)
Glycogen Molecule

Energy availability

During exercise, the two primary energy sources used include fats and carbohydrates. The prevailing sentiment is that protein is not a primary energy source. This is due to its relatively low contribution to the overall energy demands of the body during exercise. Depending on the exercise intensity, the amount and proportions of carbohydrates and fats being used will fluctuate. In other words, at any exercise intensity, carbohydrates and fats will be used as energy sources by the muscle (1). Thus, the longer and greater the intensity of exercise, the more rapidly these endogenous carbohydrates stores will be depleted.

One gram of carbohydrate contains approximately 4 kcals. 1 kcal is equivalent to 1 Calorie (uppercase C) or 1000 calories (lowercase c). A Calorie is found on nutrition labels. Depending on feeding and training status, liver glycogen can range between 200-400 kcal (~50-100 grams of carbohydrates) (2). In the skeletal muscle, this can range between 1000-3000 kcal (~250-750 grams of carbohydrates) 2. This is equivalent to your liver having one to two 50 gram Carbs Fuel Original Gels, while the skeletal muscle contains between five to 15 Carbs Fuel Original Gels. How quickly would these glycogen stores last during exercise  if they are the sole energy source and assuming an average of 575 grams are available? Well, at 100W ~5 hours, 200W ~2 hours 45 minutes, 300W ~1 hour 50 minutes, and 400W ~1 hour 20 minutes of energy*.

Due to the finite carbohydrate stores in the body compared to fat, these endogenous carbohydrates are typically the limiting energy source during endurance exercise training and competition. Therein lies the problem and why consuming carbohydrates is critical for performance.

The problem

When these carbohydrate stores become nearly depleted and blood glucose concentrations decline (hypoglycemia), the dreaded “bonk” is usually experienced. This is accompanied by the concurrent decline in performance. The duration that glycogen and blood glucose can sufficiently support performance without the need of fueling is dependent on the duration and intensity of exercise as well as fitness of the individual. Regardless, consuming exogenous carbohydrates is critical and necessary to maintain blood glucose. This provides the fuel required by the muscle for high performance, especially during prolonged endurance training and competition. Carbs Fuel anchors its product development to the extensive scientific research that has been conducted in this area. It blends the needs of athletes to determine the amount, type, and ratio of carbohydrates that should be used in its products. In doing so, the products created simplify nutrition and allow more athletes to effectively fuel their sport.


In essence, carbohydrates are simple, but critical fuel sources that are used to power the exercising muscle. However, because of the finite carbohydrate stores in the human body, performance is limited. To combat this, carbohydrates can be consumed to prolong and maintain performance during endurance exercise. These consumable carbohydrates come in different forms, which can be used in concert to create products that are designed to solve the problem at hand. 

*Energy expenditure rates (3)

  • 100W: ~8 kcal/min
  • 200 W: ~14 kcal/min
  • 300 W: ~21 kcal/min
  • 400W: ~28 kcal/min



  1. Romijn, J. A., Coyle, E. F., Sidossis, L. S., Gastaldelli, A., Horowitz, J. F., Endert, E., & Wolfe, R. R. (1993). Regulation of endogenous fat and carbohydrate metabolism in relation to exercise intensity and duration. The American journal of physiology, 265(3 Pt 1), E380–E391. https://doi.org/10.1152/ajpendo.1993.265.3.E380
  2. Hargreaves, M., & Spriet, L. L. (2020). Skeletal muscle energy metabolism during exercise. Nature metabolism, 2(9), 817–828. https://doi.org/10.1038/s42255-020-0251-4
  3. Hagerman F. C. (1992). Energy metabolism and fuel utilization. Medicine and science in sports and exercise, 24(9 Suppl), S309–S314.

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