Carbohydrate Typing: How To Use Carbs To Optimize Athlete Performance!

Carbohydrates are important to athletes. Here are a few facts and tips about carb loading, its importance, who benefits, and more.

Performance is defined as "the execution or accomplishment of work, acts, feats, etc." Today, we know a lot about how nutrition can affect the strength, speed and performance of athletes. We also know that for athletes to optimize their performance and be successful, they must consume efficient amounts of nutrients from carbohydrates, fats and proteins throughout the day.

The main question is, "How can nutrition go above and beyond for performance when taken pre, during and post intensive exercise/training?"

What Impact Does Nutrition Have On Performance?

Most of us already know that carbohydrates are the most readily available nutrient for energy production, especially during intense exercise. Although the human body can use fat, protein and carbohydrates as the principle fuels to provide energy, it is carbohydrates that is the preferred or most optimal fuel for supporting intense activity and maintaining normal blood glucose levels.

The reason for this is that carbohydrates are more oxygen-efficient than fat or protein. This is important because the amount of oxygen available to working muscles isn't unlimited—it's determined by your maximum oxygen uptake (VO2 max).

In addition and more importantly, unlike fat and protein, carbohydrate can be broken down very rapidly without oxygen to provide large amounts of extra ATP via a process known as glycolysis during intense exercise.

Since the majority of "performance athletes" tend to work at or near their anaerobic threshold, this additional energy route provided by carbohydrate is vital for maximal performance and a normal healthy blood glucose balance.

Glycogen Stores

Several decades ago, Bergstrom and Hultman (1960's) discovered that when the body's glycogen stores were depleted, fatigue sets in and performance is significantly reduced. What they also found was that when glycogen stores were depleted, then replenished properly (carbohydrate overcompensation/loading), they held more glycogen than originally.

What was also important was that the rate at which the body uses carbohydrates, or glucose, for energy depended on several factors; level of conditioning of the athlete, whether activity is aerobic or anaerobic and the athlete's diet consumption.

For a performance athlete, it is critical to keep glycogen stores packed at all times, because once they are depleted, the body will resort to its fatty acid supply as well as its amino acid supply (MUSCLE). At this time, fatty acids and amino acids (via muscle catabolism) are not optimal for energy at high levels and performance will be negatively affected.

In general, the athletes that will benefit the most from optimizing glycogen stores are endurance athletes. These include long distance runners, tri-athletes, cyclists, long distance swimmers, soccer and boxing/MMA athletes. Basically, any athletes participating in any constant event, at high intensity, lasting for 1.5-2+ hrs will benefit from carbohydrate overcompensation.

Other athletes that would benefit from a more moderate "carbohydrate loading" are football players, basketball players, track and field athletes, swimmers, rowers and runners where the intensity is moderate to high for less than 1.5 hours.

Carbohydrate Oxidation

As stated, carbohydrates are the primary energy source for intense endurance exercise; however, there is a limit to the rate at which your body can absorb them. This is believed to be the primary factor in how fast you can metabolize or burn carbohydrates consumed during exercise.

Scientists call this metabolic burning of carbohydrates carbohydrate oxidation. Based on prior studies, researchers have long believed that the maximum burn or oxidation rate of ingested carbohydrates is about one gram per minute.

In fact, current research is advising endurance/intense training athletes to consume 0.5-1.0 grams of carbohydrate per minute (intensity pending) during training or competition. Trying to consume more carbohydrates has only indicated intestinal distress and it is believed that the type of carbohydrate is the limiting factor.

If an athlete consumed 0.5-1.0 grams/min, then that would equate to 30-60g carbohydrate per minute which amounts to around 120-240kcals per hour, providing only a modest replenishment of energy compared to that being expended during training or competition. Elite endurance athletes can burn well over 1000 cals per hour which indicates that 60g/240cals/hr is hardly enough to compensate for this deficit.

Maximizing Oxidation Rates

Various current research out of the UK and Canada has indicated that a mixture of glucose and fructose during prolonged, intense cycling can maximize oxidation rates for these ingested carbohydrates at a 2:1 ratio (glucose:fructose).

These findings suggest that if an endurance athlete consumes the right blend of carbohydrates while exercising, he or she can dramatically boost the rate at which they absorb and therefore burn carbohydrates. It is believed that the glucose/fructose combination is being absorbed more rapidly and therefore producing higher rates of carbohydrate oxidation rather than glucose alone or glucose in combination with maltodextrin (glucose polymer) or sucrose.

The same Canadian team of researchers in 2004 performed another carbohydrate ingestion study on eight cyclists pedaling at 63% of VO2max for two hours. The study indicated that the carbohydrate oxidation rate when drinking a high glucose drink (1.8g per min of glucose) was no higher than when medium glucose (1.2g per min of glucose) was consumed.

More importantly, the peak and average oxidation rates of ingested glucose/fructose (1.2g of glucose + 0.6g of fructose per minute) solution were around 50% higher than both of the glucose-only drinks. These findings indicate that the maximum rate of glucose absorption into the body that can be oxidized is around 1.3g per minute.

Researchers believe that the absorption mechanism is fully saturated at 1.3g glucose/minute; therefore no further increased oxidation was indicated when given more glucose. However, since oxidation rates were increased with the addition of fructose, it's believed that fructose was absorbed from the intestine via a different mechanism transporter than glucose.

In 2006, researchers from UK performed a study that was two-fold. The first purpose was to investigate whether a glucose + fructose beverage would result in a higher carbohydrate oxidation rate and a higher fluid availability during exercise in the heat compared with the same caloric value of glucose alone.

The second purpose of the study was to examine whether ingestion of glucose at a rate of 1.5 g/min during exercise in the heat would lead to a reduced muscle glycogen oxidation rate compared with ingestion of water. One of the toughest tests for endurance athletes is training or competing in the heat, as glycogen stores are depleted faster when exercising in high temperatures.

The study concluded that athletes consuming glucose + fructose together resulted in higher oxidation rates of ingested carbohydrates than consuming glucose alone.

In addition, the beverage containing glucose + fructose proved to be more effective at replacing fluid lost during exercise than the glucose alone beverage. Researchers theorized that a mixture of glucose and fructose speeds both carbohydrate and fluid absorption, as compared to glucose alone.


Since the current research is indicating that a 2:1 Glucose:Fructose combination can increase energy output during intense training and assist with optimizing hydration, it would only make sense that the addition of anabolic amino acids would further enhance the performance and recovery.

It is well documented that BCAAs are very beneficial during and around intense training. Let's not forget that the nutritional intake for the day needs to be optimal as well. Keep in mind, we still need to consume nutrient dense foods to make sure our glycogen levels are full to perform optimally.

  1. J Appl Physiol 1983;55:230-235.Carbohydrate feeding during prolonged strenuous exercise can delay fatigue.
  2. J Appl Physiol 1986;61:165-172. Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate.
  3. Gastelu D and Hatfeild F, PhD. (1997) Dynamic Nutrition for Maximum Performance. New York: Avery Publishing Group
  4. Sports Med. 2000 Jun;29(6):407-24 Oxidation of carbohydrate feedings during prolonged exercise: current thoughts, guidelines and directions for future research
  5. Sports Med 2000;29:407-424. Oxidation of carbohydrate feedings during prolonged exercise: current thoughts, guidelines and directions for future research.
  6. Med Sci Sports Exerc 2000;32:2130-2145. American College of Sports Medicine, et al. Nutrition and athletic performance: joint position statement.
  7. Medicine & Science in Sports & Exercise. 36(9):1551-1558, September 2004.High Oxidation Rates from Combined Carbohydrates Ingested during Exercise.
  8. J Appl Physiol 2004;96:1277-1284. Oxidation of combined ingestion of glucose and fructose during exercise.
  9. J Appl Physiol 2004;96:1285-1291. Oxidation of exogenous glucose, sucrose and maltose during prolonged cycling exercise.
  10. Br J Nutr. 2005 Apr;93(4):485-92. High rates of exogenous carbohydrate oxidation from a mixture of glucose and fructose ingested during prolonged cycling exercise.
  11. J Appl Physiol 2006;100:1134-1141. Exogenous carbohydrate oxidation during ultra endurance exercise.
  12. J Appl Physiol 2006;100:807-816. Exogenous carbohydrate oxidation rates are elevated after combined ingestion of glucose and fructose during exercise in the heat.
  13. Scand J Med Sci Sports. 2007 Oct;17(5):605-10. Carbohydrate ingestion during prolonged high-intensity intermittent exercise: impact on affect and perceived exertion.